Modern treatment plants strip hormone from sewage. (Extracting Estrogens).

Reproductive hormones, both natural and the synthetic ones in contraceptive drugs, sometimes survive sewage treatment and turn up in the environment where they can affect wildlife. Modern sewage-treatment facilities, about half of those used in Europe, break down these sex hormones more effectively than older plants do.

A new study shows why: Only the modern, multiple-chamber treatment plants subject the sewage to the gamut of chemical and biological conditions required to break down different hormones.

Sewage often contains two natural estrogens, estrone (E1) and 17-beta-estradiol (E2), as well as the synthetic estrogen 17-alpha-ethinylestradiol (EE2), used in birth-control pills and patches. Scientists have determined that some estrogen passes through U.S. water-treatment plants and reaches waterways (SN: 6/17/00, p. 388), where it can cause fish to develop sexual abnormalities (SN: 1/8/94, p. 24).

Older plants have a single tank designed to remove phosphate and nitrate from sludge, but newer facilities use several such tanks and retain sludge considerably longer, says environmental chemist Thomas A. Ternes of Bundesanstalt fur Gewasserkunde in Koblenz, Germany. At a recently updated plant in Wiesbaden, Germany, for example, sludge spends 11 to 13 days in a trio of tanks rather than the 4 days or less it took in a single tank before the renovation.

Different kinds of bacteria populate the various tanks because some tanks expose sludge to oxygen and others don't. To figure out where in the newer treatment process estrogens break down, Ternes and his colleagues in Denmark and Switzerland studied sludge removed from 10 different points along the flow of sewage in the Wiesbaden plant.

The scientists found that oxygen-deprived tanks remove most of the E1 and E2 that enter them, while oxygenated tanks remove most of the EE2. Most important, all three hormones were undetectable--though not necessarily entirely absent--in the plant's effluent, the researchers report in an upcoming Environmental Science and Technology.

Estrogen removal is a fortunate side effect of multiple-tank sewage treatment, says chemist Thomas Heberer of the Technical University of Berlin. The new research shows for the first time that subjecting sludge alternately to oxygenated and oxygen-deprived conditions is highly effective at eliminating the hormones, he says. He notes that with more-sophisticated measurement techniques, Ternes' team might have measured traces of estrogen that survived the treatment process.

The study also suggests that more-costly experimental techniques for treating sewage, such as injecting ozone gas into treatment tanks or using high-tech filters, may not be necessary to remove the hormones, says Heberer. A good next step, he suggests, would be to determine whether a multiple-tank process also eliminates hormone-mimicking chemicals such as nonylphenol and bisphenol A, which have become major environmental concerns.