When you flush the toilet, you probably don’t think about the traces of the medicine and personal care products in your body that are winding up in sewage treatment plants, streams, rivers, lakes, bays and the ocean.

But Rutgers scientists have found that bacteria in sewage treatment plants may be creating new contaminants that have not been evaluated for potential risks and may affect aquatic environments, according to a study in Environmental Toxicology and Chemistry.

The scientists tested the ability of bacteria in sludge from a sewage treatment plant to break down two widely used pharmaceutical products: naproxen, a non-steroidal anti-inflammatory drug, and guaifenesin, an expectorant in many cough and cold medications. They also tested two common compounds in personal care products: oxybenzone, a key ingredient in many sunscreens, and methylparaben, a preservative in many cosmetics.

Bacteria that don’t require oxygen to grow in the sludge broke down methylparaben, but the microbes only partially broke down the three other chemicals — and created new contaminants in the process, according to the study.

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