Mercury Behavior in a Tropical Environment: The Case of Small-Scale Gold Mining in Poconé, Brazil
An estimated 50 tons of mercury (Hg) have been emitted by gold miners in the Bento Gomes river basin, in the municipality of Poconé, Brazil, since the 1980s. Since the mid-l990s, the state agency for environmental protection, FEMA (Fundação Estadual do Meio Ambiente de Mato Grosso), has enforced regulations to reduce Hg emissions to air and water and has also implemented an environmental assessment program. The objectives of this study were to evaluate efforts to reduce emissions of Hg to air and water from nine improved amalgamation centers, and to assess the pollution level in sediment at 25 sites around Poconé. In spite of the fact that retorts were used, results showed large emissions of Hg when burning amalgam, resulting in Hg air concentrations above the limit for occupational air (50 μg/m3) at all centers except one. Keeping washing water in closed systems and dumping residues in specially prepared sites reduced Hg emissions to watercourses. The average Hg concentration of fine sediments (<74 μm) in the Bento Gomes river basin was 104 ng Hg/g dry weight, three to four times higher than the background level; large amounts of Hg-contaminated sediments are re-suspended during the rainy season. In conclusion, present emissions to local watercourses have been efficiently reduced, but the use of retorts in improved amalgamation centers has not adequately reduced Hg emissions to air, which is why the use of Hg remains an occupational and environmental problem.(Submitted January 2 2003)
(Revised January 22 2004)
(Accepted February 10 2004)
c1 Department of Chemistry, Federal University of Mato Grosso, Av. Fernando C. Costa/sn, 78 090-900 Cuiabá-MT, Brazil; (fax) +55-65-815-8766; (e-mail) firstname.lastname@example.org.