http://www.monitor.net/rachel/r594.htmlTitle: #594 (04/16/98): Missing Boys
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=======================Electronic Edition========================
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. RACHEL'S ENVIRONMENT & HEALTH WEEKLY #594 .
. ---April 16, 1998--- .
. HEADLINES: .
. MISSING BOYS .
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MISSING BOYS
As we reported late in 1997 (REHW #576), the male proportion of
live births has been declining in the U.S. and Canada for at
least 20 years. Normally there are 106 males born for every 100
females, for a male proportion of 106/206 = 0.5145. This
proportion is often called the "live birth sex ratio" or simply
the "sex ratio." Several studies --some very recent[1,2] and
others dating back to the late 1980s and early 1990s --reveal
similar 20-year declines in the male proportion of live births in
England and Wales,[3] Denmark, Sweden, Finland, the Netherlands,
Germany, Chile, Argentina, Brazil, Bolivia, Peru, Paraguay,
Ecuador, Venezuela, Colombia, and Costa Rica.[4]
The declines in the male proportion of births are not large, and
by themselves they have no practical importance. Often the shift
has been from 0.515 to 0.513 or 0.512. Nevertheless, even small
shifts in the sex ratio can add up. In Canada during the last 20
years, approximately 8600 males have not been born and in their
place we have females; in the U.S. during the same period, 38,000
baby boys were replaced by baby girls. (From an environmental
perspective this is arguably beneficial because environmentally
destructive organizations tend to be dominated by men, while the
effective wing of the environmental movement is largely led by
women.)
Nevertheless, there is a very serious side to these small shifts
in sex ratio. It is extremely unlikely that similar trends in so
many different countries are due to chance. Therefore, the
altered sex ratio raises a grave public health question: what is
causing consistent biological changes in the human populations of
so many industrialized and industrializing countries? Does this
pattern signal some general change in exposures to environmental
toxicants? Now two teams of researchers --in the U.S.[1] and in
Denmark[2] --are asking whether the pattern of declining male
proportion of births is linked to a similar pattern of increasing
birth defects of the penis and testicles, increasing testicular
cancer, and declining quality and quantity of sperm.
Both groups of scientists are hypothesizing that all of these
patterns are linked to exposures to hormone-disrupting chemicals
including dioxin, pesticides, lead, solvents and smoke stack
emissions from smelters, steel foundries and incinerators.[5]
And both groups are hypothesizing that the relevant exposures are
most likely taking place before birth, in the mother's womb.
Devra Lee Davis of the World Resources Institute (Washington,
D.C), writing in the JOURNAL OF THE AMERICAN MEDICAL
ASSOCIATION,[1] acknowledges that any change in a complex
biological process, such as sex determination, probably has
several causes. She then goes on to argue, offering evidence
from many different areas of research, that the male proportion
of live births can be affected by environmental exposures:
** At the moment of conception, all embryos are destined to be
female unless something changes them into males. We all start
out female by default. For the first six to 9 weeks of life, we
all have unisex gonads. Between the 6th and 9th week, the gonads
of those with a Y chromosome specialize into testicles and begin
producing hormones that continue the process of creating a male.
If anything interferes at this stage, a female may result. Thus
sex is determined by tiny amounts of hormones circulating in the
blood of the embryo. This situation provides opportunities for
chemicals entering the mother's body ("xenobiotics") to disrupt
normal processes. And there is some evidence that chemicals
entering the mother's body do just that:
** In Seveso, Italy, in 1976, a group of people were heavily
exposed to dioxin after an explosion at a pesticide factory.
Dioxin is a potent poison, an unwanted byproduct of metal
smelters, the manufacture of paper and pesticides, and
incinerators. Between April 1977 and December 1984, 74 children
were born to parents in the zone of greatest dioxin exposure. Of
these, 48 were female and 26 male, for a male proportion of
0.351. After 1985, the male proportion of live births began to
return to normal.
** Among a group of workers applying the pesticide
dibromochloropropane (DBCP), several men became sterile.
