Draft Water Quality Criteria Methodology Revisions: Human Health

Federal RegisterAug 14, 1998

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SUMMARY: EPA is announcing the availability for public comment of draft

revisions to the Methodology for Deriving Ambient Water Quality

Criteria for the Protection of Human Health (``AWQC Methodology

Revisions'') published pursuant to Section 304(a)(1) of the Clean Water

Act (CWA). These AWQC Methodology Revisions, once finalized, will

supersede the existing Guidelines and Methodology Used in the

Preparation of Health Effect Assessment Chapters of the Consent Decree

Water Criteria Documents (``1980 AWQC National Guidelines''), published

by EPA in November 1980 (45 FR 79347, Appendix C). Today's document is

intended to satisfy the requirements of Section 304(a)(1) of the CWA

that EPA periodically revise criteria for water quality to accurately

reflect the latest scientific knowledge on the kind and extent of all

identifiable effects on health and welfare that may be expected from

the presence of pollutants in any body of water, including ground

water. These AWQC Methodology Revisions are necessitated by the many

significant scientific advances that have occurred during the past 17

years in such key areas as cancer and noncancer risk assessments,

exposure assessments, and bioaccumulation. These revisions are not

regulations and do not impose legally-binding requirements on EPA,

States, Territories, Tribes, or the public. Also published as part of

this document are draft AWQC criteria document summaries for three

contaminants that reflect the Draft AWQC Methodology Revisions.

AVAILABILITY OF DOCUMENTS: The Draft AWQC Methodology Revisions are

published below. Copies of the technical support document and the three

complete criteria documents cited in this document may be obtained from

the U.S. EPA National Center for Environmental Publications and

Information (NCEPI), 11029 Kenwood Road, Cincinnati, OH 45242 or (513)

489-8190. Materials in the public docket will be available for public

inspection and copying during normal business hours at the Office of

Water Docket, 401 M St., S.W., Washington, D.C. 20460 by appointment

only. Appointments may be made by calling (202) 260-3027 and requesting

item W-97-20. A reasonable fee will be charged for photocopies.

Selected documents supporting the Draft AWQC Methodology Revisions

will also be available for viewing by the public at the following

locations:

I. Region 1 Library, JFK Federal Building, One Congress Street, Boston,

MA 02203 (617) 565-3300

II. Region 2 Library, 290 Broadway, 16th Floor, New York, NY 10007

(212) 637-3185

III. Region 3 Library, 841 Chestnut Building, Philadelphia, PA 19107

(215) 566-5254

IV. Region 4 Library, Atlanta Federal Center, 61 Forsyth St, SW, 9th

Floor Tower, Atlanta, GA 30303-3104 (404) 347-4216

V. Region 5 Library, 77 West Jackson Boulevard, Chicago, IL 60604-3590

(312) 353-2022

VI. Region 6 Library, 1445 Ross Avenue, Dallas, TX 75202 (214) 665-6424

VII. Region 7 Information Resource Center, 726 Minnesota Avenue, Kansas

City, KS 66101-2728 (913) 551-7241

VIII. Region 8 Library, 999 18th Street, Suite 500, Denver, CO 80202-

2466 (303) 312-6746

IX. Region 9 Library, 75 Hawthorne Street, San Francisco, CA 94105

(415) 744-1517

X. Region 10 Library, 1200 Sixth Avenue, Seattle, WA 98101 (206) 553-

1289

DATES: EPA will accept public comments on the Draft AWQC Methodology

Revisions on or before December 14, 1998. Comments postmarked after

this date may not be considered.

ADDRESSES: An original and three copies of all comments and enclosures,

including references, on the draft AWQC Methodology Revisions should be

addressed to the W-97-20 Docket Clerk, Water Docket (4101), U.S. EPA,

401 M St., S.W., Washington, D.C. 20460. Electronic comments must be

submitted as a WordPerfect 5.1 or WP 6.1 file or as an ASCII file

avoiding the use of special characters. Comments and data will also be

accepted on disks in WordPerfect 5.1 or WP 6.1 or ASCII file format.

Electronic comments on this document may be filed via e-mail at: ow-

[email protected]. Commenters who want EPA to acknowledge receipt

of their comments should include a self-addressed stamped envelope. No

facsimiles (faxes) will be accepted.

FOR FURTHER INFORMATION CONTACT: Denis Borum (4304), U.S. EPA, 401 M

St. S.W., Washington, D.C. 20460 (Telephone: (202) 260-8996).

SUPPLEMENTARY INFORMATION:

List of Acronyms Used

ADI Acceptable Daily Intake.

ARAR Applicable or Relevant and

Appropriate Requirements.

ASTM American Society of Testing and

Materials.

AWQC Ambient Water Quality Criteria.

BAF Bioaccumulation Factor.

BCF Bioconcentration Factor.

BMD Benchmark Dose.

BMR Benchmark Response.

BSAF Biota-Sediment Accumulation

Factors.

BW Body Weight.

C18 Carbon-18

CDC U.S. Centers for Disease Control

and Prevention.

CR Consumption Rate.

CSFII Continuing Survey of Food Intake

by Individuals.

CTR California Toxics Rule.

CWA Clean Water Act.

DI Drinking Water Intake.

DNA Deoxyribonucleic Acid.

DOC Dissolved Organic Carbon.

DT Non-Fish Dietary Intake.

ED10 Dose Associated with a 10

Percent Extra Risk.

EMAP Environmental Modeling and

Assessment Program.

EPA Environmental Protection Agency.

FCM Food Chain Multiplier.

FDA Food and Drug Administration.

FEL Frank Effect Level.

FI Fish Intake.

FIFRA Federal Insecticide, Fungicide,

and Rodenticide Act.

FR Federal Register.

FSTRAC Federal State Toxicology and

Risk Analysis Committee.

GI Gastrointestinal.

GLI Great Lakes Water Quality

Initiative.

IARC International Agency for

Research on Cancer.

II Incidental Intake.

ILSI International Life Sciences

Institute.

IN Inhalation Intake.

IRIS Integration Risk Information

System.

kg kilogram

Kow Octanol-Water Partition

Coefficient.

L Liter.

LED10 The Lower 95 Percent Confidence

Limit on a Dose Associated with

a 10 Percent Extra Risk.

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LMS Linear Multistage Model.

LOAEL Lowest Observed Adverse Effect

Level.

LR Lifetime Risk.

MCL Maximum Contaminant Level.

MCLG Maximum Contaminant Level Goal.

MF Modifying Factor.

mg Milligrams.

ml Milliliters.

MoA Mode of Action.

MoE Margin of Exposure.

MoS Margin of Safety.

NCHS National Center for Health

Statistics.

NHANES National Health and Nutrition

Examination Survey.

NIEHS National Institute of

Environmental Health Sciences.

NOAEL No Observed Adverse Effect

Level.

NOEL No Observed Effect Level.

NPDES National Pollutant Discharge

Elimination System.

