Endocrine disruptors are chemical substances that act on the endocrine system and disrupt its functions. The term Endocrine disruptor was introduced in the Wingspread Conference Centre; Wisconsin in 1991.The work of Theo Colborn showed that the environmental chemicals disturbed the development of endocrine system. Endocrine disruption refers to the fact that there is negative interference or permanent adverse consequences beyond the range of everyday fluctuations of hormone levels.
There are various kinds of chemicals that interfere with the functioning of the hormone system. These includes hormones, plant chemicals, pesticides, chemicals used in plastic industry, pollutants etc. Some chemicals are Pervasive types widely present in the environment while some are Persistent organic pollutants. Some endocrine disruptors degrade in the environment very fast. Some chemicals are very important since these cause fatal ill effects in the body. Health effects include reproductive problems like reduced fertility, reproductive tract abnormalities, loss of fetus, brain and behavior problems, cancer etc.
Endocrine system includes specialized glands that secrete hormones directly into the blood. These hormones have target cells in which the hormones act. The hormones act on the cells through the endocrine receptors on the cells. The hormones influence all the metabolic functions of the body, growth etc. Disruption in the hormone function may seriously affect the functioning of the body. Hormones like Sex steroids, Thyroid hormones etc are subject to feed back regulation which tends to limit the sensitivity of these hormones.
The theory of endocrine disruption posits that low-dose exposure to chemicals that interact with hormone receptors can interfere with reproduction, development, and other hormonally mediated processes. Since the hormones are naturally present in the body, addition of any hormone like material from the environment into the body can have adverse effects in the body. Thus the endocrine disruptor can elicit adverse effects at much lower doses than a toxicant.
The time of exposure to endocrine disruptors is very important, since the hormone pathway is active during the different stages of development. Exposure during the early stages of the development is more important since growth and metabolism is fast during this stage. There are studies of cell cultures, laboratory animals, wildlife, and accidentally exposed humans that show that environmental chemicals cause a wide range of reproductive, developmental, growth, and behavior effects, and so while “endocrine disruption in humans by pollutant chemicals remains largely undemonstrated. While compounds that produce estrogenic, androgenic, anti androgenic, and anti thyroid actions have been studied, less is known about interactions with other hormones.
Types of endocrine disruptors
All people are exposed to chemicals with estrogenic effects in their everyday life, because endocrine disrupting chemicals are found in low doses in literally thousands of products. Chemicals commonly detected in people include DDT, Polychlorinated biphenyls (PCB’s), Bisphenol A, Polybrominated diphenyl ethers (PBDE’s), and a variety of Phthalates. There is some dispute in the scientific community surrounding the claim that these chemicals actually disrupt the endocrine system. Some researchers are investigating the health risks to children of endocrine disrupting chemicals. Bisphenol A has come under a great deal of scrutiny as it is a common component of plastic baby bottles.
Dichloro-diphenyl-trichloroethane (DDT) was first used as a pesticide against Colorado potato beetles on crops beginning in 1936.As early as 1946, the harmful effects of DDT on bird, beneficial insects, fish, and marine invertebrates were seen in the environment. Further studies found DDT in high concentrations in carnivores all over the world, the result of bio magnification through the food chain. More than sixty years ago when biologists began to study the effects of DDT on laboratory animals, it was discovered that DDT interfered with reproductive development. Recent studies suggest DDT may inhibit the proper development of female reproductive organs that adversely affects reproduction into maturity. Additional studies suggest that a marked decrease in fertility in adult males may be due to DDT exposure.
Polychlorinated biphenyls (PCBs) are a class of chlorinated compounds used as industrial coolants and lubricants. PCBs are created by heating benzene, a byproduct of gasoline refining, with chlorine. The effects of acute exposure to PCBs were well known. Direct skin contact results in a severe acne-like condition called chloracne. Exposure increases the risk of skin cancer, liver cancer, and brain cancer. Recent studies show the endocrine interference of certain PCB congeners is toxic to the liver and thyroid, increases childhood obesity in children exposed prenatally, and may increase the risk of developing diabetes.
Bisphenol A is found in some plastic water and baby bottles, plastic food containers, dental materials, and the linings of metal food and infant formula cans. It is a known endocrine disruptor, and “hundreds of studies published in the decade” have found that laboratory animals exposed to low levels of it have elevated rates diabetes, mammary and prostate cancers, decreased sperm count, reproductive problems, early puberty, obesity, and neurological problems. Some scientists believe that humans, especially infants, are currently exposed to levels that are known to cause harm in laboratory animals.
Polybrominated diphenyl ethers
Polybrominated diphenyl ethers (PBDEs) are a class of compounds found in flame retardants used in plastic cases of televisions and computers, electronics, carpets, lighting, bedding, clothing, car components, foam cushions and other textiles. Potential health concern: PBDE’s are structurally very similar to Polychlorinated biphenyls (PCBs), and have similar neurotoxic effects.
PBDEs have the potential to disrupt thyroid hormone balance and contribute to a variety of neurological and developmental deficits, including low intelligence and learning disabilities. Studies with rodents have suggested that even brief exposure to PBDEs can cause developmental and behavior problems in juveniles and exposure interfere with proper thyroid hormone regulation. Research has correlated halogenated hydrocarbons, such as PCBs, with neurotoxicity.
Phthalates are found in some soft toys, flooring, medical equipment, cosmetics and air fresheners. They are of potential health concern because they are known to disrupt the endocrine system of animals, and some research has implicated them in the rise of birth defects of the male reproductive system.
One phthalate, Bis (2-ethylhexyl) phthalate (DEHP), used in medical tubing, catheters and blood bags, may harm sexual development in male infants. Exposure to DEHP has produced a range of adverse effects in laboratory animals, but of greatest concern are effects on the development of the male reproductive system and production of normal sperm in young animals. In view of the available animal data, precautions should be taken to limit the exposure of the developing male to DEHP.
Certain alkyl phenols are degradation products from nonionic detergents. Alkyl phenol is considered to be a low-level endocrine disruptor owing to its tendency to mimic estrogen.
Other suspected endocrine disruptors include Dioxins, PCBs, furans, phenols and several pesticides , xenoestrogens, phytoestrogens etc.
Action of Endocrine disruptors
Research clearly shows that endocrine disrupting chemicals can act in a number of ways in different parts of the body. Most studies have focused on the influence of EDCs on hormone receptors, which are the parts of cells in target tissues that hormones lock on to, in order to trigger an effect. EDCs, by occupying the same receptor sites in the target cells as the natural hormone would do, can mimic the effect of a hormone or block its action. Other ways in which EDCs can work – such as disrupting hormone production, transport or breakdown – have been shown to be equally important.
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