Guidelines Establishing Test Procedures for the Analysis of Pollutants; Measurement of Mercury in Water

SUMMARY: This proposed regulation would amend the guidelines

establishing test procedures for the analysis of pollutants under the

Clean Water Act by adding Method 1631: Mercury in Water by Oxidation,

Purge and Trap, and Cold Vapor Atomic Fluorescence. EPA Method 1631 was

developed in order to measure mercury reliably at the low levels

associated with ambient water quality criteria (WQC). EPA has

promulgated WQC for mercury at 12 parts-per-trillion (ppt) in the

National Toxics Rule, and published guidance criteria for mercury at

1.8 ppt in the Water Quality Guidance for the Great Lakes System. EPA

Method 1631 would need to be used in conjunction with clean sampling

and laboratory techniques to preclude contamination at the low ppt

levels necessary for mercury determinations. EPA has developed guidance

documents on sampling and clean rooms for trace metals, including

mercury.

DATES: Comments on this proposal must be submitted on or before July

27, 1998.

ADDRESSES: Send written comments on the proposed rule to ``Method

1631'' Comment Clerk (Docket # W-98-15); Water Docket (4101);

Environmental Protection Agency; 401 M Street, SW; Washington, DC

20460. Commenters are requested to submit any references cited in their

comments. Commenters are also requested to submit an original and three

copies of their written comments and enclosures. Commenters that want

receipt of their comments acknowledged should include a self addressed,

stamped envelope. All comments must be postmarked or delivered by hand.

No facsimiles (faxes) will be accepted.

Data availability: A copy of the supporting documents cited in this

proposal is available for review at EPA's Water Docket; 401 M Street,

SW, East Tower Basement, Washington, DC 20460. For access to docket

materials, call (202) 260-3027 between 9:00 a.m. and 3:30 p.m. for an

appointment. An electronic version of Method 1631 is available via the

Internet on EPA's Internet home page at http://www.epa.gov/OST.

FOR FURTHER INFORMATION CONTACT: Maria Gomez-Taylor, Ph.D., Engineering

and Analysis Division (4303), USEPA Office of Science and Technology,

401 M Street, SW, Washington, DC 20460; or call (202) 260-1639.

SUPPLEMENTARY INFORMATION:

Potentially Affected Entities

EPA Regions, as well as States, Territories and Tribes authorized

to implement the National Pollutant Discharge Elimination System

(NPDES) program, issue permits that comply with the technology-based

and water quality-based requirements of the Clean Water Act. In doing

so, the NPDES permitting authority, including authorized States,

Territories, and Tribes, make a number of discretionary choices

associated with permit writing, including the selection of pollutants

to be measured and, in many cases, limited in permits. If EPA has

``approved'' standardized testing procedures (i.e., promulgated through

rulemaking) for a given pollutant, the NPDES permit must include one of

the approved testing procedures or an approved alternate test

procedure. Therefore, entities with NPDES permits could be affected by

the standardization of testing procedures in this rulemaking. These

entities may be affected because NPDES permits may incorporate one of

the standardized testing procedures in today's rulemaking. In addition,

when a State, Territory, or authorized Tribe provides certification of

federal licenses under Clean Water Act section 401, States, Territories

and Tribes are directed to use the standardized testing procedures.

Categories and entities that may ultimately be affected include:

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

Examples of potentially affected

Category entities

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

State and Territorial Governments States, Territories, and Tribes

and Indian Tribes. authorized to administer the NPDES

permitting program; States,

Territories, and Tribes providing

certification under Clean Water Act

section 401; Governmental NPDES

permittees.

Industry.......................... Industrial NPDES permittees.

Municipalities.................... Publicly-owned treatment works with

NPDES permits.

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

This table is not intended to be exhaustive, but rather provides a

guide for readers regarding entities likely to be affected by this

action. This table lists the types of entities that EPA is now aware

could potentially be affected by this action. Other types of entities

not listed in the table could also be affected. If you have questions

regarding the applicability of this action to a particular entity,

consult the person listed in the preceding FOR FURTHER INFORMATION

CONTACT section.

I. Authority

Today's proposal is pursuant to the authority of sections 301,

304(h), and 501(a) of the Clean Water Act (CWA), 33 U.S.C. 1314(h),

1361(a) (the ``Act''). Section 301 of the Act prohibits the discharge

of any pollutant into navigable waters unless the discharge complies

with a National Pollutant Discharge Elimination System (NPDES) permit,

issued under section 402 of the Act. Section 304(h) of the Act requires

the Administrator of the EPA to ``promulgate guidelines establishing

test procedures for the analysis of pollutants that shall include the

factors which must be provided in any certification pursuant to section

401 of this Act or permit applications pursuant to section 402 of this

Act.'' Section 501(a) of the Act authorizes the Administrator to

``prescribe such regulations as are necessary to carry out his function

under this Act.'' EPA publishes CWA analytical method regulations at 40

CFR part 136. The Administrator also has made these test procedures

applicable to monitoring and reporting of NPDES permits (40 CFR part

122, Sec. 122.21, 122.41, 122.44, and 123.25), and implementation of

the pretreatment standards issued under section 307 of the Act (40 CFR

part 403, Sec. 403.10 and 402.12).

II. Background

A. Mercury

Mercury is a toxic pollutant pursuant to section 307(a)(1) of CWA

(see the list of toxic pollutants at 40 CFR 401.15) and is a priority

pollutant as derived from the toxic pollutant list (see 40 CFR 423,

Appendix A). Available EPA approved methods for mercury

[[Page 28869]]

determine inorganic and organic forms of mercury as ``total mercury.''

B. Methods for Determination of Mercury

Methods currently approved at 40 CFR part 136 measure mercury by

purging mercury vapor from a water sample into a specially designed

chamber placed in the light beam of an atomic absorption

spectrophotometer. In contrast, EPA Method 1631 measures mercury by

purging mercury vapor from a water sample onto a gold trap and

thermally desorbing the mercury from the trap into an atomic

fluorescence spectrometer. Purging the mercury onto the gold trap

concentrates the mercury and allows water vapor from the sample to be

vented, and use of atomic fluorescence provides an increased response

compared to atomic absorption. As a result, EPA Method 1631 is

approximately 200 times more sensitive than currently approved methods

for determination of mercury.

C. Need for Improved Method for Mercury

The most sensitive currently approved methods for mercury are

capable of achieving a quantitation level of 200 ng/L (parts-per-

trillion; ppt). These methods are not sensitive enough to measure

mercury at levels called for under the National Toxics Rule (40 CFR

131.36) and the Water Quality Guidance for the Great Lakes System (60

FR 15366)--12 ppt and 1.8 ppt, respectively.

III. Summary of Proposed Rule

A. Introduction

This proposed rule would make available at 40 CFR part 136 an

additional test procedure for measurement of mercury. This rulemaking

does not propose to repeal any of the currently approved methods that

test for mercury. For an NPDES permit, the permitting authority should

decide the appropriate method based on the circumstances of the

particular effluent measured. Use of EPA Method 1631 may be specified

by the permitting authority when a permit is modified or reissued. If

the permitting authority does not specify the method to be used, a

discharger would be able to use EPA Method 1631 or any of the currently

approved methods for determination of mercury, provided that the method

chosen meets the requirements specified in the permit.

B. Summary of Proposed Method 1631

EPA Method 1631 has four procedural components: sample

pretreatment; purge and trap; desorption; and detection by atomic

fluorescence. In the sample pretreatment step, bromine monochloride

(BrCl) is added to the sample to oxidize all forms of mercury to

Hg(II). After oxidation, the sample is sequentially prereduced with

NH2OHHCl to destroy free halogens, then reduced with

SnCl2 to convert Hg(II) to volatile Hg(0). The Hg(0) is

purged from the aqueous solution with nitrogen onto a gold-coated sand

trap. The trapped mercury is thermally desorbed from the gold trap into

a flowing gas stream into the cell of a cold-vapor atomic fluorescence

spectrometer. Quality is assured through calibration and testing of the

oxidation, purging, and detection systems.

C. Sample Contamination

Trace levels of metals are ubiquitous in the environment.

Therefore, the determination of trace metals at the levels of interest

for water quality criteria necessitates the use of clean sample

handling techniques to preclude false positives arising from sample

collection, handling, or analysis. EPA has released several guidance

documents that are designed to ensure that metals data accurately

reflect actual environmental levels. The guidance documents include:

Method 1669: Sampling Ambient Water for Trace Metals at EPA Water

Quality Criteria Levels; Guidance on Establishing Trace Metals Clean

Rooms in Existing Facilities; and Guidance on Documentation and

Evaluation of Trace Metals Data Collected for Clean Water Act

Compliance Monitoring. The most serious problem faced by laboratories

conducting metals analyses at these very low levels is the potential

for sample contamination during sample collection and handling. Mercury

is particularly difficult to collect due to its ubiquity in the

environment. For example, commonly used polyethylene sample containers

are unacceptable for sample storage because atmospheric mercury would

be expected to diffuse through the walls of the container, causing

sample contamination. EPA's Method 1669 (Sampling Method) details the

rigorous sample handling and quality control (QC) procedures necessary

to produce reliable data for mercury at the levels of interest for

water quality criteria.

D. Quality Control

The quality control (QC) in EPA Method 1631 is more extensive than

the QC in currently approved methods for mercury. EPA Method 1631

contains all of the standardized QC tests proposed in EPA's

streamlining initiative (62 FR 14976) and used in the 40 CFR 136

Appendix A methods. An initial demonstration of laboratory capability

is required and consists of: (1) a method detection limit (MDL) study

to demonstrate that the laboratory is able to achieve the MDL and

minimum level of quantification (ML) specified in Method 1631; and (2)

an initial precision and recovery (IPR) test, consisting of the

analysis of four reagent water samples spiked with mercury, to

demonstrate the laboratory's ability to generate acceptable precision

and recovery.

Ongoing QC would consist of the following tests that would need to

accompany each analytical batch (i.e., a set of 20 samples or less

pretreated at the same time):

Verification of calibration of the purge and trap and

atomic fluorescence systems, to verify that instrument response has not

deviated significantly from that obtained during calibration.

Analysis of a matrix spike (MS) and matrix spike duplicate

(MSD) to demonstrate method accuracy and precision and to monitor

matrix interferences.

