Septic Systems Contaminate Groundwater with Hormone-Disrupting Chemicals in Human Waste

August 8, 2006

Research Area: 

Certain Chemicals Left Untreated May Pose Health Risks

Washington, DC – A new peer-reviewed study warns that many septic systems do not remove pollutants that may be harmful to human health from sewage before it is discharged to groundwater. Scientists from the Silent Spring Institute monitored—for the first time ever— hormone-disrupting chemicals such as natural estrogen (from urine) and alkylphenols (from detergents), as well as certain pharmaceuticals, as they passed from the septic system into groundwater.

The study looked at a typical septic system in Cape Cod, Mass., where more than 85 percent of residential and commercial properties are serviced by septic systems. Other chemicals detected included caffeine and optical brighteners (also from detergents).

The presence of hormone-disrupting chemicals in the environment has been associated with the feminization of male fish and reduced fertility in other wildlife. Further research is needed to determine whether the concentrations typically observed in the environment produce similar adverse effects on the human hormone system, and exposures during critical prenatal and childhood reproductive development stages may be of most concern. Effects on hormonally-responsive cancers are an additional concern. For example, chemicals that mimic natural estrogen may contribute to a woman’s cumulative life-time exposure to estrogen, a factor that has been linked to increased risk of developing breast cancer.

In North America, about 25 percent of the population relies on septic systems for wastewater treatment. In areas like NJ, FL, DE, MD, NY, and MA, including Cape Cod, at least a portion of the residents also rely on private, shallow groundwater wells for their drinking water. With housing density increasing, and lot size decreasing to accommodate population growth, there is an increased likelihood that wastewater coming from a household’s or neighboring household’s septic system will contaminate a drinking water well.

Lead researcher for the Silent Spring study, Chris Swartz said, “While septic systems may be effective at preventing bacterial contamination of these water supplies, the results of this study suggest that these systems do not remove hormone disrupting chemicals from septic wastewater before it infiltrates to groundwater.” And since groundwater feeds many drinking water supplies, further research is clearly needed to determine the extent and potential effects of drinking water contamination.

Previous research on hormone disruptors and other organic wastewater contaminants has focused on surface waters receiving discharges from wastewater treatment plants. In contrast, this is the first study to directly link the infiltration of these hormone disruptors into groundwater—and therefore residential well water—from on-site treatment systems, or in this case, septic systems.

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

The study will be published in the August 15 edition of Environmental Science & Technology and is posted at