Mercury contamination in Lavras do Sul, south Brazil: a legacy from past and recent gold mining

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 Hg0, 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.