URANIUM POLLUTION OF WATER RESOURCES IN MINED-OUT AND ACTIVE GOLDFIELDS OF SOUTH AFRICA - A CASE STUDY IN THE WONDERFONTEINSPRUIT CATCHMENT ON EXTENT AND SOURCES OF U-CONTAMINATION AND ASSOCIATED HEALTH RISKS

摘要

Even though mining-related uranium pollution in the Wonderfonteinspruit (WFS) has been an ongoing concern since the mid 1960s, media attention recently increased considerably focussing on pollution-related health risks that unsettle the general public. In view of recent findings that uranium (U) might be more toxic than previously thought such concerns need to be addressed. This even more so as South Africa has embarked on a nuclear expansion program aimed, amongst others, at extending mining and processing of uranium (U). This paper explores the impacts mining over the past decade had on U-pollution of water resources in the WFS catchment. The analysis is mainly based on close to 3400, mostly unpublished, values on U-concentrations of water samples gathered between 1997 and 2008. Results indicate that U-levels in water resources of the whole catchment increased markedly since 1997 even though U-loads emitted by some large gold mines in the Far West Rand were reduced. This apparent contradiction is explained by the contribution of highly polluted water decanting from the flooded mine void in the West Rand. Over the reference period, an average of some 3,5 t of dissolved U have been released into the fluvial system from monitored discharge points alone. However, since WFS dries up well before it joins the Mooi River this U-load does not usually impact on the water supply system of downstream Potchefstroom directly. It may, however, indirectly reach Potchefstroom since much of the water from the WFS recharges the underlying karst aquifer of the Boskop Turffontein Compartment (BTC) as the single most important water resource for Potchefstroom. Compared to 1997 groundwater in the BTC showed the highest relative increase in U-levels of the whole WFS catchment resulting in some 800 kg of U per year flowing into Boskop Dam as Potchefstroom's main water reservoir. Of particular concern is the fact that U-levels in the WFS are comparable to those detected in the Northern Cape (South Africa) which had been geostatistically linked to abnormal haematological values related to increased incidences of leukaemia observed in residents of the area.