Mass Balance of Mercury in a Natural Forested Amazonian Watershed (Serra do Navio, Amapa State, Brazil)

High Hg levels found in the Brazilian Amazon environ- ment have been attributed mainly to gold mining activities (Nriagu. 1992; Hylander, 1994). Forest fires also have been identified as an important Hg source (Veiga, 1994). However. recently high Hg concentrations have been found in fish and human tissues in regions where there are no known anthropogenic Hg sources (Forsberg, 1994; Fostier, 1997). These facts suggest a large variation in Hg back- ground concentrations in the Amazonian region, and/or a transport of Hg throughout the Brazilian Amazonian region. In the Amazonian region, naturally acidic rain. high air humidity. high temperature and high rainfall rates can modify processes regulating Hg biogeochemistry, acceler- ating its residence time in the environment (Lacerda. 1990). At Amapá State (northeastem Brazilian Amazon) as well as in other Amazonian regions. new gold mining fields are being opened while some older ones are still operated. Ali of them extract gold manually (garimpos) from quartzite mineral deposits. using the Hg amalgamation process to concentrare gold. This process releases Hg to the atmos- phere due to careless amalgam buming in open facilities. Resulting Hg emissions contaminate the atmosphere, soils. sediments and biota in the surrounding area and over distances of kilometers (Guimarães. 1997; Fostier. 1997). There are only scarce background measurements of Hg concentration available for the Amazonian Region (mainly soils and river sediments). and studies focused on Hg mass balance in undisturbed areas of the Amazonian environment are missing. Such studies are required for better under- standing of the Hg behaviour in this environment and for evaluating contamination risks for the regional population.Pages: 17