Linking environmental hazards to endocrine disruption

There is growing scientific evidence to suggest that humans have introduced into the environment a range of organic chemicals that adversely effect humans and wildlife by disrupting endocrine system function. Disruption occurs when the action of hormones is mimicked or blocked. Little attention has been given to environmental impacts on the body's remote signaling systems thus research is required to improve understanding of basic endocrine function throughout all stages of human development and exposures to environmental hormones and their effects at all stages of human development.

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 effects of endocrine disruption, such as reproductive dysfunction and sexual abnormalities, have been observed in wildlife populations receiving high level exposures to persistent chlorinated compounds. It is unknown to what degree humans are affected. The knowledge that many of the same hormones and their receptors exist across the animal kingdom suggests that these wildlife studies could have widespread biological implications. Current international research is focusing on the relationship between endocrine disruptors and cancer, reproductive and developmental alterations, and neurological and immunological effects. The notion of endocrine disruption is unsettling, the animal evidence is troubling, and the major uncertainties are of critical concern to the public.

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.

The European Commission has adopted (20 December 1999) a Communication on a Community Strategy for Endocrine Disrupters a range of substances suspected of interfering with the hormone systems of humans and wild life. The strategy focuses on man-made substances, including chemicals and synthetic hormones, which may harm health and cause cancer, behavioural changes and reproductive abnormalities. The objectives of the new strategy are to identify the problem of endocrine disruption, its causes and consequences and to identify appropriate policy action on the basis of the precautionary principle in order to respond quickly and effectively to the problem. The strategy points to the need for further research, international cooperation, communication to the public and appropriate policy action and identifies actions in the short, medium and long-term to meet these requirements.

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.

The following limitations inhibit endocrine disruptor study: (1) chemicals occur as mixtures; (2) the number of specific and non-specific measurable endpoints is limited; (3) the timing of effects and exposures is uncertain; (4) the applicability of animal effects are unknown: (5) the shape of the dose-response curve is uncertain; and (6) there is poor understanding of baseline neuro-endocrine action and function.
Glandular system
Type Classification:
G: Very Specific strategies