By Eric Hand, St. Louis Post-Dispatch

A Monsanto scientist says the Centers for Disease Control and Prevention goofed when it found rural Missouri men had fewer sperm and more of a Monsanto pesticide in their bodies than metropolitan men in a 2003 analysis.

The CDC stands by its analysis, which said Missouri men that tested positive for alachlor were much more likely to have low sperm counts.

While the dispute over alachlor plays on, scientists still don't know what causes differences in sperm quality around the United States and the world.

"The only thing that everybody agrees on is that there are regional differences in sperm counts," said Harry Fisch, a Columbia University urologist who a decade ago found that New York City men had some of the highest sperm counts in the world. Fisch says potential sperm killers are tough to pin down, since factors from smoking to fevers to seasonal changes can affect counts.

The regional differences are striking. New York City men had sperm counts 75 percent higher than men from the Columbia, Mo., area, according to a 2003 study led by former University of Missouri-Columbia researcher Shanna Swan.

Hypothesizing that men in agricultural areas might have higher exposures to pesticide, Swan followed up with a study that showed that Missouri men were more likely to have remnants of five pesticides in their system than men from Minneapolis. The statistically-small study of 86 men attempted to control for age and effects like smoking.

Of the five pesticides, alachlor was the most likely to be associated with poor sperm quality. Swan relied on the CDC to detect the pesticides.

But when Monsanto scientist David Gustafson tested three alachlor-positive urine samples leftover from the CDC analysis, he couldn't find any alachlor, even though he was using a more sensitive detector.

Using the more sensitive detection process, the CDC retested 14 separate urine samples saved from the original study, and found what it found before. CDC chemist Dana Barr said Gustafson might have missed the alachlor because he had to use leftover samples that were refrozen and rethawed.

Even if the alachlor was there, Gustafson said the Environmental Protection Agency has deemed it safe.

"It's not a believable result," he said.

The dispute is currently detailed in the journal Environmental Health Perspectives.

Barr said that the 2003 study never asserted alachlor was the cause of lower sperm counts. It was only correlated with them, she said. "In epidemiology, one study doesn't allow you enough evidence to conclude anything," she said.