Protection of Stratospheric Ozone: Listing of Substitutes for Ozone-Depleting Substances-n-Propyl Bromide in Adhesives, Coatings, and Aerosols

Federal RegisterMay 30, 2007

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 82

[EPA-HQ-OAR-2002-0064; FRL-8316-7]

RIN 2060-AK26

Protection of Stratospheric Ozone: Listing of Substitutes for Ozone-Depleting Substances—n-Propyl Bromide in Adhesives, Coatings, and Aerosols

AGENCY:

Environmental Protection Agency.

ACTION:

Notice of Proposed Rulemaking.

SUMMARY:

Pursuant to the U.S. Environmental Protection Agency's (EPA or “we”) Significant New Alternatives Policy (SNAP) program, this action proposes to list n-propyl bromide (nPB) as an unacceptable substitute for methyl chloroform, chlorofluorocarbon (CFC)-113, and hydrochlorofluorocarbon (HCFC)-141b when used in adhesives or in aerosol solvents because nPB in these end uses poses unacceptable risks to human health when compared with other substitutes that are available. In addition, EPA takes comment on alternate options that would find nPB acceptable subject to use conditions in adhesives or in aerosol solvents. This action also proposes to list nPB as acceptable, subject to use conditions, as a substitute for methyl chloroform, CFC-113, and hydrochlorofluorocarbon (HCFC)-141b in the coatings end use. This proposal supersedes EPA's proposal of June 3, 2003 on the acceptability of nPB as a substitute for ozone-depleting substances for aerosols and adhesives.

DATES:

Comments must be received in writing by July 30, 2007. Under the Paperwork Reduction Act, comments on the information collection provisions must be received by the Office of Management and Budget (OMB) on or before June 29, 2007. Any person interested in requesting a public hearing, must submit such request on or before June 29, 2007. If a public hearing is requested, a separate notice will be published announcing the date and time of the public hearing and the comment period will be extended until 30 days after the public hearing to allow rebuttal and supplementary information regarding any material presented at the public hearing. Inquiries regarding a public hearing should be directed to the contact person listed below.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2002-0064, by one of the following methods:

•

http://www.regulations.gov.

Follow the on-line instructions for submitting comments.

•

E-mail: A-And-R-Docket@epa.gov.

•

Mail:

Air and Radiation Docket, Environmental Protection Agency, Mailcode 6102T, 1200 Pennsylvania Ave., NW., Washington DC 20460, Attention Docket ID No. EPA-HQ-OAR-2002-0064. In addition, please mail a copy of your comments on the information collection provisions to the Office of Information and Regulatory Affairs, Office of Management and Budget (OMB),

Attn:

Desk Officer for EPA, 725 17th St., NW., Washington, DC 20503.

•

Hand Delivery:

EPA Docket Center, (EPA/DC) EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC, Attention Docket ID No. EPA-HQ-OAR-2002-0064. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for deliveries of boxed information.

Instructions:

Direct your comments to Docket ID No. EPA-HQ-OAR-2002-0064. EPA's policy is that all comments received will be included in the public docket without change and may be made available online at

http://www.regulations.gov

, including any personal information provided, unless the comment includes information claimed to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through

www.regulations.gov

or e-mail. The

http://www.regulations.gov

Web site is an “anonymous access” system, which means EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an e-mail comment directly to EPA without going through

http://www.regulations.gov

, your e-mail address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, EPA may not be able to consider your comment. Electronic files should avoid the use of special characters, any form of encryption, and be free of any defects or viruses. For additional instructions on submitting comments, go to Section I.B. of the

SUPPLEMENTARY INFORMATION

section of this document.

Docket:

All documents in the docket are listed in the

http://www.regulations.gov index.

Although listed in the index, some information is not publicly available, i.e., CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy form. Publicly available docket materials are available either electronically in

http://www.regulations.gov

or in hard copy at the Air and Radiation Docket, EPA/DC, EPA West, Room 3334, 1301 Constitution Ave., NW., Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the Air and Radiation Docket is (202) 566-1742.

FOR FURTHER INFORMATION CONTACT:

Margaret Sheppard, Stratospheric Protection Division, Office of Atmospheric Programs, Mail Code 6205J, Environmental Protection Agency, 1200 Pennsylvania Ave., NW., Washington, DC 20460; telephone number (202) 343-9163; fax number (202) 343-2362 e-mail address:

sheppard.margaret@epa.gov.

Notices and rulemakings under the SNAP program are available on EPA's Stratospheric Ozone World Wide Web site at

http://www.epa.gov/ozone/snap/regs.

SUPPLEMENTARY INFORMATION:

Table of Contents

I. General Information

A. Does this action apply to me?

B. What should I consider as I prepare my comments for EPA?

C. What acronyms and abbreviations are used in the preamble?

II. How does the Significant New Alternatives Policy (SNAP) program work?

A. What are the statutory requirements and authority for the SNAP program?

B. How do the regulations for the SNAP program work?

C. Where can I get additional information about the SNAP program?

III. What is EPA proposing today?

A. What is n-propyl bromide?

B. What industrial end uses are included in our proposed decision?

C. What is the proposed text for EPA's listing decisions?

D. What does an unacceptability determination on adhesives and aerosols mean?

E. What is the scope of the proposed determination for coatings?

IV. What criteria did EPA consider in preparing this proposal?

A. Availability of Alternatives to Ozone-Depleting Substances

B. Impacts on the Atmosphere and Local Air Quality

C. Ecosystem and Other Environmental Impacts

D. Flammability and Fire Safety

E. Health impacts and exposure

V. How did EPA assess impacts on human health?

A. Newly Available Exposure Data

B. Newly Available Data on Health Effects

C. Evaluation of Acceptable Exposure Levels for the Workplace

D. Other Analyses of nPB Toxicity

E. Community Exposure Guideline

VI. What listing is EPA proposing for each end use, and why?

A. Aerosol Solvents

B. Adhesives

C. Coatings

VII. What other regulatory options did EPA consider?

A. Alternative Option for Comment: Acceptable With Use Conditions Requiring Exposure Limit and Monitoring

B. Regulatory Options Where nPB Would Be Acceptable With Use Conditions Requiring Specific Equipment

VIII. What are the anticipated costs of this regulation to the regulated community?

IX. How do the decisions for EPA's June 2003 proposal compare to those for this proposal?

X. How can I use nPB as safely as possible?

XI. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination With Indian Tribal Governments

G. Executive Order 13045: Protection of Children From Environmental Health and Safety Risks

H. Executive Order 13211: Actions That Significantly Affect Energy Supply, Distribution, or Use

I. National Technology Transfer and Advancement Act

XII. References

I. General Information

A. Does this action apply to me?

This proposed rule would regulate the use of n-propyl bromide as an aerosol solvent and as a carrier solvent in adhesives and coatings. Businesses in these end uses that currently might be using nPB, or might want to use it in the future, include:

• Businesses that manufacture electronics or computer equipment.

• Businesses that require a high level of cleanliness in removing oil, grease, or wax, such as for aerospace applications or for manufacture of optical equipment.

• Foam fabricators that glue pieces of polyurethane foam together or foam cushion manufacturers that glue fabric around a cushion.

• Furniture manufacturers that use adhesive to attach wood parts to floors, tables and counter tops.

• A company that manufactures ammunition for the U.S. Department of Defense. Regulated entities may include:

Table 1.—Potentially Regulated Entities, by North American Industrial Classification System (NAICS) Code or Subsector

Category

NAICS code or subsector

Description of regulated entities

Industry

331

Primary Metal Manufacturing.

Industry

332

Fabricated Metal Product Manufacturing.

Industry/Military

332992

Small Arms Ammunition Manufacturing.

Industry

333

Machinery Manufacturing.

Industry

334

Computer and Electronic Product Manufacturing.

Industry

335

Equipment Appliance, and Component Manufacturing.

Industry

336

Transportation Equipment Manufacturing.

Industry

337

Furniture and Related Product Manufacturing.

Industry

339

Miscellaneous Manufacturing.

Industry

326150

Urethane and Other Foam Product (except Polystyrene) Manufacturing.

This table is not intended to be exhaustive, but rather a guide regarding entities likely to be regulated by this action. If you have any questions about whether this action applies to a particular entity, consult the person listed in the preceding section,

FOR FURTHER INFORMATION CONTACT

B. What should I consider as I prepare my comments for EPA?

1. Submitting Confidential Business Information (CBI). Do not submit this information to EPA through

www.regulations.gov

or e-mail. Clearly mark the part or all of the information that you claim to be CBI. For CBI information in a disk or CD ROM that you mail to EPA, mark the outside of the disk or CD ROM as CBI and then identify electronically within the disk or CD ROM the specific information that is claimed as CBI. In addition to one complete version of the comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.

2. Tips for Preparing Your Comments. When submitting comments, remember to:

• Identify the rulemaking by docket number and other identifying information (subject heading,

Federal Register

(FR) date and page number).

• Follow directions—The agency may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number.

• Explain why you agree or disagree; suggest alternatives and substitute language for your requested changes.

• Describe any assumptions and provide any technical information and/or data that you used.

• If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced.

• Provide specific examples to illustrate your concerns, and suggest alternatives.

• Explain your views as clearly as possible, avoiding the use of profanity or personal threats.

• Make sure to submit your comments by the comment period deadline identified.

C. What acronyms and abbreviations are used in the preamble?

Below is a list of acronyms and abbreviations used in this document.

8-hr—eight hour

ACGIH—American Conference of Governmental Industrial Hygienists

AEL—acceptable exposure limit

ASTM—American Society for Testing and Materials

BMD—benchmark dose

BMDL—benchmark dose lowerbound, the lower 95%-confidence level bound on the dose/exposure associated with the benchmark response

BSOC—Brominated Solvents Consortium

CAA—Clean Air Act

CAS Reg. No—Chemical Abstracts Service Registry Identification Number

CBI—Confidential Business Information

CEG—community exposure guideline

CERHR—Center for the Evaluation of Risks to Human Reproduction

CFC-113—the ozone-depleting chemical 1,1,2-trifluoro-1,2,2-trichloroethane, C

, CAS Reg. No. 76-13-1

CFC—chlorofluorocarbon

cfm—cubic feet per minute

CFR—Code of Federal Regulations

CNS—central nervous system

DNA—deoxyribonucleic acid

EDSTAC—The Endocrine Disruptor Screening and Testing Advisory Committee

EPA—the United States Environmental Protection Agency

FR—Federal Register

GWP—global warming potential

HCFC-141b—the ozone-depleting chemical 1,1-dichloro-1-fluoroethane, CAS Reg. No. 1717-00-6

HCFC-225ca/cb—the commercial mixture of the two ozone-depleting chemicals 3,3-dichloro-1,1,1,2,2-pentafluoropropane, CAS Reg. No. 422-56-0 and 1,3-dichloro-1,1,2,2,3-pentafluoropropane, CAS Reg. No. 507-55-1

HCFC—hydrochlorofluorocarbon

HEC—human equivalent concentration

HFC-245fa—the chemical 1,1,3,3,3-pentafluoropropane, CAS Reg. No. 460-73-1

HFC-365mfc—the chemical 1,1,1,3,3-pentafluorobutane, CAS Reg. No. 405-58-6

HFC-4310mee—the chemical 1,1,1,2,3,4,4,5,5,5-decafluoropentane, CAS Reg. No. 138495-42-8

HFC—hydrofluorocarbon

HFE—hydrofluoroether

HHE—health hazard evaluation

ICF—ICF Consulting

ICR—Information Collection Request

iPB—isopropyl bromide, C

Br, CAS Reg. No. 75-26-3, an isomer of n-propyl bromide; also called 2-bromopropane or 2-BP

—organic carbon partition coefficient, for determining the tendency of a chemical to bind to organic carbon in soil

—the concentration at which 50% of test animals die

LOAEL—Lowest Observed Adverse Effect Level

Log K

—logarithm of the octanol-water partition coefficient, for determining the tendency of a chemical to accumulate in lipids or fats instead of remaining dissolved in water

mg/l—milligrams per liter

MSDS—Material Safety Data Sheet

NAICS—North American Industrial Classification System

NIOSH—National Institute for Occupational Safety and Health

NOAEL—No Observed Adverse Effect Level

NOEL—No Observed Effect Level

nPB—ln-propyl bromide, C

Br, CAS Reg. No. 106-94-5; also called 1-bromopropane or 1-BP

NPRM—Notice of Proposed Rulemaking

NTP—National Toxicology Program

NTTAA—National Technology Transfer and Advancement Act

ODP—ozone depletion potential

ODS—ozone-depleting substance

OEHHA—Office of Environmental Health Hazard Assessment of the California Environmental Protection Agency

OMB—U.S. Office of Management and Budget

OSHA—the United States Occupational Safety and Health Administration

PCBTF—parachlorobenzotrifluoride, CAS Reg. No. 98-56-6

PEL—Permissible Exposure Limit ppm-parts per million

RCRA—Resource Conservation and Recovery Act

RFA—Regulatory Flexibility Act

RfC—reference concentration

SIP—state implementation plan

SNAP—Significant New Alternatives Policy

TCA—the ozone-depleting chemical 1,1,1-trichloroethane, CAS Reg. No. 71-55-6; also called methyl chloroform, MCF, or 1,1,1

TCE—the chemical 1,1,2-trichloroethene, CAS Reg. No. 79-01-6, C2Cl3H; also call trichloroethylene

TERA—Toxicological Excellence for Risk Assessment

TLV—Threshold Limit Value(tm)

TSCA—Toxic Substances Control Act

TWA—time-weighted average

UMRA—Unfunded Mandates Reform Act

U.S.C.—United States Code

VMSs—volatile methyl siloxanes

VOC—volatile organic compound

II. How does the Significant New Alternatives Policy (SNAP) program work?

A. What are the statutory requirements and authority for the SNAP program?

Section 612 of the Clean Air Act (CAA) authorizes EPA to develop a program for evaluating alternatives to ozone-depleting substances, referred to as the Significant New Alternatives Policy (SNAP) program. The major provisions of section 612 are:

•

Rulemaking

—Section 612(c) requires EPA to promulgate rules making it unlawful to replace any class I (chlorofluorocarbon, halon, carbon tetrachloride, methyl chloroform, and hydrobromofluorocarbon) or class II (hydrochlorofluorocarbon) substance with any substitute that the Administrator determines may present adverse effects to human health or the environment where the Administrator has identified an alternative that (1) reduces the overall risk to human health and the environment, and (2) is currently or potentially available.

•

Listing of Unacceptable/Acceptable Substitutes

—Section 612(c) also requires EPA to publish a list of the substitutes unacceptable for specific uses. We must publish a corresponding list of acceptable alternatives for specific uses.

•

Petition Process

—Section 612(d) grants the right to any person to petition EPA to add a substitute to or delete a substitute from the lists published in accordance with section 612(c). EPA has 90 days to grant or deny a petition. Where the Agency grants the petition, we must publish the revised lists within an additional six months.

•

90-day Notification

—Section 612(e) requires EPA to require any person who produces a chemical substitute for a class I substance to notify the Agency not less than 90 days before new or existing chemicals are introduced into interstate commerce for significant new uses as substitutes for a class I substance. The producer must also provide the Agency with the producer's health and safety studies on such substitutes.

•

Outreach

—Section 612(b)(1) states that the Administrator shall seek to maximize the use of federal research facilities and resources to assist users of class I and II substances in identifying and developing alternatives to the use of such substances in key commercial applications.

•

Clearinghouse

—Section 612(b)(4) requires the Agency to set up a public clearinghouse of alternative chemicals, product substitutes, and alternative manufacturing processes that are available for products and manufacturing processes which use class I and II substances.

B. How do the regulations for the SNAP program work?

On March 18, 1994, EPA published the original rulemaking (59 FR 13044) that described the process for administering the SNAP program and issued the first acceptability lists for substitutes in the major industrial use sectors. These sectors include: Refrigeration and air conditioning; foam blowing; solvents cleaning; fire suppression and explosion protection; sterilants; aerosols; adhesives, coatings and inks; and tobacco expansion. These sectors comprise the principal industrial sectors that historically consumed large volumes of ozone-depleting substances.

Anyone who plans to market or produce a substitute for an ozone-depleting substance (ODS) in one of the eight major industrial use sectors must provide the Agency with health and safety studies on the substitute at least 90 days before introducing it into

interstate commerce for significant new use as an alternative. This requirement applies to the person planning to introduce the substitute into interstate commerce, typically chemical manufacturers, but may also include importers, formulators or end-users when they are responsible for introducing a substitute into commerce.

