The impact of post gold mining on mercury pollution in the West Rand region, Gauteng, South Africa

Abstract

The impact of historical use of mercury (Hg) for the extraction of gold was assessed in watersheds from an abandoned mine in Randfonetin, a town located at 45km west of Johannesburg (South Africa), which has a long history of gold mining, and its surroundings. The majority of analyzed waters at the site were acidic with pH ranging between 2.9 and 5.0. Elevated total Hg concentrations (HgTOT) were measured in waters (up to 223ngHgL−1; mean: 52ngHgL−1) as well as in surface sediments (up to 2580μgHgkg−1; mean: 970μgHgkg−1) from the old mine site. The Krugersdorp Game Reserve watersheds which are directly downstream from the mine drainage appear to become impacted by the pollution from historic gold mines. The high HgTOT measured in a borehole (223ngHgL−1) suggests a groundwater contamination in the area.Hg transported downstream from the mine site is also susceptible to methylation. Relatively high CH3Hg+ (MHg) values were measured in waters (up to 2ngMHgL−1) and surface sediments (up to 10μgMHgkg−1) with significant enrichment in bulk sediments. The methylation of Hg seems to be controlled by factors such as the inorganic Hg content, redox potential and the organic matter content.Sequential extraction procedures together with geochemical modeling have demonstrated the predominance of nonsoluble Hg species (91–95%) in studied soils and the existence of a number of Hg species in watersheds. Diverse mechanisms were proposed to explain both vertical and horizontal transport of Hg at the site.