The last two decades have witnessed growing scientific concerns and public debate over the potential adverse effects that may result from exposure to a group of chemicals that have the potential to alter the normal functioning of the endocrine system in wildlife and humans.
Concerns regarding exposure to these EDCs are due primarily to
1) adverse effects observed in certain wildlife, fish, and bird ecosystems;
2) the increased incidence of certain endocrine-related human diseases;
3) endocrine disruption resulting from exposure to certain environmental chemicals observed in laboratory experimental animals.
In 1993, Colborn et al. pointed out that industrial-derived endocrine-disrupting chemicals, have been released into the environment and they hypothesized that prenatal or early postnatal exposure could result in permanent and irreversible damage to wildlife and humans. EDCs encompass a variety of chemical classes, including natural and synthetic hormones, plant constituents, pesticides, compounds used in the plastics industry and in consumer products, and other industrial by-products and pollutants. They are often pervasive and widely dispersed in the environment. Some are persistent, can be transported long distances across national boundaries, and have been found in virtually all regions of the world.
Concerns regarding EDC have generated a vast number of divergent research studies conducted under various conditions and examining various outcomes. It is extremely rare that a single study could provide all the necessary relevant information to link a particular exposure scenario to a particular health outcome in wildlife or humans. The fact that many endocrine effects are subtle or even cryptic at birth, and are not exhibited until adolescence or even later in life, complicates the study of causality. An even more complicating fact is that EDCs can act at multiple sites via multiple mechanisms of action. Receptor-mediated mechanisms have received the most attention, but other mechanisms (e.g., hormone synthesis, transport, and metabolism) have been shown to be equally important. Furthermore delayed effects of low-dose early-life stage exposure have been shown for many vertebrate species that occurred long after the exposure ceased. For most associations reported between exposure to EDCs and a variety of biologic outcomes, the mechanism(s) of action are poorly understood. This makes it difficult to distinguish between direct and indirect effects and primary versus secondary effects of exposure to EDCs. It also indicates that considerable caution is necessary in extrapolating from in vitro data to in vivo effects, in predicting effects from limited in vivo data, and in extrapolating from experimental data to the human situation.
A collective weight of evidence is essential in determining under what conditions observed effects resulting from exposure to EDCs occur via endocrine mediated mechanisms. Therefore, it is essential to evaluate the entire body of relevant knowledge. The intensity of the concerns and lack of consensus among scientists can best be ameliorated by an objective evaluation of the available scientific data on the potential adverse effects of these chemicals from an international perspective. Countries lacking the necessary infrastructure to monitor and evaluate these chemicals express a particular need for an objective international assessment. Furthermore, due to current intense research on EDC, an international collaboration should also consecutively integrate new data as they become available and make this information accessible for policy makers.