Environmental Distribution of Mercury Related to Land Use and Physicochemical Setting in Watersheds of the Apalachicola-Chattahoochee-Flint River Basin
During 1992 and 1993, a survey was conducted to determine the distribution of mercury (Hg) in bed sediments and aquatic biota in surface-water bodies of the Apalachicola-Chattahoochee-Flint River basin. The objective of the survey was to relate broad-scale patterns in mercury distribution to watershed land use and physicochemical setting. Concentrations of Hg in fine sediments (less than 63 micrometers particle size) were determined at 41 surface-water sites, and in whole tissue of aquatic biota (Asiatic clams or mosquitofish) at 34 of these sites. Typical background Hg levels in fine sediments ranged from 0.04 to 0.08 micrograms per gam (gg/g). Among all sites sampled in this study, mean Hg concentration in fine sediment was 0.13, and concentrations ranged from 0.04 to 0.56 μg/g. Mercury was detected in tissue at all but two sites. Mercury concentration in tissue ranged from less than detection to 2.6 tg/g of dry weight. Mean Hg concentration in clam tissue was 0.44 'ug/g, dry weight, and mean concentration in mosquitofish tissue was 0.15 μg/g, dry weight. Although the highest concentrations of Hg in sediment were measured in urban watersheds , in the Piedmont Province, the highest concentrations of Hg in clam tissue were measured at sites in Coastal Plain watersheds draining mostly forest or agricultural land, and where sediment Hg concentrations were relatively low. Coastal Plain sites are characterized by physicochemical settings that enhance the formation of methylmercury—the form of Hg that most rapidly bioaccumulates. Comparison of Hg concentrations in sediment and tissue suggests that Hg as methylmercury may be more available to aquatic biota in the Coastal Plain than in the Piedmont. Greater bioavailability of Hg in the Coastal Plain is supported by consumption advisories for fish caught in widely distributed water bodies in the Coastal Plain.