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Three chemicals in farm pesticidesmost commonly found in the Midwesthave been linked to poor sperm quality in rural Midwesterners and probably are consumed through drinking water, according to a University of Missouri study. 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.
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.
Shanna Swan, research leader and an expert in reproduction and the environment at the University of Missouri 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.
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, 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.