Trace element contaminants associated with historic gold mining in sediments of dams and pans across Benoni, South Africa

As a historic gold mining area, the City of Benoni has numerous water bodies close to major tailings dams and mine dumps. Here we assess spatial patterns in the sediment geochemistry of five dams and four natural pans within a 5-km radius of the core mining area to determine the degree of contamination7 by mining-associated pollutants. XRF analysis was used with a geoaccumulation index to assess the degree of contamination above background levels. Prevailing winds blow from the north and north-west with less dominant winds from the east. Sediment concentrations of As, Cu, Pb, Ni and Zn are highly correlated across the region, suggestive of a common source. Except for one pan showing evidence of local industrial pollution, the most contaminated sites are the dams to the west of the mine dumps where concentrations of As, Cu, Pb and Zn increase towards the central mining area, with highest trace metal concentrations in Kleinfontein Dam, adjacent to a reworked mine dump. Sites upwind of the central mining area showed little evidence of mining-related contamination. Trace contaminant concentrations in sediments of these dams are much greater than those found in the nearby Springs-Blesbokspruit wetlands adjacent to more recently active mines. The potential risks to aquatic ecosystems and recreational users of these urban and suburban water bodies from these wind-blown, legacy mining contaminants merit further investigation.