THE INCREASING NITRATE HAZARD IN GROUNDWATER IN THE RURAL AREAS

The occurrence of nitrate in drinking water presents a serious hazard for infants and, at higher levels, also for livestock. However, the illness is not a notifiable disease and local statistics are unavailable. Concern exists that the symptoms may not be recognised. The AIDS epidemic has introduced an urgency into the matter as HIV positive mothers are urged not to breastfeed. These infants now run the risk of their formulas being prepared with nitrate contaminated water. In South Africa, high nitrate concentrations in groundwater occur mainly in a wide band stretching northeasterly from the Northern Cape, through the Northwest Province into the Northern Province. These areas are linked to similar areas in Namibia and Botswana which stretch over many hundreds of kilometres. In South Africa the northern parts of the provinces mentioned above, have large rural populations which are exposed to the risks involved with ingesting nitrate contaminated water. In Southern Africa, the occurrence of nitrate in groundwater can be ascribed to manure application to land, sewage sludge application to soil, wastewater irrigation, deforestation, and mineralization and mobilization of natural soil nitrogen by ploughing. Anthropogenic activities disturbing the nitrogen cycle can cause accumulation of nitrate in the groundwater over large areas. This was confirmed by nitrogen isotope determinations to be the case in the Springbok Flats. Similarly, deforestation in Cote d’Ivoire caused the appearance of nitrate in the groundwater. In semiarid to arid regions, nitrate occurs extensively in groundwater in areas where anthropogenic influences can be excluded. This indicates that accumulation can take place under certain natural conditions, but usually to lower levels than at pollution point sources. Furthermore, it is not accompanied by microbiological pollution which compounds the risk for infants. It is concluded that on-site sanitation remains a viable, or only, option for vast parts of South Africa. Not all such practices lead to groundwater pollution, but in the wrong hydrogeological and environmental conditions, the effects on groundwater can be disastrous. It is necessary to have a pragmatic approach in this regard, but where sensitive and sole source aquifer systems are at risk, alternative sanitation options have to be found. It should be noted that the occurrence of methaemoglobinaemia was mostly associated with private drinking water wells which were polluted via on-site sanitation. On the one hand, groundwater resources are not sufficiently protected, but on the other hand the nitrate standard may be too strict. Furthermore, a full understanding of the natural accumulation process is required for designing a successful groundwater protection strategy. Such a strategy will consist of a dual approach, i.e. legislation for pollution control, which is supported by an education and public awareness programme. The increasing, anthropogenic derived nitrate should largely be eliminated by voluntary actions through education. In this regard it should be recognised that control measures may take years if not decades to reduce nitrate levels in groundwater.