Down the Drain

Clean water is fundamental to life. Yet many septic systems do not rid sewage of pollutants that may be harmful to human health before discharging the sewage to groundwater—and in some cases before it contaminates drinking water wells.

Silent Spring Institute scientists made this discovery after monitoring—for the first time ever—water for hormone-disrupting chemicals such as natural estrogen and alkylphenols, as well as certain pharmaceuticals, as the water passed from the septic system into the ground. The study looked at a typical septic system on Cape Cod, where septic systems serve more than 85 percent of residential and commercial properties. Two other chemicals the researchers detected indicated the presence of sewage fallout: optical brighteners, which are found in laundry detergents, and caffeine.

The presence of hormone-disrupting chemicals in the environment has been associated with the feminization of male fish and reduced fertility in other wildlife. The scientists note that additional research is needed to determine whether the concentrations typically observed in the environment produce similar adverse effects on the human hormone system. Exposures during critical prenatal and childhood stages of reproductive development may be most critical.

Effects on hormonally responsive cancers are an additional concern. Chemicals that mimic natural estrogen, for example, may contribute to a woman’s cumulative lifetime exposure to estrogen, a factor that has been linked to an increased risk of developing breast cancer.

One in every four citizens of the United States relies on septic systems for wastewater treatment. At least a portion of the residents in a number of states—including Delaware, Florida, Maryland, Massachusetts, New Jersey, and New York—also rely on private, shallow groundwater wells for their drinking water. With housing density increasing and lot size shrinking to accommodate population growth, the likelihood is growing that wastewater from a household’s or neighboring household’s septic system will contaminate a drinking water well.

“While septic systems may be effective at preventing bacterial contamination of these water supplies,” says Chris Swartz, lead researcher for the study, “our results suggest that these systems do not remove hormone-disrupting chemicals from septic wastewater before they infiltrate into groundwater.”

And since groundwater feeds many drinking water supplies, Swartz adds, further research is needed to determine the extent and potential effects of drinking water contamination. Previous research on hormone disruptors focused on surface waters receiving discharge from wastewater treatment plants. This study was the first to directly link the infiltration of these hormone disruptors into groundwater—and therefore residential well water—from onsite treatment systems.

“Our findings should encourage communities to consider more restrictive land use policies to protect their public and private drinking water supply wells,” Swartz says. “Communities may also consider replacing onsite septic wastewater treatment systems with improved onsite technologies or centralized wastewater treatment plants, at least in densely populated areas that rely on shallow groundwater as a drinking water source.”

The study appeared in the August 15, 2006, issue of Environmental Science & Technology.