Analysis of reagent and bubbler blanks to demonstrate

freedom from contamination.

Analysis of a laboratory control sample and ongoing

precision and recovery (OPR) samples to demonstrate that the method

remains under control.

EPA Method 1631 contains QC acceptance criteria for all QC tests.

Compliance with these criteria would allow a data user to evaluate the

quality of the results. These QC acceptance criteria would increase the

reliability of results and provides a means for laboratories and data

users to monitor analytical performance, thereby providing a basis for

sound, defensible data.

E. Performance Based Measurement System

On October 7, 1997, EPA published a Notice of the Agency's intent

to implement a Performance Based Measurement System (PBMS) in all of

its programs to the extent feasible (62 FR 52098). The Agency is

currently determining the specific steps necessary to implement PBMS in

its programs and preparing an implementation plan. Because final

decisions have not yet been made concerning the implementation of PBMS

in water programs, today's proposed method does not include full

provisions for PBMS.

However, consistent with the Streamlining Initiative proposed on

March 28, 1997 (62 FR 14976), EPA Method 1631, as proposed, would

[[Page 28870]]

employ a performance-based approach to the sample preparation and

trapping systems. Analysts would be allowed to modify the sample

preparation and trapping aspects of the method provided all the

performance criteria are met. The method also allows the use of

alternate reagents and hardware provided that equivalent or superior

performance is demonstrated and all QC acceptance criteria are met.

Demonstrating equivalency involves two sets of tests, one set with

reference standards and the other with the sample matrix. The

equivalency procedures include performance of the IPR test using

reference standards to demonstrate that the results produced with the

modified procedure would meet or exceed the QC acceptance criteria in

EPA Method 1631. In addition, if the detection limit may be affected by

a modification, performance of an MDL study would be required to

demonstrate that the modified procedure could achieve an MDL less than

or equal to the MDL in EPA Method 1631 or, for those instances in which

the regulatory compliance level is greater than the ML in the method,

one-third the regulatory compliance level. (For a discussion of these

levels, see EPA Method 1631 or the Streamlining Initiative proposed in

March of 1997 (62 FR 14976).

Once EPA has made its final determinations regarding implementation

of PBMS in programs under the Clean Water Act, EPA Method 1631 would be

amended to incorporate specific provisions of PBMS. We anticipate that

such changes will be included in the final version of the method.

Commenters are encouraged to address PBMS implementation for this

method and are specifically requested to comment on the performance

characteristics of EPA Method 1631 to assist EPA in developing

practical method performance and related criteria for PBMS

implementation.

IV. Development and Validation of Method 1631

EPA Method 1631 is based on techniques published in the literature

and widely used throughout the marine chemistry community. EPA

validated the method during development in multiple single-laboratory

studies and in an interlaboratory (round-robin) method validation

study.

A. Background

In response to the need for measuring of trace metals at ambient

water quality criteria levels set forth in the National Toxics Rule,

EPA convened a panel of trace metals experts in Boston in November,

1993. The purpose of the meeting was to obtain information on modern

laboratory techniques for the analysis of trace metals. This panel

consisted of mostly marine chemists who had been making trace metals

measurements in the marine environment for more than 10 years. The

panel concluded that the technique of oxidation, purge and trap,

desorption, and atomic fluorescence would provide reliable results for

measurements of mercury at low ppt levels.

B. Initial Method Development

Initial method development was carried out under contract in a

marine chemistry laboratory recognized for expertise in measurements of

mercury at ultra-trace levels. EPA received an initial draft of the

method in late 1994. EPA revised the initial draft into EPA's

Environmental Monitoring Management Council (EMMC) format in early 1995

and added the standardized quality control (QC) used in the 40 CFR 136,

Appendix A methods. Initial QC acceptance criteria were developed from

data provided by the Agency contractor responsible for initial method

development.

C. Multiple Single-Laboratory Validation Studies

In 1996, EPA conducted studies in four laboratories to further

assess method performance and to better define the method detection

limit (MDL) and QC acceptance criteria. Each laboratory performed an

MDL study and an initial precision and recovery test. EPA revised the

draft method based on results and comments received from these studies.

Based on these data, EPA selected an MDL of 0.2 ng/L (0.2 ppt) for EPA

Method 1631. This was the highest of the MDLs achieved by any of the

laboratories. The highest MDL was selected because this MDL was well

below the 1.8 ppt ambient water quality criterion required by the Great

Lakes Initiative. EPA established a minimum level of quantitation of

0.5 ng/L and revised the QC acceptance criteria for EPA Method 1631

based on data from the four laboratories in the validation study.

Details of the studies are given in a study plan and a report of the

studies is included in the docket for today's proposed rule.

D. Interlaboratory Validation Study

In mid-1997, EPA developed a study plan to conduct an

interlaboratory validation of EPA Method 1631. The interlaboratory

validation study was conducted in late 1997. The following matrices,

forms, and levels were studied: total mercury in reagent water at four

levels; total and dissolved mercury in effluent at one level; dissolved

mercury in freshwater at four levels, and total and dissolved mercury

in seawater at one level. In addition, each laboratory performed an MDL

study to demonstrate that the MDL of 0.2 ppt could be achieved. All the

laboratories participating in the study achieved an MDL below 0.2 ppt.

Therefore, EPA believes this MDL is reasonable. The study plan and a

report of the study are contained in the Docket. Results and comments

from the study were used to evaluate the QC acceptance criteria and

revise other details of EPA Method 1631 into the version being proposed

today. The performance characteristics of the method are summarized in

Tables 1-3. EPA invites comment and additional data on the performance

characteristics of this method.

V. Status of Currently Approved Methods

This action proposes to make EPA Method 1631 available for

determination of mercury in aqueous samples ranging from seawater to

sewage effluent. Currently approved methods for determination of

mercury, EPA Methods 245.1 and 245.2, Standard Method 3112B, ASTM

Method D3223-91, USGS Method I-3462-85, and AOAC-International Method

977.22, would not be withdrawn or otherwise affected by this

regulation. EPA specifically invites comment on this aspect of the

proposal, including the possible consequences and solutions if EPA were

to withdraw such methods.

VI. Regulatory Requirements

A. Executive Order 12866

Under Executive Order 12866 (58 FR 51735 (October 4, 1993)) the

Agency must determine whether a regulatory action is ``significant''

and therefore subject to OMB review and the requirements of the

Executive Order. The Order defines ``significant regulatory action'' as

one that is likely to result in a rule that may: (1) Have an annual

effect on the economy of $100 million or more or adversely affect in a

material way the economy, a sector of the economy, productivity,

competition, jobs, the environment, public health or safety, or State,

local, or tribal governments or communities; (2) create a serious

inconsistency or otherwise interfere with an action taken or planned by

another agency; (3) materially alter the budgetary impact of

entitlements, grants, user fees, or loan programs or the rights and

obligations of recipients thereof; or (4) raise novel

[[Page 28871]]

legal or policy issues arising out of legal mandates, the President's

priorities, or the principles set forth in the Executive Order.

It has been determined that this rule is not a ``significant

regulatory action'' under the terms of Executive Order 12866 and is

therefore not subject to OMB review.

B. Unfunded Mandates Reform Act

Title II of the Unfunded Mandates Reform Act of 1995 (UMRA), P.L.

104-4, establishes requirements for Federal agencies to assess the

effects of their regulatory actions on State, local, and tribal

governments and the private sector. Under section 202 of UMRA, EPA

generally must prepare a written statement, including a cost-benefit

analysis, for proposed and final rules with ``Federal mandates'' that

may result in expenditures to State, local, and tribal governments, in

the aggregate, or to the private sector, of $100 million or more in any

one year. Before promulgating an EPA rule for which a written statement

is needed, section 205 of UMRA generally requires EPA to identify and

consider a reasonable number of regulatory alternatives and adopt the

least costly, most cost-effective, or least burdensome alternative that

achieves the objectives of the rule. The provisions of section 205 do

not apply when they are inconsistent with applicable law. Moreover,

section 205 allows EPA to adopt an alternative other than the least

costly, most cost-effective, or least burdensome alternative if the

Administrator publishes with the final rule an explanation why that

alternative was not adopted. Before EPA establishes any regulatory

requirements that may significantly or uniquely affect small

governments, including tribal governments, it must have developed under

section 203 of UMRA a small government agency plan. The plan must

provide for notifying potentially affected small governments, enabling

officials of affected small governments to have meaningful and timely

input in the development of EPA regulatory proposals with significant

Federal intergovernmental mandates, and informing, educating, and

advising small governments on compliance with the regulatory

requirements.

Today's proposed rule contains no Federal mandates (under the

regulatory provisions of Title II of the UMRA) for State, local, or

Tribal governments or the private sector. The proposed rule would

impose no enforceable duty on any State, local or Tribal governments or

the private sector. This rule proposes alternative analytical test

procedures which would merely standardize the procedures when testing

is otherwise required by a regulatory agency. Therefore, the proposed

rule is not subject to the requirements of sections 202, 203, and 205

of the UMRA. EPA invites comment on its conclusions regarding whether

alternate test procedures constitute a federal mandate.

C. Regulatory Flexibility Act

Under the Regulatory Flexibility Act (RFA), EPA generally is

required to conduct a regulatory flexibility analysis describing the

impact of the regulatory action on small entities as part of

rulemaking. However, under section 605(b) of the RFA, if EPA certifies

that the rule will not have a significant economic impact on a

substantial number of small entities, EPA is not required to prepare a

regulatory flexibility analysis. Pursuant to section 605(b) of the

Regulatory Flexibility Act, 5 U.S.C. 605(b), the Administrator

certifies that this rule will not have a significant economic impact on

a substantial number of small entities. This regulation approves an

additional test procedure (analytical method) for the measurement of

mercury. This rule makes available an alternative testing procedure for

use in compliance monitoring and data gathering but does not require

its use.

D. Paperwork Reduction Act

In accordance with the Paperwork Reduction Act, 44 U.S.C. 3501 et

seq., EPA must submit an information collection request covering

information collection requirements in proposed rules to the Director

of the Office of Management and Budget (OMB) for review and approval.

This proposed rule contains no information collection requirements.

Therefore, an information collection request will not be submitted to

OMB.

