Gender-bending PCBs.

When applied at particular times during fetal development, the hormone estrogen can turn animals that should have been males into females (SN: 1/22/94, p.56). Working with turtle eggs, a zoologist at the University of Texas at Austin has now demonstrated that at least two polychlorinated biphenyls (PCBs) possess a similar feminizing capacity.

The doses needed were small, notes Judith M. Bergeron -- around 200 micrograms per egg of either PCB, or just 10 to 100 [micro]g per egg if the two PCBs were given together. Indeed, her team reports in the September ENVIRONMENTAL HEALTH PERSPECTIVES, resulting concentrations "are comparable to average levels of PCBs found in human breast milk in industrialized nations."

The sex of many reptiles can be set by the temperature at which an egg incubates. For the red-eared sliders that Bergeron studied, hatchlings from eggs incubated at 31[degrees]C normally will all be female. Incubating those same eggs at 26[degrees]C yields exclusively male turtles. And both sexes emerge from eggs held at intermediate temperatures.

Bergeron painted slider eggs with the 11 PCBs suspected of estrogenic activity -- singly and in various combinations. When she incubated them at temperatures that should have produced predominantly or exclusively males, two PCBs proved strongly feminizing. But depending on the dose and incubation temperature, the compounds sometimes fostered only a partial sex reversal, creating "intersex" animals. These sliders sometimes developed male testes, for instance, but only in conjunction with structural antecedents of a female oviduct.

Bergeron's team "did an outstanding job of investigating a wide variety of congeners [individual PCBs] to show how even minor chemical differences can produce very different effects," says Timothy S. Gross of the University of Florida in Gainesville. Just as combinations of PCBs may prove synergistic, he adds, so may the many types of structurally different hormone-mimicking pollutants -- such as dioxins and DDT -- that can contaminate an ecosystem.

Bergeron's data don't indicate the reproductive implications for turtles of PCB-feminized gonads. However, Gross says that data from the DDT-feminized red-bellied slider turtles he's studying "are beginning to suggest that such intersex animals are not reproducing."