Importantly, those able to have children produced 3 times as many
daughters as expected.[6]
** A study of pesticide-exposed workers in the Netherlands
revealed a male proportion of 0.248, less than half the normal
proportion of male births.
** Five studies of heavily polluted residential areas in Scotland
revealed significantly diminished sex ratios. The pollutants
were emitted by metal smelters, steel foundries, and incinerators.
** In rural Minnesota, increased rates of birth defects are
reported to occur among the male children of workers who apply
pesticides, suggesting that the male fetus may be especially
vulnerable to hormone-disrupting substances. In an area with
high usage of chlorophenoxy herbicides and/or fungicides, the
male proportion among children born with defects to workers who
apply pesticides was 0.735, compared to a male proportion of
0.607 for births with defects among the general population.
Davis considers many other factors that can reduce the male
proportion of live births --age differences between the parents,
older age of father, mother under stress, multiple sclerosis,
less-frequent intercourse, and test-tube fertilizations. None of
these factors appears likely to have operated consistently in so
many countries for 20 years or more. Therefore, Davis proposes
that altered male proportion of live births should be considered
a "sentinel health event that may be linked to environmental
factors." A sentinel health event is defined as "an unusual
pattern of health in a population that signals changes in
avoidable factors. Thus," Davis writes, "changes in either a
relatively common health occurrence, such as childhood asthma, or
a relatively rare disease, such as pulmonary hypertension, can
reflect changes in avoidable exposures."
The sex ratio is not static. In many countries, the ratio
increased between 1900 and 1950 as better prenatal care reduced
the number of stillbirths, which tend to affect males
disproportionately. Thus, modern medicine has been able to avoid
stillbirths, thereby keeping more baby boys alive. But some time
between 1950 and 1970 the male proportion of live births began to
decline. Henrik Moller of the Danish National Research
Foundation[2] offers arguments similar to those of Davis, but
based on somewhat different evidence. Moller restricts his
discussion to men in Denmark, Finland, Norway, and Sweden. He
argues that the declining male proportion of live births in these
countries is closely linked to testicular cancer, and to
declining sperm quality and quantity. He suggests that all of
these effects may be caused by prenatal exposures to chemicals
that act like dioxin and the pesticide DBCP, mentioned above.
Between 1960 and 1990, the incidence of testicular cancer doubled
or more-than-doubled in each of the four Nordic countries. During
the same period, testicular cancer also increased in England and
Wales, Scotland, Australia, New Zealand, Slovenia [former
Yugoslavia], Poland, Spain, Colombia, Japan, India, and the
U.S.[7] Some of these increases may be due to better diagnosis,
but the increases were consistent in all populations, were of
similar size, and were reported by long-established cancer
registries. Testicular cancer is a well-defined entity, and it
inevitably becomes apparent, so it is unlikely to be missed.
Moller and others argue that, because testicular cancer tends to
occur young in life, whatever causes it must become effective
early, perhaps even before birth.[8] The causes of testicular
cancer are poorly understood. One recent study has found that
occupational exposure to polyvinyl chloride (PVC) increases the
likelihood of getting testicular cancer.[9]
In the four Nordic countries that Moller discusses, during the
period that testicular cancer has been increasing, the quality of
sperm has declined.[10] Sperm quality and quantity have also
declined (on average) in the U.S. and in other European
countries.[11] Moller argues that all these trends are related.
Moller conducted a case-control study of 514 Danish men with
testicular cancer, comparing them to a control group of 720 men
without cancer.[2] In both groups Moller interviewed the men and
their mothers. Among the cancer cases, he recorded the sex of
their children born up until 2 years before their cancers were
diagnosed. He found a male proportion of 0.470. Among children
born to the 720 controls, Moller found a male proportion of
0.520. Thus there was a significant reduction in the male
proportion of live births among men who would later develop
testicular cancer. Moller says his study does not close the book
on the subject --there are two other studies on record which
found different results.
In recent years the world's scientific community has been
expressing concerns about male reproductive health --increasing
birth defects of the penis and testicles, declining sperm
quantity and quality, and increasing testicular cancer --and
asking whether these phenomena all have common origins in some
sort of chemical exposures. (See REHW #438, #514.) This new
information about altered sex ratios in more than a dozen
countries simply makes the case more compelling and more urgent.