E. National Technology Transfer and Advancement Act

Under section 12(d) of the National Technology Transfer and

Advancement Act (NTTAA), the Agency is required to use voluntary

consensus standards in its regulatory activities unless to do so would

be inconsistent with applicable law or otherwise impractical. Voluntary

consensus standards are technical standards (e.g., materials

specifications, test methods, sampling procedures, business practices,

etc.) that are developed or adopted by voluntary consensus standard

bodies. Where available and potentially applicable standards are not

used by EPA, the NTTAA requires the Agency to provide Congress, through

the Office of Management and Budget (OMB), an explanation for the

reasons for not using such standards.

Proposal of EPA Method 1631 is the result of a need to determine

mercury at the low levels associated with water quality criteria for

mercury in the National Toxics Rule (40 CFR 131.36) and in the Water

Quality Guidance for the Great Lakes System (60 FR 15366). These

documents specify concentrations for mercury in the low part-per-

trillion range and the currently approved methods are not sensitive

enough to measure mercury at these levels. EPA's search of the

technical literature revealed that there are no consensus standards for

determination of mercury capable of measuring this pollutant at these

low levels. EPA invites public comments on the Agency's proposal as

well as on any other existing, potentially applicable voluntary

consensus standards that the Agency should consider for the

determination of mercury at low ppt levels.

F. Executive Order 13045: Protection of Children From Environmental

Health Risks and Safety Risks

Executive Order 13045 (62 FR 19885, April 23, 1997), applies to any

rule that (1) is likely to be ``economically significant'' as defined

under Executive Order 12866, and (2) concerns environmental health or

safety risk that the Agency has reason to believe may have a

disproportionate effect on children. If a regulatory action meets both

criteria, the Agency must evaluate the environmental health or safety

effects of the planned rule on children, and explain why the planned

regulation is preferable to other potentially effective and reasonably

feasible alternatives considered by the Agency.

This rule is not subject to E.O. 13045, ``Protection of Children

from Environmental Health Risks and Safety Risks'' because this is not

an ``economically significant'' regulatory action as defined by E.O.

12866, and because it does not involve decisions on environmental

health or safety risks that may disproportionately affect children.

VII. Request for Comments

EPA requests public comments and information on this proposed rule.

Specifically, EPA invites comment on the appropriateness of Method 1631

for the measurement of mercury at low ppt levels, the utility of EPA

Method 1631 for NPDES compliance monitoring, the MDL and QC acceptance

criteria specified in Method 1631, and EPA's proposed decision not to

withdraw other, existing, approved methods for determination of

mercury.

[[Page 28872]]

List of Subjects in 40 CFR Part 136

Environmental protection, Analytical methods, Monitoring, Reporting

and recordkeeping requirements, Waste treatment and disposal, Water

pollution control.

Dated: May 15, 1998.

Carol M. Browner,

Administrator.

In consideration of the preceding, USEPA proposes to amend title

40, chapter I of the Code of Federal Regulations part 136 as follows:

PART 136--[AMENDED]

1. The authority citation for part 136 continues to read as

follows:

Authority: Secs. 301, 304(h), 307, and 501(a) Pub. L. 95-217,

Stat. 1566, et seq. (33 U.S.C. 1251, et seq.) (The Federal Water

Pollution Control Act Amendments of 1972 as amended by the Clean

Water Act of 1977 and the Water Quality Act of 1987), 33 U.S.C. 1314

and 1361; 86 Stat. 816, Pub. L. 92-500; 91 Stat. 1567, Pub. L. 92-

217; Stat. 7, Pub. L. 100-4 (The ``Act'').

2. In Sec. 136.3, paragraph (a), Table IB.--List of Approved

Inorganic Test Procedures, is amended by revising entry 35 to read as

follows:

Sec. 136.3 Identification of test procedures.

(a) * * *

Table IB.--List of Approved Inorganic Test Procedures

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

Reference (method number or page)

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

Parameter, units and method Standard methods

EPA 1,35 18th Ed. ASTM USGS 2 Other

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

* * * * * *

*

35. Mercury--Total,4

Cold vapor, manual, or (or 245.1 3112-B D3223-91 I3462-85 3 977.22

g/L).

Automated (g/L)... 245.2 ................. ................ ................ ...........

Oxidation, purge and trap, 1631 ................. ................ ................ ...........

and atomic fluorescence

(ng/L).

* * * * * *

*

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

Table IB Notes:

\1\ ``Methods for Chemical Analysis of Water and Wastes'', Environmental Protection Agency, Environmental

Monitoring Systems Laboratory-Cincinnati (EMSL-CI), EPA-600/4-79-020, Revised March 1983 and 1979 where

applicable.

\2\ Fishman, M.J., et al, ``Methods for Analysis of Inorganic Substances in Water and Fluvial Sediments,'' U.S.

Department of the Interior, Techniques of Water--Resource Investigations of the U.S. Geological Survey,

Denver, CO, Revised 1989, unless otherwise stated.

\3\ Official Methods of Analysis of the Association of Official Analytical Chemists,'' methods manual, 15th ed.

(1990).

\4\ For the determination of total metals the sample is not filtered before processing. A digestion procedure is

required to solubilize suspended material and to destroy possible organic-metal complexes. Two digestion

procedures are given in ``Methods for Chemical Analysis of Water and Wastes, 1979 and 1983''. One (section

4.1.3), is a vigorous digestion using nitric acid. A less vigorous digestion using nitric and hydrochloric

acids (section 4.1.4) is preferred; however, the analyst should be cautioned that this mild digestion may not

suffice for all sample types. Particularly, if a colorimetric procedure is to be employed, it is necessary to

ensure that all organo-metallic bonds be broken so that the metal is in a reactive state. In those situations,

the vigorous digestion is to be preferred making certain that at no time does the sample go to dryness.

Samples containing large amounts of organic materials may also benefit by this vigorous digestion, however,

vigorous digestion with concentrated nitric acid will convert antimony and tin to insoluble oxides and render

them unavailable for analysis. Use of ICP/AES as well as determinations for certain elements such as antimony,

arsenic, the noble metals, mercury, selenium, silver, tin, and titanium require a modified sample digestion

procedure and in all cases the method write-up should be consulted for specific instructions and/or cautions.

NOTE TO TABLE IB NOTE 4: If the digestion procedure for direct aspiration AA included in one of the other

approved references is different than the above, the EPA procedure must be used.

Dissolved metals are defined as those constituents which will pass through a 0.45 micron membrane filter.

Following filtration of the sample, the referenced procedure for total metals must be followed. Sample

digestion of the filtrate for dissolved metals (or digestion of the original sample solution for total metals)

may be omitted for AA (direct aspiration or graphite furnace) and ICP analyses, provided the sample solution

to be analyzed meets the following criteria:

a. has a low COD (m capsule filter.

2.3 The sample is preserved by adding either 5 mL/L of

pretested 12N HCl or

5mL/L BrCl solution. If a sample will also be used for the

determination of methyl mercury, it should be preserved with 5 mL/L

HCl solution only.

2.4 Prior to analysis, a 100-mL sample aliquot is placed in a

specially designed purge vessel, and 0.2N BrCl solution is added to

oxidize all Hg compounds to Hg(II).

2.5 After oxidation, the sample is sequentially prereduced with

NH2OH. HCl to destroy the free halogens, and then reduced

with SnCl2 to convert Hg(II) to volatile Hg(0).

2.6 The Hg(0) is separated from solution by purging with

nitrogen onto a gold-coated sand trap (Figure 1).

2.7 The trapped Hg is thermally desorbed from the gold trap

into an inert gas stream that carries the released Hg(0) into the

cell of a cold-vapor atomic fluorescence spectrometer (CVAFS) for

detection (Figure 2).

2.8 Quality is ensured through calibration and testing of the

oxidation, purging, and detection systems.

3.0 Definitions

3.1 Total mercury--all BrCl-oxidizable mercury forms and

species found in an unfiltered aqueous solution. This includes, but

is not limited to, Hg(II), Hg(0), strongly organo-complexed Hg(II)

compounds, adsorbed particulate Hg, and several tested covalently

bound organo-mercurials (e.g., CH3HgCl,

(CH3)2Hg, and

C6H5HgOOCCH3). The recovery of Hg

bound within microbial cells may require the additional step of UV

photo-oxidation. In this Method, total mercury and total recoverable

mercury are synonymous.

3.2 Dissolved mercury--All BrCl-oxidizable mercury forms and

species found in the filtrate of an aqueous solution that has been

filtered through a 0.45 micron filter.

3.3 Apparatus--Throughout this Method, the sample containers,

sampling devices, instrumentation, and all other materials and

devices used in sample collection, sample processing, and sample

analysis that come in contact with the sample and therefore require

careful cleaning will be referred to collectively as the Apparatus.

3.4 Definitions of other terms used in this Method are given in

the glossary at the end of the Method.

4.0 Contamination and Interferences

4.1 Preventing ambient water samples from becoming contaminated

during the sampling and analysis process constitutes one of the

greatest difficulties encountered in trace metals determinations.

Over the last two decades, marine chemists have come to recognize

that much of the historical data on the concentrations of dissolved

trace metals in seawater are erroneously high because the

concentrations reflect contamination from sampling and analysis

rather than ambient levels. Therefore, it is imperative that extreme

care be taken to avoid contamination when collecting and analyzing

ambient water samples for trace metals.

4.2 Samples may become contaminated by numerous routes.

Potential sources of trace metals contamination during sampling

include: metallic or metal-containing labware (e.g., talc gloves

that contain high levels of zinc), containers, sampling equipment,

reagents, and reagent water; improperly cleaned and stored

equipment, labware, and reagents; and atmospheric inputs such as

dirt and dust. Even human contact can be a source of trace metals

contamination. For example, it has been demonstrated that dental

work (e.g., mercury amalgam fillings) in the mouths of laboratory

personnel can contaminate samples that are directly exposed to

exhalation (Reference 5).

4.3 Contamination Control.

4.3.1 Philosophy--The philosophy behind contamination control

is to ensure that any object or substance that contacts the sample

is metal free and free from any material that may contain mercury.

4.3.1.1 The integrity of the results produced cannot be

compromised by contamination of samples. This Method and the

Sampling Method give requirements and suggestions for control of

sample contamination.

