A new study by scientists from the Cary Institute of Ecosystem Studies in Millbrook, New York, Loyola University Chicago and Illinois Sustainable Technology Center, has reportedly revealed that triclosan—a synthetic antibacterial widely used in personal care products—is fueling the development of resistant bacteria in streams and rivers. Bradley Drury, et al., "Triclosan Exposure Increases Triclosan Resistance and Influences Taxonomic Composition of Benthic Bacterial Communities," Environmental Science and Technology, August 6, 2013.

Invented for surgeons in the 1960s, triclosan is an antibacterial agent designed to slow or stop the growth of bacteria, fungi and mildew. It is used in many liquid soaps and toothpastes, deodorants and cosmetics. Previous research has shown that the substance enters streams and rivers through domestic wastewater, leaky sewer infrastructure and sewer overflows, with residues apparently common in waterways throughout the United States.

In what is considered to be the first study to document triclosan resistance in a natural environment, researchers explored how bacteria living in stream and river sediments responded to triclosan in both natural and controlled settings by conducting field studies at three sites in the Chicago metropolitan region—urban North Shore Channel, suburban West Branch Dupage River and rural Nippersink Creek—and artificial stream experiments at Loyola University.

Noting that urbanization correlated with a rise in both triclosan concentrations in sediments and the proportion of bottom-dwelling bacteria resistant to triclosan, the scientists reported a "strong link between the presence of triclosan in the environment and the development of triclosan-resistant bacteria."

"The bacterial resistance caused by triclosan has real environmental consequences," said Emma Rosi-Marshall, a study author and aquatic ecologist at the Cary Institute of Ecosystem Studies. "Not only does it disrupt aquatic life by changing native bacterial communities, but it’s linked to the rise of resistant bacteria that could diminish the usefulness of important antibiotics."

The artificial stream experiments confirmed field findings that triclosan exposure triggers an increase in triclosan-resistant bacteria. In addition to the creation of these resistant bacteria, researchers also found a decrease in the diversity of benthic bacteria and a shift in the composition of bacterial communities. Most notable were a six-fold increase in cyanobacteria and a dramatic die-off of algae.