[Pharmwaste] Popular antibacterial soal ingredient's presence in env. could be cause for concern

Tenace, Laurie Laurie.Tenace at dep.state.fl.us
Thu Apr 27 12:02:49 EDT 2006


http://pubs.acs.org/subscribe/journals/esthag-w/2006/apr/science/lt_soap.html

Science News -April 26, 2006
Popular antibacterial soap ingredient's presence in environment could be
cause for concern

(go to the URL to see lots of links - Laurie)

New research suggests that large quantities of a popular ingredient in
antibacterial soap could be entering the environment through recycled sewage
sludge.
Researchers looking for emerging contaminants in wastewater treatment plants
(WWTPs) face a formidable challenge-to "find the needle in the haystack,"
says Rolf Halden, an assistant professor of environmental health sciences at
the Johns Hopkins Bloomberg School of Public Health. In a study posted today
to ES&T's Research ASAP website (DOI: 10.1021/es052245n), Halden and his
coauthors report that approximately 75% of the mass of a popular antiseptic
called triclocarban that enters a typical WWTP persists in the treated
sludge.

 
Their work is the first peer-reviewed field study of triclocarban in sewage
sludge and one of the few reports of the compound's fate during wastewater
treatment. The findings suggest that-given the high rate of sewage sludge
reuse as fertilizer-a single WWTP can return more than 1 metric ton of
triclocarban to the environment. The authors agree that their findings also
raise the question of whether triclocarban could be promoting antibiotic
resistance in bacteria in the sludge or elsewhere in the environment.

Triclocarban, commercially known as TCC, is a pesticide used extensively as
an antimicrobial additive in soaps and body washes; one survey of commercial
products found it in 30% of bar soaps. With annual production estimated at 1
million pounds or more, triclocarban is classified as a
high-production-volume chemical by the U.S. EPA.

Despite triclocarban's widespread usage-and its chemical similarity to
triclosan, another common antiseptic additive that has come under
scrutiny-relatively little is known about the compound's fate during
wastewater treatment. "I think it's surprising that no one has looked at it
before," says Shane Snyder, R&D project manager at the Southern Nevada Water
Authority. "People have done a tremendous amount of work on triclosan."

Halden and his coauthors found that triclocarban was almost entirely removed
from the WWTP's effluent after activated sludge treatment-with an average
efficiency of 97%. The compound tends to attach itself to particles in the
sludge because of its hydrophobic nature. Therefore, it remains in the
sludge; even after 19 days of anaerobic digestion, levels were as high as 51
milligrams per kilogram (mg/kg). According to Snyder, the concentration of
triclocarban in treated sludge is higher than he would have expected.

The authors propose that triclocarban's chemical structure may explain its
resistance to degradation. "Some chemicals don't withstand the anaerobic
digestion component of wastewater treatment," explains Halden, "but this
chemical does because it looks foreign to microorganisms."

In previous studies, also published in ES&T, Halden and his colleagues
documented the presence of triclocarban in streams, groundwater, wastewater,
and drinking water around Baltimore, Md. They found concentrations ranging
from 3 nanograms per liter in treated drinking water to more than 5
micrograms per liter in streams with significant raw sewage contamination.
While doing so, they developed a state-of-the-art analytical technique to
selectively identify and quantify triclocarban against the complex background
of sewage sludge.

The presence of triclocarban in sewage sludge raises questions about its fate
when the sludge is reused as biosolids. Federal regulations classify treated
sludge as biosolids on the basis of levels of pathogens and other
contaminants. According to EPA statistics, about half of the biosolids
generated from wastewater treatment are recycled to land for agriculture and
other uses.

Hans Sanderson, director of environmental safety at the Soap and Detergent
Association, comments that the research is technically sound and provides
helpful information about triclocarban's fate. He emphasizes, however, that
the results do not necessarily apply to the biosolids that meet the strictest
pathogen requirements-known as Class A biosolids-which are subject to fewer
usage restrictions. The heat treatments designed to kill pathogens in the
sludge may also change the concentration of triclocarban in the finished
biosolids. "That concentration, we don't know," says Sanderson, "but in all
likelihood it's not going to be higher than the concentration you have in the
sludge-it's probably going to be lower."

The authors say that the sludge sampled in this study would meet the Class B
biosolids standards, but they are in the process of measuring triclocarban
levels in Class A biosolids. According to Halden, "Unpublished data from the
National Biosolids Repository study show that triclocarban can withstand
additional treatment steps and remains detectable at mg/kg levels in Class A
biosolids."

The researchers are also investigating whether triclocarban is bioavailable
in soil, or whether it stays attached to particles, which would limit its
potential impact. Although relatively few data exist about the toxicity of
triclocarban, the authors report that it has been found to impair
reproduction in laboratory rats and that some of its degradation products are
carcinogenic.

To provide researchers with more information about the composition of sludge,
Halden has established the Johns Hopkins University National Biosolids
Repository. This nationwide sampling project seeks to identify synthetic
compounds-such as PCBs and PBDEs (polybrominated diphenyl ethers)-that
persist in municipal sludge and to estimate the chemical input to
agricultural soils by sludge reuse.

Halden suggests that triclocarban's antimicrobial properties give additional
cause for concern, noting that the related compound triclosan has faced
scrutiny since the late 1990s, when researchers first found that it could
promote growth of resistant strains of bacteria. The conditions under which
microbes encounter topical antiseptics like triclosan and triclocarban-at low
concentrations, for extended periods of time-are considered the most likely
to encourage resistance. But Stuart Levy, a professor at Tufts University and
the president of the Alliance for the Prudent Use of Antibiotics, cautions:
"With triclocarban, we don't have any data of its relation to antibiotic
resistance. So that makes this paper more speculative as to what [the residue
might] do in the microbial world."

The authors plan to continue their investigations into triclocarban, and they
emphasize that many unanswered questions remain. "It's kind of a detective
story," Halden says. "We noticed [triclocarban] in the streams, and we
followed it to the wastewater treatment plant and see it's not being
degraded. We're not at the end of the story." -LIZZ THRALL

Laurie J. Tenace
Environmental Specialist
Florida Department of Environmental Protection
2600 Blair Stone Road, MS 4555
Tallahassee, Florida 32399-2400
PH: (850) 245-8759
FAX: (850) 245-8811
Laurie.Tenace at dep.state.fl.us  
 
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