NTIS National Technical Information

Service.

NTR National Toxics Rule.

ODES Ocean Data Evaluation System.

PAH Polycyclic Aromatic Hydrocarbon.

PBPK Physiologically Based

Pharmacokinetic.

PCB Polychlorinated BIPHENYLS.

PCS Permits Compliance System.

Pdp Point of Departure.

POC Particulate Organic Carbon.

q1* Cancer Potency Factors.

RDA Recommended Daily Allowance.

RfC Reference Concentration.

RfD Reference Dose.

RPF Relative Potency Factor.

RSC Relative Source Contribution.

RSD Risk Specific Dose.

SAR Structure-Activity Relationship.

SAB Science Advisory Board.

SDWA Safe Drinking Water Act.

SF Safety Factor.

STORET Storage Retrieval.

TCDD-dioxin Tetrachlorodibenzo-p-dioxin.

TEAM Total Exposure Assessment

Methodology.

TEF Toxicity Equivalency Factor.

TMDL Total Maximum Daily Load.

TSD Technical Support Document.

USDA United States Department of

Agriculture.

UF Uncertainty Factor.

WQBEL Water Quality-Based Effluent

Limits.

Table of Contents

Summary of Today's Action

Appendix I. Background

A. Water Quality Criteria and Standards

1. Water Quality Criteria and the Criteria Derivation

Methodology

2. Summary of the 1980 AWQC National Guidelines

3. Water Quality Standards

B. Need for Revision of the 1980 AWQC National Guidelines

1. Scientific Advances Since 1980

2. EPA Human Health Risk Assessment Guidelines Development Since

1980

3. Differing Risk Assessment and Risk Management Approaches for

AWQC and MCLGs

C. Steps Taken toward Evaluating and Revising the 1980 AWQC

National Guidelines

1. September 1992 National Workshop

2. Science Advisory Board Review

3. FSTRAC Review

4. Water Quality Guidance for the Great Lakes System

D. Overview of AWQC Methodology Revisions, Major Changes, and

Issues

E. Risk Characterization Considerations

1. Background

2. Additional Guiding Principles

3. Risk Characterization Applied to the Revised AWQC Methodology

4. Science, Science Policy, and Risk Management

5. Discussion of Uncertainty

(a) Observed Range of Toxicity Versus Range of Environmental

Exposure

(b) Continuum of Preferred Data/Use of Defaults

Appendix II. Implementation of AWQC Methodology Revisions

A. Relationship to Other EPA Activities

B. Status of Existing 304(a) Criteria for Priority Pollutants

and Methodology

C. State and Tribal Criteria Development

D. Process for Developing New or Revised 304(a) Criteria

E. Development of Future Criteria Documents

F. Prioritization Scheme for Selecting Chemicals for Updating

G. Request for Comments

Appendix III. Elements of Methodology Revisions and Issues by

Technical Area

A. Cancer Effects

1. Background on EPA Cancer Assessment Guidelines

(a) 1980 AWQC National Guidelines

(b) 1986 EPA Guidelines for Carcinogenic Risk Assessment

Assessment Methodology for the Development of AWQC

2. Proposed Revisions to EPA's Carcinogen Risk Assessment

Guidelines

3. Revised Carcinogen Risk Assessment Methodology for Deriving

AWQC

(a) Weight-of-Evidence Narrative

(b) Dose Estimation

(1) Determining the Human Equivalent Dose

(2) Dose Adjustments for Less-than-Lifetime Exposure Periods

(3) Dose-Response Analysis

Observation

(1) Extrapolation to Low, Environmentally Relevant Doses

(2) Biologically Based Modeling Approaches

(3) Default Linear Extrapolation Approach

(4) Default Nonlinear Approach

(5) Both Linear and Nonlinear Approaches

(d) AWQC Calculation

(e) Risk Characterization

(f) Use of Toxicity Equivalence Factors (TEF) and Relative

Potency Estimates

4. Request for Comments

References for Cancer Effects

B. Noncancer Effects

1. 1980 AWQC National Guidelines for Noncancer Effects

2. Noncancer Risk Assessment Developments Since 1980

3. Issues and Recommendations Concerning the Derivation of AWQC

for Noncarcinogens

(a) Using the Current NOAEL-UF Based RfD Approach or Adopting

More Quantitative Approaches for Noncancer Risk Assessment

(1) The Benchmark Dose

(2) Categorical Regression

(3) Summary

(b) Presenting the RfD as a Single Point or as a Range for

Deriving AWQC

Effects Values

(d) Treatment of Uncertainty Factors/Severity of Effects During

the RfD Derivation and Verification Process

(e) Use of Less-Than-90-Day Studies to Derive RfDs

(f) Use of Reproductive/Developmental, Immunotoxicity, and

Neurotoxicity Data as the Basis for Deriving RfDs

(g) Applicability of Physiologically Based Pharmacokinetic

(PBPK) Data in Risk Assessment

(h) Consideration of Linearity (or Lack of a Threshold) for

Noncarcinogenic Chemicals

(i) Minimum Data Requirements

4. SAB Comments

5. Request for Comments

References for Noncancer Effects

C. Exposure

1. Policy Issues

(a) Identifying the Population Subgroup that the AWQC Should

Protect

(b) Appropriateness of Including the Drinking Water Pathway in

AWQC

Standards

(d) Setting Separate AWQC for Drinking Water and Fish

Consumption

(e) Incidental Ingestion from Ambient Surface Waters

2. Consideration of Nonwater Sources of Exposure When Setting

AWQC

(a) Background

(b) Exposure Decision Tree Approach

(d) Inclusion of Inhalation and Dermal Exposures From Household

Drinking Water Uses

(e) Inclusion of Inhalation Exposures in RSC Analysis

[[Page 43758]]

