Sludge Watch ==> Persistently Clean? Antimicrobials accumulate in municipal sludge on crops

[Maureen Reilly]

see full issue: January-February 2007 SCIENCE OBSERVER


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.


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