(May 2001)

There is now an intense and growing debate about the re-introduction of the effective, but environmentally unfriendly, chemical DDT. The reason for this is the spread of malaria, numerically the most devastating infectious disease in the world; there are 300 to 500 million human infections annually and between 1.5 and 3 million deaths each year. Only tuberculosis and HIV/AIDS can rival malaria as human plagues.

DDT, an organochlorine, was heavily used in the United States until the 1960s, when Rachel Carson’s extraordinary book "Silent Spring" showed convincingly that DDT was having a catastrophic effect on birds and other species by interfering with development of their eggs. Some bird species, such as the peregrine falcon and bald eagle, came perilously close to extinction before remedial breeding programs were undertaken.

DDT is still used throughout the world despite energetic campaigns to have it banned completely. Its advocates say it should be used extensively, but judiciously, because it is effective against the mosquitoes that carry malaria and it is inexpensive. They argue that, without its use, malaria will continue to spread and exact an even greater human and economic toll, particularly in developing countries; additionally, global warming is likely to markedly increase the range and probably the biting frequency of malaria-carrying mosquitoes. The proponents insist that DDT is the best agent we have available and that we will just have to accept its adverse environmental effects.

DDT and its chief breakdown product, DDE, appear to have estrogen-like activities and, therefore, could increase the risk of breast cancer. (The breast is a site where DDT and DDE will concentrate because the chemicals have an affinity for fatty tissue). Several studies have found higher blood concentrations of DDT or DDE or higher concentrations in breast tissue in breast cancer cases compared to controls without breast cancer. However, a large number of studies have found no such relationship.

A study by Dr. Tongzhang Zheng and his colleagues from Yale University School of Medicine and other institutions published in the American Journal of Epidemiology analyzed breast tissue for DDT and DDE in 304 cases of breast cancer, 91 women with non-cancerous abnormalities of the breast and 95 with normal breast tissue. Those with breast cancer had slightly lower concentrations of DDT and DDE.

The authors concluded, "Our results do not support the hypothesis that increasing breast tissue levels of DDT and DDE are associated with an increase in the risk of female breast cancer".

Commentary: This article is in agreement with the majority of studies concluding that there is no evidence that DDT causes human breast cancer . This is an important observation because one of the arguments used against greater use of DDT is the alleged link between human exposure and breast cancer. The evidence now available does not support such linkage, and the issue of breast cancer should not, at present, be part of the debate. Nevertheless, there are strong and persuasive arguments against use of DDT. There are alternatives to DDT; they may be less effective, but they are far less devastating to the environment.

Both sides of the debate will agree that, to control malaria, we need more research monies, new effective and non-toxic chemicals to control mosquitoes, and a malaria vaccine. Unfortunately, the vaccine that might solve the problem is still not in sight.

Zheng, T, et al. DDE and DDT in breast adipose tissue and risk of female breast cancer. American Journal of Epidemiology. Vol 150 (September 1) Pgs 453-458. 1999.