Toothpaste compounds, including triclosan, build up in toothbrushes

Toothpaste leaves your mouth feeling clean and tingly, but how does it leave your toothbrush? New research shows that compounds in toothpaste, including the antimicrobial agent triclosan, can build up in toothbrush heads and leach back out over time (Environ. Sci. Technol. 2017, DOI: 10.1021/acs.est.7b02839).

Triclosan was once a common component of antibacterial soaps and body washes in the U.S. Last year, the U.S. Food & Drug Administration gave companies a deadline of September 2017 by which to stop marketing those products, citing concerns about triclosan causing antibiotic resistance and a lack of evidence that triclosan-containing soaps were more effective than soap and water alone. The compound’s use in toothpaste is still approved, though, because of reports that it reduces gum inflammation, gingivitis, and plaque.

Because some nylons—materials commonly used in toothbrush bristles—can take up some compounds, including triclosan, researchers led by Baoshan Xing of the University of Massachusetts, Amherst, set out to determine the fate of chemicals in toothpaste. They simulated three months of tooth brushing in the lab with 22 types of manual toothbrushes, artificial saliva, and six best-selling antibacterial toothpastes containing 0.3% triclosan (3 mg/g of toothpaste).

Triclosan and other toothpaste chemicals accumulated in elastomeric toothbrush head components such as cheek and tongue cleaners, as well as nylon bristles. More than half of the toothbrushes accumulated at least 10 mg of triclosan over the simulated three-month brushing. When the researchers switched some of those toothbrushes to non-triclosan toothpastes for two weeks’ simulated brushing, triclosan leached out of the toothbrushes.

Although triclosan uptake and release did not reach harmful levels—the U.S. Environmental Protection Agency’s limit for dietary exposure is 0.3 mg/kg/day—the, the authors point out that this represents previously unrecognized sources of exposure to both humans and the environment, including transport to landfills through discarded toothbrushes.

“This study really highlights how little we know about the fate of antimicrobial chemicals,” says Erica Hartmann, a civil engineer at Northwestern University who studies antimicrobial resistance. “Every time one of these chemicals winds up in a new context, that’s another opportunity for it to have unintended consequences.”