Can phthalates subtly alter boys?

To identify a young rodent's gender without doing an elaborate test, biologists measure the distance from the animal's anus to its genital opening. This anogenital distance is slightly, but reliably, longer in males than in females--unless those males were exposed in the womb to pollutants, such as phthalates, that can alter fetal sex-hormone production. When that happens, a male's anogenital distance can become more similar to that of a female. Preliminary data suggest a similar trend in boys whose mothers were exposed during pregnancy to elevated amounts of some phthalates.

Phthalates, chemicals used in making many cosmetics, plastics, and other products, have become ubiquitous pollutants.

Epidemiologist Shanna H. Swan of the University of Missouri in Columbia and her colleagues collected urine samples from pregnant women in four U.S. cities. Tests for phthalate-breakdown products indicated that all the women had been exposed to phthalates, Swan reported. However, the amount of exposure varied from city to city. For instance, residues from certain phthalates were 40 to 90 percent higher in the women from Columbia than in those from Minneapolis.

The researchers then measured genital features in the infants, including anogenital distance, and correlated them with their moms' prenatal phthalate values.

In girls, subtle changes in anogenital distance appeared to be associated with phthalate residues in the mothers' urine. In boys, the relationship was far stronger and "highly significant," says Swan. In fact, sons of women with the highest phthalate-residue concentrations were seven times as likely to have a short anogenital distance as were boys whose mothers had the lowest phthalate exposure in the study.

No one knows whether the anatomical changes are important in the boys' reproductive lives, notes Swan. In male rodents, however, fetal-phthalate exposures have been shown to severely disrupt the development of reproductive organs (SN: 9/2/00,p. 152), and last year researchers linked phthalate exposures in men to aberrant sperm (SN: 5/31/03, p. 339) and in women, to shortened pregnancies (SN: 9/13/03, p. 173). --J.R.