The Agency has identified four possible decision categories for substitutes: Acceptable; acceptable subject to use conditions; acceptable subject to narrowed use limits; and unacceptable. Use conditions and narrowed use limits are both considered “use restrictions” and are explained below. Substitutes that are deemed acceptable with no use restrictions (no use conditions or narrowed use limits) can be used for all applications within the relevant sector end-use. Substitutes that are acceptable subject to use restrictions may be used only in accordance with those restrictions. It is illegal to replace an ODS with a substitute listed as unacceptable.

After reviewing a substitute, the Agency may make a determination that a substitute is acceptable only if certain conditions of use are met to minimize risks to human health and the environment. We describe such substitutes as “acceptable subject to use conditions.” If you use these substitutes without meeting the associated use conditions, you use these substitutes in an unacceptable manner and you could be subject to enforcement for violation of section 612 of the Clean Air Act.

For some substitutes, the Agency may permit a narrowed range of use within a sector. For example, we may limit the use of a substitute to certain end-uses or specific applications within an industry sector or may require a user to demonstrate that no other acceptable end uses are available for their specific application. We describe these substitutes as “acceptable subject to narrowed use limits.” If you use a substitute that is acceptable subject to narrowed use limits, but use it in applications and end-uses which are not consistent with the narrowed use limit, you are using these substitutes in an unacceptable manner and you could be subject to enforcement for violation of section 612 of the Clean Air Act.

The Agency publishes its SNAP program decisions in the

Federal Register

. For those substitutes that are deemed acceptable subject to use restrictions (use conditions and/or narrowed use limits), or for substitutes deemed unacceptable, we first publish these decisions as proposals to allow the public opportunity to comment, and we publish final decisions as final rulemakings. In contrast, we publish substitutes that are deemed acceptable with no restrictions in “notices of acceptability,” rather than as proposed and final rules. As described in the rule implementing the SNAP program (59 FR 13044), we do not believe that rulemaking procedures are necessary to list alternatives that are acceptable without restrictions because such listings neither impose any sanction nor prevent anyone from using a substitute.

Many SNAP listings include “comments” or “further information.” These statements provide additional information on substitutes that we determine are unacceptable, acceptable subject to narrowed use limits, or acceptable subject to use conditions. Since this additional information is not part of the regulatory decision, these statements are not binding for use of the substitute under the SNAP program. However, regulatory requirements listed in this column are binding under other programs. The further information does not necessarily include all other legal obligations pertaining to the use of the substitute. However, we encourage users of substitutes to apply all statements in the “Further Information” column in their use of these substitutes. In many instances, the information simply refers to sound operating practices that have already been identified in existing industry and/or building-code standards. Thus, many of the comments, if adopted, would not require the affected industry to make significant changes in existing operating practices.

C. Where can I get additional information about the SNAP program?

For copies of the comprehensive SNAP lists of substitutes or additional information on SNAP, look at EPA's Ozone Depletion World Wide Web site at

http://www.epa.gov/ozone/snap/lists/index.html.

For more information on the Agency's process for administering the SNAP program or criteria for evaluation of substitutes, refer to the SNAP final rulemaking published in the

Federal Register

on March 18, 1994 (59 FR 13044), codified at Code of Federal Regulations at 40 CFR part 82, subpart G. You can find a complete chronology of SNAP decisions and the appropriate

Federal Register

citations at

http://www.epa.gov/ozone/snap/chron.html.

III. What is EPA proposing today?

In this action, EPA proposes to list n-propyl bromide (nPB) as (1) unacceptable for use as a substitute for CFC-113,

methyl chloroform

and HCFC-141b

in the adhesive and aerosol solvent end uses; and (2) acceptable subject to use conditions (limited to coatings at facilities that, as of May 30, 2007, have provided EPA with information demonstrating their ability to maintain acceptable workplace exposures) as a substitute for methyl chloroform, CFC-113, and HCFC-141b in the coatings end use. This Notice of Proposed Rulemaking (NPRM) supersedes the NPRM published on June 3, 2003 (68 FR 33284) for aerosol solvents and adhesives.

CFC-113 is also referred to as Freon-113, or 1,1,2-trifluoro-1,2,2-trichloroethane. Its CAS Reg. No. is 76-13-1.

Methyl chloroform is also referred to as 1,1,1-trichloroethane, TCA, MCF, or 1,1,1. Its CAS Reg. No. is 71-55-6.

HCFC-141b is also referred to as 1,1-dichloro-1-fluoroethane. Its CAS Reg. No. is 1717-00-6.

A. What is n-propyl bromide?

n-propyl bromide (nPB), also called 1-bromopropane, is a non-flammable organic solvent with a strong odor. Its chemical formula is C

Br. Its identification number in Chemical Abstracts Service's registry (CAS Reg. No.) is 106-94-5. nPB is used to remove wax, oil, and grease from electronics, metal, and other materials. It also is used as a carrier solvent in adhesives. Some brand names of products using nPB are: Abzol®, EnSolv®, and Solvon® cleaners; Pow-R-Wash® NR Contact Cleaner, Superkleen Flux Remover 2311 and LPS NoFlash NU Electro Contact Cleaner aerosols; and Whisper Spray and Fire Retardant Soft Seam 6460 adhesives.

B. What industrial end uses are included in our proposed decision?

This proposal addresses the use of n-propyl bromide in the aerosol solvent end use of the aerosol sector and the adhesives and coatings end uses in the adhesives, coatings, and inks sector as discussed below. EPA is issuing a decision on the use of nPB in metals, electronics, and precision cleaning in a separate final rule. EPA has insufficient information for ruling on other end uses or sectors where nPB might be used (e.g., inks, foam blowing, fire suppression).

1. Aerosol Solvents

We understand that nPB is being used as an aerosol solvent in:

• Lubricants, coatings, or cleaning fluids for electrical or electronic equipment;

Lubricants, coatings, or cleaning fluids for aircraft maintenance; or

• Spinnerrette lubricants and cleaning sprays used in the production of synthetic fibers.

2. Adhesives

Types of adhesives covered under the SNAP program are those that formerly used methyl chloroform, specifically, adhesives for laminates, flexible foam, hardwood floors, tire patches, and metal to rubber adhesives. Of these applications, nPB-based adhesives have been used most widely in spray adhesives used in manufacture of foam cushions, and to a lesser degree in laminate adhesives.

3. Coatings

The SNAP program regulates the use of carrier solvents in durable coatings, including paints, varnishes, and aerospace coatings (59 FR 13118). The SNAP program currently does not regulate carrier solvents in lubricant coatings, such as silicone coatings used on medical equipment (59 FR 13119). Methyl chloroform has been used as a carrier solvent in coatings, and to a much lesser degree, HCFC-141b also has been a carrier solvent. This rule responds to a submission from a facility that is substituting methyl chloroform with nPB as an ammunition coating (sealant).

C. What is the proposed text for EPA's listing decisions?

In the proposed regulatory text at the end of this document, you will find our proposed decisions for those end uses for which we have proposed nPB as unacceptable or acceptable subject to use conditions. The proposed conditions listed in the “Use Conditions” column would be enforceable while information contained in the “Further Information” column of those tables provides additional recommendations on the safe use of nPB. Our proposed decisions for each end use are summarized below in tables 2 through 4.

Proposed Listings

Table 2.—Aerosols Proposed Unacceptable Substitutes

End Use

Substitute

Decision

Further information

Aerosol solvents

n-propyl bromide (nPB) as a substitute for CFC-113, HCFC-141b, and methyl chloroform

Unacceptable

EPA finds unacceptable risks to human health in this end use compared to other available alternatives. nPB, also known as 1-bromopropane, is Number 106-94-5 in the CAS Registry.

Table 3.—Adhesives, Coatings, and Inks Proposed Unacceptable Substitutes

Enduse

Substitute

Decision

Further information

Adhesives

n-propyl bromide (nPB) as a substitute for CFC-113, HCFC-141b, and methyl chloroform

Unacceptable

EPA finds unacceptable risks to human health in this end use compared to other available alternatives. nPB, also known as 1-bromopropane, is Number 106-94-5 in the CAS Registry.

Table 4.—Adhesives, Coatings, and Inks Substitutes That Are Proposed Acceptable Subject to Use Conditions

End Use

Substitute

Decision

Use conditions

Further information

Coatings

n-propyl bromide (nPB) as a substitute for methyl chloroform, CFC-113, and HCFC-141b

Acceptable subject to use conditions

Use is limited to coatings facilities that, as of May 30, 2007, have provided EPA information demonstrating their ability to maintain acceptable workplace exposures

EPA recommends the use of personal protective equipment, including chemical goggles, flexible laminate protective gloves and chemical-resistant clothing.

EPA expects that all users of nPB would comply with any final Permissible Exposure Limit that the Occupational Safety and Health Administration issues in the future under 42 U.S.C. 7610(a).

nPB, also known as 1-bromopropane, is Number 106-94-5 in the CAS Registry.

Note: As of May 30, 2007, the Lake City Army Ammunition Plant is the only facility using nPB in coatings that has provided information to EPA that meets this condition.

D. What does an unacceptability determination on adhesives and aerosols mean?

In this action, EPA is proposing to find nPB unacceptable as a substitute for methyl chloroform, CFC-113, and HCFC-141b for use as a carrier solvent in adhesives and as an aerosol solvent. If this proposal were to become final, it would be illegal to use nPB or blends of nPB and other solvents in adhesives or in aerosol solvent formulations as a substitute for ozone-depleting substances.

E. What is the scope of the proposed determination for coatings?

We propose to list nPB as an acceptable substitute, subject to use conditions, for methyl chloroform, CFC-113, and HCFC-141b in coatings for facilities that, as of May 30, 2007, have

provided EPA information demonstrating their ability to maintain acceptable workplace exposures. EPA has received a petition to allow use of nPB for the ammunition coating application at Lake City Army Ammunition Plant. This is the only coatings application or facility for which EPA has exposure and usage data demonstrating an ability to maintain workplace exposure levels below even the minimum level of the range of exposures that EPA is considering to be potentially acceptable (i.e., 17 to 30 ppm) (see section IV.E for an evaluation of the health risks associated with nPB). If other facilities are interested in using nPB as a substitute for methyl chloroform, CFC-113, or HCFC-141b in their coatings application, or if a person wishes to market nPB for such use, then the interested party would need to make a submission under the SNAP program.

IV. What criteria did EPA consider in preparing this proposal?

In the original rule implementing the SNAP program (March 18, 1994; 59 FR 13044, at 40 CFR 82.180(a)(7)), the Agency identified the criteria we use in determining whether a substitute is acceptable or unacceptable as a replacement for class I or II compounds:

(i) Atmospheric effects and related health and environmental impacts;

[e.g., ozone depletion potential]

(ii) General population risks from ambient exposure to compounds with direct toxicity and to increased ground-level ozone;

(iii) Ecosystem risks [e.g., bioaccumulation, impacts on surface and groundwater];

(iv) Occupational risks;

(v) Consumer risks;

(vi) Flammability; and

(vii) Cost and availability of the substitute.

In this review, EPA considered all the criteria above. However, n-propyl bromide is used in industrial applications such as electronics cleaning or spray adhesives used in foam fabrication. In those consumer products made using nPB, such as a piece of furniture or a computer, the nPB would have evaporated long before a consumer would purchase the item. Therefore, we believe there is no consumer exposure risk to evaluate in the end uses we evaluated for this rule.

Section 612(c) of the Clean Air Act directs EPA to publish a list of replacement substances (“substitutes”) for class I and class II ozone depleting substances based on whether the Administrator determines they are safe (when compared with other currently or potentially available substitutes) for specific uses or are to be prohibited for specific uses. EPA must compare the risks to human health and the environment of a substitute to the risks associated with other substitutes that are currently or potentially available. In addition, EPA also considers whether the substitute for class I and class II ODSs “reduces the overall risk to human health and the environment” compared to the ODSs being replaced. Our evaluation is based on the end use; for example, we compared nPB as a carrier solvent in adhesives to other available or potentially available adhesive alternatives.

Although EPA does not judge the effectiveness of an alternative for purposes of determining whether it is acceptable, we consider effectiveness when determining whether alternatives that pose less risk are available in a particular application within an end use. There are a wide variety of acceptable alternatives listed for aerosol solvents, but not all may be appropriate for a specific application because of differences in materials compatibility, flammability, degree of cleanliness required, local environmental requirements, and other factors.

EPA evaluated each of the criteria separately and then considered overall risk to human health and the environment in comparison to other available or potentially available alternatives. We concluded that overall, environmental risks were not sufficient to find nPB unacceptable in any of the evaluated end uses. However, the overall risks to human health, and particularly the risks to worker health, are sufficiently high in the adhesive and aerosol solvent end uses to warrant our proposal to find nPB unacceptable.

A. Availability of Alternatives to Ozone-Depleting Substances

Other alternatives are available in each end use considered in this proposal. Examples of other available alternatives for aerosol solvents that have already been found acceptable or acceptable subject to use conditions under the SNAP program include water-based formulations, alcohols, ketones, esters, ethers, terpenes, HCFC-141b, HCFC-225ca/cb, hydrofluoroethers (HFEs), hydrofluorocarbon (HFC)-4310mee, HFC-365mfc, HFC-245fa, hydrocarbons, trans-1,2-dichloroethylene, methylene chloride, trichloroethylene

(TCE), perchloroethylene

, and parachlorobenzotrifluoride (PCBTF). Of these, hydrocarbons, alcohols, blends of trans-1,2-dichloroethylene and HFEs or HFCs, and HCFC-225ca/cb are most likely to be used in the same applications as nPB. nPB is already commercially available in aerosols. Its use is primarily for electrical contact cleaning, with some use for benchtop cleaning applications (Williams, 2005).

Also called trichlorethene or TCE, C

H, CAS Reg. No. 79-01-6.

Also called PERC, tetrachloroethylene, or tetrachloroethene, C

, CAS Reg. No. 127-18-4.

Many alternatives are also available for use in adhesives, coatings, and inks: Water-based formulations, high solid formulations, alcohols, ketones, esters, ethers, terpenes, HFEs, hydrocarbons, trans-1,2-dichloroethylene, chlorinated solvents, PCBTF, and a number of alternative technologies (e.g., powder, hot melt, thermoplastic plasma spray, radiation-cured, moisture-cured, chemical-cured, and reactive liquid). Of these, the alternative adhesives most likely to be used in the same applications as nPB are water-based formulations, adhesives with methylene chloride, and flammable adhesives with acetone (IRTA, 2000). nPB is already used in adhesives, and particularly in foam fabrication and in constructing seating for aircraft (IRTA, 2000; Seilheimer, 2001).

To our knowledge, nPB is potentially available as a carrier solvent in coatings, but has not yet been commercialized, except for use by one facility, the Lake City Army Ammunition Plant. The Lake City Army Ammunition Plant evaluated twenty-nine carrier solvent alternatives to methyl chloroform and determined that nPB is the only satisfactory alternative for their application given the current process at that facility (Harper, 2005).

B. Impacts on the Atmosphere and Local Air Quality

As discussed in the June, 2003 proposal, nPB emissions from the continental United States are estimated to have an ozone depletion potential (ODP) of approximately 0.013-0.018, (Wuebbles, 2002), lower than that of the ozone depletion potential of the substances that nPB would replace—CFC-113 (ODP = 1.0), and methyl chloroform and HCFC-141b (ODPs = 0.12) (WMO, 2002). Some other acceptable alternatives for these ODSs also have low ODPs. For example, HCFC-225ca/cb has an ODP of 0.02-0.03 (WMO, 2002) and is acceptable as an aerosol solvent. There are other acceptable solvents for aerosols, adhesives, and coatings that essentially have no ODP—aqueous cleaners, HFEs, HFC-4310mee, HFC-365mfc, HFC-245fa, hydrocarbons, volatile methyl siloxanes (VMSs), methylene chloride, TCE, perchloroethylene, and PCBTF.

Based on this information, we do not believe the use of nPB within the U.S., and within the end-uses reviewed in this rulemaking, poses a significantly greater risk to the ozone layer than other available substitutes.

Comments on the June 2003 NPRM expressed concern that other countries, particularly those in equatorial regions, might assume that nPB does not pose a danger to the stratospheric ozone layer if the U.S. EPA's SNAP program finds nPB acceptable (Linnell, 2003; Steminiski, 2003). Because the ODP for nPB is higher when used in the tropics,

we recognize the concerns raised by these commenters. However, EPA is regulating use in the U.S. and cannot dictate actions taken by other countries. We believe the more appropriate forum to address this concern is through the Parties to the Montreal Protocol. At the most recent Meeting of the Parties, the Parties made the following decision with regard to n-propyl bromide, in order to “allow Parties to consider further steps regarding n-propyl bromide, in the light of available alternatives” (Decision XVIII/11):

nPB emissions in the tropics have an ODP of 0.071 to 0.100; the portions of the U.S. outside the continental U.S., such as Alaska, Hawaii, Guam, and the U.S. Virgin Islands, contain less than 1 percent of the U.S.'s businesses in industries that could use nPB. Thus, their potential impact on the ozone layer must be significantly less than that of the already low impact from nPB emissions in the continental U.S. (U.S. Economic Census, 2002a through f).

