Comparing the reproductive health of men in different areas of the United States, epidemiologist Shanna Swan came up with some baffling results: The sperm count in men from rural Missouri was far lower than in men from cities like New York, Los Angeles, and Minneapolis.
It didn't take long for Swan—a professor at the University of Missouri-Columbia at the time of study, 2003—to hypothesize that agricultural chemicals were a culprit.
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Men with higher levels of three commonly used farming pesticides—alachlor, atrazine, and diazinon—in their bodies were much more likely to have a low sperm count than men who showed low levels of the pesticides.
"The risk of poor semen quality was elevated 30 times with higher alachlor levels and 11 times with atrazine," said Swan, who is now at the School of Medicine at the University of Rochester in New York. She cautioned, however, that "the number of men we tested is small, so these numbers are not precise."
But almost none of the men with low sperm counts were farmers who had directly used the pesticides. Swan believes they were likely getting the toxins right from their own kitchen faucets.
The Missouri study bolstered a disturbing claim made by a growing cadre of scientists: Our waters—from our seas to our tap water—are becoming increasingly polluted by chemicals carried in agricultural runoff.
Humans are hardly the only creatures affected. As suggested in an episode of National Geographic's four-part TV series, Strange Days on Planet Earth, which airs tonight on PBS, a wide range of animals—from leopard frogs to Beluga whales—are suffering from waters that may be poisoned by farming chemicals.
Treating Water
In a previous study Swan found that women who drank tap water with elevated levels of certain chlorination by-products had higher miscarriage rates.
"There's no question that there are risks associated with drinking tap water," she said. "On the other hand, you have to [disinfect] the water, and we're a lot better at that in the United States than they are in [many] developing countries."
So what kind of water is the safest to drink?
"The quality of bottled water is very inconsistent," Swan said. "Tabletop filters get out some chemicals but not others. From a public health perspective, it's very difficult to recommend what people should do."
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