(f) Bioavailability of Substances from Different Routes of

Exposure

(g) Consideration of Non-water Exposure Procedures for

Noncarcinogens, Linear Carcinogens, and Nonlinear Carcinogens

3. Factors Used in the AWQC Computation

(a) Human Body Weight Values for Dose Calculations

(1) Rate Protective of Human Health from Chronic Exposure

(2) Rates Protective of Developmental Human Health Effects

(3) Rates Based on Combining Intake and Body Weight

(b) Drinking Water Intake Rates

(1) Rate Protective of Human Health from Chronic Exposure

(2) Rates Protective of Developmental Human Health Effects

(3) Rates Based on Combining Drinking Water Intake and Body

Weight

(d) Fish Intake Rates

(1) Rates Protective of Human Health from Chronic Exposure

(2) Rates Protective of Developmental Human Health Effects

(3) Rates Based on Combining Fish Intake and Body Weight

4. Request for Comments

References for Exposure

D. Bioaccumulation

1. Introduction

2. Bioaccumulation and Bioconcentration Concepts

3. Existing EPA Guidance

4. Definitions

5. Determining Bioaccumulation Factors for Nonpolar Organic

Chemicals

6. Estimating Baseline BAFs

(a) Field-Measured Baseline BAF

(b) Baseline BAF Derived from BSAFs

and FCM

(d) Calculation of a Baseline BAF from a Kow and FCM

(e) Metabolism

7. BAFs Used in Deriving AWQC

8. Inorganic Substances

9. SAB Comments

10. Issues for Public Comment

References for Bioaccumulation

E. Microbiology

1. Existing Microbiological Criteria

2. Plans for Future Work

3. SAB Comments

References for Microbiology

F. Other Considerations

1. Minimum Data Considerations

2. Site-Specific Criterion Calculation

3. Organoleptic Criteria

4. Criteria for Chemical Classes

5. Criteria for Essential Elements

Appendix IV. Summary of Ambient Water Quality Criteria for the

Protection of Human Health: Acrylonitrile

Appendix V. Summary of Ambient Water Quality Criteria for the

Protection of Human Health: 1,3-Dichloropropene

Appendix VI. Summary of Ambient Water Quality Criteria for the

Protection of Human Health: Hexachlorobutadiene

Summary of Today's Action

I. Background

Section 304(a)(1) of the Clean Water Act requires EPA to develop

and periodically revise criteria for water quality accurately

reflecting the latest scientific knowledge. In 1980, EPA published

ambient water quality criteria (AWQC) for 64 pollutants/pollutant

classes and provided a methodology for deriving the criteria. The 1980

AWQC National Guidelines for developing human health AWQC addressed

three types of endpoints: noncancer, cancer and organoleptic (taste and

odor) effects. Criteria values for the protection against noncancer and

cancer effects were estimated by using risk assessment-based

procedures, including extrapolation from animal toxicity or human

epidemiological studies. Basic human exposure assumptions were applied

to the criterion equation, such as: the exposed individual is a 70-

kilogram adult male; the assumed consumption of freshwater and

estuarine fish and shellfish is 6.5 grams/day; and the assumed

ingestion rate of drinking water is 2 liters/day. When using cancer as

the critical risk assessment endpoint, which was assumed not to have a

threshold, the AWQC were presented for information purposes as a range

of concentrations associated with specified incremental lifetime risk

levels (i.e., a range from 10-5 to 10-7). When

using noncancer effects as the critical endpoint, the AWQC reflected an

assessment of a ``no-effect'' level, since noncancer effects generally

exhibit a threshold.

Scientific Advances Since 1980

Since 1980, EPA risk assessment practices have evolved

significantly, particularly in the areas of cancer and noncancer risk

assessments, exposure assessments and bioaccumulation. In cancer risk

assessment, there have been advances with respect to the use of mode of

action information to support both the identification of carcinogens

and the selection of procedures to characterize risk at low,

environmentally relevant exposure levels. Related to this is the

development of new procedures to quantify cancer risks at low doses to

replace the current default use of the linearized multistage (LMS)

model. In noncancer risk assessment, the Agency is moving toward the

use of the benchmark dose (BMD) and other dose-response approaches in

place of the traditional NOAEL approach to estimate a reference dose or

concentration. In exposure analysis, several new studies have addressed

water consumption and fish tissue consumption. These exposure studies

provide a more current and comprehensive description of national,

regional and special population consumption patterns that EPA has

reflected in the Draft AWQC Methodology Revisions. In addition, more

formalized procedures are now available to account for human exposure

to multiple sources when setting health goals such as AWQC that have

addressed only one exposure source. With respect to bioaccumulation,

the Agency has moved toward the use of a bioaccumulation factor (BAF)

to reflect the uptake of a contaminant from all sources (e.g.,

ingestion, sediment) by fish and shellfish, rather than just from the

water column as reflected by the use of a bioconcentration factor (BCF)

as included in the 1980 methodology. The Agency has developed detailed

procedures and guidelines for estimating BAF values.

EPA Human Health Risk Assessment Guidelines Developed Since 1980

When the 1980 AWQC National Guidelines were developed, EPA had not

yet developed formal cancer or noncancer risk assessment guidelines.

Since then EPA has published several risk assessment guidelines

documents. In 1996, the Agency published Proposed Guidelines for

Carcinogen Risk Assessment (61 FR 17960) which when finalized will

supersede the carcinogenic risk assessment guidelines published in 1986

(51 FR 33992). In addition, guidelines for mutagenicity assessment were

also published in 1986 (51 FR 34006). The Agency also issued guidelines

for assessing the health risks to chemical mixtures in 1986 (51 FR

34014). With respect to noncancer risk assessment, the Agency published

guidelines in 1988 for assessing male and female reproductive risk (53

FR 24834) and in 1991 for assessing developmental toxicity (56 FR

63798). The guidelines for assessing reproductive toxicity were

subsequently updated and finalized (61 FR 56274) in 1996. In 1991, the

Agency also developed an external review draft of revised risk

assessment guidelines for noncancer health effects. In 1995, EPA also

proposed guidelines for neurotoxicity risk assessment (60 FR 52032).

In addition to these risk assessment guidelines, EPA also published

the ``Exposure Factors Handbook'' in 1989, which presents commonly used

Agency exposure assumptions and the surveys from which they are

derived. The Exposure Factors Handbook (EPA/600/P-95/002Fa) was updated

in 1997. In 1992, EPA published the revised

[[Page 43759]]

Guidelines for Exposure Assessment (57 FR 22888), which describe

general concepts of exposure assessment, including definitions and

associated units, and provide guidance on planning and conducting an

exposure assessment. Also, in the 1980s the Agency published the Total

Exposure Assessment Methodology (TEAM), which presents a process for

conducting comprehensive evaluation of human exposures. The Agency has

recently developed the Relative Source Contribution Policy, which is

currently undergoing Agency review, for assessing total human exposure

to a contaminant and allocating the RfD among the media of concern. In

1997, EPA developed draft Guiding Principles for Monte Carlo analysis.

Also, in 1986, the Agency made available to the public the

Integrated Risk Information System (IRIS). IRIS is a data base that

contains risk information on the cancer and noncancer effects of

chemicals. The IRIS assessments are peer reviewed and represent EPA

consensus positions across the Agency's program offices and regional

offices. In 1995, the Agency initiated an IRIS pilot program to test

improvements to the internal peer review and consensus processes, and

to provide more integrated characterizations of cancer and noncancer

health effects.

Differing Risk Assessment and Risk Management Approaches for AWQC and

MCLGs

Another reason for these revisions is the need to bridge the gap

between the differences in the risk assessment and risk management

approaches used by EPA's Office of Water for the derivation of AWQC

under the authority of the CWA and MCLGs (Maximum Contaminant Level

Goals) under the Safe Drinking Water Act (SDWA). Three notable

differences are with respect to the treatment of chemicals designated

as Group C possible human carcinogens--under the 1986 Guidelines for

Carcinogen Risk Assessment, the consideration of nonwater sources of

exposure when setting an AWQC or MCLG for a noncarcinogen, and cancer

risk ranges.

