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WEDNESDAY, June 18, 2003 (HealthDayNews) -- 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 sperm counts.
Swan and her colleagues report their findings in the June 18 issue of Environmental Health Perspectives.
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 says.
More information
Try the Urology Channel for fertility information or the U.S. Environmental Protection Agency to learn about pesticides.
