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Pollutants Made Worse By Bacteria

Soil microbes turn stable brominated flame retardants into more toxic forms

by Sarah Everts
June 26, 2006 | A version of this story appeared in Volume 84, Issue 26

Flame retardants may have to take some extra heat. New research shows that microorganisms present in North American and European soil break down relatively stable polybrominated diphenyl ethers (PBDEs) into more toxic molecules.

PBDEs are used in everything from carpets to electronics. The concentrations of these flame retardants in human blood serum and breast milk have been doubling every two to five years, and PBDEs are expected to become more common than PCBs in the general population, according to the Centers for Disease Control & Prevention (CDC).

Two years ago, U.S. manufacturers agreed to phase out the most potent PBDEs, penta-BDE and octa-BDEs, which are linked to fetal development and thyroid problems. Deca-BDE is considered more stable and is still widely used, although CDC lists it as a possible human carcinogen.

Lisa Alvarez-Cohen and colleagues at the University of California, Berkeley, have identified microbes in the environment that break down deca-BDE into octa-BDE and then penta-BDE (Environ. Sci. Technol., published online June 14,

"When we began the study, we were hoping to find microorganisms that would biodegrade PBDEs," says Alvarez-Cohen. "But into less toxic forms, not more toxic."

The paper identifies strains of Sulfurospirillum and Dehalococcoides as definite culprits, although other microorganisms, yet unidentified, may also be capable of the dangerous degradations.

"Microbes show enormous promise for beneficial detoxification," says Donna E. Fennell, a bioenvironmental engineer from Rutgers University. "But they are doubled-edged swords. In nature, they might be doing reactions that could result in more toxic compounds than the ones we put into the environment. This paper shows the 'yes, but' potential of microbes."

Alvarez-Cohen is looking for microorganisms that degrade these extremely toxic PBDEs further into less dangerous compounds. But it is time, she says, to reconsider policy decisions about how, or if, PBDEs should be used at all.



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