1. Group C Chemicals. Chemicals have been typically classified as

Group C--i.e., possible human carcinogens'--under the existing (1986)

EPA cancer classification scheme for any of the following reasons:

(1) Carcinogenicity has been documented in only one test species

and/or only one cancer bioassay and the results do not meet the

requirements of ``sufficient evidence.''

(2) Tumor response is of marginal significance due to inadequate

design or reporting.

(3) Benign, but not malignant, tumors occur with an agent showing

no response in a variety of short-term tests for mutagenicity.

(4) There are responses of marginal statistical significance in a

tissue known to have a high or variable background rate.

The 1986 Guidelines for Carcinogen Risk Assessment specifically

recognized the need for flexibility with respect to quantifying the

risk of Group C agents. The guidelines noted that agents judged to be

in Group C, possible human carcinogens, may generally be regarded as

suitable for quantitative risk assessment, but that case-by-case

judgments may be made in this regard.

The EPA Office of Water has historically treated Group C chemicals

differently under the CWA and the SDWA. It is important to note that

the 1980 AWQC National Guidelines for setting AWQC under the CWA

predated EPA's carcinogen classification system, which was proposed in

1984 (49 FR 46294) and finalized in 1986 (51 FR 33992). The 1980 AWQC

National Guidelines did not explicitly differentiate among agents with

respect to the weight-of-evidence for characterizing them as likely to

be carcinogenic to humans. For all pollutants judged as having adequate

data for quantifying carcinogenic risk--including those now classified

as Group C--AWQC were derived based on data on cancer incidence. In the

November 1980 Federal Register document, EPA emphasized that the AWQC

for carcinogens should state that the recommended concentration for

maximum protection of human health is zero. At the same time, the

criteria published for specific carcinogens presented water

concentrations for these pollutants corresponding to individual

lifetime cancer risk levels in the range of 10-7 to

10-5.

In the development of national primary drinking water regulations

under the SDWA, EPA is required to promulgate a health-based MCLG for

each contaminant. The Agency policy has been to set the MCLG at zero

for chemicals with strong evidence of carcinogenicity associated with

exposure from water. For chemicals with limited evidence of

carcinogenicity, including many Group C agents, the MCLG is usually

obtained using an RfD based on its noncancer effects with the

application of an additional uncertainty factor of 1 to 10 to account

for its possible carcinogenicity. If valid noncancer data for a Group C

agent are not available to establish an RfD but adequate data are

available to quantify the cancer risk, then the MCLG is based upon a

nominal lifetime excess cancer risk calculation in the range of

10-5 to 10-6 (ranging from one case in a

population of one hundred thousand to one case in a population of one

million). Even in those cases where the RfD approach has been used for

the derivation of the MCLG for a Group C agent, the drinking water

concentrations associated with excess cancer risks in the range of

10-5 to 10-6 were also provided for comparison.

It should also be noted that EPA's pesticides program has applied

both of the previously described methods for addressing Group C

chemicals in actions taken under the Federal Insecticide, Fungicide,

and Rodenticide Act (FIFRA) and finds both methods applicable on a

case-by-case basis. Unlike the drinking water program, however, the

pesticides program does not add an extra uncertainty factor to account

for potential carcinogenicity when using the RfD approach.

2. Consideration of Nonwater Sources of Exposure. The 1980 AWQC

National Guidelines for setting AWQC recommended that contributions

from nonwater sources, namely air and non-fish dietary intake, be

subtracted from the ADI, thus reducing the amount of the ADI

``available'' for water-related sources of intake. In practice,

however, when calculating human health criteria, these other exposures

were generally not considered because reliable data on these exposure

pathways were not available. Consequently, the AWQC were usually

derived such that drinking water and fish ingestion accounted for the

entire ADI (now called RfD).

In the drinking water program, a similar ``subtraction'' method was

used in the derivation of MCLGs proposed and promulgated in drinking

water regulations through the mid-1980s. More recently, the drinking

water program has consistently used a ``percentage'' method in the

derivation of MCLGs for noncarcinogens. In this approach, the

percentage of total exposure typically accounted for by drinking water,

referred to as the relative source contribution (RSC), is applied to

the RfD to determine the maximum amount of the RfD ``allocated'' to

drinking water reflected by the MCLG value. In using this percentage

procedure, the drinking water program also applies a ceiling level of

80 percent of the RfD and a floor level of 20 percent of the RfD. That

is, the MCLG cannot account for more than 80 percent of the RfD, nor

less than 20 percent of the RfD.

[[Page 43760]]

The drinking water program usually takes a conservative public

health approach of applying an RSC factor of 20 percent to the RfD when

adequate exposure data do not exist, assuming that the major portion

(80 percent) of the total exposure comes from other sources, such as

diet.

3. Cancer Risk Ranges. In addition to the different risk assessment

approaches discussed above for deriving AWQC and MCLGs for Group C

agents, different risk management approaches have arisen between the

drinking water and ambient surface water programs with respect to using

lifetime excess risk values when setting health-based criteria for

carcinogens. As indicated previously, the surface water program

historically derived AWQC for carcinogens that generally corresponded

to lifetime excess cancer risk levels of 10-7 to

10-5. The drinking water program has set MCLGs for Group C

agents based on a slightly less stringent risk range of 10-6

to 10-5, while MCLGs for chemicals with strong evidence of

carcinogenicity (that is, classified as Group A (known) or B (probable)

human carcinogen) are set at zero.

It is also important to note that under the drinking water program,

for those substances having an MCLG of zero, enforceable Maximum

Contaminant Levels (MCLs) have generally been promulgated to correspond

with cancer risk levels ranging from 10-6 to

10-4. Unlike AWQC and MCLGs which are strictly health-based

criteria, MCLs are developed with consideration given to the costs and

technological feasibility of reducing contaminant levels in water to

meet those standards.

Steps Taken Toward Evaluating and Revising the 1980 AWQC National

Guidelines

In order to begin developing a ``state-of-the-science'' approach to

revising the 1980 AWQC National Guidelines, EPA prepared an issues

paper that described the 1980 methodology, discussed areas that needed

strengthening, and proposed revisions. This paper was then distributed

for review and comment to experts at EPA headquarters, regional

offices, and laboratories; other Federal Agencies, such as the Food and

Drug Administration (FDA), the National Institute of Environmental

Health Sciences (NIEHS), and the Centers for Disease Control and

Prevention (CDC); State health organizations; Canadian health agencies;

academe; and environmental, industry, and consulting organizations.

1. September 1992 National Workshop. On September 13-16, 1992, more

than 100 invited participants discussed the critical issues in a

workshop convened in Bethesda, Maryland. Based on their expertise,

attendees were assigned to specific technical work groups. The work

group topics were cancer risk, noncancer risk, exposure, microbiology,

minimum data, and bioaccumulation. Each work group member received a

set of detailed questions that served to focus discussions on critical

factors in the 1980 AWQC National Guidelines. After the work group

members deliberated separately on their specific technical areas, all

workshop participants were given the opportunity to comment on the

proceedings. After the workshop concluded, the chairperson for each

technical work group prepared a written summary of that group's

deliberations and recommendations. Each work group participant was

given the opportunity to review and comment on the summaries; these

comments were used to prepare a draft of the proposed revision to the

methodology.

