Endocrine disruption/disruptors

It is also clear that it is difficult to relate cause and effect to any specific chemical since, with the exception of point source effluents, many waterways contain a multitude of chemicals, of which the active endocrine disruptor may not be that which has been measured in the water or tissue. For such reasons, many studies have used in vitro experiments in which isolated tissue, either from a control animal or one captured in a polluted water system, is exposed to a single pollutant in the laboratory. Such experiments have shown significant disruption to testicular activity by a wide range of xenobiotics, including cadmium, lindane, DDT, cythion, hexadrin and PCBs. ... 

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine system because of the abihty of these chemicals to mimic or block endogenous hormones, or otherwise interfere with the normal function of the endocrine system. Chemicals with this type of activity are most commonly referred to as endocrine disruptors. Some scientists believe that chemicals with the ability to disrupt the endocrine system are a potential threat to the health of humans, aquatic animals, and wildlife. Others believe that endocrine disrupting chemicals do not pose a significant health risk, particularly in light of the fact that hormone mimics exist in the natural environment. Examples of natural hormone mimics are the isoflavinoid phytoestrogens (Adlercreutz 1995 Livingston 1978 Mayr et al. 1992). 

The majority of very high concern substances will be those classified as category 1 or 2 CMRs. There are already around 850 such CMR substances based on current classifications, and it is likely that there will be another ca 500 identified from future testing. Most endocrine disrupters would require authorisation by being classified as carcinogenic or toxic for reproduction, but there is the option to add other endocrine disruptors on an ad hoc basis. 

Successful reproduction (and sex) involves many complex chemical processes that can be disrupted at various points to reduce fertility and conception. Part of this process is under control of the endocrine system, and chemicals that affect the endocrine system are termed endocrine disruptors. In the 1950s, understanding of the endocrine system led to the development of birth control pills as a way to reduce fertility in humans. This is a desirable and planned use of endocrine disruptors. Subsequently, it was discovered that a number of chemicals released into the environment could disrupt the endocrine system and reduce fertility of wildlife. Some are concerned that exposure to these chemicals, such as DDT and dioxin (TCDD), may also affect human fertility (Table 17.1). Approximately 15% of couples of reproductive age are infertile. Endocrine disruptors may also affect fetal development, causing demasculization and feminization of the offspring, which in turn cause reduced fertility in the next generation. 

Depending upon the circumstance and desired effects, endocrine-disrupting chemicals can be either good or bad. The endocrine system is a finely balanced system responsible for fertility and many of the feminine and masculine traits we are all familiar with. Endocrine disruptors are used by millions of women in the form of the pill to control fertility. Chemicals in birth control pills subtly manipulate the endocrine system to reduce fertility. Unfortunately, we now know that many chemicals are capable of influencing the endocrine systems. When these chemicals, such as DDT and TCDD, are released into the environment, they reduce the fertility of wildlife. Exposure to endocrine disruptors is linked to decreased fertility in shellfish, fish, birds, and mammals. Endocrine disruptors such as nonylphenol have been shown to feminize male fish, interfering with reproduction. Some studies have also linked exposure to endocrine disruptors to decreases in human male sperm count. Ironically, urinary metabolites of the birth control pill as well as the female hormone estrogen pass through waste treatment plants and are released into the aquatic environment, where even small concentrations cause feminization of male fish. 

A potential endocrine disruptor is a substance that might be expected to lead to endocrine disruption in an intact organism. 

The most notable coordinated effort to evaluate chemicals for potential endocrine-disrupting properties is the Endocrine Disruptor Screening Program (EDSP) directed by the EPA [37]. 

Perkins, R., Anson, J., Blair, R., Branham, W.S., Dial, S., Fang, H., Hass, B.S., Moland, C., Shi, L., Tong, W., Welsh, W., Walker, J.D., and Sheehan, D.M., The endocrine disruptor knowledge base (EDKB), a prototype toxicological knowledge base for endocrine disrupting chemicals, in Handbook on Quantitative Structure Activity Relationships (QSARs) for Predicting Chemical Endocrine Disruption Potentials, Walker, J.D., Ed., SETAC Press, Pensacola, FL, 2003 (in press). 

Thomas, P., Khan, LA. (2005). Disruption of nongenomic steroid actions on gametes and serotonergic pathways controlling reproductive neuroendocrine function by environmental chemicals. In Endocrine Disruptors Effects on Male and Female Reproductive Systems, 2nd edition (R.K. Naz, ed.), pp. 3-45. CRC Press/Taylor Francis Group, LLC, Boca Raton. 

Accepting this statement and sensational reports by the mass media, the Japan Environmental Protection Agency (JEPA) published Strategic Programs on Environmental Endocrine Disruptors in 1998 (SPEED 98) , presented JEPA s basic policy on this subject, initiated concrete countermeasures and listed about 70 substances, including SDs and STs, that are suspected of being endocrine disrupters (EDs) in a review of the literature [3]. Thereafter, researchers affiliated with the National Institute of Health Sciences (NIHS) investigated certain kinds of containers made of PS, and it was clarified that... 

The health effect of endocrine disruptors is further complicated by the fact that an endocrine disrupter or a family of endocrine disruptors may have multiple mechanisms of actions. For example, PCBs may mimic estrogen, prevent binding of thyroid hormone to thyroid binding globulin, and accelerate the metabolism and excretion of several steroid hormones. 

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