Triclosan is an indiscriminate killer, wiping out bacteria even in places where microbial communities are hard at work keeping us healthy, like sewage treatment plants. Sewage treatment plants often incorporate anaerobic digesters to reduce the volume of waste they have to deal with. Bacteria adapted to an oxygen-free environment break down organic waste, including sewage, to produce small molecules like ammonia, carbon dioxide, and methane (which can be burned as a fuel). The amount of indigestible material that’s left is much more manageable.

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It’s a win-win system, but it won’t work without bacteria—which makes the ubiquity of antibacterial products troubling. Triclosan is one of the most common antibacterial agents, popping up both where you might expect it—in hand sanitizer and anti-acne face wash—and where some you might not—lip gloss, toothpaste, dish soap, gym clothes, even pencils. A lot of that triclosan ends up down the drain and eventually makes its way to a sewage treatment plant. There, it can really mess with the plant’s bacterial tenants, according new data published in Environmental Science and Technology . Beth Mole, writing for Science News, explains “in wastewater treatment plants, the omnipresent antimicrobial can sabotage some sludge-processing microbes and promote drug resistance in others.” The solids that are left over are often spread on fields as fertilizer—antibiotic-resistant bacteria and all.

The research team, led by Paige Novak at the University of Minnesota, also found that at concentrations like those in the most triclosan-contaminated plants, methane production starts to swing erratically, suggesting that the bacterial community is close to collapsing. This problem has an easy solution, though: stop using triclosan. Trading in antibacterial soap for the regular kind isn’t likely to cause an uptick in communicable diseases: hand washing alone helps prevent the spread of illness, and studies haven’t found that antibacterial soaps make it more effective. In light of that data and others that implicate triclosan in endocrine disruption and the development of antibiotic-resistant bacteria, the FDA issued a statement in 2013 statement asking companies to justify including triclosan in their products. Triclosan isn’t the only drug that’s ending up in our waste water. Plenty of pharmaceuticals make their way down our drains, and scientists are unsure whether that poses a problem. But just like with triclosan, there are some easy solutions .

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