Sludge Watch ==> Sludge Risk: Bacteria may break deca PBDE into more toxic forms

[maureen.reilly at sympatico.ca]

Sludgewatch Admin:

It looks like the anaerobic environment of the sewage sludge digesters may 
create conditions
for some rather toxic processes..... Here is a look at the anaerobic 
breakdown of the popular flame retardant Deca PBDE into more toxic forms of 
PBDE that can accumulate in the bodies of people and animals.

Remember there were huge levels of PBDEs found in the sewage sludge of a 
little sewage treatment plant in Picton Ontario - a plant that wants to do 
agricultural land application of these sludges on the fields and vineyards 
of the Prince Edward County area east of Toronto Ontario.

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http://pubs.acs.org/subscribe/journals/esthag/40/i14/html/071506news4.html

ES&T News
Bacteria may break down popular flame retardant to produce toxics
Research published in this issue of ES&T (pp 4429–4434) documents that 
microbes can break down the large molecules of the widely used Deca PBDE 
(polybrominated diphenyl ether) flame retardant. The paper raises concerns 
about the Deca flame retardant’s safety by showing that various anaerobic 
bacteria can work in concert to dehalogenate the Deca compound to produce 
the smaller PBDE compounds that have been banned in the EU and discontinued 
in the U.S.


Stephen Zinder
Bacteria such as the Dehalococcoides shown here may be able to work in 
concert with other bacteria to attack the Deca PBDE flame retardant and 
produce small toxic PBDEs.The paper is the first to identify species of 
bacteria capable of breaking down the main constituent of the Deca flame 
retardant formulation, Deca-BDE. The study builds on previous research 
showing that the Deca flame retardant could be transformed during anaerobic 
sewage treatment.

The Deca mixture is found in electronic products such as computers and 
televisions, and it is the only PBDE formulation currently in use. Because 
of the Deca-BDE molecule’s large size, it is considered relatively inert, 
but the smaller PBDE compounds, or congeners, that have been banned and 
discontinued are persistent and bioaccumulative. The levels of these 
compounds have been rising throughout the world, especially in North 
America, and their neurotoxic effects are similar to those of PCBs, which 
they resemble chemically.

In the new paper, Lisa Alvarez-Cohen and her colleagues at the University of 
California, Berkeley, describe research they conducted with bacteria known 
to be able to dehalogenate large molecules containing chlorine. 
Sulfurospirillum multivorans are able to break down TCE (trichloroethylene), 
and the different species of Dehalococcoides used in the experiments can 
attack both chlorinated ethenes and dioxins. The new study firmly 
establishes that the Dehalococcoides bacteria can use brominated compounds 
as electron acceptors, says Lorenz Adrian, who is with the Technical 
University of Berlin’s Institute for Biotechnology and who first showed that 
the bacteria could attack dioxins.

Alvarez-Cohen’s team documented the S. multivorans bacteria’s ability to 
decompose the Deca-BDE molecules into smaller PBDE compounds containing 8 
and 9 bromine atoms.

The Dehalococcoides bacteria cannot attack the large Deca-BDE molecules, but 
they could dehalogenate PBDE compounds containing 8 bromines to produce PBDE 
compounds with 6, 5, and 4 bromines. The breakdown products included BDE-99, 
which contains 5 bromines and is often found to bioaccumulate in people and 
animals. Although these tests took place in a laboratory, Alvarez-Cohen says 
that “it is highly likely that we’ll see this kind of sequential 
transformation in the environment.”

Other researchers agree. The research raises the question of whether 
“continued production and use of the Deca may lead to ongoing exposure of 
wildlife and people to the lower brominated congeners for which we have 
toxicity concerns,” adds Linda Birnbaum, director of the experimental 
toxicology division at the U.S. EPA’s National Health and Environmental 
Effects Research Laboratory.

Andreas Gerecke, a project leader in the analytical chemistry department of 
Switzerland’s National Materials Science & Technology Laboratory (EMPA), was 
the first scientist to report that Deca-BDE was being broken down in sewage 
treatment plants. He says that “it is likely that Deca[-BDE] undergoes 
microbially mediated reductive debromination in the anaerobic environment.” 
However, he points out that the rates documented in the paper are quite 
slow.

Alvarez-Cohen acknowledges that this is true but says that she is currently 
involved in studies with additional bacteria showing “much [more rapid] 
rates of degradation.” However, scientists from the Bromine Science and 
Environmental Forum, an industry group, point out that “no degradation was 
found without TCE being added as a fuel, along with other substrates. Since 
TCE is not normally present in the environment at high concentrations (it 
oxidizes to another substance), the environmental relevance of this study is 
questionable; i.e., the conditions under which degradation was forced to 
occur are not likely to be found in the environment.”

Even so, scientists interviewed for this article agree that the paper’s 
findings are significant. Deca-BDE is also “detected at elevated levels in 
sewage sludge [and] biosolids, which can be home to multiple strains of 
bacteria,” points out Heather Stapleton, an assistant professor of 
environmental sciences and policy at Duke University. “Considering that land 
application of biosolids and soil amendment is an increasing practice, [this 
new paper’s findings warrant] further investigation.”

—KELLYN BETTS