W.E. Scott, Director, Pollution Control

Department of Environmental Affairs & Tourism, Pretoria, South Africa

DDT (1,1,1 - trichloro - 2,2 - bis (p - chlorophenylethane) is a persistent broad spectrum pesticide. In the past it has been widely used in agriculture to control a range of insect pests and disease vectors.

Residues of DDT and its metabolites (DDE and DDD) in the environment have been shown in numerous studies to result in adverse effects on wildlife reproduction. As a result of the environmental problem the insecticide has been banned in most developing countries and in some countries its use is strictly controlled.

Since 1976 DDT has not been used for any agriculture purposes in South Africa. It is currently only used for indoor malaria control in the malaria - endemic areas of three provinces, Kwa Zulu-Natal, Mpumalanga and the Northern province. For this purpose it is applied annually on the inner walls of dwellings at a coverage of 2g/m. The application of DDT starts in January every year and continues until the end of March.

Continued use of DDT and its success in malaria vector control is based on its relative low cost and lack of acute toxicity for applicators. Until recently there has not been extensive studies on sublethal effects of DDT used in Malaria control. A series of investigations sponsored by the South African Medical Research Council have produced new information on the levels of DDT in serum, breast milk and infants in the Kwazulu province. Data collected in the Malaria control area were compared with a similar area not subject to DDT treatment.

DDT and DDE were found in all serum and breast milk samples from the exposed group and DDE in most of the samples from the control group. The mean level total DDT in serum from the exposed group was 140,9 hg/kg, which is significantly higher than the 6,04 hg/kg for the control group. The mean level of total DDT in the breast milk of the exposed group was 15,83 mg/kg (milk fat) compared to the 0,69 mg/kg for the control group.

Judging from the literature it was indicated that the immunological, neurological and other systems of the infant exposed to elevated levels of DDT via breast milk may be effected.

Analysis of fish species in the malaria control area in Kwazulu province indicated generally low levels of DDT in fillet samples. No significant variations in levels of DDT in fish were observed before and after DDT application. It would appear that DDT levels in the fish do not present a health hazard to the local population.

It has been decided to phase out the use of DDT for Malaria control in South Africa over the next three years and switch to pyrethroid pesticides as an alternative. There is concern that vector resistance to the alternatives could develop.