[Federal Register Volume 63, Number 100 (Tuesday, May 26, 1998)]
[Proposed Rules]
[Pages 28868-28884]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-13783]
[[Page 28867]]
_______________________________________________________________________
Part V
Environmental Protection Agency
_______________________________________________________________________
40 CFR Part 136
Guidelines Establishing Test Procedures for the Analysis of Pollutants;
Measurement of Mercury in Water; Proposed Rule
Federal Register / Vol. 63, No. 100 / Tuesday, May 26, 1998 /
Proposed Rules
[[Page 28868]]
ENVIRONMENTAL PROTECTION AGENCY
40 CFR Part 136
[FRL-6100-5]
RIN 2040-AD07
Guidelines Establishing Test Procedures for the Analysis of
Pollutants; Measurement of Mercury in Water
AGENCY: Environmental Protection Agency (EPA).
ACTION: Proposed rule.
-----------------------------------------------------------------------
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 (<20)
b. is visibly transparent with a turbidity measurement of 1 NTU or less
c. is colorless with no perceptible odor, and
d. is of one liquid phase and free of particulate or suspended matter following acidification.
* * * * * *
*
\35\ Precision and recovery statements for the atomic absorption direct aspiration and graphite furnace methods,
and for the spectrophotometric SDDC method for arsenic are provided in Appendix D of this part titled,
``Precision and Recovery Statements for Methods for Measuring Metals''.
* * * * * * *
3. In part 136, appendix A is amended by adding EPA Method 1631 to
read as follows:
Appendix A to Part 136--Methods for Organic Chemical Analysis of
Municipal and Industrial Wastewater
* * * * *
Method 1631 Mercury in Water by Oxidation, Purge and Trap, and
CVAFS
1.0 Scope and Application
1.1 This Method is for determination of mercury (Hg) in
filtered and unfiltered water by oxidation, purge and trap,
desorption, and cold-vapor atomic fluorescence spectrometry (CVAFS).
This Method is for use in EPA's data gathering and monitoring
programs associated with the Clean Water Act, the Resource
Conservation and Recovery Act, the Comprehensive Environmental
Response, Compensation and Liability Act, and the Safe Drinking
Water Act. The Method is based on a contractor-developed method
(Reference 1) and on peer-reviewed, published procedures for the
determination of mercury in aqueous samples, ranging from sea water
to sewage effluent (References 2-5).
1.2 This Method is accompanied by Method 1669: Sampling Ambient
Water for Determination of Trace Metals at EPA Water Quality
Criteria Levels (Sampling Method). The Sampling Method guidance
document is recommended to preclude contamination during the
sampling process.
1.3 This Method is for determination of Hg in the range of 0.5-
100 ng/L and may be extended to higher levels by selection of a
smaller sample size.
1.4 The ease of contaminating ambient water samples with
mercury and interfering substances cannot be overemphasized. This
Method includes suggestions for improvements in facilities and
analytical techniques that should minimize contamination and
maximize the ability of the laboratory to make reliable trace metals
[[Page 28873]]
determinations. Section 4.0 gives these suggestions.
1.5 The detection limit and minimum level of quantitation in
this Method usually are dependent on the level of interferences
rather than instrumental limitations. The method detection limit
(MDL; 40 CFR 136, Appendix B) for Hg has been determined to be 0.2
ng/L when no interferences are present. The minimum level (ML) has
been established as 0.5 ng/L. An MDL as low as 0.05 ng/L can be
achieved for low Hg samples by using a larger sample volume, a lower
BrCl level (0.2%), and extra caution in sample handling.
1.6 Clean and ultraclean--The terms ``clean'' and
``ultraclean'' have been applied to the techniques needed to reduce
or eliminate contamination in trace metals determinations. These
terms are not used in this Method because they lack an exact
definition. However, the information provided in this Method is
consistent with the summary guidance on clean and ultraclean
techniques (References 6-7).
1.7 This Method follows the EPA Environmental Methods
Management Council's ``Guidelines and Format for Methods to Be
Proposed at 40 CFR, Part 136 or Part 141.''
