Low-Level Mercury

Criteria for Recognition by WDNR to Perform Testing

Low level mercury certification is not yet available under ch. NR 149 Laboratory Certification and Registration Code. Until it is available, laboratories with mercury certification or registration may request recognition of their low-level mercury capabilities under the emerging technology provision in s. NR 149.12(2), Wis. Adm. Code. DNR recognizes laboratories with acceptable procedures that detect mercury at or below 20 ng/L (quantification limits < 50 ng/L) under this provision. The request needs to identify the matrices and applications for which the laboratory seeks recognition.

The Department developed criteria for recognition based on the needs of the wastewater permits program and the performance criteria in method 1631. Both EPA methods 1631 and 245.7 are listed as approved methods for low level mercury in ch. NR 219, Wisconsin's equivalent to 40 CFR Part 136. As performance-based methods, these procedures may be modified; however, footnote 40 to Table B in ch. NR 219 includes explicit instructions for identifying method citations for particular modifications. Laboratories must demonstrate their ability to meet the performance criteria and be recognized for their low-level mercury capabilities prior to submitting compliance data. The necessary documentation includes:

• A copy of your SOP that includes the make and model of instrument used and any method modifications from the published procedure.
• Results with raw data for the initial demonstration of capability or IPR. Recoveries for the fortified reagent water (LCS) must fall between 79 and 121%. For method 1631, the LCS concentration is set at 5 ng/L. For less sensitive procedures, the LCS concentration should be between one and three times the limit of quantitation but should not exceed 50 ng/L.
• Results (including raw data) of method detection limit (MDL) determinations performed using reagent and wastewater. The source of the wastewater should be identified. If the laboratory is requesting recognition for other matrices, additional matrix MDLs may be necessary.
• Procedures the laboratory uses to ensure that contamination is not introduced into samples, including any carry-over studies performed.

To submit compliance data to DNR, matrix spike recoveries should fall routinely between 71 and 125%. Results outside of this range may be accepted only on a case-by-case basis.

WDNR reserves the right to revise this criteria based on data quality needs.

Contact David Webb for more information on the low level mercury listing.