2. Science Advisory Board Review. After review of the draft of the

proposed revisions to the methodology by EPA, the workshop

participants, and other relevant parties, a summary document was

submitted for review and comment to the Science Advisory Board (SAB) in

January 1993 and presented to the Drinking Water Committee of the SAB

during its meeting on February 8-9, 1993. The SAB presented its

official comments to EPA on August 12, 1993. The SAB comments have been

highlighted and addressed in each of the technical areas discussed in

Appendix III of this document. A complete copy of the document

submitted to the SAB and SAB's comments are available in the docket

accompanying this document.

3. FSTRAC Review. At the Federal State Toxicology and Risk Analysis

Committee (FSTRAC) meeting on December 1-3, 1993, in Washington, D.C.,

several State representatives presented their opinions on the

preliminary draft recommendations for revisions to the 1980 AWQC

National Guidelines. A summary of this meeting is presented in a

document entitled ``Workshop Summary: State Comments on the Preliminary

Draft Revisions of the Methodology for Deriving National Ambient Water

Quality Criteria for the Protection of Human Health.'' This document is

also available for review in the docket supporting this proposal.

4. Water Quality Guidance for the Great Lakes System. In March

1995, EPA published the Final Water Quality Guidance for the Great

Lakes System (60 FR 15366). The Great Lakes Water Quality Guidance,

developed under Section 118(c)(2) of the CWA, provides water quality

criteria for 29 pollutants as well as methodologies, policies, and

procedures for Great Lakes States and Tribes to establish consistent,

long-term protection for fish and shellfish in the Great Lakes and

their tributaries, as well as for the people and wildlife who consume

them. In developing the methodology to derive human health criteria for

the waters of the Great Lakes System, the Agency was mindful of the

need for consistency with the planned changes in the methodology for

deriving national AWQC for the protection of human health presented in

today's proposal. Throughout the following text, references are made to

comparisons of the two methodologies, national and Great Lakes Water

Quality Guidance, especially whenever differences occur due to regional

exposure assumptions made for the Great Lakes System.

Major Changes in the Draft AWQC Methodology Revisions

The proposal presents several changes from the 1980 AWQC National

Guidelines:

1. EPA's future role in developing AWQC for the protection of human

health will include the refinement of the revised methodology, the

development of revised criteria for chemicals of high priority and

national importance (including, but not limited to chemicals that

bioaccumulate, such as PCBs, dioxin, and mercury), and the development

or revision of AWQC for some additional priority chemicals. EPA does

not plan to completely revise all of the criteria developed in 1980 or

those updated as part of the proposed California Toxics Rule (CTR) 62

FR 42160, August 5, 1997. (This rule proposes for California, numeric

water quality criteria for priority toxic pollutants necessary to

fulfill the requirements of Section 303(c)(2)(b) of the CWA.) Further,

EPA intends to revise 304(a) criteria on the basis of one or more

components (e.g., BAF, fish intake, toxicological assessment) rather

than a full set of components. Appendix II of the FR document discusses

how the Agency is proposing to implement the methodology and revise the

304(a) criteria. EPA also discusses the role of 304(a) criteria in

State/Tribal adoption of water quality standards under Section 303(c)

of the CWA, EPA's responsibilities in reviewing and approving State/

Tribal standards, and EPA's duties in regards to promulgating State/

Tribal standards when necessary.

2. EPA encourages States and Tribes to use the revised methodology,

once finalized, to develop or revise AWQC to

[[Page 43761]]

appropriately reflect local conditions. EPA believes that AWQC

inherently require several risk management decisions that are, in many

cases, better made at the State and Tribal level (e.g., fish

consumption rates, target risk levels). EPA will continue to develop

and update necessary toxicological and exposure data needed in the

derivation of AWQC that may not be practical for the States or Tribes

to obtain. EPA encourages States and Tribes to use local or regional

fish consumption data when available.

3. The equations for deriving AWQC include toxicological and

exposure assessment parameters which are derived from scientific

analysis, science policy, and risk management decisions. For example,

parameters such as a field-measured BAF or a point of departure from an

animal study (in the form of a LOAEL/NOAEL/LED10) are

scientific values which are empirically measured, whereas the decision

to use animal effects as a surrogate for human effects involves

judgment on the part of the EPA (and similarly, by other agencies) as

to the best practice to follow when human data are lacking. Such a

decision is, therefore, a matter of science policy. On the other hand,

the choice of default fish consumption rates for protection of a

certain percentage of the general population, is clearly a risk

management decision. In many cases, the Agency has selected parameters

using its best judgment regarding the overall protection afforded by

the resulting AWQC when all parameters are combined. Appendix I

discusses in detail the differences between science, science policy,

and risk management. Appendix I also provides further details with

regard to risk characterization as related to this methodology, with

emphasis placed on explaining the uncertainties in the overall risk

assessment.

4. The Draft AWQC Methodology Revisions provide an alternative to

expressing AWQC as a water concentration. AWQC may also be expressed in

terms of a fish tissue concentration. For some substances, particularly

those that are expected to exhibit substantial bioaccumulation, the

AWQC derived using the above equations may have extremely low values,

possibly below the practical limits for detecting and quantifying the

substance in the water column. It may, therefore, be more practical and

meaningful in these cases to focus on the concentration of those

substances in fish tissue, since fish ingestion would be the

predominant source of exposure for substances that bioaccumulate.

5. EPA is proposing an incidental water ingestion exposure rate of

0.01 L/day to account for long-term incidental recreational ingestion

(i.e., swimming, boating, fishing) for use in those cases where AWQC

are developed for recreational waters that are not used as drinking

water sources.

6. AWQC for the protection of human health are designed to minimize

the risk of adverse effects occurring to humans from chronic (lifetime)

exposure to substances through the ingestion of drinking water and

consumption of fish obtained from surface waters. The Agency is not

recommending the development of additional water quality criteria

similar to the ``drinking water health advisories'' that focus on acute

or short-term effects, since these are not seen routinely as having a

meaningful role in the water quality criteria and standards program.

However, there may be some instances where the consideration of

short-term toxicity and exposure in the derivation of AWQC is

warranted. Although the AWQC are based on chronic health effects data

(both cancer and noncancer effects), the criteria are intended to also

be protective with respect to adverse effects that may reasonably be

expected to occur as a result of elevated short-term exposures. That

is, through the use of conservative assumptions with respect to both

toxicity and exposure parameters, the resulting AWQC values should

provide adequate protection not only for the general population over a

lifetime of exposure, but also for special subpopulations who, because

of high water- or fish-intake rates, or because of biological

sensitivities, have an increased risk of receiving a dose that would

elicit adverse effects from short-term exposures. The Agency

recognizes, however, that there may be some cases where the AWQC values

based on chronic toxicity may not provide adequate protection for a

subpopulation at special risk from such exposures. The Agency

encourages States, Tribes, and others employing the proposed

methodology to give consideration to such circumstances in deriving

criteria to ensure that adequate protection is afforded to all

identifiable subpopulations. (Appendix III discusses this in greater

detail.)

