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Guest Lecturer Discusses Health Risks of Flame

By Eddy Ball
March 2007

Linda Birnbaum
EPA Toxicologist Linda Birnbaum (Photo courtesy of Steve McCaw)

On February 8, a capacity audience of NIEHS scientists gathered for a guest lecture by former NIEHS scientist Linda S. Birnbaum, Ph.D. Birnbaum spoke on the topic of "Brominated Flame Retardants: What We Know and What We Don't."

Birnbaum is currently the director of the Experimental Toxicology Division at the Environmental Protection Agency. She is an internationally recognized authority on the potential health risks posed by the brominated chemical flame retardants that are present in consumer products found in virtually every home and workplace in North America.

The Laboratory of Pharmacology and Chemistry (LPC) and the Laboratory of Molecular Toxicology jointly sponsored Birnbaum's presentation. LPC Chemist Tom Burka, Ph.D., hosted the lecture.

Despite successful efforts to ban several kinds of brominated flame retardants (BFRs), the chemicals continue to concern environmental scientists. Products that contain banned BFRs are still in use, and concentrations of these compounds in people are rising sharply. Recent research suggests that "safer" alternatives promoted by the chemical industry may be little better than the banned chemicals.

Many of the BFRs are bio-accumulative and persistent, and function as endocrine disruptors in animals. BFRs are widely dispersed and have been found in animals living in environments where the compounds are not commonly used, such as the Arctic. "We've got lots of it in the air," Birnbaum noted as she described the worldwide distribution of the chemicals and the high levels in indoor environments.

According to Birnbaum, BFRs are very effective in preventing fire and protecting firefighters by reducing the risk of flash-over, the sudden and intense burst of flames from smoldering material that is a major cause of death among first responders. BFRs are present in such products as carpets, upholstery, plastics, styrofoam and wire insulation. Since the introduction of the compounds in the 1970s, manufacturers have used BFRs more widely in the United States than anywhere else in the world, primarily because of the stringent fire regulations in this country.

Birnbaum focused her talk on five of the most widely used BFRs. They include tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD) and three forms of polybrominated diphenyl ethers (PBDEs), known as Penta, Octa and Deca.

All of these brominated compounds cause concern among environmental scientists due to their potential toxicity or mutagenicity in animal studies and their ability to function as endocrine disruptors. However, Birnbaum devoted most of her lecture to reviewing the available information on the more volatile, persistent and potentially more dangerous PBDEs.

Because of the compounds' persistence and presence in products still in use, Penta and Octa, though no longer produced, are still a concern. New information about Deca, which industry groups have promoted as the "safer" form, suggests that it may in fact break down into Penta and Octa and pose just as much of a health risk.

PBDE levels in human milk are highest in the United States and Canada and are doubling every two to five years. In the very limited sampling performed thus far, scientists have found large inter-individual variation of levels in human milk. Data presented by Birnbaum indicate that five percent of the population, for example, has ten times the mean level, and one percent has 100 times the mean level.

Studies on PBDE exposure in animals suggest that there are potentially significant health effects. Researchers have found a strong association between PBDE levels and disruption in estrogen, androgen and thyroid hormones. The compounds may alter cell signaling, induce enzymes and be toxic to the liver and nervous system, affecting detoxification, cognitive function and development. PBDEs also appear to have additive effectives when combined with other toxins.

Birnbaum repeatedly pointed to the significant gaps in the research so far on PBDEs, especially in regard to humans. "If you don't look," she lamented, "you don't find." Throughout the lecture, Birnbaum emphasized that scientists need to understand better the mechanisms involved, the consequences of inter-individual variability and the roles of the different metabolites of PBDEs.

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