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Defective Sperm, Pesticide Tie Found

Missouri study marks the first time scientists have been able to link environmental contaminants and semen quality.

June 18, 2003|Marla Cone | Times Staff Writer

Men exposed to pesticides widely used on crops are many times more likely to have defective sperm and low sperm counts than males with little or no exposure, according to a scientific study published today .

The study provides new evidence supporting a theory that pesticides and other chemicals which mimic estrogen or block testosterone are harming human reproductive systems. It is the first time that scientists have shown a link between environmental contaminants in men's bodies and large decreases in the number and quality of their sperm.

A team led by University of Missouri-Columbia reproductive epidemiologist Shanna Swan compared men from central Missouri who had higher concentrations of two herbicides and one insecticide in their bodies with men from Missouri and the Minneapolis area who had low levels.

"Within Missouri, the pesticide score [of the men] was strongly associated with semen quality," the authors reported in the journal Environmental Health Perspectives, which is published by the National Institute of Environmental Health Sciences.

None of the men in the new study worked at or lived next to farms, where the pesticides are most commonly used. They were most likely exposed through drinking water supplied by aquifers, Swan said.

The number of men tested for pesticides -- 50 from Missouri and 36 from Minnesota -- is considered small, but scientists said the findings warrant close attention because some of those tested were found to be 30 times more likely to have defective sperm. That degree of risk is in the same range as the odds of contracting lung cancer from a lifetime of smoking cigarettes.

All the tested men, in their 20s and 30s, were fertile and recently fathered children.

"What this means is that it's harder for these men to conceive. It takes them longer," Swan said. "We also wonder what else it is doing to these men, and what it is doing to the rest of the family, the women and children?"

Sally Perrault, a reproductive toxicologist at the U.S. Environmental Protection Agency's national research lab, said the study "really raises our antennae."

Still, she said, Swan's team "hasn't proven that [the pesticides] came from the water" and that more men should be tested before the safety of the pesticides is questioned. "We should look into this more, rather than drawing real definite conclusions now," she said.

A scientific debate about sperm counts has been waged since 1992, when Danish researchers reported that men on average have half as much sperm as they did a half-century earlier, based on 61 sperm count studies, mostly in Europe and North America. Some scientists challenged the findings because there was no universal pattern.

Declining sperm counts had been reported in European, but not American, men. Since then, reproductive experts have tried to determine if chemical exposures or geographic patterns could explain the differing sperm counts.

Last fall, Swan broke new ground by reporting major differences in sperm between rural and urban areas. Men in Columbia, Mo., have significantly lower numbers of sperm -- as much as 44% less -- than men in Minneapolis, New York and Los Angeles, according to her research.

"We had trouble finding men in Missouri with good sperm quality," Swan said in an interview. "The counts in Missouri are really low."

Rex Hess, a reproductive toxicologist at University of Illinois-Urbana who was not involved in the study, said the research was so well-documented and found such a high risk that it leaves "no doubt in [his] mind that there is a link" between semen and the three pesticides, alachlor, atrazine and diazinon.

"What this means is if your sperm counts are low, [these pesticides] ought to be a top candidate," he said. "Water is so important that everybody ought to be conscious of this."

Environmentalists hope the study will increase pressure on the Bush administration to adopt stricter regulations governing the use of herbicides and insecticides. But the authors acknowledged that confirmation of the results using larger numbers of men and those from other areas is warranted.

"Given the widespread use of these pesticides, if further study confirms these findings, the implications for public health and agricultural practice could be considerable," the researchers wrote in the journal.

Scientists say it has already been well-documented over the last 20 years that farm workers and herbicide sprayers have poor semen quality.

But the new study is the first to note the condition in men who weren't working directly with pesticides. "We're not looking at exposure through home or occupational use. This is an environmental exposure of which people had no knowledge," Swan said.

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