Frederick S. vom Saal
During the last decade scientists became aware of a new type of health threat posed by environmental chemicals: the disruption of endocrine (as well as paracrine and autocrine) signals that coordinate tissue differentiation during critical periods in development. The realization that exposure of wildlife and humans to endocrine disrupting chemicals (EDCs) was occurring from plastic, pesticides and other industrial products and by-products has resulted in a new interdisciplinary field of science. An important aspect of endocrine disruption is that exposure to EDCs during development can result in permanent alternations in organ function. However, this possibility had not previously been incorporated into standard testing procedures to assess the health effects of chemicals. As a result, in 1996 the US Congress mandated that the EPA revise its testing procedures for assessing chemical safety, and the National Academy of Sciences was authorized to conduct an analysis of the science (Hormonally Active Agents in the Environment, NRC Press, 1999). This report concluded that there was convincing evidence of neurobehavioral and reproductive disruption by EDCs in wildlife and laboratory animals, and strong support for neurobehavioral effects in humans. A surprise to many is the exquisite sensitivity of developing systems to extremely small perturbations in endocrine signals that control development. This high sensitivity to very low doses of chemicals has served to create a paradigm shift in toxicology, which previously had focused on acute toxicity in response to exposure of adults to very high doses of chemicals as an endpoint, not the disruption of signalling molecules that act at low doses in differentiating tissues. This paradigm shift has produced a major media effort by the chemical industry to convince the public that chemicals which have never been tested for endocrine disrupting effects are completely safe (using exactly the same strategies employed by the tobacco and lead industries throughout the twentieth century). Chemical companies have also vigorously attacked the "precautionary principle", which is employed as a component of risk assessment throughout the rest of the industrialized world. An important outcome of research on endocrine disruption is that it has lead to a renewed awareness among scientists of the importance of epigenetic events in development. This is leading to new funding initiatives concerning the long-term health consequences of disrupting epigenetic signals during critical periods in development. However, many developmental biologists, let alone the general public and legislators, remain largely unaware of these issues. In order to reduce the risk to wildlife and humans due to exposure to EDCs, it is necessary to improve current knowledge not only within the scientific community, but on the wider political stage as well.