Only about half of the prescription drugs and other household contaminants in sewage are removed by wastewater treatment plants. These compounds, known as “chemicals of emerging concern,” (CEC) are entering the environment via wastewater treatment plants, and better water treatment is needed, according to a study by the International Joint Commission (IJC).

The IJC is a collaborative effort by the United States and Canada to protect water systems that are affected by the actions of both countries, such as the Great Lakes. The Great Lakes are the largest surface freshwater system on earth, and are being inundated with treated wastewater containing CEC.

Over the past 10 years, environmental monitoring has been concentrated on recently-discovered CEC. These compounds are found in everyday products used in homes, businesses, agriculture, and industry, including pharmaceuticals, personal care products, flame retardants, and pesticides. Between the US and Canada, more than 1,400 wastewater treatment plants discharge 4.8 billion gallons of treated water into the Great Lakes basin every day.

According to the report, “Wastewater treatment plants are among the important pathways by which CEC enter the Great Lakes, with concentrations highest in the vicinity of wastewater discharges. Treated sewage is often discharged into the nearshore waters, which also provide a source of drinking water to the public.”

In their review of 10 years of data from wastewater treatment plants worldwide, scientists found six chemicals were detected frequently in treated wastewater and had a low rate of removal (less than 25 percent chance of removing 75 percent or more). The six compounds include two antibiotics, an anti-seizure drug, an antibacterial drug, an anti-inflammatory drug, and an herbicide.

“Triclosan, an antibacterial and antifungal compound found in some soaps, toothpastes and other consumer products, has proven acutely toxic to algae and can act as a hormone disruptor in fish,” EcoWatch reports. And ingesting even low levels of antibiotics through treated water is disconcerting, as regular exposure promotes resistance.

“The compounds show up in low levels – parts per billion or parts per trillion – but aquatic life and humans aren’t exposed to just one at a time, but a whole mix,” said Antonette Arvai, a physical scientist with the IJC and lead author of the study. “We need to find which of these chemicals might hurt us.”

Chemicals found in treated wastewater may not necessarily be found in drinking water. Yet, a federal study of 74 US waterways used for drinking water found that 53 of the waterways had traces of one or more pharmaceutical, according to Environmental Health News.

Alisha is a writer and researcher with Ring of Fire. Follow her on Twitter @childoftheearth.