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ISTC Reports: Evidence of Bacterial Resistance to Triclosan Found in Sediments

ISTC reports

The latest ISTC Research Report details recent research which demonstrates that the compound triclosan, a key active ingredient in many antibacterial products, produces resistance in environmental bacteria.

Rapid urbanization in the U.S. during the 20th century has meant wastewater treatment plants today deal with unprecedented loads and complex mixtures of potential pollutants, including many antibacterial compounds found in personal care products and other consumer items.  Some of the pollutants are not completely eliminated in the wastewater treatment process.

bacterial resistance shown in natural environmentOne concern is that they may impact bacterial communities in rivers and streams receiving effluent from wastewater treatment plants. Bacteria are a critical component of the food chain and involved in many biogeochemical processes, such as the nitrogen cycle.  More needs to be known about the effects of biologically active compounds with the potential to alter these populations.

A wide range of medical and veterinary compounds, hormones, over-the-counter preparations, and chemicals used in personal care products have drawn attention from environmental scientists. Triclosan is of particular concern because it has the most widespread use.

The report titled “Ecotoxicology of Antimicrobial Pharmaceutical and Personal Care Products (PPCP) in Illinois Rivers and Streams”, authored by John Kelly, professor of biology at Loyola University Chicago, Emma Rosi-Marshall, aquatic ecologist Cary Institute for Ecosystem Studies in Millbrook, NY, and John Scott, ISTC senior chemist, was published online this week at

In field experiments, the team focused on evaluating triclosan concentrations in water along with studying bacterial abundance and diversity.  They examined water and sediment samples upstream and downstream from the discharge of a large urban waste water treatment plant (WWTP) and a smaller suburban plant, as well as from a stream in a rural woodland site in Illinois. The study showed that effluent from both WWTPs resulted in reduced abundance and diversity of bacterial communities downstream.

But the team also found that concentrated, sporadic releases of triclosan that they observed corresponded to untreated wastewater sewer overflows during high rainfall events.

There was a strong correlation between triclosan concentration in sediments and the abundance of resistant bacteria. The researchers state that this “work is the first documented link between triclosan exposure and an increase in triclosan resistance in a complex bacterial community in the environment.”

In additional laboratory controlled, artificial stream experiments with higher triclosan concentrations, a significant decrease in bacterial diversity was observed, along with a dramatic increase in triclosan-resistant bacteria. The higher concentration was intended to model sewer system failures due to aging infrastructure in the U.S. and raw sewage releases in other areas of the world.

A portion of the work also appeared in Environmental Science and Technology.

The research was supported by a grant from the Hazardous Waste Research Fund administered by the Illinois Sustainable Technology Center, a division of the Prairie Research Institute at the University of Illinois at Urbana-Champaign.


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