Photochemical Reactions and Organic Matter Binding of Mercuric Ion and Methylmercury in Surface Water

Project Staff: 

Principal Investigators: Paul R. Bloom, Department of Soil Water, and Climate, College of Agricultural, Food and Environmental Sciences; Patrick L. Brezonik, Professor, Department of Civil Engineering, Institute of Technology, University of Minnesota

Additional Staff: Abdul R. Khwaja, Research Assistant, Water Resources Science Program, University of Minnesota

Funding: 

USGS-WRRI 104B/ CAIWQ Competitive Grants Program

Project Duration: 

March 1998 - February 2001

Summary: 

Mercury (Hg) pollution is a global-scale problem with both ecological and human health implications. Thousands of lakes in Europe, Canada, and the United States, many in remote and pristine areas, contain fish with methylmercury concentrations above public health guidelines for human consumption. In spite of significant advances made over the past decade, critical gaps remain in our understanding of Hg sources, transport, and cycling processes in aquatic and terrestrial systems. Among the water chemistry factors thought to be responsible for differences in lake responses, interactions between Hg forms and natural organic matter are probably the most important. Our understanding of these interactions is based mostly on qualitative observations and statistical correlations. Quantitative, mechanistic information is lacking on this key issue.

This study will quantify the strength of binding (chemical complexation) of Hg2+ and CH3Hg+ to natural dissolved organic matter (NDOM) and determine the chemical nature of the binding. A competitive-ligand technique will be used to determine binding constants of Hg2+ and CH3Hg+ with NDOM isolated from surface waters in the Marcell Experimental Forest in northern Minnesota, a region where high Hg concentrations in fish have resulted in fish consumption advisories. The results will greatly aid in modeling of the behavior of Hg in water and in understanding the bioavailability of Hg bound to NDOM.