Mercury concentrations in surface waters from fluvial systems draining historical precious metals mining areas ink southeastern U.S.A.

This study evaluates several southern Appalachian Piedmont mining districts for Hg contamination in surface waters and determines potential relationships between Hg discharged from historical mining operations and site-specific physical factors. Water samples were collected from 3 fluvial systems that drain areas where Hg was used to amalgamate Au from ore during the 19th century. Each of the fluvial systems exhibit similar physical characteristics such as climate, vegetation, and rock type. Total Hg (HgT) determinations were made using cold vapour atomic fluorescence spectroscopy techniques. Concentrations of HgT 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 Mining District in Georgia. The correlation between HgT and total suspended solids (TSS) at the southern Appalachian sites was good with a coefficient of determination (r2) of 0.82. A clear trend between environmentally-available Fe (FeE) and HgT (r2=0.86) was also evident. The correlation between HgT and FeE most likely reflects similarities in the mechanisms that control the aqueous concentrations of both metals (i.e., the particle-reactive nature of the two elements), allowing for the sorption of Hg onto Fe-oxyhydroxides. Hence, increased loads of TSS from erosional events are probably responsible for higher stream water HgT concentrations. Vegetation at these sites, which is heavy due to the warm, humid climate of the SE, may help reduce the total amount of Hg released from contaminated mining sites to the rivers by controlling erosion, hence, decreasing the input of contaminated particles into streams and rivers.