Endocrine disrupting chemical

Our present meagre understanding of normal endocrine processes in invertebrates makes the assessment of chemical endocrine disruption in the field difficult (LeBlanc 1999). Steroid roles differ between species and sometimes sexes, and their influence may vary at different developmental stages. In most studies of invertebrates, endocrine disruption appears to involve androgenization rather than oestrogenic effects (see Box 7.2). Arthropods (crustaceans and insects), annelids and molluscs use ecdysteroids, terpenoids and vertebratelike sex steroids for endocrine control. For example, the ecdysteroid ecdysone is naturally converted to 20-hydroxyecdysone (Fig. 7.10), which induces moulting (ecdysis) in both insect larvae and crustaceans. 

The conventional definition of the endocrine system is the collection of ductless glands that secrete small amounts of hormones directly into the blood of vertebrates. The hormones are transported to other parts of the body where they have a profound effect on biological processes. Perhaps the best examples are the sex hormones oestrogen and testosterone, but there are many others. Hormones are also produced by invertebrates (e.g. moulting hormones) and even by plants (e.g. growth hormones). 

Some xenobiotic compounds can have hormonelike effects and cause disruption of the endocrine system. A compound that mimics the action of a particular hormone is termed an agonist, whereas one that blocks its activity is an antagonist. Hormone activity is governed by receptors that recognize the shape of the molecule, so potentially other molecules with suitable structural characteristics can interact with these receptors. There are other potential modes of action of endocrine disrupters. To summarize  

1 They can mimic the effects of naturally occurring hormones by recognizing their binding sites (agonists). 

2 They can reduce the effects of natural hormones by blocking their interaction with their physiological binding sites (antagonists). 

TABLE 1-2 Causative Agents in Disrupting Endocrine Functions in Animals and Humans 

Polyvinyl chloride Pentachlorophenol Plasticizers and surfactants Phthalates 

Given the complexity of endocrine systems, it is not surprising that the range of substances thought to cause endocrine disruption is wide, and includes both natural and manufactured (synthetic) chemicals. Industrial, agricultural, and municipal wastes can expose organisms in the environment to unusually high concentrations 

Dioxins, Toxic Gases, Vapors, and Their Pollutants 

Polychlorinated biphenyls (PCBs) were first synthesized in 1864, and commercial use has been active since 1929. Over 1 million tons of PCBs have been produced commercially with different trade names, such as Aroclor, Clophen, Fenchlor, and Kanechlor. There are 209 PCB isomers or types, which differ from each other in the number and relative position of the chlorine atoms on the biphenyl molecular frame. A small number of these isomers are particularly toxic and are believed to account for the bulk of PCB-induced toxicity in animals. PCBs 

A large number of individual chemicals have been demonstrated to be endocrine disruptors. EDCs include pesticides, synthetic hormones, heavy metals, plasticizers, and other industrial chemicals. Table 22.1 

Tetrahydrofuran Thiocyanate Tributyl tin Trichloroethylene Triphenyltine VM P naphtha 

In keeping with the stated purpose of this book, the endocrine disrupting effects of single chemicals are discussed briefly and serve as an introduction to a discussion of the endocrine toxic effects of chemical mixtures. 

A number of structurally different xenobiotic chemicals are estrogen mimics. These compounds include pesticides, industrial chemicals, and components of many plastics, including polystyrene and polycarbonate. Some are listed in Table 22.2. 

Ethanol has been shown to induce oxidative damage in the pituitary gland and contribute to pituitary dysfunction. Chronic exposure of laboratory animals to ethanol results in a decline in serum testosterone and decreased serum luteinizing hormone and follicle-stimulating hormone. 49  

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Issues in Environmental Science and Technology No. 12 Endocrine Disrupting Chemicals The Royal Society of Chemistry, 1999... 

Known and suspected endocrine disrupting chemicals needed to be ranked in order of priority for possible regulatory action. 

Table 2 Some known or suspected endocrine disrupting chemicals...

Culture a range of invertebrate species from the major phyla, preferably species with short life cycles. The effects of potential endocrine disrupting chemicals on growth rate, reproductive output, viability of offspring and sex ratio, and the vulnerability of different stages of the life cycle, can then be determined. 

Mechanistic studies to identify how endocrine disrupting chemicals interact with hormone systems are required. Although population effects coupled with biomarkers of exposure are strongly suggestive of endocrine disruption, the effect could be secondary to metabolic toxicity. Establishing mechanisms may avoid the need to make decisions on a weight of evidence approach alone. 

Potential Effects of Endocrine Disrupting Chemicals on Reproductive Eunction... 

There is some evidence for chemically mediated endocrine disruption in amphibians. The egg yolk protein, vitellogenin, is inducible in amphibians by exposure to DDT. " Males of the short clawed toad Xenopus laevis given 250 fig/g or 1 fig/g o,p -DDT for seven days have been shown to produce vitellogenin, although the induction was less than that achieved by treatment with 1 fig/g of either 17/1-oestradiol or diethylstilboestrol. Research has also shown that endocrine disrupting chemicals can alter sex ratios in wild populations of certain species PCB congeners and organochlorine compounds have been linked with male domination of sex ratios in polluted compared to unpolluted sites. ... 

Observed recovery in raptors has been slow owing to their lifecycle this is also an indication of the environmental movement and dispersal of endocrine disrupting chemicals from areas of intense agriculture to the aquatic environmental... 

NakadaN, Shinohara H, Murata A, Kiri K, Managaki S, Sato N, Takada H (2007) Removal of selected pharmaceuticals and personal care products (PPCPs) and endocrine-disrupting chemicals (EDCs) during sand filtration and ozonation at a municipal sewage treatment plant. Water Res 41 4373-4382... 

Collectively, the findings in experimental animals are insufficient to categorize methyl parathion as an endocrine-disrupting chemical. 

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). 

Dr. G. A. LeBlanc of North Carolina State University is evaluating effects of potentially endocrine-disrupting chemicals, including endosulfan, on steroid hormone biotransformation/elimination processes in daphnids, fish, and mice, and is constructing models of the processes. The work is being funded by the U.S. Department of Agriculture. 

Colborn T, Vom Saal FS, Soto AM. 1993. Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environ Health Perspect 101(5) 378-384. 

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