Invited Commentary Invited Commentary: Why DDT Matters Now

The insecticide 1,1,1-trichloro-2,2-bis(4-chlorophenyl) ethane (DDT) has been banned in the United States since 1972, and serum levels in the general population have fallen substantially. Why then would the Journal bother to publish two articles on DDT and health in the present issue (1, 2)? The authors of the papers allude to the significance of their contributions, but their explanations merit elaboration. In many countries, policy towards DDT for malaria vector control is being reevaluated or changing. In Uganda, whether to use DDT is now being sharply debated (3, 4). In Madagascar, South Africa, and Zambia, recent reintroduction of DDT has coincided with marked reductions in malaria morbidity and, in all likelihood, mortality (5–7). In accord with an international treaty, other countries have registered as potential users of DDT (8), but few utilize it because other methods are effective in the particular setting or because of reluctance. The reluctance to use DDT is based on concern for wildlife and humans (9)—the same reasons that led to the ban in the United States and other developed countries. About 1 million malaria deaths occur annually worldwide, and the incidence is increasing (10). The increase is due mainly to drug-resistant Plasmodium, but in some cases it may be due to reticence to use indoor residual spraying of homes with DDTwhen it is the best option for disease vector control. The indoor residual spraying with pyrethroids failed in South Africa because the mosquitoes became resistant. Mosquitoes can also become resistant to DDT’s toxicity, but they are still repelled by it (11). DDT was once used worldwide, nearly all of it for agriculture. The relatively small amounts used for control of infectious disease, however, contributed significantly to the eradication of malaria in many countries and to a substantial reduction of morbidity and mortality elsewhere (12). Whether much of the DDT used for indoor residual spraying is released into the surrounding environment is unclear. Furthermore, almost no data are available on the health effects of DDT exposure at the levels experienced by those living in sprayed homes. The data available on the potential health effects of DDT and its degradation products suggest that there may be no serious consequences of exposure at levels somewhat lower than those encountered by inhabitants of homes sprayed with DDT, though some associations require further inquiry (13). For example, animal experiments clearly indicate that neurodevelopmental effects of early life exposure to DDT are among the most sensitive outcomes (14). Several human studies that address neurodevelopment suggest there may be effects even at relatively low doses (15–17). Several early and relatively crude human studies also suggested adverse reproductive effects. The recent resurgence of interest in health effects has paralleled the recognition that DDT remains useful in selected settings. The two studies on DDT and health reported in this issue of the Journal were remarkably well done. In both, exposure was assessed by measurement of DDTand 1,1-dichloro-2,2bis(p-chlorophenyl)ethylene (DDE), which is the primary degradation product of DDT. The half-life of DDT in humans is more than 4 years; for DDE, it is probably longer, for example, 10 years (14, 18, 19). Farhang et al. (1) examined DDT and DDE during pregnancy in relation to preterm and small-for-gestational-age birth, as well as related outcomes, among 420 US women who delivered boys in the