Drugs in our sewage are an issue of continuing concern: A few years back, researchers found that treatment plants were only getting rid of about half of them.

Now, a new study suggests that the problem goes beyond a failure to eradicate the drugs: Researchers found that levels of two drugs appear to end up even higher after treatment, Environmental Health News reports.

How could this be? Well, researchers theorize that microbes in the sewage—which act as a tool for treatment plants by breaking down organic material—are also acting like tiny drug makers.

By the time drugs exit our bodies, they've already been separated into various substances; once they get into the treatment plant, the theory goes, the microbes take those ingredients and reconstruct the drugs.

That could explain why the concentrations of two drugs—carbamazepine, an anti-epileptic, and ofloxacin, an antibiotic—in the water were found to increase by an average of 80% and 120%, respectively, after sewage treatment in the Milwaukee area.

The other 46 drugs the study detected, however, didn't increase after treatment, and more research is needed to explain why. When it comes to pharmaceuticals in drinking water, the World Health Organization has reported only a "very low risk to human health." Other creatures, however, may have more to worry about.

Scientists recently found that male minnows who encounter a diabetes drug that's "ubiquitous" in our sewage end up with feminized sex organs, Environmental Health News reported last month.

To help reduce the problems of drugs in sewage, the EPA has urged people not to flush medicine down the toilet. (Maybe you shouldn't flush coffee, either.)

This article originally appeared on Newser: Microbes May Be Doing Something Wild in Our Sewage

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