AN EVALUATION OF LOW-LEVEL MERCURY ANALYTICAL TECHNIQUES

Over the past few years, the determination of low-level mercury has become a key concern in the environmental community. One outcome of the Great Lakes Initiative was the development of human health and wildlife criteria for mercury, which were set at 1.3ng/L and 1.8ng/L, respectively. The National Toxics Rule designated freshwater and marine chronic criteria as 12ng/L and 25ng/L, respectively. NPDES and state regulatory programs used mercury limits derived from these initiatives to develop part-per-trillion level, site specific limits for many POTWs throughout the country, especially those in the Great Lakes Basin. Since the analytical community was unable to quantify at these low levels using existing methodologies, EPA Methods 1631 and 245.7 were developed to meet these new ultra-low level mercury monitoring requirements.Monitoring requirements for mercury at ultra low levels brought new challenges to field and laboratory personnel. Quantitation levels were suddenly reduced by three orders of magnitude or more. Contamination minimization quickly became the primary focus for implementation of Methods 1631 and/or 245.7. Another challenge for the laboratory was to overcome the lack of robustness of Method 1631 which was initially developed for research-type work, not as a production-type method. Method 245.7 was developed, in cooperation with EPA, as a more rugged, production-type method to be used for the analysis of low part-per-trillion levels of mercury. This method just recently underwent the EPA method validation process. The entire range of concentrations typically encountered in POTW effluents is covered by Methods 1631 and/or 245.7. Each of these methods, however, has it's own set of issues.