The mere thought that long-term exposure to a pesticide might subtly erode your manhood or womanhood sounds chilling enough, but what if two such chemicals combined were hundreds or thousands of times more potent? A study raised that alarming possibility last year, but it's now under fire as other researchers have failed to reproduce it, according to a news report in today's issue of Science.*
Last June, a team led by endocrinologist John McLachlan of Tulane University in New Orleans published a report in Science (7 June 1996, p. 1489) describing how four pesticides, when paired in six different combinations, were up to 1600 times more potent than each was alone at binding to receptors for the hormone estrogen in engineered yeast cells. The results were alarming, considering that high levels of estrogenlike synthetic chemicals in a Florida lake are thought to be responsible for shrunken penises in alligators. Some controversial studies have even suggested that environmental pollutants may be responsible for a decline in human sperm count in some regions. Regulatory agencies were particularly concerned by the new study, as they faced the possibility that their chemical safety tests--which generally focus on a single compound--might be suspect.
In the months since, however, at least five teams have reported in letters to Science and Nature that they have been unable to replicate the results in other yeast and mammalian cells. McLachlan suggests that his experiment may differ from others in that his yeast cells had very low levels of receptors--only 500 per cell--while cells in other experimental systems had at least 1000. Synergy may be acutely sensitive to receptor numbers, he says.
Some experts doubt that the findings will hold up or have already written them off as unlikely to be relevant to animals or people. "If you can't reproduce [McLachlan's results], you can't ask questions or extend it any further," says Ken Korach of the National Institute of Environmental Health Sciences. "I think it's incredibly important that we resolve the issue," adds Duke University pharmacologist Donald McDonnell.