Low-level Mercury

Reporting Low-level Mercury Results

DNR identifies mercury as one of the substances that must be reported to the detection limit*. Results between the limit of detection (LOD) and limit of quantitation (LOQ) should be qualified appropriately. Most compliance programs require that laboratories report their LOD and LOQ with the analytical results.

For wastewater permit compliance, the rules (NR 106.145) specify that reported results must be above the laboratory's quantitation limit unless the concentration is below 1.3 ng/L (the lowest water quality criterion in NR 105, Wis. Adm. Code). In other words, non-detects or qualified results for concentrations between LOD and LOQ are acceptable only if the concentration is below the water quality limit.

In addition to sample results, two types of blanks must be reported with results, field blanks and method blanks. Department staff evaluate blank results as part of their data quality assessment and compliance determinations.

Correcting Results for Blanks

Method blank concentrations may be subtracted from sample results unless concentrations of mercury exceed the greater of the laboratory's LOD, 0.5 ng/L, or 5% of the sample result. Remember that method blank concentrations must be reported whether or not sample results are corrected.

Field blank results must not be subtracted from sample results.