[Pharmwaste] RE: antimicrobials accumulate in muni sludge used to fertilize crops

[Sue Dayton]

Subject: American Scientist Online Article

Published in American Scientist: 
Vist http://www.americanscientist.org/template/AssetDetail/assetid/54434 to
view the article with illustrations
 
 
Persistently Clean? 
Antimicrobials accumulate in the municipal sludge used to fertilize crops 
 
Christopher R. Brodie
 
More than a million pounds of antimicrobial chemicals from soap and
other products flow into the nation's sewers every year. Do these
compounds pose a risk? Product manufacturers say no, pointing to data
that show only traces of the two most common antibacterials, triclosan
and triclocarban, in treated wastewater. What happens to the remainder
is less certain. The stock explanation has been that the majority is
broken down during the treatment process. The fraction released into
surface water was thought to meet the same fate sooner or later. Thus,
much of the claim that these products are safe rested on the fact that
they were rendered harmless in treatment plants or just beyond. 
 
New data puncture that conclusion: 50 percent of triclosan and 76
percent of triclocarban remain unchanged by aerobic and anaerobic
digestion in a typical wastewater facility, according to a pair of
recent reports. This large intact fraction isn't going out with the
treated water--the old estimates are correct in that respect. Rather, it
is trapped in the sludge at the bottom of the treatment tanks. Most of
that sludge gets spread on the ground to fertilize pasture, forests and
human food crops.
 
Rolf U. Halden, a scientist and engineer at Johns Hopkins University,
and his coworkers are the chemical detectives behind this work, which
appeared in the June 1, 2006 issue of Environmental Science & Technology
and in Chemosphere , published online June 9, 2006. By comparing the
amounts that entered a wastewater plant with the amounts that exited or
were broken down, the Hopkins team pieced together a much more complete
picture of the life cycle of these compounds in the environment.
 
Triclosan and triclocarban are small organic molecules that give
antimicrobial properties to personal-care products such as soap,
deodorant and toothpaste as well as durable goods such as cutting
boards, baby carriers and socks. Overall, Halden's team estimates that
more than 100,000 pounds of triclosan and over 300,000 pounds of
triclocarban are spread on the ground as sludge each year in the United
States, based on data from a dozen sites around the country. Of the
total mass that enters a typical sewage-treatment facility, two percent
of triclosan and three percent of triclocarban remain in the clean-water
output. Thus, only 48 percent of triclosan and 21 percent of
triclocarban are transformed or lost in the treatment process--much less
than industry estimates. At 50 and 76 percent, respectively, sludge is
the biggest repository.
 
According to a 2002 report by the National Research Council, 63 percent
of the 5.6 million tons of dried sludge made in the United States each
year is applied to the land. (When used as fertilizer, municipal sludge
goes by the more polite name of biosolids .) This recycling is viewed as
being good for the environment, because the alternatives are
incineration, burial or (before 1992) offshore dumping. But combined
with the numbers from the National Research Council, Halden's analysis
indicates that hundreds of thousands of pounds of triclosan and
triclocarban are spread on the ground every year. Remarkably, this
massive contamination is unregulated and unmonitored. The ecological
effects are similarly unexplored.
 
In fairness, the reason that no one noticed the organic compounds (such
as triclocarban) in sludge is that the technique used to measure such
things wasn't up to the job. Sludge is a complex matrix that adheres to
and masks molecules that are strongly hydrophobic, as are triclosan and
triclocarban--so much so that this municipal gunk acted as a "chemical
black hole," according to Halden. "It used to be you could dump
[manmade] chemicals in the sludge and they'd disappear," he explains,
referring to how they became invisible to detection. But in 2004,
Halden's group described a method that allowed chemists to peer inside
the sludge, something he describes as "one of the last frontiers in
analytical chemistry."
 
What they saw was an accumulation of triclosan in the sludge up to
concentrations of 30,000 micrograms per kilogram--more than 6,000 times
more concentrated than the incoming sewage. The numbers were even higher
for triclocarban: 51,000 micrograms per kilogram in the sludge, which
worked out to 8,400 times the concentration of sewage and 300,000 times
that of the sewage treatment plant's outflow.
 
The biosolids industry is regulated by the U.S. Environmental Protection
Agency, which dictates the conditions under which the substances can be
used. But in terms of sludge composition, the EPA only set limits for
metals and certain pathogenic bacteria. There is no oversight of organic
chemicals and no categorical prohibition of the use of biosolids on food
crops. Current rules do govern the types of food that can be grown with
biosolids fertilizer, the amount of time between application and
harvest, and other practical details. But the EPA's official stance is
that the practice of growing food in dewatered municipal sludge is
acceptable.
 
And perhaps it is. Manufacturers consider triclosan and triclocarban to
be safe--even healthy, to judge by the tone of their advertisements. Some
bar soaps, for example, are five percent triclocarban by weight. With
the exceptions of triclocarban causing outbreaks of "blue-baby syndrome"
in the 1960s and ?70s (pediatricians still advise against exposing
newborns to triclocarban) and the trace amounts of dioxin, a known
carcinogen, that tag along with triclosan, the compounds have a clean
safety record in people. The problem, as any toxicologist will tell you,
is that the dose makes the poison.
 
The estimated annual production of triclocarban exceeds one million
pounds. From this massive starting amount, consider that triclosan and
triclocarban resist degradation (Halden estimates their half-life in
sediments to be 540 days) and that their chemical structure suggests
that they build up in fat, and it's easy to see the potential for
accumulation in the food chain.
 
Chemical stability by itself is hardly damning, and neither compound has
killed anyone. But direct effects on hand-washers and tooth-brushers are
not the only relevant outcomes. For example, triclosan disrupts the
functions of the endocrine system in cultured cells. Furthermore, the
risk of fueling the evolution of antibiotic-resistant bacteria--as yet
unproven--remains plausible. Halden's concern is that in sludge, the
combination of concentrated microorganisms, some of them capable of
causing disease, with extremely high concentrations of antimicrobials is
a recipe for drug resistance.
 
In the end the decision of what to do about sludge will be up to the
risk managers. The only thing environmental scientists like Halden can
do is to show their data as best they can with the resources they have.
Fortunately, the EPA seems to be listening. Their 2001 survey of
biosolids examined only metals and dioxins, but the 2006 survey (as yet
unreleased) will be more comprehensive, checking for more metals, a
short list of organics and, at least in some samples, triclocarban
specifically. Getting rid of the things that get rid of microbes may
turn out, paradoxically, to be the healthy thing to do.
 Sue Dayton
Blue Ridge Environmental Defense League
North Carolina Healthy Communities Program
PO BOX 44
Saxapahaw, NC 27340
(336) 525-2003
sdayton at swcp.com

Our lives begin to end the day we become silent about things that matter.
-  Martin Luther King Jr.