Measuring levels of an antibacterial hand soap
ingredient, triclocarban, as it passed through a wastewater
treatment facility, researchers at the
Johns Hopkins Bloomberg
School of Public Health have determined that
approximately 75 percent of the ingredient washed down the
drain by consumers persists during wastewater treatment and
accumulates in municipal sludge, which later is used as
fertilizer for crops.
Their findings are presented in a study appearing in
the online and print editions of the journal
Environmental Science & Technology. More studies are
under way to determine if triclocarban, which is toxic when
ingested, can migrate from sludge into foods, thereby
potentially posing a human health risk.
"The observed persistence of triclocarban is
remarkable," said lead author Jochen Heidler, a doctoral
candidate in the Bloomberg School's
Department of Environmental Health Sciences. "In the
plant, the chemical contained in sludge underwent
biological treatment for an average period of almost three
weeks, yet very little degradation took place."
Senior author Rolf U. Halden, assistant professor and
co-founder of the Johns Hopkins Center for Water and
Health, said, "Triclocarban does not break down easily even
under the intense measures applied during wastewater
treatment. Triclocarban is leading a peculiar double life.
Following its intended use as a topical antiseptic, we are
effectively and inadvertently using it as an agricultural
pesticide that is neither regulated nor monitored."
For the study, the researchers collected samples from
a large urban sewage treatment facility in the eastern
United States. Over a period of weeks, they tracked the
mass of triclocarban entering the plant in wastewater and
leaving it in reclaimed water and municipal sludge.
Measurements were done by isotope dilution mass
spectrometry, a cutting-edge approach in environmental
analytical chemistry. Using the acquired information on
chemical concentrations and flow volumes within the
facility, they calculated the total mass of triclocarban
entering the plant and the chemical's behavior during
According to the study, the facility was highly
effective in removing triclocarban from wastewater. Only
about 3 percent of triclocarban molecules entering the
plant were discharged into surface water along with the
treated effluent. However, very little degradation of the
triclocarban occurred, due to the compound's
polychlorinated aromatic chemical structure. Approximately
75 percent of the initial mass accumulated in sludge, where
it remained chemically unchanged. Anaerobic digestion
reduced the overall sludge volume but not the quantity of
triclocarban, thereby concentrating the antiseptic agent to
levels several thousandfold higher than those found in raw
wastewater. At the particular plant observed, 95 percent of
the sludge is recycled for other uses, such as being sold
as a soil conditioner and crop fertilizer.
"The irony is twofold," said Halden. "First, to
protect our health, we mass produce and use a toxic
chemical which the Food and Drug Administration has
determined has no scientifically proven benefit. Second,
when we try to do the right thing by recycling nutrients
contained in biosolids, we end up spreading a known
reproductive toxicant on the soil where we grow our food.
The study shows just how important it is to consider the
full life cycle of the chemicals we manufacture for use in
our daily life."
Halden's previous research determined that
triclocarban, similar to the structurally related
antimicrobial triclosan, also contaminates rivers and
streams across the United States.
The study was written by Heidler, Amir Sapkota and
Halden. Funding was provided by grants from the National
Institute of Environmental Health Sciences-Johns Hopkins
University Center in Urban Environmental Health, Maryland
Cigarette Restitution Fund, Johns Hopkins Center for
Excellence in Environmental Public Health Tracking and the
Johns Hopkins Center for a Livable Future.