Pesticides block male hormones. (Toxicology).

Product labels caution people to handle organophosphate insecticides with respect. Although designed to lethally overstimulate a bug's nerves, these chemicals can attack the human nervous system as well. Now, data suggest that these chemicals may also elicit a more subtle toxicity.

Thomas E. Wiese of Tulane and Xavier Universities in New Orleans wondered whether organophosphate pollutants that structurally resemble androgen-blocking drugs also affect people's hormone activity. So, his team did test-tube studies of a host of these pesticides, including fenitrothion, parathion, chlorothion, linuron, and ruelene.

Hormones work by docking with a specific receptor on a cell, which then responds by turning on genes. Though none of the organophosphates bound to cellular receptors for estrogens, the primary female sex hormones, all attached to androgen receptors. However, they didn't turn on genes, indicating that they don't behave like androgens. That may sound like good news, but because the insecticides to varying degrees block access to those receptors, they can interfere with normal gene activation by preventing a natural androgen, dihydrotestosterone, from docking with its receptor.--J.R.