7. For noncarcinogens, risk managers may select another value

within an RfD range rather than the default point estimate RfD value,

in criteria development, where a rationale for the range and the value

selected can be provided. General guidance for the use of values within

the RfD range is provided based on the overall uncertainty associated

with the RfD and when adverse health effects in children are not the

basis for the RfD. For example, if the IRIS RfD is 1 mg/kg/day and the

uncertainty factor (UF) is 1,000, a log-symmetrical order of magnitude

around 1 mg/kg/day could be used resulting in a range of 0.3 to 3 mg/

kg/day. If the UF were less than 1,000, the overall range would be

reduced accordingly (e.g., \1/2\ log for UFs between 100 and 1,000; and

no range for UFs of 100 or less). However, EPA would select the point

estimate as a default (the midpoint within the range) when calculating

a 304(a) criteria value for the purposes of promulgating State or

Tribal water quality standards.

8. The Draft AWQC Methodology Revisions reflect EPA's 1996 Proposed

Guidelines for Carcinogen Risk Assessment. For instance, mode of action

(MoA) information is used to determine the most appropriate low-dose

extrapolation approach for carcinogenic agents. The dose-response

assessment under the new guidelines is a two-step process. In the first

step, the response data are modeled in the range of empirical

observation. Modeling in the observed range is done with biologically

based or appropriate curve-fitting modeling. In the second step,

extrapolation below the range of observation is accomplished by

biologically based modeling if there are sufficient data or by a

default procedure (linear, nonlinear, or both). A point of departure

for extrapolation is estimated from modeling observed data. The lower

95 percent confidence limit on a dose associated with 10 percent extra

risk (i.e., LED10) is proposed as a standard point of

departure for low-dose extrapolation. If it is determined that the MoA

understanding supports a nonlinear extrapolation, the AWQC is derived

using the nonlinear default which is based on a margin of exposure

(MoE) analysis for the point of departure (e.g., the LED10)

and applying a safety factor(s) in the risk management. The linear

default would be considered for those agents that are better supported

by the assumption of linearity (e.g., direct DNA reactive mutagens) for

their MoA. A linear approach would also be applied when inadequate or

no information is available to explain the carcinogenic MoA as a

science policy choice in the interest of public health. The linear

default is a straight line extrapolation to the origin (i.e., zero

dose, zero extra risk) from the point of departure (e.g.,

LED10) identified in the observable response range. There

may be situations where it is appropriate to apply both the linear and

nonlinear

[[Page 43762]]

default procedures (e.g., for an agent that is both DNA reactive and

active as a promoter at higher doses).

9. For substances that are carcinogenic, particularly those for

which the mode of action suggests nonlinearity at low doses, the Agency

recommends that an integrated approach be taken in looking at cancer

and noncancer effects, and if one pathway does not predominate, AWQC

values should be determined for both carcinogenic and noncarcinogenic

effects. The lower of the resulting values should be used for the AWQC.

10. When deriving AWQC for noncarcinogens and nonlinear

carcinogens, a factor must be included to account for other nonwater

exposure sources so that the entire RfD, or [Point of Departure (Pdp)

divided by a safety factor (SF); (Pdp)/SF)] is not allocated to

drinking water and fish consumption alone. Guidance is provided in the

revised methodology for determining the factor, referred to as the

relative source contribution (RSC), to be used for a particular

chemical. The Agency is proposing the use of a decision tree procedure

to support the determination of the appropriate RSC value for a given

water contaminant. In the absence of data, the Agency will use 20

percent of the RfD as the default RSC in calculating a 304(a) criteria

value for the purposes of promulgating State or Tribal water quality

standards.

11. When deriving AWQC for linear carcinogens, the Agency

recommends that risk levels in the range of 10-5 to

10-6 be used for the protection of the general population.

States and Tribes can always choose a more stringent risk level, such

as 10-7. Care should be taken, however, in situations where

the AWQC includes fish intake levels based on the general population to

ensure that the risk to more highly exposed subgroups (sportfishers or

subsistence fishers) does not exceed the 10-4 level.

12. The default fish consumption values are 17.80 grams/day for the

general population, which represents the 90th percentile consumption

rate for the entire population (and approximates the average

consumption rate for sport anglers, nationally) and 86.30 grams/day for

subsistence fishers/minority anglers, which represents the 99th

percentile consumption rate for the general population and is within

the range of average intakes for subsistence fishers/minority anglers

(comments are requested on alternatively using 39.04 grams/day for

subsistence fishers/minority anglers, which is lower in the range of

averages). These values are derived from the United States Department

of Agriculture's (USDA) Continuing Survey of Food Intake by Individuals

(CSFII) from 1989-1991. These rates replace the single default value of

6.5 grams/day used in the 1980 AWQC National Guidelines. These default

values are chosen to be protective of the majority of the individuals

in those groups. However, States and Tribes are urged to use a fish

intake level derived from local data on fish consumption in place of

these default values when deriving AWQC, ensuring that the fish intake

level chosen be protective of highly exposed individuals in the

population. Consumption rates for women of childbearing age and

children younger than 14 are also provided to maximize protection in

those cases where these subpopulations may be at greatest risk.

13. All criteria should be derived using a BAF rather than a BCF,

which was used in the 1980 AWQC National Guidelines. The BAF should be

developed using the EPA methodology or any method consistent with the

EPA method. EPA's highest preference in developing BAFs are BAFs based

on field-measured data from local/regional fish.

14. EPA is neither setting organoleptic criteria nor a default

methodology for deriving such criteria. Such criteria will necessitate

case-by-case analysis.

The attached document includes six major sections: Appendix I,

which discusses the purpose of the methodology, the background

associated with the original methodology and the need for revision, and

the major changes in the revised methodology; Appendix II, which

addresses implementation issues associated with the methodology;

Appendix III, which presents the main scientific areas that make up the

methodology (cancer, noncancer, exposure, and bioaccumulation methods);

and Appendices IV through VI, which present summaries of the three

criteria developed for inclusion with the revised methodology. Complete

versions of the three criteria documents are available on the Internet

at http://www.epa.gov/OST/Rules/index.html#open.

