Chemicals from consumer products and pharmaceuticals that flow down the drain can seep from septic systems through Cape Cod’s porous soil into drinking water supplies, according to research by Silent Spring Institute. The study provides some of the first information in the U.S. about impacts of these contaminants from septic systems on groundwater used for drinking water.

In October 2009, Silent Spring Institute researchers partnered with 9 public water suppliers to collect samples from 20 wells and two distribution systems supplying drinking water on the Cape. Samples were tested for over 90 emerging contaminants, including pharmaceuticals, hormones, personal care products, herbicides, alkylphenols, flame retardants, and perfluorinated chemicals.

The researchers found that three quarters of the wells and both distribution system samples contained low levels of at least one of 18 detected chemicals. The two most commonly detected chemicals were sulfamethoxazole, an antibiotic commonly used to treat urinary tract infections and pneumonia, and PFOS, used in stain-resistant and nonstick coatings, and fire-fighting foams. Levels of sulfamethoxazole as well as the pharmaceutical dilantin in some samples were among the highest reported in US drinking water.

Septic systems are likely the main source of the chemicals detected, though some may have commercial sources. Two perfluorinated chemicals, PFOS and PFOA, used in fire-fighting foams and aviation hydraulic fluids were found at relatively high levels in Hyannis wells downslope of the airport.

None of the chemicals detected are regulated by the Safe Drinking Water Act and only three—PFOS, PFOA, and a flame retardant—have voluntary health-based guidelines developed by state and federal agencies. For the chemicals with guidelines, the highest levels measured in this study fell below the guidelines. However, current drinking water standards do not take into account that people are exposed to complex mixtures of chemicals over a lifetime or the impacts of exposures during critical windows of development, such as during pregnancy and childhood.

“While we don’t know the health effects of exposures to low levels of these chemicals,” said Dr. Laurel Schaider, Research Scientist with Silent Spring Institute, “It makes sense to exercise caution and protect drinking water supplies from sources of groundwater pollution.”