1.8 This Method is ``performance based.'' The analyst is
permitted to modify the Method to overcome interferences or lower
the cost of measurements if all performance criteria are met.
Section 9.1.2 gives the requirements for establishing method
equivalency.
1.9 Any modification of this Method, beyond those expressly
permitted, shall be considered a major modification subject to
application and approval of alternate test procedures under 40 CFR
136.4 and 136.5.
1.10 This Method should be used only by analysts who are
experienced in the use of CVAFS techniques and who are trained
thoroughly in the sample handling and instrumental techniques
described in this Method. Each analyst who uses this Method must
demonstrate the ability to generate acceptable results using the
procedure in Section 9.2.
1.11 This Method is accompanied by a data verification and
validation guidance document, Guidance on the Documentation and
Evaluation of Trace Metals Data Collected for CWA Compliance
Monitoring (Reference 8).
2.0 Summary of Method
2.1 A 100- to 2000-mL sample is collected directly into a
specially cleaned, pretested, fluoropolymer bottle using sample
handling techniques specially designed for collection of mercury at
trace levels (Reference 9).
2.2 For dissolved Hg, the sample is filtered through a 0.45-
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 <230 nm.
This PMT is isolated from outside light with a 253.7-nm interference
filter (Oriel Corp., Stamford, CT, or equivalent).
6.3.2.4 Photometer and PMT power supply (Oriel Corp. or
equivalent), to convert PMT output (nanoamp) to millivolts.
6.3.2.5 Black anodized aluminum optical block--holds
fluorescence cell, PMT, and light source at perpendicular angles,
and provides collimation of incident and fluorescent beams (Frontier
Geosciences Inc., Seattle, WA, or equivalent).
6.3.2.6 Flowmeter--with needle valve capable of reproducibly
keeping the carrier gas flow rate at 30 mL/min.
6.4 Hg purging system--Figure 2 shows the schematic diagram for
the purging system. The system consists of the following:
6.4.1 Flow meter/needle valve--capable of controlling and
measuring gas flow rate to the purge vessel at 350 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 <25 pg with a standard deviation of
<10 pg for the batch to be considered valid. If the mean is <25 pg,
the average peak measurement value is subtracted from all raw data
before results are calculated.
9.4.1.4 If Hg in the bubbler blank exceeds the acceptance
criteria in Section 9.4.1.3, the system is out of control, and the
problem must be resolved and the samples reanalyzed. Usually, the
bubbler blank is too high for one of the following reasons:
(a) Bubblers need rigorous cleaning;
(b) Soda-lime is contaminated; or
(c) Carrier gas is contaminated.
9.4.2 Reagent blanks--The Hg concentration in reagent blanks
must be determined on solutions of reagents by adding these reagents
to previously purged reagent water in the bubbler.
9.4.2.1 Reagent blanks are required when the batch of reagents
(bromine monochloride plus hydroxylamine hydrochloride) are
prepared, with verification in triplicate each month until a new
batch of reagents is needed.
9.4.2.2 Add aliquots of BrCl (0.5 mL), NH2OH (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 <2 and allowed to stand for a minimum of 24 h.
Ideally, the time that the bottles are allowed to stand should be as
close as possible to the actual time that the sample will be in
contact with the bottle. After standing, the water should be
analyzed for any signs of contamination. If a bottle shows
contamination at or above the level specified for the field blank
(Section 9.4.3), the problem must be identified, the cleaning
procedures corrected or cleaning solutions changed, and all affected
bottles recleaned.
9.4.4.2 Sampler check blanks--Sampler check blanks are
generated in the laboratory or at the equipment cleaning facility by
processing reagent water through the sampling devices using the same
procedures that are used in the field (see Sampling Method).
Therefore, the ``clean hands/dirty hands'' technique used during
field sampling should be followed when preparing sampler check
blanks at the laboratory or cleaning facility.
9.4.4.2.1 Sampler check blanks are generated by filling a large
carboy or other container with reagent water (Section 7.1) and
processing the reagent water through the equipment using the same
procedures that are used in the field (see Sampling Method,
Reference 9). For example, manual grab sampler check blanks are
collected by directly submerging a sample bottle into the water,
filling the bottle, and capping. Subsurface sampler check blanks are
collected by immersing a submersible pump or intake tubing into the
water and pumping water into a sample container.
