U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

A National Pilot Study of Mercury Contamination of Aquatic Ecosystems along Multiple Gradients

By David P. Krabbenhoft, James G. Wiener, William G. Brumbaugh, Mark L. Olson, John F. DeWild, and Ty J. Sabin

This report is available in pdf format: Krabbenhoft .pdf

ABSTRACT

Mercury (Hg) contamination of aquatic ecosystems is a global problem. However, databases for Hg in environmental samples at regional-to-national scales are few, especially for multi-media sampling that include determination of methylmercury (MeHg). A national scale pilot study to examine relations of total Hg (Hg_T) and MeHg in water, sediment and fish was conducted in the summer and fall of 1998. Samples were collected at 106 sites from 21 basins across the United States, including Alaska and Hawaii. The data showed wide ranges in concentrations, which were expected given the diverse array of environmental settings, water chemistry, and Hg loading represented by these sites. Wetland density was the single most important basin-scale factor controlling MeHg production. At low concentrations, total Hg in sediment may also influence MeHg production, but at high total Hg concentrations (>1,000 nanograms per gram; ng/g) in sediment there was little evidence of increasing MeHg production with increasing total Hg. An atmospheric Hg accumulation index was developed for differentiating areas where atmospheric Hg deposition was the dominant Hg source from areas with significant on-site sources. Four study basins along the east coast of the United States had the greatest methylation efficiency, as reflected by the MeHg/HgT ratio in sediments. Nationwide, sub-basins characterized as mixed agriculture and forest cover types had the highest methylation efficiency, whereas areas affected by mining had the lowest efficiency. This study represents a first step toward a national assessment of Hg contamination of aquatic ecosystems in the United States, however, additional data are needed to improve our resolution of the factors controlling MeHg production and bioaccumulation.