1. To request the Scientific Assessment Panel to update existing information on the ozone depletion potential of n-propyl bromide, including ozone depleting potential depending on the location of the emissions and the season in the hemisphere at that location;

2. To request the Technology and Economic Assessment Panel to continue its assessment of global emissions of n-propyl bromide, * * * paying particular attention to:

(a) Obtaining more complete data on production and uses of n-propyl bromide as well as emissions of n-propyl bromide from those sources;

(b) Providing further information on the technological and economical availability of alternatives for the different use categories of n-propyl bromide and information on the toxicity of and regulations on the substitutes for n-propyl bromide;

(c) Presenting information on the ozone depletion potential of the substances for which n-propyl bromide is used as a replacement;

3. To request that the Technology and Economic Assessment Panel prepare a report on the assessment referred to in paragraph 1 in time for the twenty-seventh meeting of the Open-ended Working Group for the consideration of the Nineteenth Meeting of the Parties. (MOP 18, 2006)

The global warming potential (GWP) index is a means of quantifying the potential integrated climate forcing of various greenhouse gases relative to carbon dioxide. Earlier data found a direct 100-year integrated GWP (100yr GWP) for nPB of 0.31 (Atmospheric and Environmental Research, Inc., 1995). More recent analysis that considers both the direct and the indirect GWP of nPB found a 100-yr GWP of 1.57 (ICF, 2003a; ICF, 2006a). In either case, the GWP for nPB is comparable to or below that of previously approved substitutes in these end uses.

Use of nPB may be controlled as a volatile organic compound (VOC) under state implementation plans (SIPs) developed to attain the National Ambient Air Quality Standards for ground-level ozone, which is a respiratory irritant. Users located in ozone nonattainment areas may need to consider using a substitute for cleaning that is not a VOC or if they choose to use a substitute that is a VOC, they may need to control emissions in accordance with the SIP. Companies have petitioned EPA, requesting that we exempt nPB from regulation as a VOC. However, unless and until EPA issues a final rulemaking exempting a compound from the definition of VOC and states change their SIPs to exclude such a compound from regulation, that compound is still regulated as a VOC. Other acceptable ODS-substitute solvents that are VOCs for state air quality planning purposes include most oxygenated solvents such as alcohols, ketones, esters, and ethers; hydrocarbons and terpenes; trichloroethylene; trans-1,2-dichloroethylene; monochlorotoluenes; and benzotrifluoride. Some VOC-exempt solvents that are acceptable ODS substitutes include HFC-245fa, HCFC-225ca/cb, HFC-365mfc and HFC-4310mee for aerosol solvents, and methylene chloride, perchloroethylene, HFE-7100, HFE-7200, PCBTF, acetone, and methyl acetate for aerosol solvents, adhesives, and coatings.

C. Ecosystem and Other Environmental Impacts

EPA considered the possible impacts of nPB if it were to pollute soil or water as a waste and compared these impacts to screening criteria developed by the Endocrine Disruptor Screening and Testing Advisory Committee (EDSTAC, 1998) (see Table 5). Available data on the organic carbon partition coefficient (K

), the breakdown processes in water and hydrolysis half-life, and the volatilization half-life indicate that nPB is less persistent in the environment than many solvents and would be of low to moderate concern for movement in soil. Based on the LC

, the acute concentration at which 50% of tested animals die, nPB's toxicity to aquatic life is moderate, being less than that for some acceptable cleaners (for example, trichloroethylene, hexane, d-limonene, and possibly some aqueous cleaners) and greater than that for some others (methylene chloride, acetone, isopropyl alcohol, and some other aqueous cleaners). The LC

for nPB is 67 milligrams per liter (mg/l), which is greater and thus less toxic than an LC

of 10 mg/l, one of EPA's criteria for listing under the Toxics Release Inventory (US EPA, 1992; ICF, 2004a). Based on its relatively low bioconcentration factor and log K

value (logarithm of the octanol-water partition coefficient), nPB is not prone to bioaccumulation. Table 5 summarizes information on environmental impacts of nPB; trans-1,2-dichloroethylene, a commonly-used solvent in blends for aerosol solvents, precision cleaning, and electronics cleaning; acetone, a commonly-used carrier solvent in adhesives; trichloroethylene, a solvent used for metals, electronics, and precision cleaning that could potentially be used in aerosol or adhesive end-uses; and methyl chloroform, an ODS that nPB would replace.

Table 5.—Ecosystem and Other Environmental Properties of

PB and Other Solvents

Property

Description of environmental property

Value for nPB

Value for trans-1,2-dichloro-ethylene

Value for acetone

Value for

trichloroethylene

Value for methyl

chloroform

, organic-carbon partition coefficient

Degree to which a substance tends to stick to soil or move in soil. Lower values (< 300)

indicate great soil mobility; values of 300 to 500 indicate moderate mobility in soil

330 (Source: ICF, 2004a)

32 to 49 (Source: ATSDR, 1996)

5.4 (Source: ATSDR, 1994)

106 to 460 (Source: ATSDR, 1997)

152 (Source: U.S. EPA, 1994a).

Break down in water

Mechanism and speed with which a compound breaks down in the environment. (Hydrolysis half-life values > 25 weeks

are of concern.)

Hydrolysis is significant. Hydrolysis half-life of 26 days (Source: ICF, 2004a)

Photolytic decomposition, dechlorination and biodegradation are significant; hydrolysis not significant (Source: ATSDR, 1996)

Biodegradation is most significant form of breakdown (Source: ATSDR, 1994)

Volatilization and biodegradation most significant, with hydrolysis relatively insignificant. Hydrolysis half-life of 10.7 to 30 months (Source: ATSDR, 1997)

Volatilization most significant; biodegradation and hydrolysis also occur (Source: ATSDR, 2004).

Volatilization half-life from surface waters

Tendency to volatilize and pass from water into the air

3.4 hours-4.4 days (Source: ICF, 2004a)

3 to 6.2 hours (Source: ATSDR, 1996)

7.8 to 18 hours (Source: ATSDR, 1994)

3.4 hours to 18 days (Source: ATSDR, 1997)

Hours to weeks (Source: U.S. EPA, 1994a).

(96 hours) for fathead minnows

Concentration at which 50% of animals die from toxicity after exposure for 4 days

67 mg/L (Source: Geiger, 1988)

108 mg/L (Source: U.S. EPA, 1980)

7280 to 8120 mg/L (Source: Fisher Scientific, 2001)

40.7 to 66.8 mg/L (Source: NPS, 1997)

52.8 to 105 mg/L (Source: U.S. EPA, 1994a).

log K

Logarithm of the octanol/water partition coefficient, a measure of tendency to accumulate in fat. Log K

values >3

indicate high tendency to accumulate

2.10 (Source: ICF, 2004a)

−0.48 (Source: LaGrega

et al.

, 2001, p. 1119)

−0.24 (Source: LaGrega

et al.

, 2001, p. 1117)

2.38 (Source: LaGrega

et al.

, 2001, p. 1127)

2.50 (Source: LaGrega

et al.

, 2001, p. 1127).

Bioconcentration factor

High factors (>1000)

indicate strong tendency for fish to absorb the chemical from water into body tissues

23 (Source: HSDB, 2004)

5 to 23 (Source: ATSDR, 1996)

<1 (Source: ATSDR, 1994)

10 to 100 (Source: ATSDR, 1997)

<9 (Source: U.S. EPA, 1994a).

Criteria from EDSTAC, 1998.

nPB is not currently regulated as a hazardous air pollutant and is not listed as a hazardous waste under the Resource Conservation and Recovery Act (RCRA). nPB is not required to be reported as part of the Toxic Release Inventory under Title III of the Superfund Amendments and Reauthorization Act. Despite this, large amounts of nPB might be harmful if disposed of in water. We recommend that users dispose of nPB as they would dispose of any spent halogenated solvent (F001 waste under RCRA). Users should not dump nPB into water, and should dispose of it by incineration. We conclude that nPB does not pose a significantly greater risk to the environment than other available alternatives, and that the use of nPB within the U.S. should not be prohibited under the SNAP program on the basis of its environmental impacts.

D. Flammability and Fire Safety

A number of commenters on the June 2003 proposal provided additional information on the flammability of nPB using standard test methods for determining flash point, such as the American Society for Testing and Materials (ASTM) D 92 open cup, ASTM D56 Tag closed cup, and ASTM D93 Pensky-Martens closed cup methods (BSOC, 2000; Miller, 2003; Morford, 2003a, 2003b, and 2003c;

Shubkin, 2003; Weiss Cohen, 2003). We agree with the commenters that by these standard test methods, nPB displayed no flash point. Thus under standard test conditions, nPB is not flammable, and it should not be flammable under normal use conditions. With its low potential for flammability, nPB is comparable to chlorinated solvents, HCFCs, HFEs, HFC-245fa, HFC-4310mee, and aqueous cleaners, and is less flammable than many acceptable substitutes, such as ketones, alcohols, terpenes, and hydrocarbons. nPB exhibits lower and upper flammability limits of approximately 3% to 8% (BSOC, 2000). A number of other solvents that are typically considered to be non-flammable also have flammability limits (for example, methylene chloride, HCFC-141b, and methyl chloroform). If the concentration of vapor of such a solvent falls between the upper and lower flammability limits, it could catch fire in presence of a flame. Such a situation is unusual, but users should take appropriate precautions in cases where the concentration of vapor could fall between the flammability limits.

E. Health Impacts and Exposure

In evaluating potential human health impacts of nPB used as a substitute for ozone-depleting substances, EPA considered impacts on both exposed workers and on the general population. Using the same approach finalized in the original SNAP rulemaking, EPA evaluated the available toxicity data using EPA guidelines to develop health-based criteria to characterize human health risks (US EPA, 1994b. Inhalation Reference Concentration Guidelines; U.S. EPA, 1991. Guidelines for Developmental Toxicity Risk Assessment; U.S. EPA, 1995a. Benchmark Dose guidelines; U.S. EPA, 1996. Guidelines for Reproductive Toxicity Risk Assessment).

To assess human health risks, EPA followed the four basic steps of risk assessment outlined by the National Academy of Sciences: hazard identification, dose-response relationship, exposure assessment, and risk characterization (NAS, 1983). First, EPA examined available studies on nPB's effects. Second, EPA considered the acceptable exposure levels for evaluating worker exposure and a community exposure guideline (CEG) for evaluating exposure to the general population based upon inhalation exposure. Third, EPA compared the acceptable exposure levels and CEG to available exposure data and projections of exposure levels to assess exposure, including new exposure data available since publication of the June 2003 NPRM. Finally, EPA decided whether there was sufficient evidence indicating that nPB could be used as safely as other alternatives available in a particular end use.

Authority To Set an Acceptable Exposure Limit

Two commenters on the June 2003 NPRM said that EPA has no jurisdiction to develop any acceptable exposure limit (AEL) designed to be applicable to a workplace environment and that only the Occupational Safety and Health Administration (OSHA) has that authority (Stelljes, 2003; Morford, 2003d). In contrast, another commenter said that EPA has the authority to set an AEL for nPB under section 612 of the Clean Air Act, has done so in the past for other chemicals (e.g., HFC-4310mee, HCFC-225ca/cb), and should require the AEL as a use condition (Risotto, 2003).

EPA believes it has the authority to calculate exposure limits for the workplace under section 612. Section 612(c) specifically states that

The Administrator shall issue regulations: providing that it shall be unlawful to replace any class I or class II substance with any substitute substance which the Administrator determines may present adverse effects to human health or the environment, where the Administrator has identified an alternative to such replacement that—

(1) reduces the overall risk to human health and the environment; and

(2) is currently or potentially available.

Thus, we must compare the risks to human health and the environment of a substitute to the risks associated with other substitutes that are currently or potentially available, as required by the Clean Air Act. In order to compare risks to human health, EPA performs quantitative risk assessments on different chemicals comparing exposure data and exposure limits, following the process described above by the National Academies of Science (NAS, 1983) and as described in the preamble to the original final SNAP rule (March 18, 1994; 59 FR 13066). Because most humans who are exposed to nPB are exposed in the workplace, the appropriate exposure data and exposure limits to protect human health must include workplace exposure data and acceptable exposure limits for the workplace. Because there is wide disparity in acceptable exposure limits for nPB developed by industry, ranging from 5 ppm to 100 ppm (Albemarle, 2003; Chemtura, 2006; Docket A-2001-07, item II-D-19; Enviro Tech International, 2006; Farr, 2003; Great Lakes Chemical Company, 2001), and because there is not a Permissible Exposure Limit for nPB set by the Occupational Safety and Health Administration, EPA believes it is appropriate to independently evaluate the human health risks associated with use of nPB in the workplace. Similarly, EPA has developed a community exposure guideline to assess the human health effects of nPB exposure to the general public.

Skin Notation

Several commenters on the June 2003 proposal stated that a skin notation for nPB is appropriate, while another commenter agreed with EPA's proposal that no skin notation was necessary (Smith, 2003; HESIS, 2003; Werner, 2003, Weiss Cohen, 2003). Rat studies indicate that dermal exposure to nPB results in neither appreciable absorption through the skin (RTI, 2005) nor systemic toxicity (Elf Atochem, 1995). Unlike methyl chloride and dichlorvos, which are absorbed through the skin and could contribute to systemic toxicity (ACGIH, 1991), EPA is not proposing to include a skin notation for nPB in the information provided to users associated with this rulemaking because of the relatively low level of absorption. The American Conference of Governmental Industrial Hygienists (ACGIH) provides no skin notation in its documentation for threshold limit values (TLVs) for several solvents, including nPB (ACGIH, 2005), methylene chloride, and perchloroethylene, and there is no evidence that absorption through the skin is greater for nPB than for the other halogenated compounds. Further, including a statement giving advice about how to reduce skin exposure in the “Further Information” column of listings is likely to be more informative to workers than a skin notation.

Given the possibility that some nPB can be absorbed through the skin in humans, and that the solvent can irritate the skin, EPA encourages users to wear protective clothing and flexible laminate gloves when using nPB and encourages vendors to include such precautions in their Material Safety Data Sheets (MSDSs). EPA requests comment on whether it would be useful, in lieu of a skin notation to add the following statement in the “further information” column of each end use where we find nPB acceptable with restrictions: “EPA recommends the use of personal protective equipment, including chemical goggles, flexible laminate protective gloves and chemical-resistant clothing, when using nPB.”

EPA also considered the potential health effects of contamination of nPB formulations with isopropyl bromide

(iPB).

In the June 2003 proposed rule, we proposed as a use condition that nPB formulations contain no more than 0.05% iPB by weight. One commenter opposed the proposed use condition, stating that it places an undue legal burden on end users, rather than the manufacturers of raw materials, that it would not benefit worker safety, and that the nPB industry has worked to reduce iPB content below 0.05% (Morford, 2003e). We agree that industry has met this contamination limit for several years without regulation. Furthermore, EPA agrees that if users are exposed to nPB concentrations no higher than the highest potentially acceptable concentration (30 ppm), a worker's exposure to iPB will be sufficiently low to avoid adverse effects. Therefore, this proposed rule does not include a use condition limiting iPB content in nPB formulations.

iPB is also referred to as 2-bromopropane, 2-propyl bromide, or 2-BP. Its CAS registry number is 75-26-3.

1. Workplace Risks

In the June 2003 NPRM, EPA proposed that an exposure limit of 25 ppm would be protective of a range of effects observed in animal and human studies, including reproductive and developmental toxicity, neurotoxicity, and hepatotoxicity. Reduction of sperm motility in rats, noted across multiple studies at relatively low exposures, was determined to be the most sensitive effect. The Agency derived an exposure limit of 18 ppm from a dose response relationship in male rat offspring (“F1 generation”) whose parents were exposed to nPB from prior to mating through birth and weaning of the litters (WIL, 2001). We then proposed to adjust this value upwards to 25 ppm based on principles of risk management, consistent with one of the original “Guiding Principles” of the SNAP program (59 FR 13046, March 18, 1994). As we discussed in the June 2003 NPRM, EPA noted that adhesives users should be able to achieve an AEL of 25 ppm and that 25 ppm was between the level based on the most sensitive endpoint (sperm motility in the F1 offspring generation at 18 ppm) and the second most sensitive endpoint (sperm motility in the F0 parental generation at 30 ppm). Following SNAP program principles, we noted that “a slight adjustment of the AEL may be warranted after applying judgment based on the available data and after considering alternative derivations” (69 FR 33295). Because the animals were exposed to nPB for some time periods that would not occur during actual occupational exposure, we stated further that “18 ppm is a reasonable but possibly conservative starting point, and that exposure to 25 ppm would not pose substantially greater risks, while still falling below an upper bound on the occupation[al] exposure limit.”