4.3.1.2 Substances in a sample cannot be allowed to contaminate

the laboratory work area or instrumentation used for trace metals

measurements. This Method gives requirements and suggestions for

protecting the laboratory.

4.3.1.3 Although contamination control is essential, personnel

health and safety remain the highest priority. The Sampling Method

and Section 5 of this Method give suggestions and requirements for

personnel safety.

4.3.2 Avoiding contamination--The best way to control

contamination is to completely avoid exposure of the sample to

contamination in the first place. Avoiding exposure means performing

operations in an area known to be free from contamination. Two of

the most important factors in avoiding/reducing sample contamination

are (1) an awareness of potential sources of contamination and (2)

strict attention to work being done. Therefore, it is imperative

that the procedures described in this Method be carried out by well-

trained, experienced personnel.

4.3.3 Use a clean environment--The ideal environment for

processing samples is a class-100 clean room. If a clean room is not

available, all sample preparation should be performed in a class-100

clean bench or a nonmetal glove box fed by mercury- and particle-

free air or nitrogen. Digestions should be performed in a nonmetal

fume hood situated, ideally, in the clean room.

4.3.4 Minimize exposure--The Apparatus that will contact

samples, blanks, or standard solutions should be opened or exposed

only in a clean room, clean bench, or glove box so that exposure to

an uncontrolled atmosphere is minimized. When not being used, the

Apparatus should be covered with clean plastic wrap, stored in the

clean bench or in a plastic box or glove box, or bagged in clean

zip-type bags. Minimizing the time between cleaning and use will

also minimize contamination.

4.3.5 Clean work surfaces'Before a given batch of samples is

processed, all work surfaces in the hood, clean bench, or glove box

in which the samples will be processed should be cleaned by wiping

with a lint-free cloth or wipe soaked with reagent water.

4.3.6 Wear gloves--Sampling personnel must wear clean, nontalc

gloves during all operations involving handling of the Apparatus,

samples, and blanks. Only clean gloves may touch the Apparatus. If

another object or substance is touched, the glove(s) must be changed

before again handling the Apparatus. If it is even suspected that

gloves have become contaminated, work must be

[[Page 28874]]

halted, the contaminated gloves removed, and a new pair of clean

gloves put on. Wearing multiple layers of clean gloves will allow

the old pair to be quickly stripped with minimal disruption to the

work activity.

4.3.7 Use metal-free Apparatus--All Apparatus used for

determination of mercury at ambient water quality criteria levels

must be nonmetallic, free of material that may contain metals, or

both.

4.3.7.1 Construction materials--Only fluoropolymer or

borosilicate glass (if Hg is the only target analyte) containers

should be used for samples that will be analyzed for mercury because

mercury vapors can diffuse in or out of other materials, resulting

in results that are biased low or high. All materials, regardless of

construction, that will directly or indirectly contact the sample

must be cleaned using the procedures in this Method and must be

known to be clean and mercury free before proceeding.

4.3.7.2 Serialization--It is recommended that serial numbers be

indelibly marked or etched on each piece of Apparatus so that

contamination can be traced, and logbooks should be maintained to

track the sample from the container through the labware to

introduction into the instrument. It may be useful to dedicate

separate sets of labware to different sample types; e.g., receiving

waters vs. effluents. However, the Apparatus used for processing

blanks and standards must be mixed with the Apparatus used to

process samples so that contamination of all labware can be

detected.

4.3.7.3 The laboratory or cleaning facility is responsible for

cleaning the Apparatus used by the sampling team. If there are any

indications that the Apparatus is not clean when received by the

sampling team (e.g., ripped storage bags), an assessment of the

likelihood of contamination must be made. Sampling must not proceed

if it is possible that the Apparatus is contaminated. If the

Apparatus is contaminated, it must be returned to the laboratory or

cleaning facility for proper cleaning before any sampling activity

resumes.

4.3.8 Avoid sources of contamination--Avoid contamination by

being aware of potential sources and routes of contamination.

4.3.8.1 Contamination by carryover--Contamination may occur

when a sample containing a low concentration of mercury is processed

immediately after a sample containing a relatively high

concentration of mercury. When an unusually concentrated sample is

encountered, a bubbler blank should be analyzed immediately

following the sample to check for carryover. Samples known or

suspected to contain the lowest concentration of mercury should be

analyzed first followed by samples containing higher levels.

4.3.8.2 Contamination by samples--Significant laboratory or

instrument contamination may result when untreated effluents, in-

process waters, landfill leachates, and other samples containing

high concentrations of mercury are processed and analyzed. This

Method is not intended for application to these samples, and samples

containing high concentrations should not be permitted into the

clean room or laboratory dedicated for processing trace metals

samples.

4.3.8.3 Contamination by indirect contact--Apparatus that may

not directly come in contact with the samples may still be a source

of contamination. For example, clean tubing placed in a dirty

plastic bag may pick up contamination from the bag and subsequently

transfer the contamination to the sample. Therefore, it is

imperative that every piece of the Apparatus that is directly or

indirectly used in the collection, processing, and analysis of

ambient water samples be thoroughly cleaned (see Section 6.1.2).

4.3.8.4 Contamination by airborne particulate matter--Less

obvious substances capable of contaminating samples include airborne

particles. Samples may be contaminated by airborne dust, dirt,

particles, or vapors from unfiltered air supplies; nearby corroded

or rusted pipes, wires, or other fixtures; or metal-containing

paint. Whenever possible, sample processing and analysis should

occur as far as possible from sources of airborne contamination.

4.4 Interferences.

4.4.1 Due to the BrCl oxidation step, there are no observed

interferences in the determination of Hg by this Method.

4.4.2 The potential exists for destruction of the gold traps if

free halogens are purged onto them, or if they are overheated (>500

deg.C). When the instructions in this Method are followed

accurately, neither of these outcomes is likely.

4.4.3 Water vapor may collect in the gold traps and

subsequently condense in the fluorescence cell upon desorption,

giving a false peak due to scattering of the excitation radiation.

Condensation can be avoided by predrying the gold trap, and by

discarding those traps that tend to absorb large quantities of water

vapor.

4.4.4 The fluorescent intensity is strongly dependent upon the

presence of molecular species in the carrier gas that can cause

``quenching'' of the excited atoms. The dual amalgamation technique

eliminates quenching due to trace gases, but it remains the

analyst's responsibility to ensure high purity inert carrier gas and

a leak-free analytical train.

5.0 Safety

5.1 The toxicity or carcinogenicity of each chemical used in

this Method has not been precisely determined; however, each

compound should be treated as a potential health hazard. Exposure to

these compounds should be reduced to the lowest possible level.

5.1.1 Chronic mercury exposure may cause kidney damage, muscle

tremors, spasms, personality changes, depression, irritability and

nervousness. Organo-mercurials may cause permanent brain damage.

Because of the toxicological and physical properties of Hg, pure

standards should be handled only by highly trained personnel

thoroughly familiar with handling and cautionary procedures and the

associated risks.

5.1.2 It is recommended that the laboratory purchase a dilute

standard solution of the Hg in this Method. If primary solutions are

prepared, they shall be prepared in a hood, and a NIOSH/MESA-

approved toxic gas respirator shall be worn when high concentrations

are handled.

5.2 This Method does not address all safety issues associated

with its use. The laboratory is responsible for maintaining a

current awareness file of OSHA regulations for the safe handling of

the chemicals specified in this Method. OSHA rules require that a

reference file of material safety data sheets (MSDSs) must be made

available to all personnel involved in these analyses (29 CFR

1917.28, Appendix E). It is also suggested that the laboratory

perform personal hygiene monitoring of each analyst who uses this

Method and that the results of this monitoring be made available to

the analyst. Additional information on laboratory safety can be

found in References 10-13. The references and bibliography at the

end of Reference 13 are particularly comprehensive in dealing with

the general subject of laboratory safety.

5.3 Samples suspected to contain high concentrations of Hg are

handled using essentially the same techniques employed in handling

radioactive or infectious materials. Well-ventilated, controlled

access laboratories are required. Assistance in evaluating the

health hazards of particular laboratory conditions may be obtained

from certain consulting laboratories and from State Departments of

Health or Labor, many of which have an industrial health service.

Each laboratory must develop a strict safety program for handling

Hg.

5.3.1 Facility--When samples known or suspected of containing

high concentrations of mercury are handled, all operations

(including removal of samples from sample containers, weighing,

transferring, and mixing) should be performed in a glove box

demonstrated to be leaktight or in a fume hood demonstrated to have

adequate airflow. Gross losses to the laboratory ventilation system

must not be allowed. Handling of the dilute solutions normally used

in analytical and animal work presents no inhalation hazards except

in an accident.

5.3.2 Protective equipment--Disposable plastic gloves, apron or

lab coat, safety glasses or mask, and a glove box or fume hood

adequate for radioactive work should be used. During analytical

operations that may give rise to aerosols or dusts, personnel should

wear respirators equipped with activated carbon filters.

5.3.3 Training--Workers must be trained in the proper method of

removing contaminated gloves and clothing without contacting the

exterior surfaces.

5.3.4 Personal hygiene--Hands and forearms should be washed

thoroughly after each manipulation and before breaks (coffee, lunch,

and shift).

5.3.5 Confinement--Isolated work areas posted with signs,

segregated glassware and tools, and plastic absorbent paper on bench

tops will aid in confining contamination.

5.3.6 Effluent vapors--The effluent from the CVAFS should pass

through either a column of activated charcoal or a trap containing

gold or sulfur to amalgamate or react mercury vapors.

5.3.7 Waste handling--Good technique includes minimizing

contaminated waste.

[[Page 28875]]

Plastic bag liners should be used in waste cans. Janitors and other

personnel must be trained in the safe handling of waste.

5.3.8 Decontamination.

5.3.8.1 Decontamination of personnel--Use any mild soap with

plenty of scrubbing action.

5.3.8.2 Glassware, tools, and surfaces--Sulfur powder will

react with mercury to produce mercuric sulfide, thereby eliminating

the possible volatilization of Hg. Satisfactory cleaning may be

accomplished by dusting a surface lightly with sulfur powder, then

washing with any detergent and water.

