Mercury and metals in South African precipitation

Even though mercury (Hg) is a global pollutant there are few studies of its concentration in the Southern Hemisphere, either in the atmosphere or in atmospheric deposition, and this is particularly true for Africa and developing nations such as South Africa. Emission inventories suggest that there is the potential for anthropogenic impact through elevated deposition in South Africa to sensitive ecosystems. To begin examining such impact, measurements of Hg and other trace metals (Al, Fe, Mn, Co, Ni, Cu, Zn, Cd and Pb) were made of rain collected using a bulk deposition collector at Cape Point, at the tip of Africa, and in Pretoria, a city within the industrial and mining heartland of South Africa. As expected, concentrations and fluxes were elevated in Pretoria, the more urban location. However, there is also evidence that Cape Point site can be impacted by regional pollution during the winter. The volume weighted mean Hg concentration at Cape Point was 10.6 ng L−1 compared to 15.8 ng L−1 in Pretoria. Comparison of rain concentrations for Hg and other metals, and relative fluxes (normalized to Al), indicate the importance of regional sources of contamination to both sites. The importance of impacted air masses at Cape Point was further investigated using ancillary data (CO and Rn) and back trajectory analysis. Overall, these results suggest that Hg and trace metal concentrations and fluxes are comparable to other locations in the world that are impacted by regional anthropogenic sources.