Since the 2003 proposal, the Agency has reviewed both information available at the time of the 2003 NPRM related to the health risks associated with nPB use, as well as more recent case studies of nPB exposures and effects in the workplace, newly published toxicological studies, comments to the June 2003 NPRM, including new risk assessments on nPB, and a new threshold limit value (TLV) issued by ACGIH.

OSHA has not developed a permissible exposure limit (PEL) for nPB that EPA could use to evaluate toxicity risks from workplace exposure. The ACGIH, an independent organization with expertise in industrial hygiene and toxicology, has developed a final workplace exposure limit of 10 ppm (ACGIH, 2005); however, as discussed below, EPA has concerns about the documentation and basis of ACGIH's derivation.

The Agency reconsidered which exposure levels are likely to protect against various health effects, based on review of all available information. We summarize benchmark dose data for a number of endpoints found in these analyses in Table 6 below. We examined these data to assess the acceptability of nPB use in the aerosol solvent, adhesive and coatings end uses reviewed in this proposed rule. These data indicate that, once uncertainty factors are applied consistent with EPA guidelines, the lowest levels for acceptable exposures would be derived for reproductive effects.

The data indicate that levels sufficient to protect against male reproductive effects (e.g., reduced sperm motility) would be in a range from 18 to 30 ppm,

in the range of 17 to 22 ppm to protect against female reproductive effects (e.g., number and length of estrous cycles), and at approximately 20 ppm for effects related to reproductive success (live litter size).

By EPA guidelines, we would apply an uncertainty factor of −10, or approximately 3, for differences between species for all health effects. We would also apply an uncertainty factor of √10 (3) for variability within the working population for reproductive and developmental effects, because, among other reasons, these conditions would not necessarily screen out an individual from being able to work, unlike for liver or nervous system effects. Therefore, for reproductive and developmental effects, we use a composite uncertainty factor of 10. See further discussion of uncertainty factors in section V.C. below.

Based on WIL, 2001, as analyzed in ICF, 2002. The equivalent values based upon Stelljes and Wood's (2004) analysis of WIL, 2001 would be slightly lower, from 16 to 28 ppm.

Table 6.—Summary of Endpoints Using Benchmark Response Modeling

Endpoint

Study

Benchmark

dose

lowerbound

(BMDL)

(ppm)

Human

equivalent

concentration

(HEC)

(ppm)

Liver Effects

Liver vacuolation in males (F

offspring generation)

WIL, 2001 as analyzed in ICF, 2002

110

116

Liver vacuolation in males (F

parent generation)

WIL, 2001 as analyzed in ICF, 2002

143

150

Liver vacuolation

ClinTrials, 1997b as analyzed in ICF, 2002 and Stelljes & Wood, 2004

226

170

Reproductive Effects—Male

Sperm motility (F

offspring generation)

WIL, 2001 as analyzed in ICF, 2002

WIL, 2001 as analyzed in Stelljes & Wood, 2004

169

156

177

164

Sperm motility (F

parent generation)

WIL, 2001 as analyzed in ICF, 2002

WIL, 2001 as analyzed in Stelljes & Wood, 2004

282

263

296

276

Prostate weight (F

parent generation)

WIL, 2001 as analyzed in TERA, 2004

190

200

Sperm count

Ichihara

et al.

, 2000b as analyzed in Stelljes & Wood, 2004

232

325

Sperm deformities (F

parent generation)

WIL, 2001 as analyzed in Stelljes & Wood, 2004

296

311

Reproductive Effects—Female

Number of estrus cycles during a 3 week period (F

parent generation)

WIL, 2001 as analyzed in ICF, 2006

162

208

170

218

Estrous cycle length (F

offspring generation)

WIL, 2001 as analyzed in TERA, 2004

400

420

Estrous cycle length (F

parent generation)

WIL, 2001 as analyzed in TERA, 2004

210

220

No estrous cycle incidence (F

offspring generation)

WIL, 2001 as analyzed in TERA, 2004

180

189

No estrous cycle incidence (F

parent generation)

WIL, 2001 as analyzed in TERA, 2004

480

504

Reproductive Effects—Reproductive Success

Decreased live litter size (F

offspring generation)

WIL, 2001 as analyzed in TERA, 2004

190

200

Decreased live litter size (F

offspring generation)

WIL, 2001 as analyzed in TERA, 2004

170

179

Pup weight gain, post-natal days 21 to 28 (F

offspring generation)

WIL, 2001 as analyzed in TERA, 2004

180

189

Developmental Effects

Fetal body weight

WIL, 2001 as analyzed in TERA, 2004

310

326

Fetal body weight

WIL, 2001 as analyzed in CERHR, 2002a

305

320

Nervous System Effects

Hindlimb strength

Ichihara

et al

, 2000a as analyzed in Stelljes and Wood, 2004

214

300

Unless explicitly stated, data are from a parental generation. Of the studies analyzed, only the WIL, 2001 study has multiple generations to be analyzed.

The benchmark response value represents a specified level of excess risk above a control response.

When considering workplace exposures, the human equivalent concentration is the BMDL, adjusted to apply to a 40-hour work week in which workers are exposed for 8 hours a day for five days per week. Animals in the WIL, 2001 study were exposed for 6 hours a day, 7 days a week. Animals in the Ichihara, 2000a and 2000b studies were exposed for 8 hours a day, 7 days a week. Animals in the ClinTrials, 1997b study were exposed for 6 hours a day, 5 days a week.

After applying an uncertainty factor of 3 for animal to human extrapolation, acceptable levels of exposure to protect against liver effects would be in the range of 39 to 57 ppm.

Omits data from those animals that have stopped estrous cycling altogether (TERA, 2004).

2. General Population Risks

EPA used a community exposure guideline of 1 ppm to assess potential risks to the general population living near a facility using nPB (see section V.E below). Of the end uses covered in this rule, use of nPB-based adhesives would result in the highest exposure levels, and so, we first examined general population exposure from adhesives. ICF Consulting modeled inhalation exposure to nPB to people living near a plant using nPB-based adhesives in several scenarios using the Agency's SCREEN3 model (US EPA, 1995b). Based on this modeling, EPA found that the exposure to individuals in the general population was below the community exposure guideline. The analysis indicates that nPB is no greater a hazard to the general population than other acceptable solvents under the SNAP program. For further discussion, see the risk screen for nPB (ICF, 2006a).

Representatives from a state environmental agency and from a potential user of nPB have asked EPA whether we had developed a reference concentration (RfC). We clarify that the community exposure guideline is a value developed by the SNAP program for our risk assessment of nPB following EPA's RfC Guidelines. However, it is not a formal RfC developed by EPA's National Center for Environmental Assessment and is not in IRIS. At this time, EPA does not have plans to issue an official RfC for nPB.

V. How did EPA assess impacts on human health?

A. Newly Available Exposure Data

Since publication of the June 2003 NPRM, EPA has received additional information on exposure levels in each end use discussed in this proposal.

In the adhesives end use, we considered new exposure modeling based on information from site visits to facilities using spray adhesives (ICF, 2006a). These data predicted that:

• At average rates of ventilation and adhesive application, average workplace exposures would be approximately 60 ppm.

• Average adhesive application rates and poor ventilation rates resulted in average exposures of approximately 250 ppm.

• High (90th percentile) adhesive application rates and average ventilation rates resulted in average exposures of approximately 600 ppm.

• In the worst case scenario with high adhesive application rates and poor ventilation, average workplace exposures would be as high as 2530 ppm.

We compared the modeled data in the four exposure scenarios to measured exposure data in three health hazard evaluations by the National Institute for Occupational Safety and Health (NIOSH) (NIOSH 2002a, 2002b, 2003a).

Our understanding is that North Carolina OSHA received complaints from workers and requested that NIOSH evaluate health hazards at these three facilities. NIOSH found average exposure levels of 68 ppm, 116 ppm, 127 ppm, and 195 ppm for sprayers actively using the adhesive prior to installation of state-of-the-art ventilation systems (NIOSH 2002a, 2002b, 2003a). The plant with an average exposure level of 68 ppm for sprayers (9 samples) had an average exposure level comparable to the average concentration of 60 ppm in the modeling scenario with average adhesive rates and average ventilation levels. The other plants with average exposure levels of 116 to 127 ppm (20 samples), and of 195 ppm (36 samples) for sprayers had exposure levels between the average modeled exposure for a facility with average adhesive application rates and average ventilation (60 ppm) and the average modeled exposure for a facility with average adhesive application rates and poor ventilation (250 ppm). Based on this comparison, EPA believes the modeled exposure levels are a reasonable predictor of actual exposure based on current industry practice in the adhesive end use.

In the aerosol solvent end use, we received a study on workplace exposure levels of nPB-based aerosols from a commenter (Linnell, 2003). This study was performed to simulate typical exposure levels in a number of situations where nPB might be used in the workplace while using different types of ventilation equipment, rather than using data from current industry users of nPB-based aerosols in their actual manufacturing or maintenance processes. As discussed below in section VI.A., we are concerned that the exposure data and ventilation levels in this study may not be representative of use of nPB-based aerosols in industry. Personal breathing zone samples taken from the collars of workers showed 8-hour time-weighted average (TWA) exposures of 5.5, 13, and 32 ppm for workers using 310 g of nPB from a spray can

(Linnell, 2003). The two higher exposure levels occurred in the absence of any local or regional ventilation; the use of both local and regional ventilation equipment with ventilation levels around 1900 ft

/min was associated with the lowest exposure level. Short-term exposures of 370, 1,100 and 2,100 ppm taken from a room with regional ventilation at 640 cubic feet per minute (cfm), when averaged over an 8-hour period, resulted in exposures of 12, 34, and 66 ppm (Linnell, 2003). EPA considers the highest of these 8-hour values, 66 ppm, not to be representative of worker exposure from inhalation because the measurement was taken from the worker's wrist, rather than from his breathing zone. Another short-term exposure value of 190 ppm, taken from a vented booth with local ventilation at 472 cfm, in addition to the regional ventilation of 640 cfm, resulted in an 8-hour exposure of 6 ppm. Similar measurements were made in another study we considered in developing the June 2003 NPRM: Eight hour (8-hr) TWA exposures of 11.3, 15.1, 17.0, and 30.2 ppm with regional ventilation of 300 cubic feet per minute from a fan for the entire room (Confidential submission, 1998).

Unlike samples measured directly in the breathing zone, area samples measured in the study are not considered representative of actual exposure and are not discussed here. Short-term measurements taken over 15 minutes from personal samplers, although in some cases extremely high, are not discussed in detail here because available toxicity information does not indicate need for a short-term exposure limit for nPB in addition to the 8-hr TWA limit (ACGIH, 2005; ERG, 2004). Additional information on these other samples is in the occupational exposure assessment for aerosols in the risk screen for nPB (ICF, 2006a).

Another commenter submitted information on aerosol exposures for a number of other available alternative aerosols (Werner, 2003). While these data do not include nPB, based on the properties of aerosol solvents, we believe it is reasonable to compare concentrations of these different chemicals to potential nPB exposures. The study compared concentrations of eight different chemicals that are acceptable under the SNAP program in aerosol formulations: HFE-7100, HFE-7200, trans-1,2-dichloroethylene, HCFC-225ca and -225cb, acetone, pentane, and HFC-134a. In this study, with ventilation of only 48 cfm, 8-hr TWA exposure from the different chemicals varied from 35.5 ppm to 194.0 ppm,

below the recommended exposure levels for these particular chemicals (ICF, 2006a) but above the range of exposure levels that EPA would consider acceptable for nPB.

These measurements can be converted to estimates of nPB exposure by multiplying the measured concentration of the alternate chemical by the molecular weight of the same alternate chemical and dividing this by the molecular weight of nPB, 123. After performing this calculation, the equivalent exposure levels for nPB vary from 29.5 ppm to 394.4 ppm.

In addition, we considered new information from modeling of nPB exposures (ICF, 2006a). The modeling examined exposure levels that would be expected at ventilation levels of 450 cfm, 625 cfm, and 1350 ppm, considering the molecular weight of the compound and the composition of different aerosol blends. EPA's SNAP program has previously used these same levels to calculate potential aerosol exposures, based upon exposure levels expected during benchtop cleaning. In a space with an air exchange rate of 450 ft

/minute or less,

EPA's modeling predicts 8-hour average exposure of approximately 16 to 17 ppm if a user sprays 450 g of nPB (approximately 1 lb),

and corresponding higher exposure values at higher spray rates (e.g., 33 ppm if the amount of nPB sprayed is 900 g) (ICF, 2006a). Exposure values were predicted to be lower at higher ventilation rates.

This corresponds roughly to a regional or room fan at low levels or natural air currents in an open area. Confined areas would have even lower air exchange rates with higher exposure levels.

We consider use of 1000 g/day to be the high end of typical use, based on the setup of one of the exposure studies (Confidential Submission, 1998). The typical aerosol solvent user in the electronics industry uses a can per day (Williams, 2005). This is comparable to or slightly less than the spray rate assumed in the modeling.

Since the June 2003 NPRM, EPA received a new submission for nPB in coatings (Lake City Army Ammunition Plant, 2003). The Lake City Army Ammunition Plant provided data on workplace exposure to nPB (Lake City Army Ammunition Plant, 2004). The mean exposure at this facility was 3.7 ppm. Out of 31 samples taken, 25 (approximately 80%) were below 5 ppm. Only one of 31 samples had an exposure level above 10 ppm, and that exposure value was approximately 21 ppm.

B. Newly Available Data on Health Effects

Since publication of the June 2003 NPRM, EPA has examined additional occupational (Table 7) and animal (Table 8) studies that have become available:

Table 7.—Recent Studies on

PB Occupational Exposure

Case Study

Sample size/population

Exposure data

Observations

Remarks

Beck and Caravati, 2003

6 foam cushion factory workers (gluers)

Exposure during 30-40 hr/wk for a 3-month period. Exposure measured in one day was a mean of 130 ppm (range, 91-176 ppm)

Lower leg weakness accompanied by pain and difficulty with standing and walking, numbness of legs and feet, hyperreflexia and hypertonicity of lower extremities, dizziness and shortness of breath, and peripheral neurotoxicity. Measured serum bromide levels were elevated, range 44-170 mg/dL

Small sample size studied. Possible interference or synergistic effects from other adhesive ingredients (1,2-epoxybutane and styrene-butadiene).

Majersik

et al.

, 2004; Majersik

et al.

, 2005 *

6 foam cushion factory workers (gluers)

5-8 hr/day for at least 2 years with mean air concentration of 130 ppm on last day of study. Measurements taken over 9 hours (equivalent to 92-127 ppm with mean of 108 ppm for an 8-hour TWA)

Subacute onset of lower extremity pain, difficulty walking, and high serum bromide levels in blood. Neurotoxic symptoms persisted for at least 2 years after exposure ended

Follow-up to Beck and Caravati (2003). Chronic nPB exposure associated with incapacitating neurotoxic syndrome. Initial report from Utah OSHA indicated erroneously that workers were not spraying while measurements were taken. In fact, adhesives were being sprayed and fans were being used only for portions of the day that measurements were taken, making measurements likely to be representative of conditions during the past several months at the plant.

Ichihara

et al.

, 2004a

37 chemical plant workers (24 males and 13 females)

12 hour shifts over 2-day period, mean concentration of 82 ppm (range, 0-170 ppm)

Mucosal irritation (nose, throat), headache, dizziness, constipation, intoxication, and feeling light-headed or heavy-headed. Four female workers complained of disruption or cessation of menstruation. No severe chronic symptoms of neurological damage at less than 170 ppm. Several workers had hemoglobin and hematocrit values outside of the normal range and were diagnosed with mild anemia; most of these cases also showed signs of iron deficiency

Inadequate exposure characterization and exposure to other potential toxicants, small sample size, and no appropriate control group. Healthy worker effect possible, where more sensitive workers left the factory between 1996 and 1999.

Ichihara

et al.

, 2004b

27 female chemical plant workers (23 age matched with 23 females from a beer factory control group)

1-day exposure period, range of exposure, 0.34-49 ppm

Responses indicated anxiety, fatigue, confusion, tension, and depression. Changes in menstrual status but not statistically significant. Effects on peripheral and central nervous system—diminished vibration sensation of the foot; significantly longer distal latency in the tibial nerve; decreased values in sensory nerve conduction velocity in the sural nerve; and lower scores on memory and perceptual tests. No comparable effects seen in control group

No long-term exposure measurements, small sample size; lack of controls for age, height, and body-weight. Low B vitamin levels in normal range in some workers but researchers concluded this did not cause observed neurological effects. Additionally, the study did not indicate any significant differences in the prevalence of menstrual cycle abnormalities.