This document proposes revisions to EPA's 1980 methodology for the

development of water quality criteria to protect human health. The

revisions reflect scientific advancements since 1980 in a number of

areas, including cancer and noncancer risk assessments, exposure

assessments and bioaccumulation. When final, the revised methodology

will provide guidance to States, Tribes, and the public on the approach

that EPA expects to take in developing recommended human health

criteria. The revised methodology also will provide guidance to States

and Tribes that they may use in developing human health criteria as

part of their water quality standards; States and Tribes use such

standards in implementing a number of environmental programs, including

setting discharge limits in NPDES permits. The revised methodology does

not substitute for the Clean Water Act or EPA's regulations; nor is it

a regulation itself. Thus, the revised methodology cannot impose

legally-binding requirements on EPA, States, or the public, and may not

apply to a particular situation based upon the circumstances. EPA and

State decisionmakers retain the discretion to use different,

scientifically defensible, methodologies to develop human health

criteria. EPA may change the methodology in the future.

This criteria methodology incorporates scientific advancements made

over the past two decades. The use of this methodology is an important

component of the Agency's efforts to improve the quality of the

Nation's waters. EPA believes the methodology will enhance the overall

scientific basis of water quality criteria. Further, the methodology

should help States and Tribes address their unique water quality issues

and risk management decisions, and afford them greater flexibility in

developing their water quality programs.

Dated: August 3, 1998.

J. Charles Fox,

Acting Assistant Administrator for Water.

Appendix I. Background

A. Water Quality Criteria and Standards

1. Water Quality Criteria and the Criteria Derivation Methodology

EPA published the availability of ambient water quality criteria

(AWQC) documents for 64 toxic pollutants and pollutant categories

identified in Section 307(a) of the Clean Water Act (CWA) in the

Federal Register on November 28, 1980 (45 FR 79318). The November 1980

Federal Register document also summarized the criteria documents and

discussed in detail the methods used to derive the AWQC for those

pollutants. The AWQC for those 64 pollutants and pollutant categories

were published pursuant to Section 304(a)(1) of the CWA:

``The Administrator, * * * shall develop and publish, * * *,

(and from time to time thereafter revise) criteria for water quality

accurately reflecting the latest scientific knowledge (A) on the

kind and extent of all identifiable effects on health and welfare

including, but not limited to, plankton, fish, shellfish, wildlife,

plant life, shorelines,

[[Page 43763]]

beaches, esthetics, and recreation which may be expected from the

presence of pollutants in any body of water, including ground water;

(B) on the concentration and dispersal of pollutants, or their

byproducts, through biological, physical, and chemical processes;

and (C) on the effects of pollutants on the biological community

diversity, productivity, and stability, including information on the

factors affecting rates of eutrophication and rates of organic and

inorganic sedimentation for varying types of receiving waters.''

The AWQC published in November 1980 provided two essential types of

information: (1) discussions of available scientific data on the

effects of the pollutants on public health and welfare, aquatic life,

and recreation; and (2) quantitative concentrations or qualitative

assessments of the levels of pollutants in water which, if not

exceeded, will generally ensure adequate water quality for a specified

water use. Water quality criteria developed under Section 304(a) are

based solely on data and scientific judgments on the relationship

between pollutant concentrations and environmental and human health

effects. The 304(a) criteria do not reflect consideration of economic

impacts or the technological feasibility of meeting the chemical

concentrations in ambient water. As discussed below, 304(a) criteria

may be used as guidance by States and Tribes to establish water quality

standards, which ultimately provide a basis for controlling discharges

or releases of pollutants.

The 1980 AWQC were derived using guidelines and methodologies

developed by the Agency for calculating the impact of waterborne

pollutants on aquatic organisms and on human health. Those guidelines

and methodologies consisted of systematic procedures for assessing

valid and appropriate data concerning a pollutant's acute and chronic

adverse effects on aquatic organisms, nonhuman mammals, and humans. The

guidelines and methodologies were fully described in Appendix B (for

protection of aquatic life and its uses) and Appendix C (for protection

of human health) of the November 1980 Federal Register document.

This revised methodology addresses the development of AWQC to

protect human health; a similar process to revise the methodology for

deriving AWQC for the protection of aquatic life is currently underway

at the Agency. When finalized, the Agency intends to use the revised

AWQC human health methodology to both develop new AWQC for additional

chemicals and to revise existing AWQC. Appendices IV-VI are summaries

of criteria developed using the revised methodology. These AWQC were

developed to demonstrate the different risk assessment and exposure

approaches presented in the revised methodology. The complete criteria

documents are available from NTIS or on EPA's Internet web site. In

addition, EPA intends to derive AWQC for the protection of human health

for several chemicals of high priority, including but not limited to,

PCBs, lead, mercury, arsenic, and dioxin, within the next several

years. EPA anticipates that the focus of 304(a) criteria development

will be criteria for bioaccumulative chemicals and chemicals considered

highest priority by the Agency. The Draft AWQC Methodology Revisions

presented here are also intended to provide States and Tribes

flexibility in setting water quality standards by providing

scientifically valid options for developing their own water quality

criteria that consider local conditions. States and Tribes are

encouraged to use the methodology once it is finalized to derive their

own AWQC. However, the revised methodology also defines the default

factors EPA intends to use in evaluating and determining consistency of

State water quality standards with the requirements of the CWA. The

Agency intends to use these default factors to calculate water quality

criteria when promulgating water quality standards for a State or Tribe

under Section 303(c) of the Act.

2. Summary of the 1980 AWQC National Guidelines

The 1980 AWQC National Guidelines for developing AWQC for the

protection of human health addressed three types of endpoints:

noncancer, cancer, and organoleptic (taste and odor) effects. Criteria

values for protection against noncancer and cancer effects were

estimated by using risk assessment-based procedures, including

extrapolation from animal toxicity or human epidemiological studies.

Basic human exposure assumptions were applied, such as: the exposed

individual is a 70-kilogram adult male; the assumed consumption of

freshwater and estuarine fish and shellfish is 6.5 grams per day; and

the assumed ingestion rate of drinking water is 2 liters per day.

When using cancer as the critical risk assessment endpoint, which

has been assumed not to have a threshold, the AWQC were presented as a

range of concentrations associated with specified incremental lifetime

risk levels 1 (i.e., a range from 10-5 to

10-7). When using noncancer effects as the endpoint, the

AWQC reflected an assessment of a ``no-effect'' level, since noncancer

effects generally exhibit a threshold. The risk assessment-based

procedures used to derive the AWQC to protect human health were

specific to whether the endpoint was cancer or noncancer. The key

features of each procedure are described briefly in the following

sections.

---------------------------------------------------------------------------

\1\ Throughout this document, the term ``risk level'' regarding

a cancer assessment endpoint specifically refers to an upper-bound

estimate of excess lifetime cancer risk.

