Worldwide concern has arisen that certain environmental contaminants as well as some naturally occurring compounds have the potential to disrupt the endocrine system which regulates vital processes including development, growth, metabolism and reproduction. Several pieces of interesting evidence indicating possible increasing trends of adverse effects on the reproductive capability of animals, wildlife as well as humans have been forthcoming. The last two decades has witnessed growing scientific concerns and public debate over the potential adverse effects that may result from exposure to a group of chemicals that have the potential to alter the normal functioning of the endocrine system in wildlife and humans.
In the early 1990’s, an interdisciplinary group of scientists in the United states started a discussion about chemicals with a potential to specifically induce adverse effects on the endocrine systems of both human and wildlife. The result, the “Wingspread Consensus Statement”, triggered further debate in both the USA and Europe. The general public was confronted with this issue by television through programs like the 1993 BBC Horizon documentary with striking title “Assault on the Male” and the well known 1996 publication “Our Stolen Future” by Theo Colborn, Dumanoski and Myers.
- What are endocrine disruptors???
Endocrine disruptors have been defined as exogenous agents that interfere with the production, release, transport, metabolism, binding, action or elimination of natural hormones in the body responsible for the maintenance of homeostasis and regulation of developmental processes (Kavlock et al., 1996). In 1996, the European Commission defined an endocrine disrupter as “an exogenous substance that causes adverse health effects in an intact organism, or its progeny, consequent to changes in endocrine function” (European Commission, 1996).
EDCs are suspected to interact with the endocrine systems and as such disturb hormone homeostasis. The endocrine system acts by releasing hormones which in effect trigger actions in specific target cells. Almost all biological development unfolds as a sequence of events, orchestrated and controlled by biochemical signaling mechanisms that activate gene expression. Key among these signaling mechanisms are hormones; chemical messenger molecules that are produced in one part of the body and transported to another where they enter a cell and in concert with other intracellular complexes, initiates gene expression. Interference with any step in these signaling processes during development can result in adverse effects ranging from obvious birth defects to subtle changes that only become manifest long after exposure has occurred. High doses of endocrine disrupting chemicals (EDCs) can result in overt toxicity, such as cell death, but at lower levels, they can alter the expression of genes, resulting in endocrine system changes that become permanent during critical periods of development. In addition, different EDCs can interfere with different signaling pathways using different mechanisms, and when combined with other chemicals in mixtures, this can result in a wide variety of possible outcomes, most of which would be difficult to detect statistically.
Disruptors are divided into three categories:
Mimics - These disruptors are perceived by the body as genuine hormones because they elicit the same chemical reaction as natural hormones.
Blockers - These disruptors, by blocking the cell receptors, prevent naturally occurring hormones from affecting cells in the usual way.
Triggers – These disruptors elicit unusual or abnormal reactions in cells.
- Endocrine Disrupting Chemicals (EDCs)
Given the complexity of endocrine systems, the range of substances thought to cause endocrine disruption is wide and varied, and includes both natural (chiefly originated from plants called phytoestrogens) and manufactured chemicals (called xenoestrogens). Chemical classes demonstrating endocrine disrupting properties includes: Pesticides (insecticides such as o, p’DDT, endosulphan, dieldrin, methoxychlor, kepone, dicofol, toxaphene, chlordane, herbicides such as alachlor, atrazine and nitrofen; fungicides such as benomyl, mancozeb and tributyltin; nematocides such as aldicarb) Bisphenol-A and phthalates, Pharmaceuticals (Drug estrogens-birth control pills, DES, cimetidine), nonylphenol, octylphenol, industrial chemicals (polychlorinated biphenyls), dioxin, benzopyrene and heavy metals (lead, mercury and cadmium). Furthermore, some of the endocrine-disrupting chemicals, in particular the organochlorine pesticides, PCBs and dioxins, are persistent in the environment, taking years or even decades to degrade. The recent discovery suggests extremely low, environmentally relevant doses of EDCs can elicit a physiological response that alters organism development and function.