Scientists are observing with increasing alarm that some very common hormone-mimicking chemicals can have grotesque effects.

A widely used herbicide acts as a female hormone and feminizes male animals in the wild. Thus male frogs can have female organs, and some male fish actually produce eggs. In a Florida lake contaminated by these chemicals, male alligators have tiny penises.

These days there is also growing evidence linking this class of chemicals to problems in humans. These include breast cancer, infertility, low sperm counts, genital deformities, early menstruation and even diabetes and obesity.

Philip Landrigan, a professor of pediatrics at Mount Sinai School of Medicine, says that a congenital defect called hypospadias — a misplacement of the urethra — is now twice as common among newborn boys as it used to be. He suspects endocrine disruptors, so called because they can wreak havoc with the endocrine system that governs hormones.