Mercury concentrations in surface waters from fluvial systems draining historical precious metals mining areas in southeastern USA

This study evaluates several southern Appalachian Piedmont mining districts for Hg contamination in surface waters and determines potential relationsh ips between Kg discharged from historical mining operations and site-specif ic physical factors. Water samples were collected from 3 fluvial systems th at drain areas where Hg was used to amalgamate Au from ore during the 19th century. Each of the fluvial systems exhibit similar physical characteristi cs such as climate, vegetation, and rock type. Total Hg (Hg-T) determinatio ns were made using cold vapour atomic fluorescence spectroscopy techniques. Concentrations of Hg-T in the southern Appalachian Piedmont range from 1-3 ng l(-1) in waters of the Arbacoochee, Alabama, and South Mountains, North Carolina, Mining Districts to 13 ng l(-1) in waters of the Dahlonega Minin g District in Georgia. The correlation between Hg, and total suspended soli ds (TSS) at the southern Appalachian sites was good with a coefficient of d etermination (r(2)) of 0.82. A clear trend between environmentally-availabl e Fe (Fe-E) and Hg-T (r(2)=0.86) was also evident. The correlation between HET and Fe-E most likely reflects similarities in the mechanisms that contr ol the aqueous concentrations of both metals (i.e., the particle-reactive n ature of the two elements), allowing for the sorption of Hg onto Fe-oxyhydr oxides. Hence, increased loads of TSS from erosional events are probably re sponsible for higher stream water Hg-T concentrations. Vegetation at these sites, which is heavy due to the warm, humid climate of the Southeastern U. S.A., may help reduce the total amount of Hg released from contaminated min ing sites to the rivers by controlling erosion, hence, decreasing the input of contaminated particles into streams and rivers. These southern Appalachian mining sites used Hg amalgamation techniques sim ilar to those used in other precious metals mining districts, such as the h ighly contaminated Comstock Au-Ag district in Nevada, yet Hg-T concentratio ns are orders of magnitude lower; This difference in concentration between the southern Appalachian districts and the Comstock district may correlate to the relative amounts of HE that were used in each. However, other variab les were evaluated to determine if physio-chemical differences such as clim ate could influence Hg-T concentrations in surface waters of the two areas. (C) 1999 Elsevier Science Ltd. All rights reserved.