A new study of exposure to potentially harmful flame retardant compounds reveals household dust as the main source to humans rather than animal and dairy products as had previously been supposed.

Miriam Diamond

PBDEs (polybrominated diphenyl ethers) are widely used as flame-retardant additives in electronics and soft furnishings. They have been detected in humans across the globe, but North Americans appear to suffer the greatest exposure. Little is known about the specific toxic effects of PBDEs. Indeed, they may have no serious effects at all, but some researchers say that the increasing presence of the compounds in human tissue is cause for concern nevertheless. They cite studies that show an association between exposure to PBDEs and delayed puberty (acting as a thyroid-active agent) and neurodevelopmental problems such as poor memory that worsens with age.Now, Miriam Diamond and her colleagues at the University of Toronto have used a computer model to show that contrary to popular opinion, PBDE exposure occurs mainly through exposure to household dust rather than through consumption of animal and dairy products contaminated with the compounds.

“Our work is good news and bad news,” says Diamond. “Good news because we've identified the main route of exposure to PBDEs - house dust; bad news because we need more action to remove PBDEs from household products and replace them with alternatives that are effective in reducing hazards related to fires and that do not accumulate in the environment.”

PBDEs are released into the environment at their manufacturing sources and also through everyday product wear and tear, which is the presumed source of the chemicals in house dust, according to Diamond. PBDEs were detected in household dust from sixteen homes tested in the Washington DC area and one home in Charleston, South Carolina. Now, Diamond and her colleagues have built on that study by carrying out a more sophisticated analysis of all potential exposure pathways, including food, soil, dust and inhalation of indoor and outdoor air.

By using a combination of measured concentrations and computer modeling, the Toronto team estimated the emissions and fate of PBDEs in the Toronto area.

Toddlers tend to have high levels of PBDEs, which is most likely because they are frequently bringing toys and other objects from the floor to their mouths, the researchers suggest. Breast-feeding infants have higher levels of PBDEs than all other ages, which is consistent with earlier research revealing high levels of PBDEs in the breast milk of women across North America. “We hypothesize that women with very high PBDE concentrations in breast milk may be super-exposed,” Diamond says. “Given evidence from the literature, it seems likely that if one reduces one's exposure, then presumably the breast milk concentrations will fall.”

Diamond suggests a number of steps that people can take to minimize exposure, such as frequent house cleaning and improved ventilation. “It seems to me that any measures one takes to minimize dust will reduce exposures,” she says.

Officials in the US and Canada are still debating the fate of flame retardants, although the main US manufacturer has discontinued production of two types of PBDEs - the penta and octa formulations - as part of a voluntary agreement with the US Environmental Protection Agency. The European Union has banned the penta and octa formulations and is currently considering a voluntary phase-out and further study on a third type, the deca formulation.

Environ Sci Technol., 2005; http://dx.doi.org/10.1021/es048267b

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