Toxic Leftovers: Microbes convert flame retardant

Bacteria can break down a common flame retardant into more-toxic forms, researchers report. Besides finding more degradation products than earlier work had, the new study is the first to identify specific bacterial strains capable of the feat, the team says.

Polybrominated diphenyl ethers (PBDEs) are a family of flame-retardant chemicals found in products such as electronics, automobiles, and furniture. The chemicals have 1 to 10 bromine atoms and come in 209 versions. Manufacturers use deca-BDE, which has 10 bromine atoms, or mixtures dominated by penta-BDEs, with their 5 bromines, or octa-BDEs, with 8 bromines.

The chemicals’ effects go beyond fire resistance (SN: 10/25/03, p. 266: New PCBs?). Studies in rats and mice have found that penta- and octa-BDEs disrupt development. Deca-BDE is considered less harmful, although the Environmental Protection Agency has listed it as a possible human carcinogen.

The toxins are ubiquitous in the environment, turning up in soil, water, and even human-breast milk.

The European Union and California have banned penta- and octa-BDEs, and the sole U.S. manufacturer has volunteered to stop making these forms (SN: 11/01/03, p. 275: Flaming Out? Days may be numbered for two fire retardants). Deca-BDE remains in production and in wide use.

Lisa Alvarez-Cohen of the University of California, Berkeley and her colleagues were looking for a way to use bioremediation to eliminate the chemicals. They reasoned that various strains of anaerobic bacteria that can remove chlorine atoms from chemicals might also lop off bromines to detoxify the PBDEs.

The group tested whether several different bacterial cultures could break down either deca-BDE or an octa-BDE mixture in the laboratory. The researchers found that the bacteria converted the chemicals into more-toxic forms.

“We were quite surprised to see the production of all these very toxic intermediates,” says Alvarez-Cohen.

For example, Sulfurospirillum multivorans converted deca-BDE into eight- and seven-bromine forms but could not break down the octa-BDE mixture. Dehalococcoides ethenogenes transformed the octa-BDE mixture into five-, six-, and seven-bromine forms but did not alter deca-BDE. When other microbes were added to D. ethenogenes, the mixture also produced two- and four-bromine PBDEs. Among the breakdown products were several especially toxic forms.

While other researchers have reported the microbial debromination of deca-BDE in anaerobic sewage sludge to nine- and eight-bromine forms, “this is the first time anything beyond octa has been shown,” says Alvarez-Cohen. Her group’s work appears in the July 15 Environmental Science & Technology.

“Lots of folks weren’t that concerned about deca-BDE because it was portrayed as being stable,” notes Robert C. Hale of the Virginia Institute of Marine Science in Gloucester Point. But the new research, coupled with other published examples of fish and sunlight converting deca-BDEs to less-brominated forms, is “a real reason for concern,” he says. “We haven’t seen massive amounts of debrominated products out there yet, but it may be a question of time.”

Aimee Cunningham

Aimee Cunningham is the biomedical writer. She has a master’s degree in science journalism from New York University.

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