Distribution of anthropogenic mercury in French Guyana river sediments downstream from gold mining sites

Abstract
Total mercury concentrations in French Guyana river sediments were determined near gold mining sites and compared to unaffected reference sites. In small meter-size rivers the anthropogenic impact is localized and characterised by high total mercury peak concentrations in the mg/kg dry weight range (St. Elie site). The mercury load is more diluted in larger water streams such as the Inini river system where a mercury gradient was observed along a 50 km flow path downstream with 510, 295, 261 ng/g total mercury concentrations in the sediments at 0, 35 and 50 km distance from the Dorlin mining site. Sediments situated upstream the gold mining sites compared to the geochemical background concentrations indicating that thé impact related to atmospheric deposition is relatively insignificant. The mercury content of upstream sediments compare to the mercury load of unaffected soils and river sediments collected in distant virgin sites (less than 400 ng/g total mercury).