A survey of Cr(VI) contamination of surface water in the proximity of ferrochromium smelters in South Africa

Abstract

South Africa holds approximately three-quarters of the world’s viable chromite ore reserves and is one of the largest ferrochrome producers. It is impossible to completely exclude oxygen from all high-temperature ferrochrome production steps, which results in the unintentional possibility of generating small amounts of Cr(VI) species that are generally considered as carcinogenic. In this study, Cr(VI) levels present in surface water within the vicinity of ferrochrome smelters located in the Bushveld Igneous Complex were monitored for a period of 1 year. The results indicated that surface water in the proximity of ferrochrome smelters was mostly unaffected by Cr(VI) pollution. Two surface water sampling sites were consistently impacted by relatively low level Cr(VI) pollution (annual mean values of 4.4 and 6.3 μg/ℓ, respectively), with no values in excess of the 50 μg/ℓ drinking water limit recorded. However, at two other surface water sampling sites, maximum Cr(VI) concentrations of 198 and 220 μg/ℓ were measured. The median Cr(VI) concentrations for these two sites were 1.8 and 1.9 μg/ℓ, respectively, indicating that Cr(VI) pollution of the surface water at these sites was erratic and most likely due to surface run-off. Although drinking water pollution was not the main focus of this paper, results indicated that drinking water in the proximity of most FeCr smelters was not polluted by Cr(VI). However, the annual mean Cr(VI) concentration of drinking water that originated from a borehole at one drinking water sampling site was 45.3 μg/ℓ, with several months exceeding the 50 μg/ℓ limit. Significant steps have, however, already been taken to remedy the situation.

Keywords: Cr(VI); hexavalent chromium; surface water; drinking water; South Africa; ferrochromium industry