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| Analytical MethodsUnited States Environmental ProtectionAgencyOffice of Water4303EPA-821-F-99-010May 1999 Guidelines Establishing Test Procedures for Analysis of Pollutants;Measurement of Mercury in Water (EPA Method 1631, RevisionB); Final Rule
**Summary**

*EPA announces publication of a final rule approving the use of EPA Method 1631, Revision B,for the determination of mercury in EPA's wastewater program (40 CFR part 136).  Approval ofthis method supports EPA's efforts to make available an additional analytical method capable ofmeasuring mercury accurately at ambient water quality criteria levels.*

**Background on Testing Methods**

The U.S. Environmental Protection Agency (EPA) publishes analytical testing methods that areused by industrial and municipal facilities to analyze chemical and biological components ofwastewater, drinking water, sediment, and other environmental samples (for the purpose of datagathering and compliance monitoring under the Clean Water Act and the Safe Drinking WaterAct).

**Purpose of Final Rule for Method 1631**

EPA proposed approval of Method 1631 on May 26, 1998 (63 FR 28867) and published a Noticeof Data Availability (NODA) on March 5, 1999 (64 FR 10596).  The NODA includes additionaleffluent data supporting the use of EPA Method 1631, Revision B, for effluent samples.  In thefinal rule, EPA is formally approving Method 1631, Revision B, at 40 CFR Part 136.

This action provides an additional testing procedure for compliance monitoring under theNPDES program (CWA section 402); ambient water quality monitoring; CWA section 401certifications; development of effluent limitations guidelines, pretreatment standards and newsource performance standards in EPA's water programs; and general laboratory use. 

This rulemaking does not repeal any of the currently approved test methods for mercury. Each permitting authority must decide which method is appropriate for its needs.

**Highlights of Method 1631**

Method 1631 allows determination of mercury at a minimum level (ML) of 0.5 ng/L (parts-per-trillion; ppt), approximately 400 times lower than the level achieved by other mercury methodspreviously approved at 40 CFR Part 136.  Determination of mercury at low ppt levels isnecessary to support measurements at the ambient water quality criteria for mercury published inthe National Toxics Rule as 12 ppt (40 CFR 131.36) and in the Final Water Quality Guidance forthe Great Lakes System as 1.3 ppt (60 FR 15366).
BENEFITS OF METHOD 1631, REVISION BAllows determination of mercury at 0.5 ng/L
- Improved accuracy and precision at low levels    Supports measurements at ambient water quality criteria levelsPerformance-based
- Includes standardized QC  **Components of Method 1631, Revision B**  Method 1631, Revision B, has four components: (1) sample pretreatment, (2) purge and trap, (3)desorption, and (4) detection of mercury by atomic fluorescence.  In the sample pretreatmentstep, bromine monochloride (BrCl) is added to the sample to oxidize all forms of mercury toHg(ll).  After oxidation, the sample is sequentially prereduced with NH2OH HCl to destroy freehalogens, then reduced with SnCl2 to convert Hg(ll) to volatile Hg(0).  The Hg(0) is purged fromthe aqueous solution onto a gold-coated sand trap.  The trapped mercury is thermally desorbedfrom the gold trap into a flowing gas stream into the cell of a cold-vapor atomic fluorescencespectrometer.  Quality is assured through calibration and testing of the oxidation, purging, anddetection systems.  Method 1631, Revision B, contains QC acceptance criteria for all standardized QC tests. Compliance with these criteria will allow the data user to evaluate the quality of the results.  Thisrequirement increases the reliability of results produced and provides a means for laboratoriesand data users to monitor analytical performance, thereby providing a basis for sound, defensibledata.  **Changes Since Proposal**  The Agency revised the proposed version of  Method 1631 based on public comments.  Thefollowing modifications are included in Method 1631, Revision B.  CHANGES INCLUDED IN METHOD 1631, REVISION BA change in sample holding time from 6 months to 28 days.
- A change in MS/MSD performance criteria for recovery from 75-125% to 71-125%.    A change resulting in the removal of the option to report laboratory-determined MDLs and MLs.
**Performance-based Features of Method 1631**

Since Method 1631, Revision B, is performance-based, it encourages advances in analyticaltechnology and may reduce the cost of analysis.  The analyst is permitted to modify the methodto overcome interferences or lower the cost of measurements, provided that all methodequivalency and performance criteria are met.  This performance-based approach is consistentwith EPA's streamlining proposal (March 28, 1997; 62 FR 14976) and the Agency'sperformance-based measurement system policy (October 6, 1997; 62 FR 52098).

**Additional Information and Copies**

For additional information concerning this action you may contact Maria Gomez-Taylor at theU.S. Environmental Protection Agency, Mail Code 4303T, 1200 Pennsylvania Avenue NW, Washington, DC 20460; at 202 566-1005; or at email: [email protected].

The Federal Register notice contains instructions on how to obtain additional information andhow to review the public record for this rulemaking.  The complete text of the Federal Registernotice containing Method 1631, Revision B, may be viewed or downloaded on the Internet at http://www.epa.gov/waterscience/methods/1631.html.

Also, you may obtain copies of Method 1631, Revision B, through the USEPA National ServiceCenter for Environmental Publications and Information (NSCEP), 11029 Kenwood Road,Cincinnati, OH  45242 (ph. 1-800-490-9198) or on the Internet at http://www.epa.gov/ncepi/.

 

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