Nemhauser, 2005 *

Foam cushion factory workers (gluers) in North Carolina

In 1999 study, 16 workers exposed to mean air concentration of 116 ppm, and 12 sprayers exposed to mean concentration of 108 ppm with range of 58 to 254 ppm. In 2001 study, 13 workers exposed to nPB mean air concentration of 46 ppm and 12 sprayers were exposed to mean concentration of 101 ppm, with range of 38 to 281 ppm

Higher exposure to nPB and dose-dependent relationship among those who reported anxiety, headache, and ataxia. No reproductive abnormalities reported in medical survey for men or women. Semen analysis found no differences between exposed and unexposed workers

Small sample sizes studied with moderate worker participation. Healthy worker effect likely occurred: Those that had most significant health effects had already removed themselves from workplace by the time of the study. No arsenic found at the plant. Neurotoxic effects caused by nPB. See related Health Hazard Evaluation (HHE): NIOSH, 2003a.

NIOSH, 2003a

16 workers in 1999 evaluation; 13 workers in 2001 follow-up evaluation

1999 Initial Site Visit: Geometric mean nPB concentration (from personal samples), 81.2 (range, 18-254 ppm); 2001 follow-up: Geometric mean, 81.2 ppm (range, 7-281 ppm)

Most workers exposed to nPB levels > 25 ppm. Exposure concentrations lower in 2001 than 1999, but difference not statistically significant. Headache, anxiety, feeling drunk associated with nPB exposure. Hematological endpoints unaffected in exposed group. No correlation of nPB exposure with sperm or semen indices or with neurological abnormalities

Arsenic was not attributed to occupational exposure. The National Institute for Occupational Safety and Health (NIOSH) stated that neurological symptoms may have been related to excess exposure to nPB, but that no other effects could conclusively be related to nPB exposure.

Raymond and Ford, 2005 *

4 foam cushion factory workers (gluers) in North Carolina

Exposure study conducted 9 months after index patient became ill indicated workers exposed to mean nPB air concentration of 116 ppm. 4 workers exposed for 2-3 weeks before initial symptoms detected

Dizziness, numbness, ocular symptoms, lower extremity weakness and unsteady gait, weakness, hypesthesia, and ataxic gait in all four workers. Symptoms decreased over time but after six years, at least one worker re-exposed twice at other furniture plants; one or more still suffer from ataxia

Small sample size, possible confounding effect from arsenic.

Toraason

et al.

, 2006

41 and 22 foam cushion factory workers (gluers) at 2 facilities

1-3 days up to 8 hrs per day, with concentrations of 0.2-271 ppm at facility A, 4-27 ppm at facility B

No statistically significant differences in DNA damage with worker's nPB exposure. In vitro results showed nPB increased DNA damage

Authors find limited evidence that nPB poses a “small risk” for DNA damage.

* Presentation at North American Congress of Clinical Toxicology on September 14, 2005.

Table 8.—Recent Animal Studies of

PB Effects

Citation

Population/sample size

Exposure

Observations

Comments

Fueta

et al.

, 2002

24 male Wistar rats (12 control, 12 exposed)

6 hr/day, 5 day/wk for 8 weeks at 700 ppm

No apparent morphological defects in the brain

Only one exposure concentration was used (which is higher than the level already associated with other toxic effects in rodents [400 ppm]) and a shorter exposure duration (8 weeks) was used than the other subchronic studies that have shown effects (13 weeks).

Fueta

et al.

, 2004

58 male Wistar rats (29 experimental and 29 in control group)

6 hr/day, 5 day/wk for 4 to 8 weeks, 700 ppm

No apparent morphological defects in the brain. Chronic inhalation changes brain enzyme levels and electrical activity that is reversible after exposure

Unclear how nPB and/or its metabolites directly act on receptors or channels in the brain.

Furuhashi

et al.

, 2006

80 Wistar rats (pups and their dams)

(1) 8 hr/day (4 hr, followed by 2.5-hr rest period, followed by 4 hr exposure), 7 day/wk during gestation and nursing at 0, 100, 400, 800 ppm in first experiment

(2) Dams exposed (800 ppm) during gestation (Group A), offspring not exposed during nursing. Offspring of Group (B) of unexposed dams were nursed by exposed dams. Offspring in control groups C and D not exposed

(1) At 800 ppm: most rat offspring died within 2 days of birth or in utero;. body weights of dams significantly lower, organ weights of offspring significantly lower after weaning at 800 ppm in males, and 800 and 400 ppm in females. Most sperm and estrous indicators did not differ among the groups, although the rate of sperm arrival to the cauda epididymis was significantly lower in the 400 ppm group. Inconsistent or no changes in biochemical indicators

(2) Second experiment No difference in body weights and pregnancy endpoints between exposed (800 ppm) and unexposed dams. Live offspring at birth, survival rates, body weights, significantly decreased, number of dead offspring, significantly increased in 800-ppm groups

Authors concluded that exposure to nPB during pregnancy and lactation adversely affects growth and survival of offspring. Low numbers of offspring in 400- and 800-ppm exposure groups prevent statistical testing

EPA comments: Study design inconsistent with guidelines for developmental studies, so comparisons to previous studies are difficult. The mechanism for the adverse effects observed is not known (e.g., indirect exposure through milk, changes in nursing behavior, changes in milk production, exposure in utero, changes in the intrauterine environment)

Honma

et al.

, 2003

Fisher 344 male rats

8 hr/day, 7day/wk for three weeks exposed to 0, 10, 50, 200 or 1000 ppm (5 rats/dosage and 5 different tests)

3 week exposure to greater than 50 ppm temporarily increased locomotor activity and ambulatory and rearing behaviors in male rats

Neurological effects shown to be transient and reversible at ≥ 200 ppm (Ichihara

et al.

, 2000) or absent after 28 days of exposure at concentrations ≥ 400 ppm (ClinTrials, 1997a) or after 90 days of exposure at concentrations up to 600 ppm (ClinTrials, 1997b) in other studies. Human studies are limited by co-exposures and poor estimates of exposure concentrations. Thus, EPA is not using this endpoint as the basis of an AEL.

Ishidao

et al.

, 2002

30 male Wistar rats

6 hr/day, 5 day/wk with test groups (10/dose) exposed to 700 ppm for 4 and 12 weeks and 1500 ppm for 3 and 4 weeks

nPB is metabolized rapidly in the rat following exposures to nPB at concentrations ≥ 700 ppm for at least 3 weeks

Exposure levels are higher than in some other studies and are much higher than concentrations seen in the workplace. nPB metabolism appears to be different following multiple exposures as compared to acute exposures (see RTI, 2005; ICF, 2006b).

NTP, 2003

Female and male B6C3F1 mice and Fischer 344 rats

0, 62.5, 125, 250, 500 (rats and mice), 1000 (rats) ppm for 90 days

Early mortality in mice at 500 ppm accompanied by liver and lung cell degeneration and cytoplasmic vacuolization. Cytoplasmic vacuolization also in rat liver cells ≥ 250 ppm (males) and ≥ 500 ppm (females), with increased severity at higher doses. No adverse central nervous system (CNS) effects or histopathology reported

Unpublished study. Conclusions drawn from a review of raw data from the National Toxicology Program (NTP) Web site. In general, the severity of effects (in non-reproductive organs) is slightly higher at lower concentrations in male rats than in females.

RTI, 2005/Garner

et al.

, 2006

Female and male B6C3F1mice and Fisher 344N rats, four to six animals in each test trial

Exposure via several injection routes (intraperitoneal, intravenous, cannuliz-ation), inhalation, and dermal. Injection conducted via bolus dosing at 5, 20, or 100 mg/kg body weight. Inhalation concentrations of 70, 240, 800, and 2700 ppm administered in a single acute exposure. A dose of 96 mg/kg was applied to a shaved area on the backs of six male rats with a non-occlusive charcoal filter covering (that is, one that does not prevent evaporation)

nPB cleared by mice after 48 hours as follows: 45% as volatiles in the breath, 28% as CO

in the breath, 26% in urine, <3% in feces, and 2% retained in the body. Distribution was similar in male rats, although amounts in urine and volatiles in breath were higher in mice. At higher doses, the amount of nPB excreted in urine and as CO

decreased, with a much greater change in rats compared to mice

• After pretreatment with a cytochrome P450 inhibitor, a decrease in nPB cleared as CO

(80%) and urine (40%); pretreatment with a glutathione inhibitor reduced nPB cleared as CO

by 10% and urine by 4%

• The Vmax, a measure of the maximum initial rate of an enzyme-catalysed reaction, is 0.227 for male rats, 0.143 for female rats, 0.329 for male mice and 0.234 for female mice. Half-lives were comparable between males and females at ≤ 800 ppm

• For rats exposed to nPB through skin, 37% of the dose was excreted in volatiles, 1.2 % in urine, 1.7% as CO

, and 35.7% was on the applicators or in the skin washes. Only 0.32% remained in tissues. Airborne concentrations of nPB in the chamber were 4 to 10 ppm after dosing

The study authors concluded that:

• nPB administered via intraperitoneal injection or inhalation is eliminated mostly through the breath, with urine as a secondary path.

• Metabolism of nPB appears to be primarily through cytochrome P450 enzymes (CYP2E1), particularly in mice; glutathione conjugation still plays an important role in rats.

• At high concentrations, female rats may have a decreased capacity to metabolize nPB compared to male rats.

• nPB decreases glutathione levels in the liver after a one-time exposure to nPB at concentrations as low as 70 ppm.

• nPB is not appreciably absorbed (~3-27%) in rats following dermal application.

EPA agrees with these points, except we found that gender differences were only apparent in rats at very high concentrations (2700 ppm and greater). We also note that:

• Inhalation tests were only one-time exposures at very high concentrations (240 to 2700 ppm), and thus, are not comparable to long-term dosing at the lower levels expected in the workplace.

• Results of dermal testing are not conclusive because of potential for inhalation exposure.

Sohn

et al.

, 2002

40 male and 40 female Sprague-Dawley rats

6 hr/day, 5 day/wk for 13 weeks, test groups (10/sex/dose) were exposed to 0, 200, 500 or 1250 ppm

No effects on mortality, activity, weight gain, food consumption, urinalysis, or histological effects in the brains and spinal cords

The differences between the various studies may be due to variability in exposure methodology and achieved concentrations of nPB.

Stump, 2005*

125 female/125 male rats in first generation and 100 female/100 male rats in offspring generation

Both test groups of 25 male rats/ 25 female rats exposed to 0, 100, 200, 250, 500 and 750 ppm nPB for 10 weeks

Decreased litter size at 250 and 500 ppm in both generations. Decreased fertility at 100 and 250 ppm in offspring generation

Complete infertility at 750 ppm.

Reproductive effects seen in both rat sexes which is a strong signal of reproductive toxicity potential in humans. The author considers 100 ppm to be a lowest observed adverse effect level (LOAEL). This is a presentation of data from WIL, 2001.

Wang

et al.

, 2003

36 male Wistar rats

8 hr/day, 5 day/wk for 12 weeks, test groups ( 9 rats) were exposed to 0, 200, 400 or 800 ppm

Decrease in creatine kinase in the spinal cord (17% at ≥ 200 ppm) and brain (15-28% at ≥ 400 ppm) at 200, 400, and 800 ppm. No physical or behavioral changes observed

Small study size. No behavioral changes or physical symptoms were observed in the animals, so the toxicological relevance of the decrease in creatine kinase is questionable.

Yamada

et al.

, 2003

40 female Wistar rats

8 hr/day, 7 day/wk with test groups (9/dose) exposed to 0, 200, 400, or 800 ppm for 12 weeks

All rats at 800 ppm became seriously ill after 7 weeks of exposure. Significant decrease in antral follicles at ≥ 200 ppm, and a decrease in the number of female rats exhibiting regular estrous cycles in 400-ppm females during 7-9 weeks of exposure and at 2-3 weeks at the 800-ppm dose

Data suggest that nPB is affecting the maturation of ovarian follicles. A no observed adverse effect level (NOAEL) of 200 ppm is identified with a LOAEL of 400 ppm for the changes in estrus cycles.

* Presentation at North American Congress of Clinical Toxicology on September 14, 2005

• In general, the recent animal studies collectively show a range of effects associated with nPB exposure that are qualitatively consistent with previously published findings. (Exceptions to this are the negative results regarding central nervous system toxicity in the NTP (2003) study and the Sohn (2002) study on rats.) Some general conclusions we draw from the new studies include:

• Case reports of nPB exposure in the workplace indicate that severe, possibly irreversible, neurological effects may occur at sustained concentrations of approximately 100 ppm or greater (Beck and Caravati, 2003; Majersik

et al

, 2004; Majersik

et al.

, 2005; Ichihara

et al.

, 2002a; Miller, 2005; Raymond and Ford, 2005). In other cases, similar or higher concentrations up to 170 ppm caused less severe nervous system effects (Nemhauser, 2005; NIOSH, 2003a; Ichihara, 2004a). Some neurological effects occurred in workers at levels of less than 50 ppm (Ichihara

et al.

, 2004b). Because of design and methodological limitations, such as small numbers of subjects and limited exposure information, these studies do not provide a sufficient quantitative basis to derive an acceptable exposure limit.

• Data on female rats indicate that nPB affects the maturation of ovarian follicles and the ovarian cycle (Yamada

et al.

, 2003), consistent with previously reviewed data (WIL , 2001; Sekiguchi

et al.

, 2002).

• Some data on occupation exposure suggest that workers exposed to nPB may have experienced menstrual disorders (Ichihara

et al.

, 2002; Ichihara

et al.

, 2004b). However, the data are not statistically significant and are not sufficient to conclude that nPB exposure caused these female reproductive effects.

• Data on DNA damage in workers exposed to nPB was not statistically significant (Toraason

et al.

, 2006).

• Metabolic data on mice and rats indicate some species differences. Metabolism of nPB appears to be primarily through cytochrome P450 enzymes, particularly in mice; glutathione conjugation also plays a role, and a bigger role for rats than for mice (RTI, 2005).

• New data from toxicological studies on nervous system effects remain inconsistent and equivocal concerning the level at which nervous system effects occur (Fueta

et al.

, 2002; Fueta

et al.

, 2004; Honma

et al.

, 2003; Ishidao

et al.

, 2002, NTP, 2003; Sohn

et al.

2002, Wang

et al.

, 2003).

A number of commenters on the June 2003 NPRM suggested that EPA should consider neurotoxicity as the endpoint in deriving an AEL for nPB (Linnell, 2003; Werner, 2003; Rusch and Bernhardt, 2003, Rusch, 2003). In particular, they requested that EPA consider the study conducted by Wang (2003) and epidemiological data on neurotoxic effects of nPB. As discussed above, the data on neurotoxic effects of nPB on workers are limited and are not sufficient to determine acceptable levels of exposure. In the study on rats by Wang

et. al.

(2003), measurements found a decrease in enzymes in the spinal cord and brain at 200, 400, and 800 ppm, but the animals displayed no physical or behavioral changes. Because of the lack of physical symptoms or behavioral changes, EPA does not believe that the decrease in enzyme levels in the central nervous system are toxicologically relevant. Other studies examining neurological effects of nPB showed those effects to be transient and reversible at and above 200 ppm (Ichihara

et al.

, 2000a). Exposures of 200 ppm and above for three weeks had no effect on memory, learning function, or coordination of limbs (Honma, 2003); the effect of spontaneous locomotor activity seen in this study at 50 ppm and above was not considered adverse by the authors. In other studies, neurological effects were absent after extended periods of exposure-after 28 days of exposure at concentrations> 400 ppm (ClinTrials, 1997a) and after 90 days of exposure at concentrations up to 600 ppm (ClinTrials, 1997b). Thus, although neurological effects have been associated with nPB exposure, the data are currently insufficient to quantify and determine acceptable exposure levels based on this endpoint.

One commenter on the June 2003 NPRM requested that EPA evaluate a study by Yamada

et al.

(2003), a study published just prior to the June 2003 NPRM. In response to the comment, EPA reexamined Yamada

et al.

, 2003 and re-evaluated the literature (Ichihara

et al.

, 1999, 2002, 2004a,b; Sekiguchi, 2002, Yamada

et al.

, 2003; WIL, 2001) to assess potential reproductive toxicity in females (ICF, 2006a, Att. A). A peer review of these effects is in the public docket (ICF, 2004b). Multiple benchmark analyses found a statistically significant decrease in the number of estrous cycles and increase in estrous cycle length associated with nPB exposure, consistent with other reproductive endpoints, namely reductions in sperm motility, decreased live litter size, and change in prostate weight (ICF, 2002a; ICF, 2006a; Stelljes and Wood, 2004; TERA, 2004).

