Another emasculating pesticide found.

Exposure in the womb to any of several chemicals can derail the normal sexual and behavioral development of male animals. Most of the agents scientists have identified as possessing this capacity--such as dioxin (SN: 5/30/92, p.359)--appear to exert their gender-bending properties by mimicking the actions of estrogen, a female sex hormone (SN: 1/8/94, p.24). But as described in the June TOXICOLOGY AND APPLIED PHARMACOLOGY, such changes also can result when a chemical blocks the activity of androgens, or male sex hormones.

A team of North Carolina-based researchers administered vinclozolin -- a systemic fungicide used to protect fruits, vegetables, ornamental plants, and turf -- to pregnant rats. Daily exposures of up to 200 milligrams per kilogram of body weight occurred from the 14th day of pregnancy through the third day following the birth of each rat's litter.

Year-old male offspring exhibited a range of reproductive abnormalities. Effects witnessed in those exposed to the highest doses included undescended testes, a cleft phallus, infertility, and hypospadias (a partially unfused phallus). The males also developed a "vaginal pouch" -- a structure characteristic of the female reproductive tract. Overall, the most-exposed animals suffered not only demasculinization, but also feminization, explains L. Earl Gray Jr. of the Environmental Protection Agency's reproductive toxicology branch in Research Triangle Park, N.C., a coauthor of the new report.

Vinclozolin fostered the changes by binding to -- and blocking -- androgen receptors in reproductive tissue, notes another of the study's investigators, William R. Kelce of ManTech Environmental Technology in Research Triangle Park.

Though the fungicide can bind to these receptors, its breakdown products bind to them 10 to 100 times more effectively. Indeed, the concentration of these by-products needed to block the receptors appears to be the same as that found in the blood of the pregnant rats treated with vinclozolin. As such, the team argues, any assessment of this pesticide's health effects should consider not only the parent compound, but also its breakdown products in soil, leaves of treated plants, and animals exposed to the fungicide.

Some researchers suspect an increasing incidence of hypospadias, low sperm production, and undescended testes in men may trace to estrogen-mimicking pollutants (SN: 1/22/94, p.56). Because vinclozolin produces such effects in male animals without involving an estrogenic pathway, the new report suggests that toxicologists begin focusing more attention on this antiandrogenic route -- and agents that employ it.