disruption in invertebrates.
A produces superfemale snails
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.
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
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.
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.
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.
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