The prevalence of environmental compounds, both synthetic and naturally occurring, with endocrine disrupting properties has opened many doors in research area for scientists. It has generated debate among regulatory agencies, and the general public about the potential long term risks they pose for human and wildlife (Patisaul et al., 2009). These substances interfere with metabolism, hormone biosynthesis, or changing normal homeostatic control or reproduction into deviating forms. They are present in our surrounding environment, food, and consumer products. A broad class of molecules such as organochlorinated pesticides and industrial chemicals such as, plastics and plasticizers, fuels, and many other chemicals are represented as endocrine disruptor chemicals (EDCs) (Diamanti-Kandarakis et al.,2009).
In the endocrine system, these environmental pollutants are very active biologically and disrupt the function of endogenous hormones (Robins et al., 2011). Endocrine-disrupting chemicals were focused very well in 1991 when a group of scientists at a Wingspread work session has given conclusion about these chemicals. They have defined these compounds as the compound introduced into the environment by human activity are able to disrupt the endocrine system of animals, including fish, wildlife, and humans. Because of the hormones' crucial role in controlling development, endocrine disruptions have profound effects (Hotchkiss et al., 2008).
This paper has three objectives: (1) to discuss about the Endocrine System and endocrine disruptor chemicals, (2) to discuss the mode of action of endocrine disrupting chemicals and the effects of endocrine disruptors on human, and wildlife (3) to discuss the sources, and routes of exposure to endocrine disruptors (4) to discuss the future perspective for endocrine disruptors.
The Endocrine System
The human body has complex systems, including the circulatory, digestive, and muscular systems and each of these systems functions importantly. The body has two control systems: nervous system and endocrine system. Endocrine system is made of a group of organs called endocrine glands. These endocrine glands are present in various parts of the body. These glands release hormones that act as chemical messengers and travel through the blood. These hormones control the responses, such as growth, reproduction, metabolic rate, blood glucose levels, salt, and water balance (Rushton, 2009). The site of the neurons that control neuroendocrine system is the hypothalamus. Hormones are produced by the hypothalamic neural cells and these hormones are important for a crucial homeostatic regulatory function. These homeostatic regulatory functions can be disturbed if the actions of these hormones are interfered with any chemicals that mimic or antagonize the functions of hormones (Gore, 2010).
A synthetic chemicals that when get absorbed into body either mimic or block hormones and disturb the body's normal functions. These chemicals disrupt these functions through altering normal hormone levels, stopping or stimulating the production of hormones, or changing the way of hormones travel through the body. Thus, these chemicals affect the control systems of the body by interfering with hormones (NRDC, 1998).
Mode of Action of Endocrine Disruptors
The mechanisms of the endocrine disruptors by which they affect cellular activity are not clear. They exert their effects by altering genomic responses (Robins et al., 2011). Most of the actions of endocrine disruptors exert on lipid (steroid) or amino acid derived (thyroid) hormones, and very few act on synthesis or signaling of peptide/protein hormones. But common effects are observed through steroid receptors on peptide/protein hormones. Genes are directly affected by the endocrine disruptors but this mode of action is not explored well. Some estrogenic actions are DNA damage that leads to malignant differentiation of affected cells. They show epigenetic impact (Gore, 2010). These compounds act as either agonists or antagonists of the steroidal sex hormones, estrogens or androgens and by that way it interferes with reproduction. By interfering with steroidal signaling, most endocrine disruptors disrupt reproduction (Uzumcu and Zachow, 2007). Some characteristics of endocrine disruptors make them more interesting, such as, the basis for adult diseases including cancer is formed after exposure to endocrine disruptors during critical developmental time. These chemicals also affect the offspring of affected person by epigenetic modifications. Finally, multiple endocrine systems are affected by a complex mixture of these compounds and thus, make this disruption more complicated (Ma, 2009).
Effects of EDCs on Human and wildlife
Numerous effects can be seen after exposure to endocrine disruptors on humans. These effects include depressed circulating thyroid hormone, abnormal thyroid cytology, delayed cognitive development, altered sensory and motor abilities, reproductive impairment, and compromised neural functions (Steinberg et al. 2008). These chemicals affect human sexual maturation and thyroid activity in youth (Schell et al., 2010). Some chemicals such as, phthalates are known to alter the germ cell development in human fetus (Lambrot et al., 2008).
Some invertebrates, fish, and wildlife population are also affected by endocrine disruptors. They cause imposex, unsustainability of the wild population, infertility, adverse effect in reproduction and development in wild life population (Hotchkiss, et.al., 2008).
Endocrine Disrupting chemicals and Their Sources
A variety of classes of chemicals are known to be endocrine disruptors. These classes include pesticides, industrial by-products and chemicals used in manufacturing-particularly plastics, many other chemicals that are present in the environment or are in widespread use. Some of these chemicals include dioxin and dioxin- like compounds, diethylstilbestrol, polychlorinated biphenyls, DDT, DDE, bisphenol A, phthalates, and some pesticides. (Robins et al. 2011). The material most commonly used to make the clear plastic bottles is known as polyethylene terephthalate (PET) and these PET bottles are useful as containers for soda beverages, sport drinks, and condiments such as vinegar and salad dressing. These plastic containers introduce endocrine disrupting chemicals into foods and beverages (Sax, 2009). Especially for younger children, the indoor environment is known to be a significant source of these kinds of chemicals. In this polluted world, the indoor dust is contaminated with EDCs such as polychlorinated biphenyls, polybrominated diphenyl ethers, and phthalates and thus, indoor dust may contribute to overall exposure of these chemicals to the children (Hwang et al. 2008). The waste water effluents also contain large amount of endocrine disruptor in it (Huang and Sedlak, 2000).
Routes of Exposure to Endocrine disruptors
Direct contact with pesticides, other chemicals and ingestion of contaminated water, food, or air, can be the route of exposure (NRDC, 1998). Some important issues are there to understand the consequences of exposure to EDCs. Knowledge of age at exposure is important to understand the mechanism of action of EDCs. There are different consequences of exposure of an adult to that of the developing fetus and infants. After exposure to these chemicals, the latency period will be started and then after some period of time, manifestation of disorder will be observed. Exposure to the mixtures of these EDCs results into additive or synergistic response (Diamanti-Kandarakis et al., 2009).
Endocrine disruptors are the emerging topic in science researches. Knowledge regarding these chemicals and its mode of actions is too little. Very few information is available about the link between exposures to potential endocrine disrupting chemicals and their effects on human and wildlife. The awareness of the risk of the endocrine disruptors should be increased by the public education about the sources of EDC and their adverse effects on health (Hwang et al., 2008). The site and mechanism of action of these chemicals are required additional research to understand them. It requires more developed, improved methods for detecting these chemicals. The use of molecular mechanisms can be helpful to provide biomarkers for various disease risks from ED exposure as well as it can provide opportunities for therapeutic intervention (Schell and Gallo, 2010).