Study: Microbes Transform 'Safest' PBDEs Into More Harmful Compounds

Bacteria in the soil can break down the most commonly used flame-retardant compound in the United States into more toxic forms that could be harmful to humans, according to a study published on June 14 on the Web site of the American Chemical Society journal, Environmental Science & Technology.

The finding, by a team of environmental engineers at the University of California, Berkeley, suggests these transformations could complicate efforts to reduce or eliminate the most problematic polybrominated diphenyl esters (PBDEs) from the environment.

"This study, for the first time, establishes that microbes found in every-day settings can degrade relatively stable forms of PBDEs, making them far less stable and potentially more toxic," said Lisa Alvarez-Cohen, PhD, the study's corresponding author. "It implies that current and planned bans of the most toxic forms of PBDEs may be ineffectual if the less toxic forms are rendered more toxic when released into the environment."

In laboratory animals, high blood levels of PBDE are associated with cancer, lowered immunity, thyroid problems, and learning and memory difficulties. Although PBDE levels in people haven't reached the levels of laboratory animals, Alvarez-Cohen said that scientists are concerned because they are rising in humans at an exponential rate, doubling every two to five years.

In 2004, EPA announced a voluntary agreement that would end the U.S. manufacture and sale of penta-BDEs and octa-BDEs, two potent forms of PBDEs linked to health problems in animals. Deca-BDE, the most commonly used form of PBDE, remains on the market because it is considered more stable and less readily absorbed into the body, Alvarez-Cohen said. Laboratory studies, however, have shown that over time, both deca- and octa-BDEs can break down into potentially more harmful forms, including penta- and tetra-BDEs.

This new study supports the notion that this process also could occur in the real world, raising concerns about the continued manufacture and use of deca-BDEs, Alvarez-Cohen said. In their study, Alvarez-Cohen and her colleagues exposed octa-BDE and deca-BDE to five types of anaerobic bacteria commonly found in the soil. Based on previous research with other compounds, they anticipated that the bacteria would break down deca-BDEs into benign components. Instead, the microbes transformed deca-BDEs into octa-BDEs and the octa-BDEs into the more harmful penta- and tetra-BDEs.

"Now that we understand that certain PBDEs found in the environment can be transformed into more toxic forms, we need to make more intelligent policy decisions with respect to how, or even if, we should use these compounds," Alvarez-Cohen said.

PBDEs are used in televisions, computers, wire insulation, upholstery and many other products containing plastic and foam. If these products overheat, PBDEs release atoms called bromines that sap oxygen from the air, preventing a fire. Over time, PBDEs can leach into the air, soil and sediment, and move up through the food chain. These compounds have been detected in fruits and vegetables, meats, dairy products and even household dust.

Additional information on PBDEs can be found at http://www.epa.gov/oppt/pbde.

Lisa Alvarez-Cohen: http://www.ce.berkeley.edu/~alvcohen

This article originally appeared in the 06/01/2006 issue of Environmental Protection.

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