Undigested, discarded medication in septic tanks is leading to water pollution.

According to a study in a recent issue of the journal Ground Water, pharmaceuticals are being found in septic tanks and, consequentially, ground water, due to incomplete human metabolism and excretion into the waste stream or by disposal of unused medications in the toilet or down the sink.

This screening-level study investigated the occurrence of pharmaceuticals in areas receiving wastewater from septic tanks located in sand and gravel deposits in Missoula, Mont.

Many pharmaceutical and pharmaceutically active compounds (e.g. caffeine) persist through the human body and are resistant to conventional wastewater treatment practices. They often are detected in aquatic environments such as lakes, rivers and ground water, which can receive direct inputs of treated wastewater.

"We don't know what toxicological effects these detectable concentrations of pharmaceuticals pose, although typical concentrations in one liter of ground water are usually much lower than a typical human therapeutic dose," says lead author Emily Godfrey.

While such low concentrations do not appear to pose a threat to human health, this research may help frame policy on the disposal of expired or unused compounds.