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, 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, as
well as from local water filtration and wastewater
treatment plants. From the samples, Halden and his summer
research intern, Daniel H. Paull, now a graduate student in
the Chemistry Department in the
Krieger School of Arts and Sciences, 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 every day in the checkout line of
the grocery store," Halden said.
The study was written by Halden and Paull. The
research was supported by the National Institute for
Environmental Health Sciences through the Johns Hopkins
Center in Urban and Environmental Health, the Maryland
Cigarette Restitution Program Research Grant, the Johns
Hopkins Bloomberg School of Public Health Faculty
Innovation Award and the Johns Hopkins
Center for a
Livable Future.