Reproductive effects are seen in males, females, and offspring, and in different generations of the two-generation study (WIL, 2000). They also are consistent with results seen in one-generation reproductive studies, such as Ichihara

et al.

(2000b) and Yamada (2003). See Table 6 above in section IV.E.1. for a more complete list of the different health effects. EPA believes that the preponderance of the data indicate that exposure levels sufficient to protect against male reproductive effects (

e.g.

, reduced sperm motility) would be in a range from 18 to 30 ppm, in the range of 17 to 22 ppm to protect against female reproductive effects (

e.g.

, number and length of estrous cycles), and at approximately 20 ppm for effects related to reproductive success (live litter size). We have not determined what specific level within those ranges (an overall range of 17 to 30 ppm) is most appropriate for evaluating whether a substitute may be used safely and consider these exposure levels to be potentially acceptable. Therefore, we assessed the acceptability of nPB by considering whether it could be used safely in the three end-uses. For end-uses with likelihood of exposures above the range we are considering, while following typical industry practices, we are proposing an unacceptability determination. For end-uses that as their normal practice meet exposure levels below the range we are considering, we are proposing an acceptability determination. It is not necessary for 100% of exposure data for an end use to be above or below the range of 17 to 30 ppm in order to make a determination on the acceptability of an end use because there may be occasional cases that are not following common industry practices. Unusual events would not indicate the industry's likelihood of keeping exposures at safe levels, and thus, should not be the determining factor in our decision. Rather, we consider the overall likelihood that typical industry use would consistently result in acceptably low or unacceptably high exposures.

In the June 2003 NPRM, EPA used a BMDL of 169 ppm as a point of departure for developing an AEL. Some commenters stated that data from the F1 generation is inappropriate for calculating occupational exposure, citing statements from toxicologists, such as, “occupational exposure involves adults only.” They also stated that EPA has not required this for other chemicals and that the resulting value is more conservative than what is normal and appropriate for industrial toxicology (Morford, 2003f, Ruckriegel, 2003). Others stated that sperm motility effects on the F1 generation are appropriate to consider (Risotto, 2003; Farr, 2003), particularly because of the

potential for

in utero

effects and because of the consistent presence of these reproductive effects in both generations and at multiple levels. EPA acknowledges that using data from the F1 offspring generation may be conservative because the pups in the F1 generation were exposed to nPB between weaning and sexual maturity (WIL, 2001). During occupational exposure, this period of exposure would not occur because children under age 16 are not allowed to work in industrial settings. However, EPA believes that because of the potential for

in utero

C. Evaluation of Acceptable Exposure Levels for the Workplace

To calculate acceptable exposure levels for nPB, EPA uses standard risk assessment methods delineated in Agency guidance (U.S. EPA, 1994b) in evaluating data, choosing a benchmark dose level or a NOAEL, and making the adjustments and uncertainty factors prescribed to account for differences in the duration of exposure and in sensitivity between and within species.

Adjustment for Occupational Exposure Pattern

To account for differences between the exposure pattern used in the WIL study (6 hours per day for 7 days per week) when compared to a typical workweek of 8 hours per day and 5 days a week, a “human equivalent concentration” (HEC) is first calculated by adjusting the benchmark dose level:

(BMDL in ppm × 6 hours/8 hours) × 7 days/5 days = HEC (ppm)

HECs for the major health endpoints are shown in Table 6 above in section IV.E.1.

Uncertainty Factors

According to EPA risk assessment guidance for reference concentrations (RfC) (EPA 1994a), uncertainty factors of up to 10 may be applied to the HEC for each of the following conditions:

(1) Data from animal studies are used to estimate effects on humans;

(2) Data on healthy people or animals are adjusted to account for variations in sensitivity among members of the human population (inter-individual variability);

(3) Data from subchronic studies are used to provide estimates for chronic exposure;

(4) Studies that only provide a LOAEL rather than a NOAEL or benchmark dose; or

(5) An incomplete database of toxicity information exists for the chemical.

EPA believes that two uncertainty factors are appropriate for this database to account for that: (1) Physiological differences between humans and rats; and (2) variability within the working population. The rationale for the use of these two uncertainty factors is described below.

EPA RfC guidelines state that an uncertainty factor of 10 may be used for potential differences between study animals and humans. This factor of 10 consists in turn of two uncertainty factors of 3—the first to account for differences in pharmacodynamics

and the second to account for differences in pharmacokinetics

between the study of animal and humans. (The value of three is the square root of 10 rounded to one digit, with 10 representing an order of magnitude (EPA,1994a). In practice, EPA uses the square root of 10 when there are two or four uncertainty factors of 3, yielding a total uncertainty factor of 10 or 100, and we use a value of 3 when multiplying by an uncertainty factor of 10). By EPA RfC guidelines (U.S. EPA, 1994b), no adjustment for differences in pharmacokinetics is necessary in this instance because the blood/air partition coefficient

for nPB in the human (7.1) is less than in the rat (11.7), indicating that the delivered dose of nPB into the bloodstream in rats is slightly higher than in humans. Consistent with Appendix J of EPA's RfC guidelines for an inhaled compound that exerts its effects through the bloodstream, EPA applies an uncertainty factor of 1 for pharmacokinetics.

Pharmacodynamics refers to the biochemical and physiological effects of chemicals in the body and the mechanism of their actions.

Pharmacokinetics refers to the activity or fate of chemicals in the body, including the processes of absorption, distribution, localization in tissues, biotransformation, and excretion.

The blood/air partition coefficient is the ratio of a chemical's concentration between blood and air when at equilibrium.

However, EPA recognizes that the lack of an uncertainty adjustment for pharmacokinetic differences between animals and humans rests on a default approach applied to category 3 gases described in Appendix J of its guidelines for deriving an inhalation RfC. This default approach assumes that nPB's toxicokinetics follow a model in which: (1) The toxicity is directly related to the inhaled parent compound in the arterial blood, and (2) the critical metabolic pathways scale across species, with respect to body weight, in the same way as the ventilation rate. Given the hypothesized metabolic pathways for nPB (ICF, 2002a; CERHR, 2002a), it is plausible that toxicity in rats may be related to a reactive metabolite in the target tissue rather than the blood level of the parent compound. EPA is not aware of any quantitative data on nPB metabolism in humans, or evidence implicating the biologically active agent or mode of action. Some commenters on the June 2003 NPRM stated that EPA should use an uncertainty factor of 1 or 2 to extrapolate from animals to humans (Weiss Cohen, 2003), while others suggested uncertainty factors of 2 or 3 for pharmacokinetics, or an overall uncertainty factor of 10 for rat to human extrapolation because of a lack of information on the metabolism and mode of action of nPB and because the rat is an insensitive model for effects on male reproduction in humans (Werner, 2003; Rusch and Bernhardt, 2003). Commenters provided no data to indicate that (1) the toxicity is not directly related to the inhaled parent compound in the arterial blood, or (2) the critical metabolic pathways do not scale across species, with respect to body weight, in the same way as the ventilation rate. Recent studies provide additional data regarding metabolism of nPB in rats and mice (RTI, 2005), but data on human metabolism are still lacking.

One analysis of these metabolic data suggested that mice are less sensitive to the effects of nPB than rats and hypothesized that humans would also be less sensitive than rats (Stelljes, 2005). However, this analysis makes numerous assumptions about toxic nPB metabolites and metabolic activation pathways that have not been confirmed by experimental data. A review of this

analysis is available in the public docket (ICF, 2006c). Despite the difference in metabolic pathways for nPB in mice and rats (RTI, 2005), EPA finds no significant species-specific differences in toxicity exist between rats and mice at inhaled concentrations <500 ppm for 13 weeks (NTP, 2003; ICF, 2006b). These metabolic and subchronic inhalation studies conducted under the National Toxicology Program did not specifically examine for reproductive toxicity or nPB metabolism in target organs that control reproductive function. In summary, there are little available data about the metabolic activation or reactive metabolites responsible for reproductive toxicity in rodents. Similarly, for nPB, there is little information available about differences and similarities between rodents and humans. Given this circumstance, EPA assumes, in the absence of evidence to the contrary, that nPB toxicity is directly related to the inhaled parent compound in the arterial blood and that the critical metabolic pathways scale across species in a manner similar to the ventilation rate. Therefore, the Agency is proposing to apply an uncertainty factor of 1 to account for interspecies differences in pharmacokinetics.

EPA requests additional data and comment from the public on the pharmacokinetics, metabolism, and mode of action of nPB that will help determine whether an interspecies uncertainty factor greater than the default value of 1 is warranted to account for pharmacokinetics. If data become available indicating that nPB does not conform to the constraints assumed by the default pharmacokinetic model in the RfC guidelines, we would revise our risk assessment for nPB as necessary, and apply an uncertainty factor for pharmacokinetics consistent with the RfC guidelines in extrapolating from animal to humans. Depending on the resulting difference in the acceptable exposure levels, we would also revise our acceptability determinations accordingly. Given the available data on the blood/air partition coefficient and EPA RfC guidance in the absence of other information, EPA is applying the same rationale used for other compounds reviewed under EPA's SNAP program with a comparable amount of data where an uncertainty factor of 1 for pharmacokinetics was applied. To account for uncertainty in pharmacodynamics of nPB, EPA is applying the default uncertainty factor of 3. This follows the procedures in EPA's RfC guidelines for situations where there are no data to compare pharmacodynamics in rats versus humans (U.S. EPA, 1994b). Recently published data on humans and rodents do not decrease the uncertainty regarding the pharmacodynamics of nPB; therefore, modification of the uncertainty factor of 3 for differences between species is not justified.

One commenter stated that EPA did not cite any data that describes the size, condition, or very existence of a subpopulation of men especially sensitive to the effects of nPB. In addition, this commenter asserted that sensitive populations are not traditionally considered when deriving an occupational exposure limit, and that EPA has never mentioned a concern with sensitive subpopulations in previous SNAP reviews.

EPA disagrees with the comments. There are preexisting reproductive conditions as well as significant variability in fertility among otherwise healthy adults in the workplace. Women over age 35 and men over age 40 have fertility rates up to three times lower than those of people in their twenties, with effects on the ovarian cycle and on sperm motility as major factors changing with increasing age for women and men, respectively (Dunson

et al.

, 2002). Adding damage from other factors, such as smoking or occupation exposure to chemicals such as nPB, therefore, can potentially harm an individual's ability to reproduce further (Dunson,

et al.

2002). In addition, we note that EPA has used uncertainty factors in the past to protect sensitive subpopulations on other chemicals reviewed under the SNAP program (e.g., trifluoroiodomethane at 69 FR 58907, October 1, 2004). For deriving AELs from health endpoints such as liver effects and neurotoxicity, the SNAP program typically has assigned an uncertainty factor of 1 for sensitive subpopulations because we assume that individuals who are especially susceptible to these effects will have greater difficulty working than most people. However, there is no connection between the ability to reproduce and the ability to work in the industrial sectors discussed in this rule. Thus, we find it appropriate to apply an uncertainty factor greater than 1 for reproductive effects.

Some commenters on the June 2003 NPRM said that an uncertainty factor of 1 is appropriate for variability within the working population because sensitive subpopulations will not be present in the working population (Stelljes, 2003, Morford, 2003f). Other commenters stated that there will be very little difference in variability between the worker population and the general population and that it is unclear why EPA selected an uncertainty factor of 3 instead of 10 (Werner, 2003). Commenters suggested uncertainty factors for variability in the working population of 1, 2, and 5 (Stelljes, 2003; Weiss Cohen, 2003; Werner, 2003).

EPA's RfC guidelines recommend an uncertainty factor of 10 to account for intraspecies variability within the general population. However, in deriving an acceptable exposure limit, EPA's focus is on worker exposure, which excludes some particularly vulnerable populations, such as children, most adolescents, and the elderly. Thus, we believe that a full uncertainty factor of 10, as for the general population, may be higher than necessary to protect workers. However, because of variability in reproductive function due to factors present among workers, such as aging, smoking, and sexually transmitted disease, and because there is no screening of workers that would make workers more likely to have healthy reproductive systems than non-workers of the same age, we believe than an uncertainty factor of 1 is not sufficiently protective. Under EPA guidelines, 3 is a default value for an uncertainty factor where there is indication that a value less than an order of magnitude (10) but greater than one is appropriate, and where the available data are not sufficiently quantified to select a specific value. Therefore, EPA is again proposing to assign an uncertainty factor of 3 to account for difference between individuals in the working population.

The uncertainty factors of 3 for animal-human extrapolation and 3 for variability within the human working population (each representing the square root of ten, half an order of magnitude) yield a composite uncertainty factor of 10. This factor was applied to all HECs derived from reproductive studies summarized in Table 6 in section IV.E.1 above. The resultant values are higher than the value that would have been obtained had EPA used the TLV of 10 ppm developed by the ACGIH. EPA believes that the benchmark dose approach more accurately characterizes the observed effects and provides a more robust utilization of the data.

D. Other Analyses of nPB Toxicity

Analyses Reviewed During Preparation of June 2003 NPRM

One commenter on the June 2003 NPRM stated that documents by Drs. Doull, Rozman, Stelljes, Murray, Rodricks, and the KS Crump Group were not acknowledged (Morford, 2003f, g, and h). EPA specifically mentioned

and responded to the occupational exposure limit recommendations from Drs. Rozman, Doull, and Stelljes in the preamble to the June 2003 NPRM at 68 FR 33298-33299. In addition, EPA included more detailed written responses to these derivations and the evaluation by Dr. Rodricks in the online docket prior to proposal (EPA-HQ-OAR-2002-0064-0017, -0018, and -0019). We considered these documents in preparation of the June 2003 proposal as well as this proposal.

In general, we disagree that the neurotoxicity endpoint selected by Drs. Rozman and Doull is the most appropriate endpoint for setting an AEL and we agree with Dr. Stelljes that sperm motility in the F1 offspring generation of the WIL, 2001 2-generation study is an appropriate endpoint. We agree with a number of these documents that data from the F1 generation may be conservative because workplace exposure would not include exposure to the F1 animals during the four-week period from weaning to sexual maturity. However, EPA believes that because of the potential for

in utero

effects that would only be seen in the offspring generation, looking only at the F0 parental generation could underestimate the adverse health impacts of a chemical. Therefore, it was appropriate for us to consider effects seen in both the F0 parental generation and the F1 offspring generation. Further, effects on sperm motility in the parental and offspring generations are seen at levels generally consistent with multiple reproductive effects seen in both generations and both sexes exposed to nPB, such as estrous cycle length, lack of estrous cycling, the number of estrous cycles in a 3-week period, and the number of live pup births (TERA, 2004; ICF, 2006a; SLR International, 2001; Stelljes and Wood, 2004). We believe that the document from the K. S. Crump group, a survey of the ratio of points of departure to TLVs set by the ACGIH, is not relevant now that the ACGIH has issued a TLV specifically for nPB. ACGIH appears to set an AEL for nPB that is a factor of 10 lower than the endpoint cited as lowest (100 ppm for effects on pup weight) (ACGIH, 2005). Thus, ACGIH has used an approach for nPB consistent with the total uncertainty factor of 10 assigned by EPA. In general, we find that these documents submitted by the commenter assigned uncertainty factors in a manner inconsistent with EPA guidance. This would result in a higher AEL than we would determine following the approach EPA has used on other chemicals, as well as an AEL that in our view would not sufficiently protect human health from nPB's effects because of multiple sources of uncertainty in available data (

e.g.

, variability within the working population, differences between animals and humans in how nPB affects the reproductive system).

Since the 2003 NPRM, a number of reviews of nPB toxicity have been issued, several of which include recommendations for occupational exposure limits. CERHR, 2003a and 2004a are similar to CERHR, 2002a, the expert panel report for nPB for the Center for the Evaluation of Risks to Human Reproduction (CERHR). CERHR, 2003b and 2004b are similar to CERHR, 2002b, the CERHR expert panel's report for iPB. These documents discuss the usefulness of data in available studies for assessing nPB's health impacts and establish No Observed Adverse Concentration levels of 100 ppm for both male and female reproductive effects in animals, but do not derive an AEL. Rozman and Doull, 2005 derived an AEL of 25 ppm for nPB based on neurotoxicity, using more recent information than Rozman and Doull, 2002.

