The insecticide DDT (dichlorodiphenytrichloroethane) has been in the public mind ever since Rachel Carson’s Silent Spring was published in 1962. Growing awareness of its environmental effects, persistence, biomagnification in food chains, and presence in humans (including in breast milk) led to severe restrictions being placed on its use, particularly in the developed world. However, its effectiveness against malaria-carrying mosquitoes led to the continued use of DDT in many areas of the world, including within residences. Now a new paper by Hidrik Bouwman, Henk van den Berg and Herik Kylin reviews the current state of knowledge about the risks vs. benefits of DDT.
The paper is an excellent example of the need to balance risks and benefits, rather than simplistically only looking at the harm that a chemical can do (or conversely, only looking at the benefits and ignoring potential harm).
The paper reviews recent information on human health effects of DDT exposure, and particularly epidemiological studies. It was noted that, of 22 epidemiological reviewed, 12 showed significant relationships between exposure to DDT (or its metabolite DDE) with conditions such as Type 2 diabetes, blood hormone levels, birth mass, a type of pancreatic cancer, and fertility. The authors also concluded that exposures are often high in areas where DDT is applied in dwellings, and breast milk levels often exceed tolerable daily intakes recommended by agencies such as WHO.
However, at the same time, the authors noted that malaria control measures, which include the use of DDT, significantly improve community health. As a result, an outright ban on DDT in tropical regions at this time would have greater negative consequences than continuing to use it.
While there may be a net benefit to using DDT, that doesn’t mean that the status quo should be maintained. It is important to look for ways to reduce human exposure to DDT, without sacrificing the benefits. For example, the authors note that commercial DDT includes two separate DDT isomers, one of which is endocrine-active, along with other components; it may be possible to eliminate the endocrine-active o,p’-DDT while still retaining its desired effects on mosquitoes. They also suggest that changes in how DDT is applied and the use of risk management strategies to reduce exposures to pregnant mothers, breast-feeding mothers, fetuses, babies and toddlers may reduce the adverse effects. As a long-term goal, developing a safer alternative to DDT would be worthwhile.
This paper is an example of the type of thought process used routinely by government agencies for a wide range of decisions. For example, a new medical drug may have side effects, but if it treats a much more serious condition then the benefits may outweigh the adverse effects, and the drug would be allowed for the treatment of the serious condition, unless a safer alternative is available. Even things like the vehicles we drive are subject to this sort of decision-making; we know that vehicles emit harmful pollutants (not to mention the adverse effects of car accidents, and the costs of vehicle infrastructure), but the generally accepted position is that the benefits of rapid transportation outweigh these adverse effects.
Bouwman, H., van den Berg, H., & Kylin, H. (2011). DDT and Malaria Prevention: Addressing the Paradox Environmental Health Perspectives DOI: 10.1289/ehp.1002127