Daily News Archive
April 28, 2006
Antibacterial Soap Ingredient Found in Recycled
Sewage Sludge Used on Crops
(Beyond Pesticides, April 28, 2006) Researchers
at the Johns Hopkins Bloomberg School of Public Health measured levels
of an antibacterial hand soap ingredient, triclocarban, as it passed
through a wastewater treatment facility. They 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 underway
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 PhD 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, PhD, 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 Hopkins 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 treatment.
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 thousand-fold 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 Dr. 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."
Dr. Halden's previous research determined that triclocarban, similar
to the structurally related antimicrobial triclosan,
also contaminates rivers and streams across the United States.