[Pharmwaste] Antimicrobials accumulate in the municipal sludge used to fertilize

[Tenace, Laurie]

http://www.americanscientist.org/template/AssetDetail/assetid/54434

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.

click for full image and caption 
  

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.  

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  
 
view our mercury web pages at: 
http://www.dep.state.fl.us/waste/categories/mercury/default.htm 

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