The latest in a series of controversial studies has found an association between exposure to pesticides and poor semen quality in American men living in rural areas. The study is the most recent volley in the endocrine disrupter debate, which concerns how some environmental pollutants may affect fertility, hormones, and the endocrine system.
Researchers have reported in the past on differences in sperm health and viability among men in cities and rural regions. Last April, researchers at several institutions published results from the Study for Future Families, which showed that men in rural Columbia, Missouri, had poorer semen quality than men in New York City, Los Angeles, and Minneapolis--although all groups were fertile (Science, 27 October 2000, p. 695). The report's authors concluded then that pesticide exposure might explain the differing semen quality, although they didn't test for the chemicals directly.
To better establish a link between pesticides and sperm, the original group of researchers, led by epidemiologist and statistician Shanna Swan of the University of Missouri School of Medicine in Columbia, tested for metabolites from 15 pesticides in the men's urine. The team looked only at a subset of the original 400 men, selecting 86 in Minneapolis and rural Missouri.
Swan's team found that the Missouri men were more likely to test positive for metabolites from at least one agricultural pesticide. Furthermore, high amounts of several of the pesticides correlated with poorer semen quality, the researchers report on 18 June in Environmental Health Perspectives. For example, men with a high level of alachlor, an herbicide, were 30 times more likely to have poor semen quality. At least three pesticides, however, revealed the opposite pattern: Men with high levels were less likely to have below-normal semen quality.
"It's a very significant study," says reproductive toxicologist Rex Hess of the University of Illinois, Urbana-Champaign, who says it's the best work he's seen correlating pesticide levels with semen quality. Although these men were fertile, Hess says he's especially troubled because the pesticides can block the hormone estrogen, which he's found to be necessary for sperm development. He points out, though, that more men need to be tested to validate the study's results.
The controversy continues, though. "Many things affect sperm quality," says urologist Harry Fisch of Columbia Presbyterian Medical Center in New York City. "What this study says is that you can be exposed to pesticides and still be fertile." Moreover, the differences between the Minneapolis and Missouri cohorts could be explained by genetics, not environmental toxins, he says.