The Stelljes and Wood (2004) analysis is similar in its results to SLR International (2001), a study by the same authors. EPA previously reviewed SLR International, 2001 in developing the June 2003 NPRM. Both studies by Stelljes and Wood concluded with a recommended AEL of 156 ppm, based on male reproductive effects and uncertainty factors of 1 in driving the AEL. Stelljes (2005) reviews RTI's 2005 study on metabolism of nPB in mice and rats and other literature and speculates that humans should be less sensitive to nPB than either mice or rats based on differences in metabolite production. Stelljes (2005) recommends that no uncertainty factor is required to extrapolate from animals to humans and that an uncertainty factor of no more than 2 is appropriate to account for differences within the working population. All of these documents assigned uncertainty factors in a manner that is not sufficiently supported by the available data and that is inconsistent with EPA's guidance. For example, Stelljes (2005) discusses metabolic data in rats and mice from RTI, 2005 and concludes that on this basis, the uncertainty factor for extrapolation from animals to humans should be 1. However, the metabolic data relate to pharmacokinetics—the activity of chemicals in the body—and do not address EPA's proposed uncertainty factor of 3 related to pharmacodynamics (the biochemical and physiological effects of chemicals in the body and the mechanism of their actions). Using the AEL from one of these documents would result in a higher, less protective AEL than we would determine following the approach EPA has used for other chemicals under the SNAP program and would not consider multiple sources of uncertainty in health effects (i.e., variability within the working population and differences between animals and humans in how nPB affects the reproductive system). Thus, we are concerned that the AELs based on these documents would not be sufficiently protective and would result in an inappropriate acceptability decision. Detailed reviews of these documents are available in the public docket.

Toxicological Excellence in Risk Assessment (TERA), 2004 reviews other AEL derivations for nPB, performs a benchmark dose (BMD) analysis, and recommends an AEL of 20 ppm based on live litter size. This analysis is consistent with EPA guidance for BMD modeling and for assigning uncertainty factors. A review of this document is available in the public docket (ICF, 2004c).

ICF (2004b, 2006a) derived an AEL for nPB based upon female reproductive effects. ICF (2004b, 2006a) discussed the relevant literature (Ichihara

et al.,

1999, 2002, 2004a, 2004b; Sekiguchi, 2002; Yamada

et al.

, 2003; WIL, 2001) and calculated mean estrous cycle length and the mean number of estrous cycles occurring during a three-week period at different exposure levels in the WIL, 2001 2-generation study. ICF (2004b, 2006a) found statistically significant reductions in the number of estrous cycles in a three-week period, both including and excluding females that had stopped their estrous cycles, at 250, 500, and 750 ppm in the F0 parental generation and at 500 and 750 ppm in the F1 generation. ICF (2004b, 2006a) conducted BMD modeling and calculated BMDL values of the number of estrous cycles in a three-week period that varied from 102 to 208 ppm, depending upon the model used and the benchmark criteria selected. All data were calculated based on the mean reductions in estrous cycle number calculated from the WIL, 2001 study. Values were calculated for the F0 generation; the number of data for the F1 generation was too small for statistical analysis. The BMDLs that ICF calculated for the number of estrous cycles in a three-week period were 162 ppm and 208 ppm, depending on the benchmark response criteria (10% change in response vs. one standard

deviation) and using a linear-heterogeneous model.

The California Environmental Protection Agency's Office of Environmental Health Hazard Assessment (OEHHA) listed both nPB and iPB as reproductive toxins on the basis of developmental, male reproductive, and female reproductive toxicity under the State's Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition 65 (OEHHA, 2006). Under this law, California is required to list chemicals known to be carcinogenic or to be reproductive toxins and to update that list at least annually.

The American Conference of Government Industrial Hygienists (ACGIH) issued a recommended Threshold Limit Value

(TLV) of 10 ppm (time-weighted average) for nPB (ACGIH, 2005). ACGIH summarized numerous studies showing different effects of nPB and identified no observed effect levels (NOELs) of 200 ppm for hepatotoxicity (ClinTrials, 1997b) and less than 100 ppm for developmental toxicity, as evidenced by decreased fetal weight (Huntingdon Life Sciences, 2001).

OSHA has not developed a permissible exposure limit (PEL) for nPB that EPA could use to evaluate toxicity risks

from workplace exposure. In prior SNAP reviews, EPA has used ACGIH TLVs where available in assessing a chemical's risks and determining its acceptability if OSHA has not set a PEL. ACGIH is recognized as an independent, scientifically knowledgeable organization with expertise in issues of toxicity and industrial hygiene. However, in this case, EPA believes that ACGIH's TLV for nPB of 10 ppm has significant limitations as a reliable basis for an acceptable exposure limit, especially given the availability of other, more comprehensive analyses described in this proposal. First, according to the authors of the Huntingdon Life Sciences study, the decrease in fetal weight was an artifact of sampling procedure that biased the data (test animals were only sacrificed at the end of the day rather than at random). The CERHR expert panel excluded “aberrantly low” fetal weights from one litter in this study and calculated a BMDL greater than 300 ppm for this endpoint after removing those outlier data (CERHR, 2002a, 2003a, and 2004a). TERA calculated a similar BMDL when analyzing the same data set (TERA, 2004). Further, the reference list in the documentation on the TLV indicates that ACGIH did not review and evaluate all the studies available prior to the development of the recommended exposure limit. For example, key supporting articles that reported disruption of estrous cycles (Yamada

et al.

, 2003 and Sekiguchi

et al.

, 2002) were not discussed in the TLV documentation. Further, ACGIH did not provide sufficient reasoning for the selection of the chosen endpoint over others (e.g., reproductive toxicity and/or neurotoxicity). The lack of discussion of applied uncertainty factors also prevents a determination of how ACGIH arrived at a TLV of 10 ppm. In summary, EPA is not basing its proposed acceptability determination for nPB on the ACGIH TLV because: (1) Other scientists evaluating the database for nPB did not find the reduced pup weight to be the most sensitive endpoint; (2) benchmark dose (BMD) analysis of the reduced pup weight data (CERHR, 2002a; TERA, 2004) results in a higher BMDL (roughly 300 ppm) than those for reproductive effects; and (3) ACGIH may not have reviewed the complete body of literature as several studies discussing neurotoxicity and female reproductive effects were omitted from the list of references. A number of reviews of this document are available in the public docket (ICF, 2004d; O'Malley, 2004).

Vendors of nPB-based products have recommended a wide range of exposure limits, from 5 ppm to 100 ppm (Albemarle, 2003; Chemtura, 2006; Docket A-2001-07, item II-D-19; Enviro Tech International, 2006; Farr, 2003; Great Lakes Chemical Company, 2001).

We note that, even if EPA had selected the ACGIH TLV as our basis for assessing the risks of nPB, we would have proposed the same determinations. In the specific coatings application that we propose to find acceptable subject to use conditions at the Lake City Army Ammunition Plant, exposure data showed an ability to meet an exposure level of 10 ppm, with the vast majority of measurements below that value. Thirty-four of 35 samples had concentrations below 10 ppm, and the mean concentration for the plant was less than 4 ppm (Lake City Army Ammunition Plant, 2004). For the aerosol and adhesive end uses, it would be even more difficult to achieve an exposure level of 10 ppm than to achieve a level in the range that EPA is considering (17 to 30 ppm). Thus, we would have proposed the same decisions for nPB of acceptable, subject to use conditions for coatings and unacceptable for aerosols and adhesives using the ACGIH's TLV of 10 ppm to assess health risks. Despite some flaws in its derivation, the TLV of 10 ppm is less than two-fold lower than the low end of the range of acceptable exposure levels based on the most sensitive reproductive endpoints. This small difference is well within the uncertainty required to extrapolate a benchmark dose from an experimental study in rats to an occupational exposure limit in humans.

E. Community Exposure Guideline

In this proposal, EPA is using a community exposure guideline (CEG) of 1 ppm to evaluate potential health risks among populations living near facilities using nPB. This community exposure guideline is an estimate of a continuous inhalation exposure (averaged over 24 hours per day, 7 days per week) to the general public (including sensitive subgroups) that is likely to be without an appreciable risk of adverse health effects during a lifetime.

Based on EPA risk assessment guidelines (US EPA, 1994b), the CEG was derived using the lowest BMDL from effects listed in Table 6 as the point of departure (110 ppm for vacuolation in the liver of animals in the F1 generation of WIL, 2001). The HEC was calculated as follows:

110 ppm x (6 hours exposure in study/24 hours avg time) x (7 days/7 days) = 28 ppm

EPA used an uncertainty factor of 3 for extrapolation from animals to humans, as discussed above in section VI.A, and an uncertainty factor of 10 for variability within the general population, consistent with EPA's RfC guidelines. Dividing the HEC of 28 ppm by 30 yields a community exposure guideline of approximately 1 ppm. If we had used sperm motility (HEC of 42 ppm based on a BMDL of 169 ppm) or number of estrous cycles (HEC of 40 ppm based on a BMDL of 162 ppm) as starting points, we would calculate the same approximate CEG value. We note that, following RfC guidelines, EPA's community exposure guideline includes a number of conservative assumptions, including exposure adjustments to protect an individual exposed for up to 24 hours a day for 70 years (U.S. EPA, 1994b, p. 1-5).

EPA evaluated general population exposure using EPA's SCREEN3 (U.S. EPA, 1995b) air dispersion model to assess the likely maximum concentration of nPB from single sources.

EPA used data collected from

actual facilities (Swanson, 2002) to characterize two scenarios: (1) A typical large, high-use adhesive application facility where the closest resident is 100 meters away; and (2) a smaller facility with average-use adhesive application in an urban area, where the nearest resident is only 3 meters away. The results indicated that modeled exposures in either scenario did not exceed the CEG of 1 ppm. The highest exposure modeled was 0.24 ppm at a distance of 3 meters away from the source in the urban scenario, while most other exposures were at least an order of magnitude lower (ICF, 2003; ICF, 2006a). Because the community exposure guideline was not exceeded for any of the exposure scenarios in this conservative screening approach, EPA has concluded that nPB exposure to populations living close to facilities using nPB is not a concern for purposes of determining the acceptability of nPB under the SNAP program.

We performed the modeling for a facility using nPB-based adhesives because the nPB emissions from this type of facility were expected to be higher than those from facilities using nPB for other end uses. Thus, if a facility using adhesives would not result in emissions exceeding the CEG, facilities using nPB in aerosols or in metals, electronics, or

precision cleaning also would not result in emissions exceeding the CEG.

VI. What listing is EPA proposing for each end use, and why?

In this rule, EPA is proposing to find nPB unacceptable in adhesive and aerosol solvent end uses, and acceptable subject to use conditions in the coatings end use. The proposed listings, summarized in Table 9, are intended to allow the use of nPB where it does not pose a human health risk significantly greater than other substitutes and prohibit nPB's use where nPB exposure cannot be maintained, or is unlikely to be maintained, at even the highest level considered in this proposal (i.e., 30 ppm). We also are taking comment on an alternate approach of finding nPB acceptable subject to use conditions in the above end uses (see Section VII.A).

Table 9.—Proposed Decisions by End Use and Sector

For nPB in this sector and end use:

Our proposal is to list nPB as:

And our proposed alternate approach is:

Aerosols:

Aerosol solvents

Unacceptable

Acceptable, subject to use conditions.

Adhesives, Coatings, and Inks:

Coatings

Acceptable, subject to use conditions

Acceptable, subject to use conditions.

Adhesives

Unacceptable

Acceptable, subject to use conditions.

Use of nPB in this end use is limited to coatings at facilities that, as of May 30, 2007, have provided EPA information demonstrating their ability to maintain acceptable workplace exposures (i.e., the Lake City Army Ammunition Plant).

Use conditions would include proposed requirements that users must (1) meet an exposure limit of 20 ppm on an eight-hour time-weighted average, (2) monitor workers' exposure to nPB using a personal breathing zone sampler on an eight-hour time-weighted average initially and periodically (every 6 months or longer, depending on the concentration during initial monitoring), and (3) keep records of the worker exposure data on site at the facility for at least three years from the date of the measurement.

A. Aerosol Solvents

In this rule, EPA proposes to find nPB unacceptable in the aerosol solvent end use. There are a number of aerosol solvent alternatives that do not pose any risk for ozone depletion or for ground level smog formation.

EPA's greatest concern with nPB-based aerosols is that users of nPB as an aerosol solvent cannot reliably maintain exposures at sufficiently low levels to ensure that workers are protected. This finding is based on measured exposure data and model estimations indicating the likelihood of elevated concentrations associated with nPB-based aerosols given typical ventilation conditions. A number of other acceptable solvent alternatives are available that can be used at exposure levels below their respective acceptable exposure limits.

Smog, also known as ground-level ozone, is produced from emissions of volatile organic compounds that react under certain conditions of temperature and light.

Ventilation conditions are an important consideration in evaluating potential risks within this end-use category. “Benchtop cleaning” of individual parts, which is feasible under exhaust hoods or in spray booths with adequate ventilation, comprises 25% or less of the market involving ODS substitutes for aerosols (U.S. EPA, 2004). According to industry information and several commenters, the majority of the market for nPB-based aerosols involves in-place applications requiring a portable aerosol, such as cleaning energized electrical contacts and switches, maintenance in underground mines, or cleaning active elevator motors (CSMA, 1998; U.S. EPA, 2004; Williams, 2005). These applications often occur in tightly confined spaces where it is not feasible to install ventilation equipment or remove parts to ventilated areas (CSMA, 1998; Linnell, 2003; Werner, 2003). Other acceptable substitutes, such as blends of HFEs or HFCs and trans-dichloroethylene, are available in these end uses. One commenter also suggested that a user of an nPB-based aerosol will assume that they are being provided with a product that offers similar margins of safety as the product being replaced (i.e., HCFC-141b) and therefore can be used under the same conditions (Werner, 2003).

The likelihood that nPB aerosol solvents would be used in poorly ventilated spaces is of particular concern given the likelihood of elevated exposure levels. The exposure data from aerosol solvent use are extremely limited. These data are from simulations of a number of situations where nPB might be used, such as benchtop cleaning of electronics and cleaning automotive brakes, rather than data from facilities currently using nPB in manufacturing or maintenance processes. Thus, the available exposure data may not be representative of ventilation levels normally used with nPB-based aerosols and may not adequately represent exposure levels during in-place cleaning, industry's most common application for nPB-based aerosols. The distribution of exposure levels in the seven samples ranging from 5.5 to 32 ppm corresponded to the range of ventilation rates reported—0, 300, 640, and 1900 cfm—with the highest ventilation rate resulting in the lowest exposure levels and the lower ventilation levels resulting in the values above 30 ppm. The ventilation rate most consistent with use in a confined space for in-place cleaning, 0 cfm, resulted in half the exposures (one of two) exceeding 30 ppm. The highest ventilation rate, 1900 cfm, occurred at a vented booth, which would not be feasible to install for in-place cleaning applications—the majority of applications for nPB-based aerosols. The middle ventilation rates of 300 and 640 cfm occurred during use of a fan for an entire room (regional ventilation), as might be expected for benchtop cleaning (Confidential submission, 1998), but not for in-place cleaning in confined spaces. In modeling nPB exposure from aerosol solvent use at a low ventilation rate of

450 cfm, a level that might be expected during benchtop cleaning, 8-hour average concentrations of 16.5 to 33 ppm are predicted, depending on the amount of nPB used (ICF, 2006a). Exposure levels for confined spaces with even lower ventilation rates, as we would expect for in-place cleaning, would be even higher, likely exceeding the high end of the range that EPA is considering. Short-term exposures of 370 and 1,100 ppm taken from workers' collars in a room with regional ventilation at 640 cfm, when averaged over an 8-hour period, resulted in exposure levels of 12 and 34 ppm. These exposures occurred as a result of using nPB over a period up to 15 minutes, so it is likely that users would have greater exposure than 30 ppm if they used nPB for longer than 15 minutes per day, as with multiple uses. The available data sets have a small sample size, may not be representative of in-place cleaning in confined spaces, and do not provide EPA with convincing data that nPB is likely be used safely, at exposure levels at or below the highest level in the range we are considering for evaluation of acceptability.

EPA is concerned that many, and perhaps most, uses of nPB aerosol solvents result in a high probability of exposures at or above even the upper end of the range of exposures that the Agency is considering to be potentially acceptable. EPA is aware of no data on ventilation levels demonstrating that most users of aerosol solvents, or of nPB in particular, would use aerosols in locations with sufficiently high ventilation levels to protect human health (e.g., 1900 cfm or greater). We request data on worker exposure levels, typical ventilation rates, and patterns for usage of nPB-based aerosols, considering both benchtop and in-place use.

