Water Quality Seminar Series Jointly sponsored by Institute of Natural Resource Sustainability (INRS) and Dept. of Natural Resources and Environmental Sciences (NRES) March 31, 2009 Noon – 1 PM Illinois Natural Resources Building (Illinois State Geological Survey) Room 101 (SE corner) 615 E. Peabody (Coffee and cookies will be provided) Total Dissolved Methylmercury in Freshwaters? Intercomparison of a Novel Analytical Method with Distillation/Ethylation in Samples from Freshwater Systems by Robert J.M. Hudson Department of Natural Resources and Environmental Sciences University of Illinois A novel method for analyzing methylmercury (MeHg) in filtered water samples has been developed at the University of Illinois and tested in geochemical studies conducted in the Grand Calumet, the Piasa Creek watershed, and other locations. The method combines a new analytical system – Hg-thiourea complex ion chromatography – with a novel method of sample preparation – thiourea-catalyzed SPE. It has proved to be viable for large scale large scale field studies and to yield geochemically meaningful results. In conjunction with these field studies, an intercomparison of dissolved MeHg measurements made using the new method and a sophisticated variant of the accepted standard method was conducted on selected split samples. The distillation/ethylation results, which were obtained at Trent University using speciated isotope dilution, were systematically lower in a significant fraction of samples. We hypothesize that these differences are due to the occurrence of a highly-stable complex between MeHg and reduced sulfur compounds in natural waters that is not always detected when using distillation/ethylation.