Bacteria in sewage can change estrogens' chemical makeup.

Gomes, RL, MD Scrimshaw and JN Lester. 2009. Fate of conjugated natural and synthetic steroid estrogens in crude sewage and activated sewage sludge batch studies. Environmental Science & Technology doi: 10.1021/es801952h.

Bacteria in sewage can chemically transform estrogenic compounds, converting them to back to their original chemical form as the sewage travels toward treatment plants after the compounds have been excreted by people. This conversion makes the bacteria more amenable to being filtered out of the water by  treatment.

The findings open the door to exploring new ways in which the estrogens that are more resistant to bacterial modification could be changed at the sewage treatment plant to make them easier to remove from the water.

Not all of the estrogens, however, can be changed. Which are depends on time, temperature and whether the estrogens are synthetic or natural, the researchers report.

Recent research has shown that human-related estrogens are found in lakes, rivers and other waterways, likely arriving there from water that has passed through the sewage treatment process. The hormones can affect the health and reproduction of  fish and other creatures that call the water home. Fish with both male and female gonads, as well as feminized male fish, have been reported in species living downstream from treatment plant outflows. Some studies have linked these abnormalities to the estrogen hormones found in sewage.

The estrogens are mainly excreted from people through their urine. They can be natural estrogens or synthetic ones, such as those found in birth control pills or hormone replacement therapy.

Before estrogens can leave the human body, they are chemically transformed, or metabolized.  The body tacks on a molecule that allows the hormones to pass into the urine rather than remain in fat or blood.

Researchers in England examined what happens to these estrogens in the wastewater after they enter sewage treatment plants. In a series of experiments, they better defined how bacteria further chemically modify the estrogens in the sewage.

They found that several things happen. Certain types of metabolized estrogens are converted back to their original form by the bacteria in the sewage. Other types of metabolized estrogens are more resistant to modification and remain unchanged or are altered in different ways.

This is not as worrisome as it sounds. The bacteria in our own digestive systems perform the same kinds of chemical modifications on the foods we eat and the drugs we take. It is likely that the bacteria in our digestive systems are the same ones acting on the estrogens in wastewater, the authors speculate.