Mercury in sediments from gold and copper exploitation areas in the Camaqua River Basin, Southern Brazil

Mercury concentrations were determined in stream sediments from the Camaqua River Basin, located in the shield region of the state of Rio Grande do Su l, southern Brazil. The resulting geochemical data show that overbank flood plain deposits exhibit higher concentrations than sediments collected from the active channel bed. In addition, higher Hg concentrations were measured in the fine(<63 <mu>m) sediment fraction of the samples. Total Hg concentr ations in the fine fraction of active stream sediments from Lavras do Sul C ounty, which have been influenced by past gold mining activities, have decr eased during the last five years to values less than or equal to 142 ng g(- 1). However, in a settling pond containing abandoned mine wastes, the Hg co ncentration of a bulk sample remained exceptionally high (5220 ng g(-1)). P reliminary speciation results show that Hg-0 is the predominant species in most of the samples. This was the form of Hg released by the gold amalgamat ion activities in the area, and appears to be relatively stable under the e xisting E-h and pH conditions. (C) 2000 Elsevier Science Ltd. All rights re served.