Elevated mercury concentrations in soils, sediments, water, and fish of the Madeira River basin, Brazilian Amazon: a function of natural enrichments?

Previous site-specific investigations have found that mercury concentration s in water, sediments, and biota of the Brazilian Amazon are elevated above global averages, and that these concentrations are a direct result of wide spread mercury amalgamation mining operations conducted by non-organized pr ospectors. In order to assess the regional impacts of Hg contamination from these non-organized gold mining activities, water, sediments, and fish wer e systematically collected in 1997 along a 900-km reach of the Madeira Rive r. The sampling program extended from the Amazon River upstream to Porto Ve lho, the site of historic and ongoing mercury amalgamation mining. Mercury concentrations were found to be elevated above global averages in all sampl ed media. However, the geochemical data suggest that the high mercury level s are due largely to natural sources and natural biogeochemical processes, and that the impacts of anthropogenically released mercury from mine sites is relatively localized. (C) 2000 Elsevier Science B.V. All rights reserved .