Module 3: Toxicology - Section 18: Reproductive Health Disorders in the Workplace

TOX 18.4 Reproductive Health Hazards - Endocrine Disruptors

3. Endocrine disruptors:

Endocrine disruptors refer to a variety of manufactured chemicals that may cause health abnormalities by interfering with the normal hormonal balance of humans or animals. Traditional wisdom is that endocrine disruptors (also described as "hormonally active agents") are chemicals that, by virtue of some structural similarity to normal hormones, can also bind to the receptor sites. However, once bound, these chemicals do not elicit the normal biochemical response; they alter the activity of the endocrine system, either by mimicking (enhancing) or by blocking (inhibiting) normal hormonal functions. The most commonly studied chemicals that may fit this category are polychlorinated biphenyls (PCBs), dioxins, and persistent pesticides. The four main disease categories attracting the most attention in endocrine disruptors research are reproductive, carcinogenic, neurologic, and immunologic health outcomes.

3.1 Cancer:

The relationship between pregnant women exposed to DES (synthetic oestrogen used to prevent miscarriage) and subsequent reproductive organ cancers in female offspring is well documented. The occurrence of certain cancers at hormonally sensitive sites in the body has been increasing over time in industrialised countries. Although some of the apparent increases may be due to improvement in our ability to detect cancer, it does not explain all the increases. This has led to suggestions that the general populations’ widespread exposure to endocrine disrupting chemicals could be damaging human health. There appear to be an increased incidence for endocrine-mediated cancers such as breast, testicular, prostate tumours and thyroid cancers. Thus far, there is no definite chemical being associated with the increase in these tumours but there is an argument that the increases are roughly linked in time with the increased use and release of industrial chemicals into the environment.

3.2 Nervous system function:

Information from human and experimental animal studies clearly shows that exposure to certain endocrine disrupting chemicals such as PCB’s, particularly before birth, can harm the development of the nervous system, neuro-endocrine function, and behaviour. Current studies are concentrating on several suspect chemical groups that may act via an endocrine-medicated neurotoxicity: PCBs, dioxins, DDT, and other chlorinated pesticides and metals. It should be noted that for the male reproductive system to function normally, an intact neurologic system is needed. Thus, the results of these studies may have an impact on related reproductive research.

3.3 Immune Function:

The immune system is involved in fighting infections and in allergic reactions. Exposure to environmental chemicals, including certain endocrine disrupting chemicals such as DES which is a powerful synthetic oestrogen, or PCB’s and doxins, has shown to alter human and animal immunity. It is however not clear whether this occurs via endocrine disruption. The suggestion of possible immuno-suppression comes from the fact that certain endocrine disruptors (for example, DES, PCBs, dioxins) alter the types of lymphocytes present in the blood stream. Laboratory animals and wildlife have demonstrated such changes in association with exposure to DES, PCBs, carbamate, organochlorine pesticides, and organic and heavy metals. As was noted earlier, infection and associated immunologic disturbances are considered a risk factor for male infertility.

3.4 Reproductive Abnormalities:

Possible reproductive effects of endocrine disrupting chemicals include decrease in sperm quality (count, proportion of normal sperm, semen volume), impaired fertility and abnormalities of male sex organs (cryptochidism and hypospadias).

There are well-documented reports of human reproductive effects (semen abnormalities) from exposure to endocrine disruptors. For example, kepone exposure at a US pesticide factory led to workers with oligospermia. Also, wildlife and experimental animals with offspring showing feminisation, demasculinisation, and abnormalities in sexual behaviour and development demonstrate endocrine-disrupting chemicals in their environment. Further studies are being conducted to better understand this situation.

Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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