Wash And Wonder

When microbe-averse consumers wash their hands with soap containing the widely used antibacterial agent triclocarban (TCC), much of the biocide likely ends up intact in the sludge of wastewater treatments plants from where the sludge is reused as fertilizer, according to measurements at a state-of-the-art plant in the U.S. (Environ. Sci. Technol., published online April 26, dx.doi.org/10.1021/es052245n).

Last October, a Food & Drug Administration panel concluded there is at present no scientifically discernible benefit from using antimicrobial soap instead of plain soap. To senior author Rolf U. Halden of Johns Hopkins University Center for Water & Health, this assessment amplifies the importance of tracing the environmental fates of TCC, produced at a rate of 1 million lb or so per year, and related high-volume antiseptic compounds, such as triclosan, in personal care products.

Halden and his colleagues have yet to chronicle TCC movement beyond the sludge at a single treatment plant. This means they cannot discern from their reported data whether TCC in sludge poses actual hazards, such as contributing to the development of antibiotic-resistant bacteria.

"I see sludge as an early warning matrix," Halden notes. For him, the ability of TCC, used commercially as a pesticide and biocide for decades, to withstand a gauntlet of physical, chemical, and biological cleaning processes at a modern wastewater treatment plant is a signal that the compound can persist in the environment.

"This is an important topic, but we need to decide what to be concerned about and what not to," says Hans Sanderson, director of environmental safety at the Soap & Detergent Association. In light of the looming threat of a bird flu pandemic as well as public health risks posed by other infectious diseases, "why remove an extra health protection in consumers' homes?"

Halden stresses that he is a big fan of the public health benefits of hand washing with regular soap, but questions the need for antibacterial soap.

Using a combnation of liquid chromatography and mass spectrometry to separate, identify, and measure TCC in the complex liquid and solid matrices of the unnamed treatment plant, Halden's group found that most of the roughly 3.7 kg of TCC entering the plant each day sorbed onto wastewater particulates. That enabled the biocide to bypass several treatments including chlorination and sand filtration.?? But the compound even survived 19 days of an anaerobic microbial digestion process. As much as 76% of the incoming TCC ended up in sludge at levels of about 50 ppm. That could amount to more than a ton of TCC per year accumulating at each of the larger plants among the U.S.'s 18,000 or so treatment facilities, Halden notes.

Reflecting a growing concern about what happens to ingredients in pharmaceuticals and personal care products that go down the drain, the Environmental Protection Agency plans this summer to conduct a nationwide survey of sewage sludge that will look for the presence of 20 analytes. TCC and the related antibacterial agent triclosan are not now among them, notes Rick Stevens, national biosolids coordinator for EPA's Office of Water. "We haven't finalized the list, and we might add them," he says.