Endocrine signals can be mimicked, blocked and amplified by environmental hazards. A transient environmental signal at a key moment in body development may impart a massive, chronic, latent, or even transgenerational effect on the organism and/or its progeny. The same substance, acting as an agonist (i.e., promoting an effect) in one setting or time, may act as an antagonist (i.e., preventing the effect) in another location of the body or time in development.
The body has three systems in which cells are known to communicate remotely with one another. The immune system cells signal through cytokines, antibodies, and other cells (e.g. macrophages or dentritic cells). The nervous system cells signal other cells through specialized appendages and neurotransmitters. The endocrine system cells signal one another and other cells in the body through chemical messengers (hormones) that often work through a receptor mechanism.
The potential effect from endocrine disruptors include: reproductive behaviors, metabolism, sexual differentiation of the brain, learning/memory, neuroteratogenic effects, and psychomotor development. The chemicals considered of greatest potential endocrine disruptor activity are: PCBs, dioxins, triazine herbicides, DDT, Dithiocarbamates, tamoxiphen, and phytoestrogens.
The endocrine system consists of a set of glands and the hormones they produce, which help guide the development, growth, reproduction and behaviour of animals and human beings. There is growing concern about a range of man-made substances which are designed for use in industry, agriculture and consumer goods as well as substances produced as a by-product of industrial processes. These substances are now suspected of interfering with the endocrine system.
In March 1999, the Scientific Committee for Toxicity, Ecotoxicity and the Environment (SCTEE) issued a report, "Human and Wildlife Health Effects of Endocrine Disrupting Chemicals, with emphasis on Wildlife and on Ecotoxicology test methods". The report identifies a "potential global problem" for wildlife. It also states that "impaired reproduction and development causally linked to endocrine disrupting substances are well-documented in a number of wildlife species and have caused local and population changes".
In May 1997, at the Summit Meeting of the Environment Leaders of the G8 countries, a Declaration was adopted encouraging international coordination in research efforts on endocrine disruption. In May 1999, at the EU-US Transatlantic Environment Conference on Chemicals in Stresa, Italy, emphasis was likewise placed on the need to coordinate research programmes and also to ensure harmonisation via OECD.
Humans and mice exposed in utero to the potent synthetic estrogen, diethylstilbestrol (DES), exhibit altered reproductive tract structure and function. These same exposures to an adult have no measurable effect. This DES experience and other such "experiments in nature" have suggested concern for the effects of environmental hormones on children's development.