5.3.9 Laundry--Clothing known to be contaminated should be

collected in plastic bags. Persons who convey the bags and launder

the clothing should be advised of the hazard and trained in proper

handling. If the launderer knows of the potential problem, the

clothing may be put into a washer without contact. The washer should

be run through a cycle before being used again for other clothing.

5.3.10 Wipe tests--A useful method of determining cleanliness

of work surfaces and tools is to wipe the surface with a piece of

filter paper. Extraction and analysis by this Method can achieve a

limit of detection of less than 1 ng per wipe. Less than 0.1

g per wipe indicates acceptable cleanliness; anything

higher warrants further cleaning. More than 10 g on a wipe

constitutes an acute hazard and requires prompt cleaning before

further use of the equipment or work space, and indicates that

unacceptable work practices have been employed.

6.0 Apparatus and Materials

Disclaimer: The mention of trade names or commercial products in

this Method is for illustrative purposes only and does not

constitute endorsement or recommendation for use by the

Environmental Protection Agency. Equivalent performance may be

achievable using apparatus, materials, or cleaning procedures other

than those suggested here. The laboratory is responsible for

demonstrating equivalent performance.

6.1 Sampling equipment.

6.1.1 Sample collection bottles-Fluoropolymer or borosilicate

glass, 125-to 1000-mL, with fluoropolymer or fluoropolymer-lined

cap.

6.1.2 Cleaning.

6.1.2.1 New bottles are cleaned by heating to 65-75 deg.C in 4

N HCl for at least 48 h. The bottles are cooled, rinsed three times

with reagent water, and filled with reagent water containing 1% HCl.

These bottles are capped and placed in a clean oven at 60-70 deg.C

overnight. After cooling, they are rinsed three more times with

reagent water, filled with reagent water containing 0.4% (v/v) HCl,

and placed in a mercury-free class-100 clean bench until dry. The

bottles are tightly capped (with a wrench), double-bagged in new

polyethylene zip-type bags until needed, and stored in wooden or

plastic boxes until use.

6.1.2.2 Used bottles known not to have contained mercury at

high levels are cleaned as above, except for only 6-12 h in hot 4 N

HCl.

6.1.2.3 Bottle blanks should be analyzed as described in

Section 9.4.4.1 to verify the effectiveness of the cleaning

procedures.

6.1.3 Filtration Apparatus.

6.1.3.1 Filter--0.45-m, 15-mm diameter capsule filter

(Gelman Supor 12175, or equivalent).

6.1.3.2 Peristaltic pump--115-V a.c., 12-V d.c., internal

battery, variable-speed, single-head (Cole-Parmer, portable,

``Masterflex L/S,'' Catalog No. H-07570-10 drive with Quick Load

pump head, Catalog No. H-07021-24, or equivalent).

6.1.3.3 Tubing--styrene/ethylene/butylene/silicone (SEBS) resin

for use with peristaltic pump, approx \3/8\-in ID by approximately 3

ft (Cole-Parmer size 18, Catalog No. G-06464-18, or approximately

\1/4\-in OD, Cole-Parmer size 17, Catalog No. G-06464-17, or

equivalent). Tubing is cleaned by soaking in 5-10% HCl solution for

8-24 h, rinsing with reagent water in a clean bench in a clean room,

and drying in the clean bench by purging with metal-free air or

nitrogen. After drying, the tubing is double-bagged in clear

polyethylene bags, serialized with a unique number, and stored until

use.

6.2 Equipment for bottle and glassware cleaning.

6.2.1 Vat, 100-200 L, high-density polyethylene (HDPE), half

filled with 4 N HCl in reagent water.

6.2.2 Panel immersion heater, 500-W, all-fluoropolymer coated,

120 vac (Cole-Parmer H-03053-04, or equivalent).

Warning: Read instructions carefully!! The heater will maintain

steady state, without temperature feedback control, of 60-75 deg.C

in a vat of the size described. However, the equilibrium temperature

will be higher (up to boiling) in a smaller vat. Also, the heater

plate MUST be maintained in a vertical position, completely

submerged and away from the vat walls to avoid melting the vat or

burning out!

6.2.3 Laboratory sink--in class-100 clean area, with high-flow

reagent water (Section 7.1) for rinsing.

6.2.4 Clean bench--class-100, for drying rinsed bottles.

6.2.5 Oven--stainless steel, in class-100 clean area, capable

of maintaining 5 deg.C in the 60-70 deg.C temperature

range.

6.3 Cold vapor atomic fluorescence spectrometer (CVAFS): The

CVAFS system used may either be purchased from a supplier, or built

in the laboratory from commercially available components.

6.3.1 Commercially available CVAFS--Tekran (Toronto, ON) Model

2500 CVAFS, or Brooks-Rand (Seattle, WA) Model III CVAFS, or

equivalent.

6.3.2 Custom-built CVAFS (Reference 14). Figure 2 shows the

schematic diagram. The system consists of the following:

6.3.2.1 Low-pressure 4-W mercury vapor lamp.

6.3.2.2 Far UV quartz flow-through fluorescence cell--12 mm x

12 mm x 45 mm, with a 10-mm path length (NSG Cells, or

equivalent).

6.3.2.3 UV-visible photomultiplier (PMT)--sensitive to 50

mL/min.

6.4.2 Fluoropolymer fittings--connections between components

and columns are made using 6.4-mm OD fluoropolymer tubing and

fluoropolymer friction-fit or threaded tubing connectors.

Connections between components requiring mobility are made with 3.2-

mm OD fluoropolymer tubing because of its greater flexibility.

6.4.3 Acid fume pretrap--10-cm long x 0.9-cm ID fluoropolymer

tube containing 2-3 g of reagent grade, nonindicating, 8-14 mesh

soda lime chunks, packed between wads of silanized glass wool. This

trap is cleaned of Hg by placing on the output of a clean cold vapor

generator (bubbler) and purging for 1 h with N2 at 350

mL/min.

6.4.4 Cold vapor generator (bubbler)--200-mL borosilicate glass

(15 cm high x 5.0 cm diameter) with standard taper 24/40 neck,

fitted with a sparging stopper having a coarse glass frit that

extends to within 0.2 cm of the bubbler bottom (Frontier

Geosciences, Inc. or equivalent).

6.5 The dual-trap Hg(0) preconcentrating system.

6.5.1 Figure 2 shows the dual-trap amalgamation system

(Reference 5).

6.5.2 Gold-coated sand traps--10-cm long x 6.5-mm OD x 4-mm

ID quartz tubing. The tube is filled with 3.4 cm of gold-coated 45/

60 mesh quartz sand (Frontier Geosciences Inc., Seattle, WA, or

equivalent). The ends are plugged with quartz wool.

6.5.2.1 Traps are fitted with 6.5-mm ID fluoropolymer friction-

fit sleeves for making connection to the system. When traps are not

in use, fluoropolymer end plugs are inserted in trap ends to

eliminate contamination.

6.5.2.2 At least six traps are needed for efficient operation,

one as the ``analytical'' trap, and the others to sequentially

collect samples.

6.5.3 Heating of gold-coated sand traps--To desorb Hg collected

on a trap, heat for 3.0 min to 450-500 deg.C (a barely visible red

glow when the room is darkened) with a coil consisting of 75 cm of

24-gauge Nichrome wire at a potential of 10-14 vac. Potential is

applied and finely adjusted with an autotransformer.

6.5.4 Timers--The heating interval is controlled by a timer-

activated 120-V outlet (Gralab, or equivalent), into which the

heating coil autotransformer is plugged. Two timers are required,

one each for the ``sample'' trap and the ``analytical'' trap.

6.5.5 Air blowers--After heating, traps are cooled by blowing

air from a small

[[Page 28876]]

squirrel-cage blower positioned immediately above the trap. Two

blowers are required, one each for the ``sample'' trap and the

``analytical'' trap.

6.6 Recorder--Any multi-range millivolt chart recorder or

integrator with a range compatible with the CVAFS is acceptable. By

using a two pen recorder with pen sensitivity offset by a factor of

10, the dynamic range of the system is extended to 10\3\.

6.7 Pipettors--All-plastic pneumatic fixed-volume and variable

pipettors in the range of 10 L to 5.0 mL.

6.8 Analytical balance capable of weighing to the nearest 0.01

g.

7.0 Reagents and Standards

7.1 Reagent water--18-M minimum, ultrapure deionized

water starting from a prepurified (distilled, reverse osmosis, etc.)

source. Water should be monitored for Hg, especially after ion

exchange beds are changed.

7.2 Air--It is very important that the laboratory air be low in

both particulate and gaseous mercury. Ideally, mercury work should

be conducted in a new laboratory with mercury-free paint on the

walls. Outside air, which is very low in Hg, should be brought

directly into the class-100 clean bench air intake. If this is not

possible, air coming into the clean bench can be cleaned for mercury

by placing a gold-coated cloth prefilter over the intake.

7.2.1 Gold-coated cloth filter: Soak 2 m\2\ of cotton gauze in

500 mL of 2% gold chloride solution at pH 7. In a hood, add 100 mL

of 30% NH2OHHCl solution, and homogenize into the

cloth with gloved hands. The material will turn black as colloidal

gold is precipitated. Allow the mixture to set for several hours,

then rinse with copious amounts of deionized water. Squeeze-dry the

rinsed cloth, and spread flat on newspapers to air-dry. When dry,

fold and place over the intake prefilter of the laminar flow hood.

Caution: Great care should be taken to avoid contaminating the

laboratory with gold dust. This could cause interferences with the

analysis if gold becomes incorporated into the samples or equipment.

The gilding procedure should be done in a remote laboratory if at

all possible.

7.3 Hydrochloric acid--trace-metal purified reagent-grade HCl

containing less than 5 pg/mL Hg. The HCl should be preanalyzed for

Hg before use.

7.4 Hydroxylamine hydrochloride--Dissolve 300 g of

NH2OHHCl in reagent water and bring to 1.0 L.

This solution may be purified by the addition of 1.0 mL of

SnCl2 solution and purging overnight at 500 mL/min with

Hg-free N2.

7.5 Stannous chloride--Bring 200 g of

SnCl22H2O and 100 mL concentrated HCl

to 1.0 L with reagent water. Purge overnight with mercury-free

N2 at 500 mL/min to remove all traces of Hg. Store

tightly capped.

