Regional atmospheric Cr(VI) pollution from the Bushveld Complex, South Africa

Abstract

Hexavalent chromium, Cr(VI), is a proven human carcinogen. Of interest in this paper was the regional atmospheric pollution of Cr(VI) from the ferrochromium and related industries located in the western Bushveld Complex (wBC) of South Africa. A significant fraction of the world's ferrochromium and platinum group metals is produced in this region. Particulate matter (PM), in two size fractions, i.e. PM2.5 (≤2.5 μm) and PM2.5−10 (2.5–10 μm), was sampled for a full calendar year at a regional background site, which is situated downwind of the wBC on the dominant anti-cyclonic recirculation route of air mass over the South African interior. Results indicated that Cr(VI) concentrations in air masses that had passed over the regional background were below the detection limit of the analytical technique applied, but that Cr(VI) in air masses that had passed over the wBC were elevated and had a median concentration of 4.6 ng/m3. The majority of Cr(VI) was found to be in the finer size fraction (PM2.5), which could be explained by the nature of Cr(VI)-containing PM being emitted by the sources in the wBC and the atmospheric lifetimes of different PM size fractions. The results further indicated that it is possible that not only pyrometallurgical sources in the wBC, but also other combustion sources outside the wBC contributed to the observed atmospheric Cr(VI) concentrations.