For example, DDT has been shown to cause reproductive failure in western
gulls in California.
18 The poor breeding success was characterized by a reduced
number of adult males, a highly skewed sex ratio (e.g., female to male ratios of
3.85 on Santa Barbara Island), and female–female pairing of some of the excess
females. Researchers suggest that the causes for the observed poor breeding
success might include DDT contamination, causing the thinning of eggshells
and also abnormal development of the reproductive system in embryos leading
to breeding failure in the adult birds.
Research conducted in the past two decades indicate that certain persistent
toxicants may be producing adverse effects in wildlife, including birds and
mammals, and in humans, by disrupting the endocrine system. Some of the
effects include reproductive and developmental abnormalities, increases in
certain hormone-related cancers, such as breast, testis, and prostate cancers,
and decreases in wildlife populations.
Similarly, a number of other reports have indicated that sperm counts in
men worldwide have decreased about 50% since 1940. Over the same period,
the incidence of prostate cancer in some countries has doubled, while that of
testicular cancer has tripled. There are also indications that birth defects in the
male reproductive tract have increased over the past several decades.
Furthermore, since 1940, the incidence of female breast cancer has risen in
the U.S. and Western Europe. Studies also show that endometriosis (the
growth outside the uterus of cells that normally line the uterus), formerly a rare
condition, now afflicts five million American women. Women who are afflicted
by the disease in their reproductive years frequently suffer infertility.
In the animal world, a study of alligators on Lake Apopka in Florida found
that the young were often unable to hatch, and that males that did hatch had
abnormally small penises. An active program of research followed the
observation, and a large number of reports related to the subject have been
published. Many scientists agree that at least part of the reason for the
observed conditions may be the introduction into the environment since 1940
of xenobiotics that block or mimic the action of estrogen.
Such chemicals may act on the adult human or animal and cause cancer or
endometriosis. The consequences may be even more widespread and devastating when estrogen mimics accumulate in the mother. The estrogen mimics may
then be transferred to the egg or fetus, disrupting the hormone balance of the
developing offspring and causing reproductive abnormalities or changes that
set the stage for cancer in adulthood. (Further discussion of endocrine
disruption is presented in Chapter 14.)
4.5 REFERENCES
1. Black, V.J. and Unsworth, M.H., Stomatal responses to sulfur dioxide and
vapor pressure deficit, J. Exp. Bot., 31, 667, 1980.
62
Environmental Toxicology
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-004.3d]
Ref: 4365 MING-HO YU Chap-004 Page: 62 45-64
gulls in California.
18 The poor breeding success was characterized by a reduced
number of adult males, a highly skewed sex ratio (e.g., female to male ratios of
3.85 on Santa Barbara Island), and female–female pairing of some of the excess
females. Researchers suggest that the causes for the observed poor breeding
success might include DDT contamination, causing the thinning of eggshells
and also abnormal development of the reproductive system in embryos leading
to breeding failure in the adult birds.
Research conducted in the past two decades indicate that certain persistent
toxicants may be producing adverse effects in wildlife, including birds and
mammals, and in humans, by disrupting the endocrine system. Some of the
effects include reproductive and developmental abnormalities, increases in
certain hormone-related cancers, such as breast, testis, and prostate cancers,
and decreases in wildlife populations.
Similarly, a number of other reports have indicated that sperm counts in
men worldwide have decreased about 50% since 1940. Over the same period,
the incidence of prostate cancer in some countries has doubled, while that of
testicular cancer has tripled. There are also indications that birth defects in the
male reproductive tract have increased over the past several decades.
Furthermore, since 1940, the incidence of female breast cancer has risen in
the U.S. and Western Europe. Studies also show that endometriosis (the
growth outside the uterus of cells that normally line the uterus), formerly a rare
condition, now afflicts five million American women. Women who are afflicted
by the disease in their reproductive years frequently suffer infertility.
In the animal world, a study of alligators on Lake Apopka in Florida found
that the young were often unable to hatch, and that males that did hatch had
abnormally small penises. An active program of research followed the
observation, and a large number of reports related to the subject have been
published. Many scientists agree that at least part of the reason for the
observed conditions may be the introduction into the environment since 1940
of xenobiotics that block or mimic the action of estrogen.
Such chemicals may act on the adult human or animal and cause cancer or
endometriosis. The consequences may be even more widespread and devastating when estrogen mimics accumulate in the mother. The estrogen mimics may
then be transferred to the egg or fetus, disrupting the hormone balance of the
developing offspring and causing reproductive abnormalities or changes that
set the stage for cancer in adulthood. (Further discussion of endocrine
disruption is presented in Chapter 14.)
4.5 REFERENCES
1. Black, V.J. and Unsworth, M.H., Stomatal responses to sulfur dioxide and
vapor pressure deficit, J. Exp. Bot., 31, 667, 1980.
62
Environmental Toxicology
[16:54 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-004.3d]
Ref: 4365 MING-HO YU Chap-004 Page: 62 45-64