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Endocrine disruption in invertebrates. bisphenol A produces superfemale snails Most animal life on earth lack backbones... they are invertebrates. This includes animals as different as mollusks, lobsters, insects, starfish, spiders and sea cucumbers, to name just few. Like vertebrates, invertebrates depend upon chemical signalling from hormones to regulate growth and development. And like vertebrates, they are therefore vulnerable to endocrine disruption. Many of the hormones used by invertebrates have their counterparts in vertebrates, but others are quite distinct. Thus the patterns of vulnerability to endocrine disruption among invertebrates could be similar in some respects but wildly different in others. But because invertebrates are vitally important in many instances to healthy ecosystems, their vulnerability to endocrine disruption should be of intense interest to people. The Society of Environmental Toxicology and Chemistry (SETAC) convened a workshop in 1998 to review what is known about endocrine disruption effects in invertebrates. The proceedings were published in 1999 as a volume edited by Dr. Peter L. deFur, Mark Crane, Christopher Ingersoll and Lisa Tattersfield. Few invertebrates have been studied expressly for endocrine disruption, other than insects in which a great deal of work has been undertaken specifically to develop pesticides that interfere with insect hormones. The best example of accidental (as opposed to pesticides, which are purposeful) disruption is the effect of tributyltin (TBT) on marine snails: TBT interferes with hormone metabolism in snails, increasing the levels of androgens. One effect is called "imposex," where a female snail develops both female and male genital systems, and the male organs are superimposed physically over the female organs. The other effect is "intersex," observed in the periwinkle Littorina littorea,in which the female organs are modified toward a male form, although not completely. The most fully developed cases of intersex and imposex result in female sterilization. The effects of these types of endocrine disruption have been shown to alter sex ratio of the populations affected, reduce the numbers of juveniles, and in extreme cases, reduction and elimination of the population at heavily contaminated locations. TBT is used in marine paints to eliminate "fouling" (in which marine organisms attach themselves to boat hulls). It is also used in fungicides and thus can enter marine ecosystems in agriculturaly run-off. TBT is extremely potent.
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Billinghurst, Z, AS Clare, T Fileman, J Mcevoy, J Readman, and MH Depledge. 1998. Inhibition of barnacle settlement by the environmental oestrogen 4-nonylphenol and the natural oestrogen 17b oestradiaol. Marine Pollution Bulletin 36(10):833-839. Billinghurst et al. discovered that both natural estrogen and the estrogen mimic 4-nonylphenol interfere with the ability of barnacles to settle from ocean waters (which they inhabit for the first portion of their life, as larvae) to the rocky substrate they inhabit as adults. The authors were unsure of the mechanism of action with some of the results indicating either that the estrogen and nonylphenol were acting through different mechanisms or that there was a nonmonotonic dose response relationship within the range of concentrations examined. |