7.6 Bromine monochloride (BrCl)--In a fume hood, dissolve 27 g

of reagent grade KBr in 2.5 L of low-Hg HCl. Place a clean magnetic

stir bar in the bottle and stir for approximately 1 h in the fume

hood. Slowly add 38 g reagent grade KBrO3 to the acid

while stirring. When all of the KBrO3 has been added, the

solution color should change from yellow to red to orange. Loosely

cap the bottle, and allow to stir another hour before tightening the

lid.

Warning: This process generates copious quantities of free

halogens (Cl2, Br2, BrCl), which are released

from the bottle. Add the KBrO3 slowly in a fume hood!

7.7 Stock mercury standard--NIST-certified 10,000-ppm aqueous

Hg solution (NIST-3133). This solution is stable at least until the

NIST expiration date.

7.8 Secondary Hg standard--Add approx 0.5 L of reagent water

and 5 mL of BrCl solution (Section 7.6) to a 1.00-L class A

volumetric flask. Add 0.100 mL of the stock mercury standard

(Section 7.7) to the flask and dilute to 1.00 L with reagent water.

This solution contains 1.00 ``g/mL (1.00 ppm) Hg. Transfer

the solution to a fluoropolymer bottle and cap tightly. This

solution is considered stable until the NIST expiration date.

7.9 Working Hg standard--Dilute 1.00 mL of the secondary Hg

standard (Section 7.8) to 100 mL in a class A volumetric flask with

reagent water containing 0.5% by volume BrCl solution (Section 7.6).

This solution contains 10.0 ng/mL and should be replaced monthly.

7.10 IPR and OPR solutions--Using the working Hg standard

(Section 7.9), prepare IPR and OPR solutions at a concentration of 5

ng/L Hg in reagent water.

7.11 Nitrogen--Grade 4.5 (standard laboratory grade) nitrogen

that has been further purified by the removal of Hg using a gold-

coated sand trap.

7.12 Argon--Grade 5.0 (ultra high-purity, GC grade) that has

been further purified by the removal of Hg using a gold-coated sand

trap.

8.0 Sample Collection, Preservation, and Storage

8.1 Before samples are collected, consideration should be given

to the type of data required, (i.e., dissolved or total), so that

appropriate preservation and pretreatment steps can be taken. The pH

of all aqueous samples must be tested immediately before aliquotting

for processing or direct analysis to ensure the sample has been

properly preserved.

8.2 Samples are collected into rigorously cleaned fluoropolymer

bottles with fluoropolymer or fluoropolymer-lined caps. Borosilicate

glass bottles may be used if Hg is the only target analyte. It is

critical that the bottles have tightly sealing caps to avoid

diffusion of atmospheric Hg through the threads (Reference 4).

Polyethylene sample bottles must not be used (Reference 14).

8.3 Collect samples using guidance provided in the Sampling

Method (Reference 9). Procedures in the Sampling Method are based on

rigorous protocols for collection of samples for mercury (References

4 and 14).

Note: Discrete samplers have been found to contaminate samples

with Hg at the ng/L level. Therefore, great care should be exercised

if this type of sampler is used to collect samples. It may be

necessary for the sampling team to use other means of sample

collection if samples are found to be contaminated using the

discrete sampler.

8.4 Sample filtration--For dissolved Hg, samples and field

blanks are filtered through a 0.45 m capsule filter

(Section 6.1.3.1). The Sampling Method gives the filtering

procedures.

8.5 Preservation--Samples are preserved by adding either 5mL/L

of pretested 12N HCl or 5 mL/L BrCl solution. If a sample will also

be used for the determination of methyl mercury, it should be

preserved with 5 mL/L HCl solution only. Acid- and BrCl-preserved

samples are stable for a minimum of 6 months.

8.5.1 Samples may be shipped to the laboratory unpreserved if

they are (1) collected in fluoropolymer bottles, (2) filled to the

top with no head space, (3) capped tightly, and (4) maintained at 0-

4 deg.C from the time of collection until preservation. The samples

must be acid-preserved within 48 h after sampling.

8.5.2 Samples that are acid-preserved may lose Hg to coagulated

organic materials in the water or condensed on the walls (Reference

15). The best approach is to add BrCl directly to the sample bottle

at least 24 hours before analysis. If other Hg species are to be

analyzed, these aliquot must be removed prior to the addition of

BrCl. If BrCl cannot be added directly to the sample bottle, the

bottle must be shaken vigorously prior to sub-sampling.

8.5.3 Handling of the samples in the laboratory should be

undertaken in a mercury-free clean bench, after rinsing the outside

of the bottles with reagent water and drying in the clean air hood.

Note: Due to the potential for contamination, it is recommended

that filtration and preservation of samples be performed in the

clean room in the laboratory. However, if circumstances in the field

prevent overnight shipment of samples, samples should be filtered

and preserved in a designated clean area in the field in accordance

with the procedures given in Sampling Method 1669 (Reference 9).

8.6 Storage--Sample bottles should be stored in clean (new)

polyethylene bags until sample analysis. Refrigeration at 0--4 deg.C

is not necessary once samples are preserved. If properly preserved,

samples can be held up to 6 months before analysis.

9.0 Quality Control

9.1 Each laboratory that uses this Method is required to

operate a formal quality assurance program (Reference 16). The

minimum requirements of this program consist of an initial

demonstration of laboratory capability, ongoing analysis of

standards and blanks as a test of continued performance, and the

analysis of matrix spikes (MS) and matrix spike duplicates (M.SD) to

assess accuracy and precision. Laboratory performance is compared to

established performance criteria to determine that the results of

analyses meet the performance characteristics of the Method.

9.1.1 The analyst shall make an initial demonstration of the

ability to generate acceptable accuracy and precision with this

Method. This ability is established as described in Section 9.2.

9.1.2 In recognition of advances that are occurring in

analytical technology, the

[[Page 28877]]

analyst is permitted certain options to improve results or lower the

cost of measurements. These options include automation of the dual-

amalgamation system, single-trap amalgamation (Reference 17), direct

electronic data acquisition, calibration using gas-phase elemental

Hg standards, changes in the bubbler design (including substitution

of a flow-injection system), or changes in the detector (i.e.,

CVAAS) when less sensitivity is acceptable or desired. Changes in

the principle of the determinative technique, such as the use of

colorimetry, are not allowed. If an analytical technique other than

the CVAFS technique specified in this Method is used, that technique

must have a specificity for mercury equal to or better than the

specificity of the technique in this Method.

9.1.2.1 Each time this Method is modified, the analyst is

required to repeat the procedure in Section 9.2. If the change will

affect the detection limit of the Method, the laboratory is required

to demonstrate that the MDL (40 CFR Part 136, Appendix B) is lower

than one-third the regulatory compliance level or lower than the MDL

of this Method, whichever is higher. If the change will affect

calibration, the analyst must recalibrate the instrument according

to Section 10.

9.1.2.2 The laboratory is required to maintain records of

modifications made to this Method. These records include the

following, at a minimum:

9.1.2.2.1 The names, titles, addresses, and telephone numbers

of the analyst(s) who performed the analyses and modification, and

the quality control officer who witnessed and will verify the

analyses and modification.

9.1.2.2.2 A narrative stating the reason(s) for the

modification(s).

9.1.2.2.3 Results from all quality control (QC) tests comparing

the modified method to this Method, including the following:

(a) Calibration (Section 10).

(b) Initial precision and recovery (Section 9.2).

(c) Analysis of blanks (Section 9.4).

(d) Matrix spike/matrix spike duplicate analysis (Section 9.3).

(e) Ongoing precision and recovery (Section 9.5).

(f) Quality control sample (Section 9.6).

(g) Method detection limit (Section 9.2.1).

9.1.2.2.4 Data that will allow an independent reviewer to

validate each determination by tracking the instrument output to the

final result. These data are to include the following:

(a) Sample numbers and other identifiers.

(b) Processing dates.

(c) Analysis dates.

(d) Analysis sequence/run chronology.

(e) Sample weight or volume.

(f) Copies of logbooks, chart recorder, or other raw data

output.

(g) Calculations linking raw data to the results reported.

9.1.3 Analyses of MS and MSD samples are required to

demonstrate the accuracy and precision and to monitor matrix

interferences. Section 9.3 describes the procedure and QC criteria

for spiking.

9.1.4 Analyses of blanks are required to demonstrate acceptable

levels of contamination. Section 9.4 describes the procedures and

criteria for analyzing blanks.

9.1.5 The laboratory shall, on an ongoing basis, demonstrate

through analysis of the ongoing precision and recovery (OPR) sample

and the quality control sample (QCS) that the system is in control.

Sections 9.5 and 9.6 describe these procedures, respectively.

9.1.6 The laboratory shall maintain records to define the

quality of the data that are generated. Sections 9.3.7 and 9.5.3

describe the development of accuracy statements.

9.1.7 The determination of Hg in water is controlled by an

analytical batch. An analytical batch is a set of samples oxidized

with the same batch of reagents, and analyzed during the same 12-

hour shift. A batch may be from 1 to as many as 20 samples. Each

batch must be accompanied by at least three bubbler blanks (Section

9.4), an OPR sample, and a QCS. In addition, there must be one MS

and one MSD sample for every 10 samples (a frequency of 10%).

9.2 Initial demonstration of laboratory capability.

9.2.1 Method detection limit--To establish the ability to

detect Hg, the analyst shall determine the MDL determined according

to the procedure at 40 CFR 136, Appendix B using the apparatus,

reagents, and standards that will be used in the practice of this

Method. The laboratory must produce an MDL that is less than or

equal to the MDL listed in Section 1.5 or one-third the regulatory

compliance limit, whichever is greater. The MDL should be determined

when a new operator begins work or whenever, in the judgment of the

laboratory, a change in instrument hardware or operating conditions

would dictate that the MDL be redetermined.

9.2.2 Initial precision and recovery (IPR)'To establish the

ability to generate acceptable precision and recovery, the analyst

shall perform the following operations:

9.2.2.1 Analyze four replicates of the IPR solution (5 ng/L,

Section 7.10) according to the procedure beginning in Section 11.

9.2.2.2 Using the results of the set of four analyses, compute

the average percent recovery (X), and the standard deviation of the

percent recovery (s) for Hg.

