NEW SOURCE IDENTIFICATION OF MERCURY CONTAMINATION IN THE GREAT-LAKES

Investigations of two Great Lakes estuaries for new sources of mercury contamination revealed previously unmeasured high concentrations in water, sediments, and precipitation. For the St. Louis River estuary, the highest water and sediment mercury concentrations occurred near a regional wastewater treatment facility. Analysis of waste streams showed that the highest levels were associated with the incineration process where sewage sludge is burned by using refuse-derived fuel from municipal garbage, and from municipal wastewater inputs. The total mass of mercury entering the St. Louis River estuary (Minnesota and Wisconsin) is estimated from upstream, wastewater, and precipitation sources. Drought conditions and lake seiche combined to push elevated mercury concentrations “upstream”, exposing more than 80% of the estuary to mercury contamination. The highest water concentrations in the Fox River/Green Bay (Wisconsin) estuary occurred immediately downstream from the DePere Dam and originated from sediment sources and/or unidentified discharges. Investigation of contamination of water samples by Kemmerer and Van Dorn water samplers showed that plastic components contained up to 0.2% mercury that leached into the samples. A new sampler was devised to correct the problem. The detection limit for U.S. EPA methodology for mercury analysis of water (No. 245) has been lowered from 25 ng of Hg/L to an average of 2 ng of Hg/L by using a standardized protocol of standard solutions and blanks and by prescreening reagents for the lowest mercury content to achieve a reagent blank value of ~4 ng of Hg/L. These low detection limits create opportunities to identify new sources of mercury contamination. The identification of incineration of municipal refuse as a major source of mercury emissions to the environment may lead to additional discoveries across the United States, where more than 150 facilities have been built. © 1990, American Chemical Society. All rights reserved.