Saturday, January 22, 2005

Anti-bacterial additive widespread in U.S. waterways

Many rivers and streams in the United States are believed to contain a toxic antimicrobial chemical whose environmental fate was never thoroughly scrutinized despite large scale production and usage for almost half a century, according to an analysis conducted by researchers at the Johns Hopkins Bloomberg School of Public Health. The chemical, triclocarban, has been widely used for decades in hand soaps and other cleaning products, but rarely was monitored for or detected in the environment. The new findings suggest that triclocarban contamination is greatly underreported. The study is published in the current online edition of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society.

"We've been using triclocarban for almost half a century at rates approaching 1 million pounds per year, but we have essentially no idea of what exactly happens to the compound after we flush it down the drain," said the study's lead author, Rolf U. Halden, PhD, PE, assistant professor in the School's Department of Environmental Health Sciences and founding member of its Center for Water and Health.

The nationwide assessment of triclocarban contamination is based in part on an analysis of water samples collected from rivers in and around Baltimore, Md., as well as from local water filtration and wastewater treatment plants. From the samples, Dr. Halden and his summer research intern, Daniel H. Paull, now a graduate student in the Chemistry department at Johns Hopkins University, observed the occurrence of triclocarban in the environment correlated strongly with that of triclosan, another commonly used antimicrobial chemical that has been studied in much greater detail because it is more easily detectable.

Using an empirical model and published data on the environmental occurrence of triclosan, the researchers predicted triclocarban concentrations for 85 U.S. streams. The study results suggest that the antimicrobial contaminant is present in 60 percent of the U.S. water resources investigated, thereby making it the fifth most frequent contaminant among 96 pharmaceuticals, personal care products and organic wastewater contaminants evaluated.

To determine the validity of the analysis, the researchers compared their predicted nationwide levels of contamination to experimentally measured concentrations in the Greater Baltimore region, and found no statistically significant differences. The results also show that the levels of triclocarban in water resources nationwide are much higher than previously thought.

In surface water from the Baltimore region, the researchers detected triclocarban at concentrations of up to 6.75 micrograms per liter (parts-per-billion). This maximum concentration was 28 fold higher than previously reported levels, which are currently used by the U.S. Environmental Protection Agency for evaluation of the ecological and human health risks of triclocarban.

"Along with its chemical cousin triclosan, the antimicrobial compound triclocarban should be added to the list of polychlorinated organic compounds that deserve our attention due to unfavorable environmental characteristics, which include long term persistence and potential bioaccumulation. Triclocarban, for example, has an estimated half life of 1.5 years in aquatic sediments. Do the potential benefits of antimicrobial products outweigh their known environmental and human health risks? This is a scientifically complex question consumers, knowingly or unknowingly, answer to everyday in the checkout line of the grocery store," said Dr. Halden.

Source : Eurekalert

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