--Peter Montague
(National Writers Union, UAW Local 1981/AFL-CIO)
===============
[1] Devra Lee Davis and others, "Reduced Ratio of Male to Female
Births in Several Industrial Countries," JOURNAL OF THE AMERICAN
MEDICAL ASSOCIATION Vol. 279, No. 13 (April 1, 1998), pgs.
1018-1023.
[2] Henrik Moller, "Trends in sex-ratio, testicular cancer and
male reproductive hazards: Are they connected?" APMIS [ACTA
PATHOLOGICA, MICROBIOLOGICA ET IMMUNOLOGICA SCANDINAVICA] Vol.
106 (1998) pgs. 232-239.
[3] H.O. Dickinson and L. Parker, "Why is the sex ratio falling
in England and Wales? " JOURNAL OF EPIDEMIOLOGY AND COMMUNITY
HEALTH Vol. 50 (1996), pgs. 227-230.
[4] M.F. Feitosa and H. Krieger, "Demography of the Human Sex
Ratio on Some Latin American Countries," HUMAN BIOLOGY Vol. 64,
No. 4 (August 1992), pgs. 523-530.
[5] F.L.R. Williams and others, "Low Sex Ratios of Births in
Areas at Risk From Air Pollution from Incinerators, as Shown by
Geographical Analysis and 3-Dimensional Mapping," INTERNATIONAL
JOURNAL OF EPIDEMIOLOGY Vol. 21, No. 2 (1992), pgs. 311-319.
[6] G. Potashnik and others, "Dibromochloropropane-induced
Reduction of the Sex-ratio in Man." ANDROLOGIA Vol. 16, No. 3
(1984), pgs.213-218.
[7] David Forman and Henrik Moller, "Testicular Cancer." CANCER
SURVEYS Vol. 19/20 pgs. 323-341.
[8] Anders Ekbom and Olof Akre, "Increasing incidence of
testicular cancer --birth cohort effects," APMIS [ACTA
PATHOLOGICA MICROBIOLOGICA ET IMMUNOLOGICA SCANDINAVICA] Vol. 106
(1998). pgs. 225-231. And see H. Moller, "Clues to the Aetiology
of Testicular Germ Cell Tumours from Descriptive Epidemiology,"
EUROPEAN UROLOGY Vol. 23 (1993), pgs. 8-13.
[9] Lennart Hardell and others, "Occupational exposure to
polyvinyl chloride as a risk factor for testicular cancer
evaluated in a case-control study," INTERNATIONAL JOURNAL OF
CANCER Vol. 73 (1997), pgs. 828-830.
[10] Erik Bendvold, "Semen Quality in Norwegian Men over a
20-Year Period," INTERNATIONAL JOURNAL OF FERTILITY Vol. 34, No.
6, (1989), pgs. 401-404. And: Erik Bostofte and others, "Has the
Fertility of Danish Men Declined Through the Years in Terms of
Semen Quality? A Comparison of Semen Qualities between 1952 and
1972," INTERNATIONAL JOURNAL OF FERTILITY Vol. 28, No. 2, (1983),
pgs. 91-95.
[11] Shanna H. Swan and others, "Have sperm densities declined?
A reanalysis of the global trend data," ENVIRONMENTAL HEALTH
PERSPECTIVES Vol. 105 (1997), pgs. 1228-1232.
Descriptor terms: sex ratio; male reproductive health;
testicular cancer; cancer; carcinogens; pvc; semen; birth
defects; cryptorchidism; undescended testicles; devra davis;
england; denmark; sweden; finland; netherlands; germany; chile;
argentina; brazil; bolivia; peru; paraguay; ecuador; venezuela;
colombia; cost rica; canada; u.s.; hormone-disrupters; wri; jama;
dibromochloropropane; dbcp; pesticides; kenrik moller; norway;
wales; scotland; incineration; australia; new zealand; slovenia;
poland; spain; japan; india;
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