Study of the geochemical distribution of heavy metals in sediments in areas impacted by coal mining

This study evaluated the geochemical distribution and potential mobility of heavy metals in sediments impacted by coal extraction in the Candiota Region of Brazil. Sampling was performed in Candiota stream and tributaries, at eleven sites, in February and June 2000. The silt/clay fraction of sediments was analyzed by total and sequential extraction schemes established by the EPA and European Commission, respectively. The results indicated higher mobility for manganese, intermediary for nickel, zinc, copper, and lower for iron, chromium, and aluminum. The mouth of Poacd Stream, most affected by mining activities, presented an increase of iron in the oxidizable fraction, as well as zinc, nickel, and copper, suggesting association with sulfides and presence of pyrite in the sediments. The same behavior was observed in the Candiota Strewn, after the entrance of the Poaca. Due to a lower pH (4.3) caused by mining acid drainage, at the mouth of Poaca Stream, manganese content decreased in sediments and increased ten times in the water column.