9.4.4.2.2 The sampler check blank must be analyzed using the
procedures in this Method. If mercury or any potentially interfering
substance is detected in the blank at or above the level specified
for the field blank (Section 9.4.3), the source of contamination or
interference must be identified, and the problem corrected. The
equipment must be demonstrated to be free from mercury and
interferences before the equipment may be used in the field.
9.4.4.2.3 Sampler check blanks must be run on all equipment
that will be used in the field. If, for example, samples are to be
collected using both a grab sampling device and a subsurface
sampling device, a sampler check blank must be run on both pieces of
equipment.
9.5 Ongoing precision and recovery (OPR)--To demonstrate that
the analytical system is within the performance criteria of this
Method and that acceptable precision and accuracy is being
maintained within each analytical batch, the analyst shall perform
the following operations:
9.5.1 Analyze the OPR solution (5 ng/L, Section 7.10) followed
by a bubbler blank prior to the analysis of each analytical batch
according to the procedure beginning in Section 11. An OPR also must
be analyzed at the end of an analytical run or at the end of each
12-hour shift. Subtract the peak height (or peak area) of the
bubbler blank from the peak height (or area) of the OPR and
calculate the concentration for the blank-subtracted OPR.
9.5.2 Compare the concentration recovery with the limits for
ongoing precision and recovery in Table 2. If the recovery is in the
range specified, the analytical system is control and analysis of
samples and blanks may proceed. If, however, the concentration is
not in the specified range, the analytical
[[Page 28879]]
process is not in control. Correct the problem and repeat the
ongoing precision and recovery test. All reported results must be
associated with an OPR that meets the Table 2 performance criteria
at the beginning and end of each batch.
9.5.3 The laboratory should add results that pass the
specification in Section 9.5.2 to IPR and previous OPR data and
update QC charts to form a graphic representation of continued
laboratory performance. The laboratory should also develop a
statement of laboratory data quality by calculating the average
percent recovery (Ra) 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 (<0.01%) may occur. Bubblers that
contain such samples should be blanked prior to proceeding with low
level samples.
11.3 Desorption of Hg from the gold trap.
11.3.1 Remove the (sample) trap from the bubbler, place the
Nichrome wire coil around the trap and connect the trap into the
analyzer train between the incoming Hg-free argon and the second
gold-coated (analytical) sand trap (Figure 2).
11.3.2 Pass argon through the sample and analytical traps at a
flow rate of approximately 30 mL/min for approximately 2 min to
drive off condensed water vapor.
11.3.3 Apply power to the coil around the sample trap for 3
minutes to thermally desorb the Hg (as Hg(0)) from the sample trap
onto the analytical trap.
11.3.4 After the 3-min desorption time, turn off the power to
the Nichrome coil, and cool the sample trap using the cooling fan.
11.3.5 Turn on the chart recorder or other data acquisition
device to start data collection, and apply power to the Nichrome
wire coil around the analytical trap. Heat the analytical trap for 3
min (1 min beyond the point at which the peak returns to baseline).
11.3.6 Stop data collection, turn off the power to the Nichrome
coil, and cool the analytical trap to room temperature using the
cooling fan.
11.3.7 Place the next sample trap in line and proceed with
analysis of the next sample.
Note: Do not heat a sample trap while the analytical trap is
still warm; otherwise, the analyte may be lost by passing through
the analytical trap.
11.4 Peaks generated using this technique should be very sharp
and almost symmetrical. Mercury elutes at approximately 1 minute and
has a width at half-height of about 5 seconds.
11.4.1 Broad or asymmetrical peaks indicate a problem with the
desorption train, such as improper gas flow rate, water vapor on the
trap(s), or an analytical trap damaged by chemical fumes or
overheating.
[[Page 28880]]
11.4.2 Damage to an analytical trap is also indicated by a
sharp peak, followed by a small, broad peak.