9.2.2.3 Compare s and X with the corresponding limits for

initial precision and recovery in Table 2. If s and X meet the

acceptance criteria, system performance is acceptable and analysis

of samples may begin. If, however, s exceeds the precision limit or

X falls outside the acceptance range, system performance is

unacceptable. Correct the problem and repeat the test (Section

9.2.2.1).

9.3 Matrix spike (MS) and matrix spike duplicate (MSD)--To

assess the performance of the Method on a given sample matrix, the

laboratory must spike, in duplicate, a minimum of 10% (1 sample in

10) from a given sampling site or, if for compliance monitoring,

from a given discharge. Therefore, an analytical batch of 20 samples

would require two pairs of MS/MSD samples (four spiked samples

total).

9.3.1 The concentration of the spike in the sample shall be

determined as follows:

9.3.1.1 If, as in compliance monitoring, the concentration of

Hg in the sample is being checked against a regulatory compliance

limit, the spiking level shall be at that limit or at 1-5 times the

background concentration of the sample (as determined in Section

9.3.2), whichever is greater.

9.3.1.2 If the concentration of Hg in a sample is not being

checked against a limit, the spike shall be at 1-5 times the

background concentration or at 1-5 times the ML in Table 2,

whichever is greater.

9.3.2 To determine the background concentration (B), analyze

one sample aliquot from each set of 10 samples from each site or

discharge according to the procedure in Section 11. If the expected

background concentration is known from previous experience or other

knowledge, the spiking level may be established a priori.

9.3.2.1 If necessary, prepare a standard solution to produce an

appropriate level in the sample (Section 9.3.1).

9.3.2.2 Spike two additional sample aliquots with the spiking

solution and analyze these aliquots as described in Section 11.1.2

to determine the concentration after spiking (A).

9.3.3 Calculate the percent recovery (R) in each aliquot using

the following equation:

[GRAPHIC] [TIFF OMITTED] TP26MY98.116

Where:

A = Measured concentration of analyte after spiking

B = Measured concentration of analyte before spiking

T = True concentration of the spiking

9.3.4 Compare percent recovery (R) with the QC acceptance

criteria in Table 2.

9.3.4.1 If results of the MS/MSD are similar and fail the

acceptance criteria, and recovery for the OPR standard (Section 9.5)

for the analytical batch is within the acceptance criteria in Table

2, an interference is present and the results may not be reported

for regulatory compliance purposes. If the interference can be

attributed to sampling, the site or discharge should be resampled.

If the interference can be attributed to a method deficiency, the

analyst must modify the method, repeat the test required in Section

9.1.2, and repeat analysis of the sample and MS/MSD. However, when

Method 1631 was written, there were no known interferences in the

determination of Hg using this Method. If such a result is observed,

the laboratory should investigate it thoroughly.

9.3.4.2 If the results of both the spike and the OPR test fall

outside the acceptance criteria, the analytical system is judged to

be not in control. The laboratory must identify and correct the

problem and reanalyze the sample batch.

9.3.5 Relative percent difference between duplicates'Compute

the relative percent difference (RPD) between the MS and MSD results

according to the following equation using the concentrations found

in the MS and MSD. Do not use the recoveries calculated in Section

9.3.3 for this calculation because the RPD is inflated when the

background concentration is near the spike concentration.

[[Page 28878]]

[GRAPHIC] [TIFF OMITTED] TP26MY98.112

Where:

D1 = concentration of Hg in the MS sample

D2 = concentration of Hg in the MSD sample

9.3.6 The RPD for the MS/MSD pair must not exceed the

acceptance criterion in Table 2. If the criterion is not met, the

system is judged to be out of control. The problem must be

identified and corrected immediately, and the analytical batch

reanalyzed.

9.3.7 As part of the QC program for the laboratory, method

precision and accuracy for samples should be assessed and records

maintained. After analyzing five samples in which the recovery

passes the test in Section 9.3.4, compute the average percent

recovery (Ra) and the standard deviation of the percent

recovery (sr). Express the accuracy assessment as a

percent recovery interval from Ra - 2sr to

Ra + 2sr. For example, if Ra = 90%

and sr = 10% for five analyses, the accuracy interval is

expressed as 70--110%. Update the accuracy assessment regularly

(e.g., after every five to ten new accuracy measurements).

9.4 Blanks--Blanks are critical to the reliable determination

of Hg at low levels. The sections below give the minimum

requirements for analysis of blanks. However, it is suggested that

additional blanks be analyzed as necessary to pinpoint sources of

contamination in, and external to, the laboratory.

9.4.1 Bubbler blanks--Bubbler blanks are analyzed to

demonstrate freedom from system contamination. At least three

bubbler blanks must be run per analytical batch. One bubbler blank

must be analyzed following each OPR. The mean bubbler blank for an

analytical batch, if within acceptance criteria, is subtracted from

all raw data for that batch prior to the calculation of results.

9.4.1.1 Immediately after analyzing a sample for Hg, place a

clean gold trap on the bubbler, purge and analyze the sample a

second time using the procedure in Section 11, and determine the

amount of Hg remaining in the system.

9.4.1.2 If the bubbler blank is found to contain more than 50

pg Hg, the system is out of control. The problem must be

investigated and remedied, and the samples run on that bubbler must

be reanalyzed. If the blanks from other bubblers contain less than

50 pg Hg, the data associated with those bubblers remain valid.

9.4.1.3 The mean result for all bubbler blanks (from bubblers

passing the specification in Section 9.4.1.2) in an analytical batch

(at least three bubbler blanks) is calculated at the end of the

batch. The mean result must be 2OH (0.2

mL) and SnCl2 (0.5 mL) to previously purged reagent water

in the bubbler.

9.4.2.3 The presence of more than 25 pg of Hg indicates a

problem with the reagent solution. The purging of certain reagent

solutions, such as SnCl2 or NH2OH with

mercury-free nitrogen or argon can reduce Hg to acceptable levels.

Because BrCl cannot be purified, a new batch should be made from

different reagents and should be tested for Hg levels if the level

of Hg in the BrCl solution is too high.

9.4.3 Field blanks.

9.4.3.1 Analyze the field blank(s) shipped with each set of

samples (samples collected from the same site at the same time, to a

maximum of 10 samples). Analyze the blank immediately before

analyzing the samples in the batch.

9.4.3.2 If Hg or any potentially interfering substance is found

in the field blank at a concentration equal to or greater than the

ML (Table 2), or greater than one-fifth the level in the associated

sample, whichever is greater, results for associated samples may be

the result of contamination and may not be reported for regulatory

compliance purposes.

9.4.3.3 Alternatively, if a sufficient number of field blanks

(three minimum) are analyzed to characterize the nature of the field

blank, the average concentration plus two standard deviations must

be less than the regulatory compliance limit or less than one-half

the level in the associated sample, whichever is greater.

9.4.3.4 If contamination of the field blanks and associated

samples is known or suspected, the laboratory should communicate

this to the sampling team so that the source of contamination can be

identified and corrective measures taken before the next sampling

event.

9.4.4 Equipment blanks--Before any sampling equipment is used

at a given site, the laboratory or cleaning facility is required to

generate equipment blanks to demonstrate that the sampling equipment

is free from contamination. Two types of equipment blanks are

required: bottle blanks and sampler check blanks.

9.4.4.1 Bottle blanks--After undergoing the cleaning procedures

in this Method, bottles should be subjected to conditions of use to

verify the effectiveness of the cleaning procedures. A

representative set of sample bottles should be filled with reagent

water acidified to pH a) and the standard deviation of the

percent recovery (sr). Express the accuracy as a recovery

interval from Ra--2sr to Ra +

2sr. For example, if Ra = 95% and

sr = 5%, the accuracy is 85-105%.

9.6 Quality control sample (QCS)--The laboratory must obtain a

QCS from a source different from the Hg used to produce the

standards used routinely in this Method (Sections 7.7-7.10). The QCS

should be analyzed as an independent check of system performance

9.7 Depending on specific program requirements, the laboratory

may be required to analyze field duplicates and field spikes

collected to assess the precision and accuracy of the sampling,

sample transportation, and storage techniques. The relative percent

difference (RPD) between field duplicates should be less than 20%.

If the RPD of the field duplicates exceeds 20%, the laboratory

should communicate this to the sampling team so that the source of

error can be identified and corrective measures taken before the

next sampling event.

10.0 Calibration and Standardization

10.1 Establish the operating conditions necessary to purge Hg

from the bubbler and to desorb Hg from the traps in a sharp peak.

Further details for operation of the purge and trap and desorption

and analysis systems is given in Sections 11.3 and 11.4,

respectively. The entire system is calibrated using standards

traceable to NIST standard reference material, as follows:

10.1.1 Calibration.

10.1.1.1 The calibration must contain five or more non-zero

points and the results of analysis of two bubbler blanks. The lowest

calibration point must be at the Minimum Level (ML).

10.1.1.2 Standards are analyzed by the addition of aliquots of

the Hg working standard (Section 7.9) directly into the bubblers.

Add a 50 L aliquot of the working standard and 0.5 mL

SnCl2 to the bubbler. Swirl to produce a standard of 0.5

ng/L. Purge under the optimum operating conditions (Section 10.1).

Sequentially follow with aliquots of 0.1, 0.5, 2.5, and 10 mL of the

working standard plus 0.5 mL SnCl2 to produce standards

of 1, 5, 25, and 100 ng/L.

10.1.1.3 For each point, subtract the mean peak height or area

of the bubbler blanks for the analytical batch from the peak height

or area for the standard. Calculate the calibration factor

(CFx) for Hg in each of the five standards using the mean

bubbler-blank-subtracted peak height or area and the following

equation:

[GRAPHIC] [TIFF OMITTED] TP26MY98.113

Where:

AX=peak height or area for Hg in standard

ABBpeak height or area for Hg in bubbler blank)

CX=concentration of standard analyzed (ng/L)

10.1.1.4 Calculate the mean calibration factor

(CFm), the standard deviation of the calibration factor

(SD), and the relative standard deviation (RSD) of the calibration

factor, where RSD = 100 x SD/CFm.

10.1.1.5 If RSD 15%, calculate the recovery for the

lowest standard (0.5 ng/L) using CFm. If the RSD

15% and the recovery of the lowest standard is in the

range of 75-125%, the calibration is acceptable and CFm

may be used to calculate the concentration of Hg in samples. If RSD

> 15% or if the recovery of the lowest standard is not in the range

of 75-125%, recalibrate the analytical system and repeat the test.

