ABSTRACT
An attempt is made, in this work, to establish approximate gold production and, consequently, mercury emission rates in Lavras do Sul during the 20th century, after a description of the historical background of the study area. The identification of two heavily polluted sites ('hot spots') shows the persistence of Hg contamination originated in the early 1900s until the 1950s, as well as more recent soil pollution, from the 1980s. The evaluation of natural and anthropogenic residual contamination is approached by the study of Hg concentrations in mineralized rock samples, in soil samples neighboring mining wastes and milling facilities and in stream sediments. Anthropogenic contamination in soil samples reached 110,000 ng/g Hg in bulk samples and 506,000 ng/g Hg in the silt-clay fraction, of which 82-83% as Hg(0), and 16-18% associated to the sulfide/residual fraction, according to complementary speciation analyses. The association of Hg with base metal sulfides may be contributing to local background concentrations varying from 140 to 207 ng/g in stream sediments.
ABSTRACT
The genotoxicity of river water and sediment including interstitial water was evaluated by microscreen phage-induction and Salmonella/microsome assays. Different processes used to fractionate the sediment sample were compared using solvents with different polarities. The results obtained for mutagenic activity using the Salmonella/microsome test were negative in the water and interstitial water samples analysed using the direct concentration method. The responses in the microscreen phage-induction assay showed the presence of genotoxic or indicative genotoxic activity for at least one water sample of each site analysed using the same concentration method. Similar results were obtained for interstitial water samples, i.e. absence of mutagenic activity in the Salmonella/microsome test and presence of genotoxic activity in the microscreen phage-induction assay. Metal contamination, as evidenced by the concentrations in stream sediments, may also help explain some of these genotoxic results. Stream sediment organic extracts showed frameshift mutagenic activity in the ether extract detected by Salmonella/microsome assay. The concentrates evaluated by microscreen phage-induction assay identified the action of organic compounds in the non-polar, medium polar and polar fractions. Thus, the microscreen phage-induction assay has proven to be a more appropriate methodology than the Salmonella/microsome test to analyse multiple pollutants in this ecosystem where both organic compounds and heavy metals are present.
