Given
the central role that hormones play in guiding the development of
the reproductive system and then in controlling its activities once
developed, it is not surprising that a major focus of endocrine
disruption research has been on reproductive health. Our Stolen
Future reviews many studies, especially experimental work with
laboratory animals, that document endocrine disruption of the reproductive
system. These include reductions in fertility, alterations in sexual
behavior, deformations of the reproductive tract and reproductive
diseases.
Research
reported since the publication of Our Stolen Future has continued
to explore these themes. The animal literature has emphasized mechanistic
understanding of how endocrine disruptors work, with new revelations
on the exquisite sensitivity
of the developing fetus to chemical hijacking. Research on mixtures
showing fetal loss in mice
even to very low levels of herbicides suggests that current regulatory
toxicology is probably failing to protect public health.
The
research on people has attempted to resolve several controversies
(for example, whether sperm count
is declining, and if so, why?), to determine whether several reproductive
system cancers (especially
breast cancer) are linked to organochlorine contaminants, and to
establish trends in reproductive tract disorders in men
and women, for example,
hypospadias and endometriosis. Analysis suggests that sperm declines,
hypospadias, cryptorchidism and testicular cancer are different
manifestations of the same syndrome, testicular
dysgenesis syndrome.
Now
some scientists have even begun to question whether the "demographic
transition" ... the decline in birth rates associated with
improving economic conditions... may have an involuntary component
linked to contamination-impaired reproduction. The traditional explanation
is that as economies improve and childhood survival increases, women
make voluntary choices to have smaller family sizes. More...
Concerns
have also been raised about links between cryptorchidism in people
(affecting about 3% of newborn males) and in utero exposure
to organochlorines. Research is firming up those links and also
revealing their molecular basis. More...
New
issues have arisen, also, which based on animal studies may involve
endocrine disruption, including reductions in the age of puberty
and changes in the human sex ratio.
A recent study even suggests
eating contaminated fish may impair a woman's ability to conceive
children.
Another
new study shows that women
within a few miles of where pesticides are used on agricultural
fields have an increased risk of having their fetus dying during
pregnancy.
Experimental
studies in the laboratory have proven crucial to revealing important
impacts, identifying human health endpoints that should be examined,
clarifying mechanisms, and exploring questions about sensitivity
to low doses and to mixtures. They have also been essential to documenting
different types of endocrine disruption and to establishing which
compounds have hormonal effects.
Some
points of entry:
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