Potential endocrine disrupters

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

The liver plays an important role in the endocrine system. The concentrations of hormones in plasma, and the activity of the glands which secrete them, are determined by the rate at which they are deactivated by the liver. The liver also has a major function in female reproduction since it is the target tissue of ovarian estrogen, to which it responds by producing the yolk protein vitellogenin. " Xenobiotics that affect either of these functions can therefore be considered to be potential endocrine disrupters. 

There is now very clear evidence that a wide range of anthropogenic chemicals can be considered as potential endocrine disrupters in fish (Table 1), but it is rather less clear whether they cause actual endocrine disruption in intact animals... 

Fish have many advantages as experimental models in the study of endocrine disruption, and although they do have some significant differences in their endocrine system to that of mammals, the underlying basis is very similar. Chemicals which are shown to be either actual or potential endocrine disrupters... 

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. 

For methyl parathion, most of the information on health effects in humans is derived from cases of acute exposure to relatively high concentrations of the pesticide. Such reports have not addressed the issue of the potential endocrine-disrupting capacity of methyl parathion in humans. An added complication in determining whether methyl parathion has endocrine-disrupting capabilities in humans is the fact that humans are seldom exposed to a single pesticide. 

The potential endocrine-disrupting capacity of methyl parathion in wildlife has also been examined, and results of some recent studies are summarized below. 

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. 

Analysis of potential endocrine disrupters, such as alkylphenols (degradation products of non-ionic surfactants), diphenolalkanes (cumylphenol, bisphenol-A, bisphenol-F) and benzophenones (from the paper industry) with RPLC-SSI-QITMS in the negative ion mode has been described [631]. 

The designation potential endocrine disrupter has been proposed for chemical products with an endocrine-disruption ability that is demonstrated in an in vitro assay but not confirmed in an in vivo animal model. To date, most of the available information on chemical products with endocrine disrupter activity has been generated by in vitro experiments [10]. Various existing tests and bioassays of very different types have been proposed by distinct international bodies to identify hormonal... 

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]. 

A firm assessment of the risk to humans is not possible at present because of a lack of relevant data about the effects of exposure to endocrine disrupters. While high levels of exposure to some chemicals thought to have endocrine disrupting properties could theoretically increase the risk of reproductive and developmental disorders, no direct evidence is available at present. Further investigation of the relationship between potential endocrine disrupters and human health is needed. In particular, the levels of exposure of humans to such chemicals must be reliably established. 

Walker data set — Walker et al., developed a database that contains a large and diverse collection of known pesticides and industrial chemicals, as well as some food additives and drugs (Walker et al., 2003). The database contains 92,964 Chemical Abstract Service (CAS) Registry numbers of chemicals that will probably have to be evaluated for their potential endocrine disruption. A final data set of 58,391 chemicals was processed by our system after eliminating those chemicals for which structures were not available (Walker et al., 2003) and/or 3D structures could not be generated (Hong et al., 2002). 

TABLE 33.1. Examples of Known and Potential Endocrine Disrupting Chemicals (EDCs) and Their Postulated Mechanisms... 

Information on any other adverse effects to the environment should be included where available, such as environmental fate (exposure), ozone depletion potential, photochemical ozone creation potential, endocrine disrupting potential and/or global warming potential. 

Human exposure to single endocrine-disrupting chemicals is generally considered to be low, and the compounds arc much less potent than the natural hormones. However, humans are expected to be exposed to a mixture of potential endocrine-disrupting chemicals. Hence, potential additive or synergistic effects have to be considered to assess the human risk. Furthermore, in vivo potency is often different from in vitro potency since the mcchani.sm.s of hormonal action of chemicals may not be adequately reflected by the in vitro assays. 

Many of the molecules used as sunscreens such as 4-methylbenzylidene camphor and octyl methoxycinnamate, in fact, show estrogenic activity and are potential endocrine disrupters. The product is normally supplied as aqueous white liquid dispersion containing approximately... 

Brominated flame retardants are widely used as polymer additives in plastics, electric appliances, and textile and polyurethane foams. Some of the technical flame retardant products contain brominated organic compounds, including polybrominated biphenyls (PBBs) and polybrominated diphenyl ethers. These compounds are structurally similar to PCBs and, therefore, their chemical properties, persistence, bioaccumulation, and distribution in the environment follow similar patterns. Moreover, they have potential endocrine disrupting properties and there are concerns over their exposure health effects. 

---