10.2 Ongoing precision and recovery--Perform the ongoing

precision and recovery test (Section 9.5) to verify calibration

prior to and after analysis of samples in each analytical batch.

11.0 Procedure

Note: The following procedures for analysis of samples are

provided as guidelines. Laboratories may find it necessary to

optimize the procedures, such as drying time or potential applied to

the Nichrome wires, for the laboratory's specific instrumental set-

up.

11.1 Sample Preparation.

11.1.1 Pour a 100-mL aliquot from a thoroughly shaken,

acidified sample, into a 125-mL fluoropolymer bottle. If BrCl was

not added as a preservative (Section 8.5), add the amount of BrCl

solution (Section 7.6) given below, cap the bottle, and digest at

room temperature for a 12 h minimum.

11.1.1.1 For clear water and filtered samples, add 0.5 mL of

BrCl; for brown water and turbid samples, add 1.0 mL of BrCl. If the

yellow color disappears because of consumption by organic matter or

sulfides, more BrCl should be added until a permanent (12-h) yellow

color is obtained.

11.1.1.2 Some highly organic matrices, such as sewage effluent,

will require high levels of BrCl (i.e., 5 mL/100 mL of sample), and

longer oxidation times, or elevated temperatures (i.e.; place sealed

bottles in oven at 50 deg.C for 6 h). The oxidation always must be

continued until a permanent yellow color remains.

11.1.2 Matrix spikes and matrix spike duplicates--For every 10

or fewer samples, pour two additional 100-mL aliquots from a

randomly selected sample, spike at the level specified in Section

9.3, and process in the same manner as the samples. There should be

2 MS/MSD pairs for each analytical batch of 20 samples.

11.2 Hg reduction and purging--Place 100 mL of reagent water in

each bubbler, add 1.0 mL of SnCl2, and purge with Hg-free

N2 for 20 min at 300-400 mL/min (Figure 1).

11.2.1 Connect a gold sand trap to the output of the soda lime

pretrap, and purge the water another 20 min to obtain a bubbler

blank.

11.2.2 Add 0.2 mL of 30% N H2OH to the BrCl-oxidized sample in

the 125-mL fluoropolymer bottle. Cap the bottle and swirl the

sample. The yellow color will disappear, indicating the destruction

of the BrCl. Allow the sample to react for 5 min with periodic

swirling to be sure that no traces of halogens remain.

Note: Purging of free halogens onto the gold trap will result in

damage to the trap and low or irreproducible results.

11.2.3 After discarding the water from the standards, connect a

fresh trap to the bubbler, pour the reduced sample into the bubbler,

add 0.5 mL of 20% SnCl2 solution, and purge the sample

onto a gold sand trap with N2 for 20 min.

11.2.4 When analyzing Hg samples, the recovery is quantitative,

and organic interferents are destroyed. Thus, standards, bubbler

blanks, and small amounts of high-level samples may be run directly

in the water of previously purged samples. After very high samples,

a small degree of carryover (s = peak height (or area) for Hg in sample

ABB = peak height (or area) for Hg in bubbler blank

CFm = mean calibration factor (Section 10.1.1.5)

Vs = sample volume in liters

12.3 Calculate the concentration of Hg in the reagent blank

(CRB), in ng/L, using the equation in Section 12.2 and

substituting the peak height or area resulting from the reagent

blank for As. If the Hg in the reagent blank is

attributable to Hg in the BrCl, correct the concentration of Hg in

the reagent blank by the volume of BrCl used for the particular

sample (Section 11.1.1.2) using the following equation:

[GRAPHIC] [TIFF OMITTED] TP26MY98.115

where:

VBS = volume of BrCI solution used in sample (Section

11.1.1.2)

VBRB = volume of BrCI solution used in reagent blank

(Section 9.4.2.2)

12.4 Reporting

12.4.1 Report results for Hg at or above the ML, in ng/L, to

three significant figures. Report results for Hg in samples below

the ML as 0.2 ng/L, or as required by the regulatory authority or

in the permit.

12.4.2 Report results for Hg in samples and reagent blanks

separately, unless otherwise requested or required by a regulatory

authority or in a permit. If blank correction is requested or

required, subtract the concentration of Hg in the reagent blank from

the concentration of Hg in the sample to obtain the net sample Hg

concentration.

12.4.3 If the laboratory achieved an MDL lower than 0.2 ng/L

(Section 1.5), a new ML may be calculated by multiplying the

laboratory-determined MDL by 3.18 and rounding the result to the

number nearest to (1, 2, or 5) x 10n, where n is an

integer. Results below these levels should be reported as above

using the lower MDL and ML.

13.0 Method Performance

13.1 This method was tested in 12 laboratories using reagent

water, freshwater, marine water and effluent (Reference 18). The

quality control acceptance criteria listed in Table 2 were verified

by data gathered in the interlaboratory study, and the method

detection limit (MDL) given in Section 1.5 was verified in all 12

laboratories. In addition, the techniques in this Method have been

intercompared with other techniques for low-level mercury

determination in water in a variety of studies, including ICES-5

(Reference 19) and the International Mercury Speciation

Intercomparison Exercise (Reference 20).

13.2 Precision and recovery data for reagent water, freshwater,

marine water, and secondary effluent are given in Table 3.

14.0 Pollution Prevention

14.1 Pollution prevention encompasses any technique that

reduces or eliminates the quantity or toxicity of waste at the point

of generation. Many opportunities for pollution prevention exist in

laboratory operation. EPA has established a preferred hierarchy of

environmental management techniques that places pollution prevention

as the management option of first choice. Whenever feasible,

laboratory personnel should use pollution prevention techniques to

address their waste generation. When wastes cannot be reduced

feasibly at the source, the Agency recommends recycling as the next

best option. The acids used in this Method should be reused as

practicable by purifying by electrochemical techniques. The only

other chemicals used in this Method are the neat materials used in

preparing standards. These standards are used in extremely small

amounts and pose little threat to the environment when managed

properly. Standards should be prepared in volumes consistent with

laboratory use to minimize the disposal of excess volumes of expired

standards.

14.2 For information about pollution prevention that may be

applied to laboratories and research institutions, consult Less is

Better: Laboratory Chemical Management for Waste Reduction,

available from the American Chemical Society's Department of

Governmental Relations and Science Policy, 1155 16th Street NW,

Washington DC 20036, 202/872-4477.

15.0 Waste Management

15.1 The laboratory is responsible for complying with all

Federal, State, and local regulations governing waste management,

particularly hazardous waste identification rules and land disposal

restrictions, and for protecting the air, water, and land by

minimizing and controlling all releases from fume hoods and bench

operations. Compliance with all sewage discharge permits and

regulations is also required.

15.2 Acids, samples at pH n, where n is an integer.

17.9 Must--This action, activity, or procedural step is

required.

17.10 Quality Control Sample (QCS)--A sample containing Hg at

known concentrations. The QCS is obtained from a source external to

the laboratory, or is prepared from a source of standards different

from the source of calibration standards. It is used as an

independent check of instrument calibration.

17.11 Reagent Water--Prepared from 18 M ultrapure

deionized water starting from a prepurified source. Reagent water is

used to wash bottles, as trip and field blanks, and in the

preparation of standards and reagents.

17.12 Regulatory Compliance Limit--A limit on the concentration

or amount of a pollutant or contaminant specified in a nationwide

standard, in a permit, or otherwise established by a regulatory

authority.

17.13 Shall--This action, activity, or procedure is required.

17.14 Should--This action, activity, or procedure is suggested,

but not required.

17.15 Stock Solution--A solution containing an analyte that is

prepared from a reference material traceable to EPA, NIST, or a

source that will attest to the purity and authenticity of the

reference material.

17.16 Ultraclean Handling--A series of established procedures

designed to ensure that samples are not contaminated during sample

collection, storage, or analysis.

18.0 Tables and Figures

Table 1.--Lowest Ambient Water Quality Criterion for Mercury and the Method Detection Limit and Minimum Level of

Quantitation for EPA Method 1631

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

Method detection limit (MDL) and minimum

Lowest ambient water level (ML)

Metal quality criterion \1\ -------------------------------------------

MDL\2\ ML\3\

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

Mercury (Hg)................................. 1.8 ng/L 0.2 ng/L 0.5 ng/L

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

\1\ Lowest water quality criterion for the Great Lakes System (60 FR 15366, March 23, 1995). The lowest

Nationwide criterion is 12 ng/L (40 CFR 131.36).

\2\ Method detection limit (40 CFR 136, Appendix B).

\3\ Minimum level of quantitation (see Glossary).

Table 2.--Quality Control Acceptance Criteria for Performance Tests in

EPA Method 1631

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

Acceptance criteria Section Limit (%)

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

Initial precision and recovery (IPR).......... 9.2.2 ...........

Precision (s)............................. 9.2.2.3 21

Recovery (X).............................. 9.2.2.3 79-121

Ongoing precision and recovery (OPR).......... 9.5.2 77-123

Matrix spike/matrix spike duplicate (MS/MSD).. 9.3 ...........

Recovery.................................. 9.3.4 75-125

Relative percent difference (RPD)......... 9.3.5 24

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

[[Page 28882]]

Table 3.--Precision and Recovery for Reagent Water, Fresh Water, Marine

Water, and Effluent Water Using Method 1631

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

* Mean

Matrix recovery * Precision

(%) (% RSD)

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

Reagent water................................. 98.0 5.6

Fresh water (filtered)........................ 90.4 8.3

Marine water (filtered)....................... 92.3 4.7

Marine water (unfiltered)..................... 88.9 5.0

Secondary effluent (filtered)................. 90.7 3.0

Secondary effluent (unfiltered)............... 92.8 4.5

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

* Mean percent recoveries and RSDs are based on expected Hg

concentrations.

BILLING CODE 6560-50-P

[[Page 28883]]

[GRAPHIC] [TIFF OMITTED] TP26MY98.107

[[Page 28884]]

[GRAPHIC] [TIFF OMITTED] TP26MY98.108

[FR Doc. 98-13783 Filed 5-22-98; 8:45 am]

BILLING CODE 6560-50-C