Treatment plants may only be getting rid of about half the drugs and other "chemicals of emerging concern" that turn up in our sewage, a study finds. Officials in a joint US-Canadian study of the Great Lakes assessed 42 of these chemicals using a decade's worth of data, Scientific American reports. They found that while acetaminophen, caffeine, and the natural estrogen estriol were well-removed, others slipped by. They include an herbicide and anti-bacterial, anti-inflammatory, and anti-seizure drugs, as well as two antibiotics.
"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," says the study's lead author. It's not certain just how all the chemicals may affect aquatic or human life, Scientific American notes, and just because a drug appears in sewage doesn't indicate it's in the water we drink. Still, a number of chemicals found have been linked to health issues, either for fish or for us. For instance, "even at low levels you don’t want to have people ingest antibiotics regularly, because it will promote resistance," the author says.