Estimation of appropriate background concentrations for assessing mercury contamination in fish

One goal of environmental restoration at contaminated industrial or hazardous waste sites is the prevention of any further release of contaminants. As a consequence of successful remediation, it is hoped that elevated contaminant concentrations in biota will return to levels characteristic of environments uncontaminated by point sources. To evaluate the efficacy of such an environmental cleanup, it is necessary to know what background contaminant concentrations would typify uncontaminated conditions in the systems of interest. An accurate estimate of an appropriate background mercury concentration in fish is needed to determine the extent to which industrial mercury discharges produce elevated mercury concentration in fish in receiving waters, and to determine the concentration in fish that would represent restoration to uncontaminated status. Losses of large quantities of mercury in the 1950s at the U.S. Department of Energy (DOE) facilities in Oak Ridge, Tennessee resulted in continued chronic contamination of several small streams and the downstream river/reservoir system. mercury concentrations in axial muscle of fish exceed 1 μg/g wet wt. near the source, and decline to much lower concentrations 20 km downstream in Watts Bar Reservoir. Although remedial efforts are underway, the facility remains a continuing source of mercury contamination to the downstream waters. This study measures mercury concentration in bluegill and redbreast sunfish from streams and reservoirs near Oak Ridge, TN that are presumed to be relatively unimpacted by anthropogenic point sources of mercury to determine appropriate background levels in fish to apply in evaluating local contaminated streams and reservoirs. 16 refs., 1 fig., 1 tab