Tied To Semen Trouble
Three chemicals in farm pesticides
have now been linked to poor sperm quality in rural Midwesterners.
Missouri men exposed to high amounts
of the substances are far more likely than men with less contact
to have diluted or deformed and sluggish sperm. Each of the semen
problems can reduce the ability of sperm to reach and fertilize
an egg and could make conception harder, the researchers say.
However, all the men in the latest study were fathers, so the
impact of the chemicals on fertility, if any, is uncertain.
"These chemicals are among
the most commonly used throughout the Midwest," says research
leader Shanna Swan, an expert in reproduction and the environment
at the University of Missouri.
The chemicals -- two plant killers
and an insecticide -- most likely reach men through the water
supply. Drinking water in some areas of the Midwest contains significant
levels of the substances. Swan says her future work will focus
on whether the pesticides affect female fertility. She is now
analyzing evidence from men in Iowa City, where the chemicals
are also common and where, in the 1970s, researchers found low
Swan and her colleagues report
their findings in the June 18 issue of Environmental Health
In a previous study, also in the
environmental journal, Swan's group found more rural men than
city dwellers had under-performing sperm, and she suggested the
connection might involve exposure to pesticides. This time, she
and her colleagues identified the particular substances within
farm chemicals that appear to be causing problems with semen.
To do so, they tested urine samples
of 86 men in Minnesota and Missouri for breakdown products of
15 popular pesticides. Several were associated with unhealthy
sperm traits but three stood out.
The three chemicals are the bug
spray diazinon -- used to fight ants and other insects -- and
two weed killers, alachlor and atrazine. Missouri men (though
not Minnesotans) exposed to high levels of each substance in their
urine were many times more likely than those with less exposure
to have abnormal sperm. Alachlor had the strongest connection:
High levels of exposure to the herbicide were associated with
a 30-fold increased risk of diluted or struggling sperm.
Atrazine, the most commonly detected
herbicide in the U.S. drinking water, has been shown to disrupt
the proper development of frogs. Another study found a link between
exposure to the chemical and prostate cancer, Swan says.
John Heinze, executive director
of the Environmental Health Research Foundation, calls the latest
study "interesting." But, he says, there are reasons
to be cautious about the conclusions.
None of the three chemicals have
been shown in animal studies to adversely affect sperm quality.
"You would expect to see that in an animal study that uses
massive doses," he says. And, all of the men had children,
so the impact of the substances on male fertility doesn't appear
to be that strong, says Heinze, whose group receives funding from
the chemicals and plastics industries, as well as from government
and other private sources.
The U.S. Geological Survey has
found higher than recommended levels of the three chemicals in
Midwest groundwater. Neither water processing plants nor home
filtering devices remove them, Swan says.
In a bit of good news, Swan's group
found no evidence that the widespread insect killer DEET and other
pesticides used around the home affected sperm quality. However,
she observes, DEET is typically absorbed through the skin, not
ingested in drinking water like atrazine, alachlor and diazinon.
Rex Hess, a reproductive biologist
at the University of Illinois in Urbana, calls the new findings
"quite interesting." Although the study doesn't prove
the pesticides cause semen trouble, Hess believes the hormone
estrogen could provide a connection.
In 1997, Hess published a paper
in Nature showing that the hormone estrogen played an important
role in healthy sperm quality. That's because the molecule regulates
how much water is in semen, and thus how concentrated with sperm
a man's semen is -- the higher the better.
Atrazine has been shown to interfere
with estrogen, Hess says. As a result, it could dilute semen and
suppress fertility. "It could have that effect," he
Try the Urology
Channel for fertility information or the U.S.
Environmental Protection Agency to learn about pesticides.
Reference Source 101