EPA has found numerous other aerosol solvents acceptable. These aerosol solvents can be used safely in a manner consistent with their respective acceptable exposure limits. This is highlighted in a study comparing concentrations of eight different chemicals that are acceptable under the SNAP program in aerosol formulations: HFE-7100, HFE-7200, trans-1,2-dichloroethylene, HCFC-225ca and -225cb, acetone, pentane, and HFC-134a. In this study, with ventilation of only 48 cfm, 8-hr TWA exposure from the different chemicals varied from 35.5 ppm to 194.0 ppm, and all chemicals met their respective recommended exposure levels (ICF, 2006a). As discussed above in section V.A, when these concentrations are adjusted for the chemicals' respective molecular weights, they would correspond to nPB concentrations of 29.5 to 394.4 ppm, which is at or above even the highest level the Agency would consider acceptable. The ventilation level in this study is closer to what we would expect in a confined space where fans or vents cannot be installed, as for in-place cleaning. Based on these considerations, the Agency believes that nPB used as an aerosol solvent would impose significantly more risk to human health than other alternatives available for this end use.

B. Adhesives

EPA proposes to find nPB unacceptable in the adhesive end use. As for aerosol solvents, we found that some alternative adhesive formulations could reduce particular environmental risks more than nPB, such as generation of ground level “smog” or ozone depletion potential. However, we find the greatest concern in this end use is with nPB's human health effects. We propose to find nPB unacceptable in adhesives because it poses significantly greater risk to human health as compared to other available alternatives in this end use.

In the June 2003 NPRM, we initially proposed to find nPB acceptable in adhesives based on the SNAP program principle that “EPA does not intend to restrict a substitute if it poses only marginally greater risk than another substitute * * *. The Agency also does not want to intercede in the market's choice of available substitutes, unless a substitute has been proposed or is being used that is clearly more harmful to human health and the environment than other alternatives.” (68 FR 33294, citing the original March 18, 1994 SNAP rule at 59 FR 13046). At the time of the proposal, we considered data from NIOSH monitoring and health hazard evaluations for three facilities using nPB-based adhesives. At two of the three facilities, NIOSH worked together with the companies to install state-of-the-art ventilation equipment. Looking at exposure data from all workers after ventilation improvements, we believed it would be possible for facilities to meet the proposed AEL of 25 ppm (68 FR 33294).

• One public commenter suggested that EPA should reconsider whether industrial exposures consistently occur and/or can be controlled to a level at or below 25 ppm (Werner, 2003). We reevaluated the exposure data for the two plants that had improved their ventilation, focusing on exposure to the workers that receive the highest exposures because they directly spray the nPB-based adhesive. We found that, even in the best case, a substantial number of workers spraying nPB-based adhesives would be exposed above the highest level in the range we are considering.

• NIOSH investigators initially reported that mean exposures to nPB ranged from 60 to 381 ppm (8-hour time weighted averages) at three different foam-fabrication facilities using nPB-based adhesives (NIOSH, 2000a, 2000b, 2001, 2002a, 2002b, 2003a). In one facility, average (mean) nPB exposures were reduced from 169 ppm to 19 ppm, following installation of ventilation equipment (NIOSH, 2000b). Although use of spray booths at this facility reduced the average exposure level to 19.4 ppm for all workers, the majority of the sprayers directly using nPB-based adhesives still would be exposed at unacceptably high levels. Out of fourteen sprayers at the Custom Products facility:

• Six, or 43% of sprayers, would be exposed to more than 30 ppm.

• Nine, or 64% of sprayers, would be exposed to more than 25 ppm.

• Ten, or 71% of sprayers, would be exposed to more than 20 ppm.

• Eleven, or 79% of sprayers, would be exposed to more than 15 ppm.

• Thirteen, or 93% of sprayers, would be exposed to more than 10 ppm.

At another facility using nPB-based adhesives, the average exposure was reduced from 58 pm to 19 ppm after the company installed ventilation recommended by NIOSH (NIOSH, 2001). Data on exposure for sprayers found fewer individuals receiving high exposures than at the facility monitored in NIOSH (2000b), but 65% (22 of 34) of exposure samples for sprayers were higher than 15 ppm, 33% (11 of 34) were higher than 20 ppm and 15% (5 of 34) were higher than 25 ppm after improving ventilation.

Overall, 42% of sprayers in these two facilities using nPB-based adhesives were exposed to concentrations of nPB greater than 20 ppm (21 of 48 workers) and 23% (14 of 48 workers) were exposed to more than 25 ppm, even after installing state-of-the-art ventilation with assistance from NIOSH. Sprayers had significantly higher individual exposures than workers who did not work directly with the nPB-based adhesive.

In response to public comment and additional information available to EPA since the June 2003 NPRM, we now propose that use of nPB-based adhesives poses significantly higher risks to human health than other available adhesives. Since the June 2003 NPRM, there have been a number of reports of

workers working with nPB-based adhesives that have suffered adverse, persistent neurological effects that resulted in hospitalization (Beck and Caravati, 2003, and Majersik

et al.

, 2004, 2005; Calhoun County, 2005; Miller, 2005; Raymond and Ford, 2005). Based on data from actual facilities using adhesives, it is estimated that a facility using nPB with average adhesive application rates and average ventilation rates would have exposure levels of approximately 60 ppm on an 8-hr time-weighted average (ICF, 2006a). Modeling of exposures at high adhesive application rates and average or lower ventilation rates resulted in exposures of approximately 250 to 2530 ppm (ICF, 2006a). We believe these modeling results show that most adhesive users would exceed acceptable exposure levels by significant margins and that it is unlikely that adhesive users would be able to use nPB safely.

Considering the exposure data for nPB-based adhesives, we believe it is unlikely that, even with improved ventilation, adhesive users could reduce exposures to acceptable levels on a consistent basis. In the best case seen, a facility with low to average initial exposure levels was able to reduce exposures to the middle of the range EPA is considering after extensive assistance from NIOSH in installing state-of-the-art ventilation. We expect that many facilities will begin with higher exposure levels and will not have the same level of assistance to improve ventilation, thus making it unlikely that they would achieve acceptable exposures. Given the information above, we are concerned that nPB-based adhesives cannot be reliably used in a manner that protects human health. We request comment and further data on whether it is feasible to use nPB-based adhesives with worker exposure levels consistently at or below any of the values in the range of exposure levels that EPA is considering potentially acceptable (i.e., 17 to 30 ppm).

The available information indicates that all acceptable carrier solvents in adhesives other than nPB have projected or actual exposure less than the appropriate workplace exposure limit EPA used in finding those substitutes acceptable. Examples of other carrier solvents currently used in adhesives and acceptable under the SNAP Program include hydrocarbon solvents, acetone, methylene chloride, and water. EPA finds that there are other available alternatives that pose significantly less risk to human health and the environment compared to nPB in the adhesives end use.

During the public comment period on the June 2003 NPRM, one commenter representing the adhesives industry stated that there are some small but critical applications that require nonflammability and high solvency (Collatz, 2003). The commenter did not specify what those applications are, and whether there was information showing that other types of adhesives, such as those using water, flammable solvents, or methylene chloride, are technically infeasible in these applications. We request comment and data on whether there are any unique applications in the adhesives end use for which there are no technically feasible alternatives other than nPB and thus, for which nPB should be allowed. If so, and if determined that nPB should be unacceptable except where no other substitutes are feasible, we would consider finding nPB acceptable subject to narrowed use limits, with requirements for each end user to perform a demonstration that there are no other technically feasible alternatives for their particular site, to install local exhaust ventilation equipment designed to reduce exposures to acceptable levels and to perform worker exposure monitoring. Alternatively, if there was sufficient information provided during the public comment period showing that there are applications in which nPB can be safely used, we would consider finding nPB acceptable in adhesives, subject to use conditions requiring installation of local exhaust ventilation and worker exposure monitoring. This would allow for use of nPB in any applications where it may be used safely if any such applications exist.

C. Coatings

We are proposing to find nPB acceptable, subject to use conditions, for facilities that, as of May 30, 2007, have provided EPA information demonstrating their ability to maintain workplace exposure levels below even the minimum level of the range of exposures that EPA is considering to be potentially acceptable (i.e., 17 to 30 ppm). The SNAP submission with information on coatings was made for a single facility and EPA is unaware of anyone else interested in using nPB in this end use. Therefore, there are currently no analyses indicating whether nPB would pose significantly greater risks in any coating applications other than this facility. Workplace exposure levels to nPB from ammunition sealant at Lake City Army Ammunition Plant ranged from less than 1 ppm up to 21 ppm on an eight-hour time-weighted average. Thirty-four of 35 samples had concentrations below 10 ppm, and the mean concentration for the plant was less than 4 ppm (Lake City Army Ammunition Plant, 2004). The vast majority of measurements show worker exposure well below the lowest level in the range of exposures that EPA is considering. Thus, we believe that nPB can be used as safely as other acceptable solvents used at their acceptable exposure limits under the conditions at this facility.

Other acceptable substitutes for ozone-depleting substances in coatings, in general, include oxygenated solvents, hydrocarbon solvents, terpenes, hydrofluoroethers 7100 and 7200, benzotrifluorides (include parachlorobenzotrifluoride), monochlorotoluenes, trans-1,2-dichloroethylene, chlorinated solvents, water-based formulations, and high-solids formulations. In the particular application for ammunition coatings, the submitter evaluated a large number of alternatives and found that n-propyl bromide was the only one of 29 solvents tested that could meet performance specifications at this facility (Harper, 2005). Thus, it is not clear that there are other substitutes available for this specific application, and exposure data show that in this specific application, nPB can be used in a way that does not pose significantly greater risks to human health compared to other acceptable substitutes in the coatings end use.

VII. What other regulatory options did EPA consider?

EPA considered several different options, but we prefer the approach proposed in this rule. We also take comment on the options discussed below.

A. Alternate Option for Comment: Acceptable With Use Conditions Requiring Exposure Limit and Monitoring

We also take comment on a proposed alternate approach in which nPB would be acceptable subject to use conditions in all the end uses addressed in this action. Under this alternate approach, users would meet an exposure limit, monitor exposure of workers using nPB, and keep records to demonstrate compliance with these requirements. For purposes of this alternative proposal, we selected 20 ppm to use as an exposure limit above which use would be unacceptable, and 10 ppm as an action level that allows reduced exposure monitoring, for the reasons discussed below in section VII.A.1, “Use Conditions and Their Rationale.” However, we are soliciting comment on whether a different exposure level within the 17 to 30 ppm range should

be selected. The following requirements would apply at each facility where nPB is used:

Exposure Limit

The owner or operator would be required to ensure that workers using nPB are exposed to no more than 20 ppm on an 8-hour time-weighted average. The exposure limit could be met through engineering controls (e.g., ventilation equipment), work practices, or reduced use of nPB.

Initial Worker Exposure Monitoring

For each facility where nPB is used, the owner or operator of the facility would be required to ensure that personal breathing zone air samples of each nPB user's exposure would be collected on an eight-hour, time-weighted average initially within 90 days after a final rule becomes effective. Monitoring measurements may be taken with an organic chemical monitoring badge on the collar or a tube filled with charcoal on the collar.

Periodic Exposure Monitoring

(1) The owner or operator of the facility would be required to ensure that personal breathing zone air samples of user exposure are collected periodically on an eight-hour, time-weighted average depending on the results of the most recent set of exposure data. A monitoring program could be instituted by the company or by the nPB supplier for that facility. Periodic sampling requirements would be based on the most recent monitoring results, as follows:

Table 10.—Alternative Approach Exposure Levels and Periodic Exposure Monitoring

If exposure measurements for nPB are at this level:

Then the owner or operator:

all measurements at or below 10 ppm

is not required to perform periodic exposure monitoring.

all measurements at or below 20 ppm, with some measurements above 10 ppm

must take personal breathing zone samples again at least once in the next six months.

at least one measurement above 20 ppm

must stop using nPB in the application exceeding the exposure limit until exposure data show that 20 ppm can be consistently met in the vast majority of cases.

unknown, in cases of new workplace conditions increasing exposure or new applications of nPB

must take personal breathing zone samples as a test before using nPB in new industrial applications or conditions, or within 7 days of an emergency caused by a leak, rupture or breakdown, and use this value to determine the next time monitoring is required.

(2) For periodic monitoring, the owner or operator would be allowed either to monitor each nPB user's exposure, or to monitor exposure of a representative nPB user in each job classification in a work area during every work shift, where the monitored nPB user is expected to have the highest exposure.

(3) The owner or operator would be allowed to discontinue the periodic 8-hour TWA monitoring for nPB users at the facility where at least two consecutive sets of measurements taken at least seven days apart are below 10 ppm.

Monitoring for New Conditions or Applications

Whenever there is a change in workplace conditions that may increase exposure or whenever a new application of nPB is introduced, the owner or operator would be required to take personal breathing zone samples accounting for all nPB users as a test before using nPB in manufacturing or repair. These could be either samples for each nPB user or samples representing each job classification in a work area during a work shift, so long as the samples are based on the user with the likely highest exposure. Examples of changes in workplace conditions that may increase exposure include changes in production, process control equipment, or work practices, or a leak, rupture, or other breakdown.

Examples of introduction of a new application of nPB include aerosol contact cleaning in a location with regional ventilation or natural ventilation, where previous measurements were carried out on workers in a location with local ventilation. If the change occurs because of an unpredictable emergency, then the owner or operator would need to ensure exposure monitoring takes place within 7 days of the change.

See 29 CFR 1910.1052(d)(4)(i).

Sampling Methods and Accuracy

Exposure samples would be required to be analyzed either by NIOSH method 1003 for halogenated hydrocarbons or method 1025 for 1-bromopropane and 2-bromopropane or by another method that is accurate to ±25% at the 95 percent confidence level.

Recordkeeping Requirements

The owner or operator of the facility would be required to keep records of the monitored exposure data at the facility for at least three years from the date the measurements were taken for purposes of this rule. These records would be required to be made available in the event of a facility inspection or a request for the data by EPA. Note that the EPA's recordkeeping requirement does not affect OSHA's standard on access to employee exposure and medical records, which requires retaining any exposure records for at least 30 years (29 CFR 1910.1020(d)(ii)).

The regulatory listings by end-use under this alternate approach that the Agency requests comment on would be as follows:

BILLING CODE 6560-50-P

EP30MY07.000

EP30MY07.001

BILLING CODE 6560-50-C

1. Use Conditions and Their Rationale

The major provisions of the use conditions and the related issues that EPA considered in developing the alternate approach that we are taking comment on are as follows:

Exposure limit. A requirement to meet a workplace exposure limit would be an interim measure to ensure that nPB will be used safely until OSHA issues a final permissible exposure limit (PEL) under the Occupational Safety and Health Act. In the event that OSHA issues a final PEL, it would supersede EPA's exposure limit. EPA is specifically deferring to OSHA, and has no intention to assume responsibility to displace OSHA's authority under Public Law 91-596. EPA's exposure limit would not pre-empt the authority of OSHA to take regulatory or enforcement action with respect to exposure to this substance. This is made clear by the Clean Air Act under which EPA would promulgate this regulation (Subchapter VI—Stratospheric Ozone Protection), which provides at 42 U.S.C. 7610 in pertinent part: “* * * this chapter [Chapter 85—Air Pollution Prevention] shall not be construed as superseding or limiting the authorities, under any other provision of law, of the Administrator or any other Federal officer, department, or agency.” By issuing an exposure limit for nPB, EPA's intention would be to fill existing regulatory gaps during the interim period of substitution away from ozone-depleting compounds and provide the needed margin of protection for human health and the environment until OSHA develops other regulatory controls or standards under appropriate authorities.

As discussed above in section IV.E.1, EPA is considering exposures within the range of 17 to 30 ppm as potentially acceptable in order to determine whether nPB may be used safely in each end use. For purposes of having a clear compliance target under this alternative approach for public comment, we are using 20 ppm as the exposure limit above which use would be unacceptable. We chose this value because we expect it to be protective against the reproductive and developmental effects identified previously (live litter size, sperm motility, estrous cycles).

Worker exposure monitoring.

The worker exposure monitoring requirements under the use conditions in the alternate approach were modeled after OSHA's requirements for monitoring for methylene chloride. 29 CFR 1910.1052(d). We expect that the regulated community would be familiar with this approach and there might be fewer changes for regulated businesses if OSHA later were to establish a workplace standard for nPB. Because the exposure limit would be an 8-hr TWA value that is derived from studies that measured exposure via inhalation, the proposed use conditions require the owner or operator to monitor 8-hr TWA values that measure workers' exposure in the breathing zone (e.g., samples from a worker's collar). We are not proposing to monitor short-term exposures because acute, short-term exposures of nPB are not of significant health concern, so long as long-term exposures are below the 8-hour TWA limit or potentially acceptable exposure levels (ERG, 2004).

Option for monitoring representative set of workers.

Personal breath zone samples could be taken either from each worker using nPB or from a representative

set of exposed workers expected to have the highest exposur

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