11.4.3 If the analytical trap has been damaged, the trap and
the fluoropolymer tubing downstream from it should be discarded
because of the possibility of gold migration onto downstream
surfaces.
11.4.4 Gold-coated sand traps should be tracked by unique
identifiers so that any trap producing poor results can be quickly
recognized and discarded.
12.0 Data Analysis and Calculations
12.1 Calculate the mean peak height or area for bubbler blanks,
``BB'' (n = at least 3).
12.2 Calculate the concentration of Hg in ng/L (parts-per-
trillion; ppt) in each sample according to the following equation:
[GRAPHIC] [TIFF OMITTED] TP26MY98.114
where:
As = 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 <0.5 ng/L, or as required by the regulatory authority or
in the permit. Report results for Hg in reagent blanks at or above
the ML, in ng/L, to three significant figures. Report results for Hg
in reagent blanks below the ML but at or above the MDL to two
significant figures. Report results for Hg not detected in reagent
blanks 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 <2, and BrCl solutions must be
neutralized before being disposed of, or must be handled as
hazardous waste.
15.3 For further information on waste management, consult Less
is Better: Laboratory Chemical Management for Waste Reduction, both
available from the American Chemical Society's Department of
Government Relations and Science Policy, 1155 16th Street NW,
Washington, DC 20036.
16.0 References
1. Bloom, Nicolas, Draft ``Total Mercury in Aqueous Media'',
Frontier Geosciences, Inc., September 7, 1994.
2. Fitzgerald, W.F.; Gill, G.A. ``Sub-Nanogram Determination of
Mercury by Two-Stage Gold Amalgamation and Gas Phase Detection
Applied to Atmospheric Analysis,'' Anal. Chem. 1979, 15, 1714.
3, Bloom, N.S; Crecelius, E.A. ``Determination of Mercury in Sea
water at Subnanogram per Liter Levels,'' Mar. Chem. 1983, 14, 49.
4. Gill, G.A.; Fitzgerald, W.F. ``Mercury Sampling of Open Ocean
Waters at the Picogram Level,'' Deep Sea Res 1985, 32, 287.
5. Bloom, N.S.; Fitzgerald, W.F. ``Determination of Volatile
Mercury Species at the Picogram Level by Low-Temperature Gas
Chromatography with Cold-Vapor Atomic Fluorescence Detection,''
Anal. Chim. Acta. 1988, 208, 151.
6. Guidance on Establishing Trace Metal Clean Rooms in Existing
Facilities, U.S. Environmental Protection Agency, Office of Water,
Office of Science and Technology, Engineering and Analysis Division
(4303), 401 M Street SW, Washington, DC 20460, January 1996, EPA
821-B-96-001.
7. Trace Metal Cleanroom, prepared by Research Triangle Institue
for U.S. Environmental Protection Agency, 26 W. Martin Luther King
Dr., Cincinnati, OH 45268, RTI/6302/04-02 F.
8. Guidance on the Documentation and Evaluation of Trace Metals
Data Collected for Clean Water Act Compliance Monitoring, U.S.
Environmental Protection Agency, Office of Water, Office of Science
and Technology, Engineering and Analysis Division (4303), 401 M
Street SW, Washington, DC 20460, July 1996, EPA 821-B-96-004.
9. Method 1669, ``Method for Sampling Ambient Water for
Determination of Metals at EPA Ambient Criteria Levels,'' U.S.
Environmental Protection Agency, Office of Water, Office of Science
and Technology, Engineering and Analysis Division (4303), 401 M
Street SW, Washington, DC 20460, April 1995 with January 1996
revisions.
10. ``Working with Carcinogens,'' Department of Health,
Education, and Welfare, Public Health Service. Centers for Disease
Control. NIOSH Publication 77-206, Aug. 1977, NTIS PB-277256.
11. ``OSHA Safety and Health Standards, General Industry,'' OSHA
2206, 29 CFR 1910.
12. ``Safety in Academic Chemistry Laboratories,'' ACS Committee
on Chemical Safety, 1979.
