A recent paper in Environmental Health Perspectives by Cohn, BA, MS Wolff, PM Cirillo and RI Sholtz.2007. DDT and breast cancer in young women, provides important new data on the significance of age at exposure.
This was a prospective study of blood from young women that was collected between 1959 and 1967 and stored by freezing, combined with an analysis of their current medical records. The median time to diagnosis of breast cancer after the sample was taken of 17 years.
In summary it shows that women who are exposed to relatively high levels of DDT before mid-adolescence are 5 times more likely to develop breast cancer later in life than women with lower exposures. Exposure after adolescence does not increase risk.
Rachel Carson proposed as early as 1962 that DDT might be linked to breast cancer and she died of the disease herself. Since then most studies have failed to find an increased risk. However most of these studies have involved measuring contamination levels after cancer has been diagnosed, and then comparing these ‘cases’ with’controls’ matched for age.
However toxicological experiments with animals, have consistently suggested that early exposure from fetal life to puberty, especially when tissues are developing rapidly, can be important contributors to cancer risk. Yet in previous human studies, effects of DDT on carcinogenicity were not proven. The reason, according to Cohn et al is “Prior studies collected blood when women were of middle age or much older.” It is also “the first study specifically designed, a priori, to consider whether age at exposure may modify DDT effects on breast cancer.” Because DDT was first widely introduced in the US in 1945, a woman’s age in 1945 is an indicator of the youngest possible age at which a woman could have been exposed to DDT. Women who reached puberty before 1945 could not have been exposed to the pesticide during development up to puberty.
DDT continues to be used in some African countries to fight malaria. For example, DDT is effective in prevention when used to spray annually inside huts. This use was sanctioned in the UN Stockholm Convention on Persistent Organic Pollutants as a public health exception. In a reversal of 30 years of policy, the World Health Organization endorsed DDT spraying for malaria control. see http://news.bbc.co.uk/2/hi/science/nature/5350068.stm for more detail and other articles.
Within the International Society of Doctors for the Environment Dr. Paul Saoke, Executive Director, Physicians for Social Responsibility in Kenya opposes DDT usage. Dr. Jamidu Katima, Director of the Tanzanian public interest group AGENDA and Co-Chair of the International POPs Elimination Network says “WHO’s decision to increase use of DDT threatens the health of children and families already plagued with malaria, and directly undermines an important global treaty”
What conclusion can we draw? DDT is a transboundary poison and its accumulation has grave consequences for all life. In fact DDT is one of 12 initial chemicals targeted for global phaseout under the Stockholm Convention on Persistent Organic Pollutants (POPs) because they are toxic, persist in the environment, travel around the globe, and build up in our bodies. The treaty, which has been adopted by 127 countries and is supported by public health and environmental advocates around the world, allows interim DDT use for malaria control in countries that request it and mobilizes funds for safe and effective malaria control and prevention strategies that do not rely on DDT. Malaria is an appalling disease with huge mortality and every possible method is needed to save life and suffering. There can be no conclusion other than the need for the wealthy, fortunate countries of the world to increase their expenditure on the development of malarial treatments, which are not profitable to our market driven pharmaceutical industries
We acknowledge that some of the material for this article was taken from Environmental Health Sciences.