---------------------------------------------------------------------------

Cancer effects. If human or animal studies on a contaminant

indicated that it induced a statistically significant carcinogenic

response, the 1980 AWQC National Guidelines treated the contaminant as

a carcinogen and derived a low-dose cancer potency factor from

available animal data using the linearized multistage model (LMS). The

LMS, which uses a linear, nonthreshold assumption for low-dose risk,

was used by the Agency as a science policy choice in protecting public

health, and represents the most plausible upper limit for low-dose

risk. The cancer potency factor, which expresses incremental, lifetime

risk as a function of the rate of intake of the contaminant, was then

combined with exposure assumptions to express that risk in terms of an

ambient water concentration. In the 1980 AWQC National Guidelines, the

Agency presented a range of contaminant concentrations corresponding to

incremental cancer risks of 10-7 to 10-5 (that

is, a risk of one additional case of cancer in a population of ten

million to one additional cancer case in a population of one hundred

thousand, respectively). The risk range was presented for information

purposes and did not represent an Agency judgment on ``acceptable''

risk level. The Agency stated in 1980 that: ``for the maximum

protection of human health from the potential carcinogenic effects due

to exposure of Chemical X through ingestion of contaminated water and

aquatic organisms, the ambient water concentration should be zero based

on the nonthreshold assumption for this chemical. However, zero level

may not be attainable at the present time. Therefore, the levels which

may result in incremental cancer risk over the lifetime are estimated

at 10-5, 10-6, and 10-7.''

Noncancer effects. If the pollutant was not considered to have the

potential for causing cancer in humans (this was later defined as a

known, probable, or possible human carcinogen by the 1986 Guidelines

for Cancer Risk), the 1980 AWQC National Guidelines treated the

contaminant as a noncarcinogen, and a criterion was derived using a

threshold

[[Page 43764]]

concentration for noncancer adverse effects. The criteria derived from

noncancer data were based on the Acceptable Daily Intake (ADI) (now

termed the reference dose [RfD]). ADI values were generally derived

using no-observed- adverse-effect level (NOAEL) data from animal

studies, although human data were used whenever available. The ADI was

calculated by dividing the NOAEL by an uncertainty factor to account

for uncertainties inherent in extrapolating toxicological data from

animal studies to humans. In accordance with the National Research

Council recommendations of 1977, safety factors (later termed

uncertainty factors) of 10, 100, or 1,000 were used, depending on the

quality and quantity of the data.

Organoleptic effects. Organoleptic characteristics were also used

in developing criteria for some contaminants to control undesirable

taste and/or odor imparted by them to ambient water. In some cases, a

water quality criterion based on organoleptic effects would be more

stringent than a criterion based on toxicologic endpoints. The 1980

AWQC National Guidelines emphasized that criteria derived for

organoleptic endpoints are not based on toxicologic information, have

no direct relationship to adverse human health effects and, therefore,

do not necessarily represent approximations of acceptable risk levels

for humans.

3. Water Quality Standards

Under Section 303 of the CWA, States have the primary

responsibility to establish water quality standards, defined under the

Act as designated beneficial uses of a water segment and the water

quality criteria necessary to support those uses. Additionally, Native

American Tribes authorized to administer the water quality standards

program under 40 CFR 131.8 establish water quality standards for waters

within their jurisdictions. This statutory framework allows States and

Tribes to work with local communities to establish appropriate

designated uses, and adopt criteria to protect those designated uses.

Section 303 provides for EPA review of Water Quality Standards and for

promulgation of a superseding Federal rule in cases where State or

Tribal standards are not consistent with the applicable requirements of

the CWA, or in situations where the Agency determines Federal standards

are necessary to meet the requirements of the Act. Section 303(c)(2)(B)

specifically requires States and Tribes to adopt AWQC for toxics for

which EPA has published criteria under Section 304(a), and for which

the discharge or presence could reasonably be expected to interfere

with the designated use adopted by the State or Tribe. In adopting such

criteria, States and Tribes must establish numerical values based on

one of the following: (1) 304(a) criteria; (2) 304(a) criteria modified

to reflect site-specific conditions; or, (3) other scientifically

defensible methods.

In order to avoid confusion, it must be recognized that the Act

uses the term ``criteria'' in two separate ways. In Section 303(c), the

term is part of the definition of a water quality standard. That is, a

water quality standard is composed of designated uses and the criteria

necessary to protect those uses. Thus, States and Tribes are required

to adopt regulations which contain legally enforceable criteria.

However, in Section 304(a) the term criteria is used to describe the

scientific information that EPA develops to be used as guidance in the

State, Tribal, or Federal adoption of water quality standards pursuant

to 303(c). Thus, two distinct purposes are served by the

304(a)criteria. The first is as guidance to the States and Tribes in

the development and adoption of water quality criteria which will

protect designated uses, and the second is as the basis for

promulgation of a superseding Federal rule when such action is

necessary.

B. Need for Revision of the 1980 AWQC National Guidelines

l. Scientific Advances Since 1980

Since 1980, EPA risk assessment practices have evolved

significantly, particularly in the areas of cancer and noncancer risk

assessments, exposure assessments, and bioaccumulation. In cancer risk

assessment, there have been advances with respect to the use of mode of

action information to support both the identification of carcinogens

and the selection of procedures to characterize risk at low,

environmentally relevant exposure levels. Related to this is the

development of new procedures to quantify cancer risk at low doses to

replace the current default use of the LMS model. (See discussion in

Appendix III, Section A.) In noncancer risk assessment, the Agency is

moving toward the use of the benchmark dose (BMD) and other dose-

response approaches in place of the traditional NOAEL approach to

estimate a reference dose or concentration. A BMD is calculated by

fitting a mathematical dose-response model to data using appropriate

statistical procedures. (See discussion in Appendix III, Section B.)

In exposure analysis, several new studies have addressed water

consumption and fish-tissue consumption. These studies provide a more

current and comprehensive description of national, regional, and

special-population consumption patterns that EPA has reflected in the

Draft AWQC Methodology Revisions presented today. In addition, more

formalized procedures are now available to account for human exposure

from multiple sources when setting health goals such as AWQC that

address only one exposure source. (See discussion in Appendix III,

Section C.)

With respect to bioaccumulation, the Agency has moved toward the

use of a bioaccumulation factor (BAF) to reflect the uptake of a

contaminant from all sources (e.g., ingestion, sediment) by fish and

shellfish, rather than just from the water column as reflected by the

use of a bioconcentration factor (BCF) as included in the 1980

methodology. The Agency has also developed detailed procedures and

guidelines for estimating BAF values. (See discussion in Appendix III,

Section D.)

2. EPA Human Health Risk Assessment Guidelines Development Since 1980

When the 1980 AWQC methodology was developed, EPA had not yet

developed formal cancer or noncancer risk assessment guidelines. Since

then EPA has published several risk assessment guidelines documents. In

1996, the Agency proposed revised guidelines for carcinogenic risk

assessment (61 FR 17960) which when finalized will supersede the

carcinogenic risk assessment guidelines published in 1986 (51 FR

33992). In addition, guidelines for mutagenicity assessment were also

published in 1986 (51 FR 34006). The Agency also issued guidelines for

assessing the health risks to chemical mixtures in 1986 (51 FR 34014).

With respect to noncancer risk assessment, the Agency published