Mercury distribution in waters and fishes of the upper Madeira rivers and mercury exposure in riparian Amazonian populations

In this paper, the results of mercury concentrations in two abiotic compart ments (river water and suspended particles) and two biotic compartments (fi sh and human hair) from the upper Madeira rivers of the Bolivian Amazon bas in are presented. Because of the local hydrological regimes and a high depo sition rate in the plain, due to the presence of a subsidence zone at the b ottom of the Andean piedmont, in the dry season, the highest mercury concen trations and fluxes were not found in rivers where mining activities took p lace (2.25-6.99 ng l(-1); and 1.07-8.67 mg Hg d(-1) km(-2)), but at the out let of the Andean basins exploited for their alluvial gold (7.22-8.22 ng l( -1); and 9.47-9.52 mg Hg d(-1) km(-2)). The total mercury concentrations me asured in surface waters of the upper Beni basin varied during the dry seas on, from 2.24 to 2.57 ng l(-1) in the glacial waters of the Zongo river, to 7.00 ng l(-1) in the Madeira River at Porto Velho and 9.49-10.86 ng l(-1) at its confluence with the Amazon. The results obtained from fish indicate, on one hand, that 86% of the piscivorous fishes collected in the Beni rive r were contaminated, and, on the other hand, their high mercury concentrati ons could exceed by almost four times the WHO (1976) safety limit. In the B eni River, the mercury concentrations found in omnivorous and mud-feeding f ish ranged from 0.02 to 0.19 mu g g(-1) (wet wt.), and in piscivorous fish, from 0.33 to 2.30 mu g Hg g(-1) (wet wt.). The mercury accumulated by carn ivorous fishes was mainly present in its organic form; methylmercury repres ented 73-98% of the total mercury analysed. Eighty persons were studied in the entire Bolivian Amazonian basin. Unlike the gold miners, who are more a ffected by tropical diseases, such as malaria and yellow fever, the indigen ous people living on the banks of the Beni river, present elevated levels o f mercury(9.81 mu g g(-1) on average). We observed an increase in contamina tion in youngs children still being breast-fed, confirming that hair mercur y concentration in babies was significantly affected by maternal mercury co ntamination during pregnancy. These results show that the major health impa cts caused by mercury affect people who are not working directly in gold mi ning activities but who have a regular fish diet. (C) 2000 Elsevier Science B.V. All rights reserved.