13. ``Standard Methods for the Examination of Water and
Wastewater,'' 18th ed. and later revisions, American Public Health
Association, 1015 15th Street NW, Washington, DC 20005. 1-35:
Section 1090 (Safety), 1992.
[[Page 28881]]
14. Bloom, N.S. ``Trace Metals & Ultra-Clean Sample Handling,''
Environ. Lab. 1995, 7, 20.
15. Bloom, N.S. ``Influence of Analytical Conditions on the
Observed `Reactive Mercury,' Concentrations in Natural Fresh
Waters.'' In Mercury as a Global Pollutant; Huckabee, J. and Watras,
C.J., Eds.; Lewis Publishers, Ann Arbor, MI: 1994.
16. ``Handbook of Analytical Quality Control in Water and
Wastewater Laboratories,'' U.S. Environmental Protection Agency.
Environmental Monitoring Systems Laboratory, Cincinnati, OH 45268,
EPA-600/4-79-019, March 1979.
17. Liang, L.; Bloom, N.S. ``Determination of Total Mercury by
Single-Stage Gold Amalgamation with Cold Vapor Atom Spectrometric
Detection,'' J. Anal. Atomic Spectrom. 1993, 8, 591.
18. ``Results of the EPA Method 1631 Validation Study,''
February, 1998. Available from the EPA Sample Control Center, 300 N.
Lee St., Alexandria, VA, 22314; 703/519-1140.
19. Cossa, D.; Couran, P. ``An International Intercomparison
Exercise for Total Mercury in Sea Water,'' App. Organomet. Chem.
1990, 4, 49.
20. Bloom, N.S.; Horvat, M.; Watras, C.J. ``Results of the
International Mercury Speciation Intercomparison Exercise,'' Wat.
Air. Soil Pollut., in press.
17.0 Glossary
The definitions and purposes below are specific to this Method,
but have been conformed to common usage as much as possible.
17.1 Ambient Water--Waters in the natural environment (e.g.,
rivers, lakes, streams, and other receiving waters), as opposed to
effluent discharges.
17.2 Analytical Batch--A batch of up to 20 samples that are
oxidized with the same batch of reagents and analyzed during the
same 12-hour shift. Each analytical batch must also include at least
three bubbler blanks, an OPR, and a QCS. In addition, MS/MSD samples
must be prepared at a frequency of 10% per analytical batch (one MS/
MSD for every 10 samples).
17.3 Bubbler Blank--Analyzed to demonstrate freedom from system
contamination. Immediately after analyzing a sample, water in the
bubbler is purged and analyzed using the same procedure as for the
samples to determine Hg. The blank is somewhat different between
days, and a minimum of three bubbler blanks must be analyzed per
analytical batch. The average of the results for the three bubbler
blanks is subtracted from the result of analysis of each sample to
produce a final result.
17.4 Intercomparison Study--An exercise in which samples are
prepared and split by a reference laboratory, then analyzed by one
or more testing laboratories and the reference laboratory. The
intercomparison, with a reputable laboratory as the reference
laboratory, serves as the best test of the precision and accuracy of
the analyses at natural environmental levels.
17.5 Matrix Spike (MS) and Matrix Spike Duplicate (MSD)--
Aliquots of an environmental sample to which known quantities of the
analyte(s) of interest is added in the laboratory. The MS and MSD
are analyzed exactly like a sample. Their purpose is to quantify the
bias and precision caused by the sample matrix. The background
concentrations of the analytes in the sample matrix must be
determined in a separate aliquot and the measured values in the MS
and MSD corrected for these background concentrations.
17.6 May--This action, activity, or procedural step is allowed
but not required.
17.7 May not--This action, activity, or procedural step is
prohibited.
17.8 Minimum Level (ML)--The lowest level at which the entire
analytical system must give a recognizable signal and acceptable
calibration point for the analyte. It is equivalent to the
concentration of the lowest calibration standard, assuming that all
method-specified sample weights, volumes, and cleanup procedures
have been employed. The ML is calculated by multiplying the MDL by
3.18 and rounding the result to the number nearest to (1, 2, or 5) -
10n, 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.
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[FR Doc. 98-13783 Filed 5-22-98; 8:45 am]
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