News Coverage
PBDEs in dust and dryer lint
Published January 12, 2005
Research recently posted to ES&T 's Research ASAP website (es0486824) provides the strongest hypothesis to date for the source of the very high levels of brominated flame retardants being found in the blood and breast milk of U.S. residents. Heather Stapleton of the National Institute of Standards and Technology says the study also shows that young children in the most contaminated homes may be ingesting enough polybrominated diphenyl ethers (PBDEs), which are suspected to be endocrine disrupters, from dust to raise public health concerns.
New research suggests that the PBDEs used as flame retardants in consumer goods such as couches are escaping from the products they are used to protect and attaching themselves to people's clothes. Children are at particularly high risk of taking up the chemicals, which are suspected to be endocrine disrupters, from PBDEs in house dust.
Although most people's main exposure to persistent, bioaccumulative chemicals is through food, recent analyses of the PBDE content of food (Environ. Sci. Technol. 2004 ,38 ,5306-5311) cannot fully account for the levels of the chemicals being found in the most highly exposed segments of the population, Stapleton says. "PBDEs are very unusual in that we have seen some people with levels 50 times higher than the median," explains Linda Birnbaum, director of the U.S. EPA's Experimental Toxicology Division. In the case of dioxin, for example, which is like most other persistent and bioaccumulative chemicals, about 5% of the population has levels that are 2 times the median, and 1% has levels that are 3 times the median, she says. By comparison, 5% of the population has PBDE levels 10 times the median.
Stapleton's research shows that the dust in U.S. homes can contain very high levels of PBDEs. She found flame retardants in the dust of all 16 homes she tested in the Washington, D.C., metropolitan area, as well as in the one Charleston, S.C., home she sampled. Stapleton analyzed for 22 different PBDE compounds, or congeners, and found that the homes contained 780-30,100 nanograms (ng) of total PBDEs per gram of dry mass. As has been the case with human milk and blood, the levels of PBDEs in the U.S. dust were nearly an order of magnitude higher than the amounts measured in European homes.
Stapleton's results are the first to be published in a peer-reviewed journal, but they are similar to the levels in 10 U.S. homes that were reported in a study by the Environmental Working Group, an environmental nonprofit. Arnold Schecter of the University of Texas School of Public Health and colleagues also reported similar findings at the international brominated flame retardants and dioxin meetings.
The PBDEs levels in the U.S. house dust are in line with what's being found in dust in the 70 randomly selected Canadian homes that have already been analyzed for PBDEs in indoor air (Environ. Sci. Technol. 2004, 38,386A-387A ), says Tom Harner of the Meteorological Service of Canada. Taken together with Harner's research into the levels of PBDEs in indoor air-which shows that air emissions cannot completely explain the highest levels in people-the dust studies confirm that "we need to consider indoor exposure as a route," Stapleton says.
"House dust could definitely be a source of exposure to PBDEs through inhalation, ingestion, and dermal uptake," Birnbaum agrees. "Ingestion of dust is likely to be the dominant intake route for both [non-nursing] children and adults, compared to dietary intake," Harner adds.
Stapleton also found that the percentage of congeners associated with the Deca PBDE formulation, the only PBDEs that are being included in U.S. goods as of this year, varies to a "surprising" degree in the tested homes. This may reflect differing manufacturing practices for the electronic goods the Deca flame retardants are used to protect, such as computers, televisions, and stereo equipment, she says. "Smaller houses or apartments have more Deca in their dust," she adds.
By using EPA estimates of how much dust a toddler between the ages of 1 and 4 can be expected to take up, Stapleton and her colleagues determined that children in homes with high levels of PBDEs could be ingesting as much 1180ng of PBDEs from dust each day. She warns that this is sufficiently close to the levels that cause behavioral effects in laboratory animals to highlight the need for more data on indoor exposure to PBDEs. This is particularly true for children, because previous studies have revealed that nursing infants may already be consuming a high dose. PBDEs are slated for evaluation by the Children's Environmental Exposure Research Study program, which is currently undergoing additional peer review (Environ. Sci. Technol. 2005 ,39 ,40A).
Exactly how the PBDEs are escaping from consumer products remains unclear, but Stapleton attempted to glean more information about one potential route by looking for PBDEs in dryer lint.
"Possible sources [of PBDEs] seem to be your couch, your rugs, your mattress-almost everything you sit upon in your home," Stapleton explains. "The [PBDEs] are very hydrophobic-they're sticky-[so the obvious question is] are they sticking to your clothes? If you put your hand on your pants and then eat a potato chip, is that then transferring them from your hand into your body?" She figured that if PBDEs were attached to people's clothes, they'd show up in dryer lint.
Stapleton was surprised by what she found. "The levels were higher than I expected to see," she says. "If anything, those are low estimates, because we expect some to be taken off in the washing cycle before it even hits the dryer," she says. She acknowledges that at least some dryers could contain Deca as a flame retardant, but the "fact that we see Penta and Deca levels in some of these dryer lint samples suggests that it's most likely associated with the dust," she says.
In the meantime, another researcher investigating PBDEs in dust, Miriam Diamond of the University of Toronto in Canada, says that the chemicals may have the largest impact on people of lower socioeconomic status. "High exposure and presumably high levels in milk [and] blood could be transient if sources are reduced [and] ventilation improved," she says. "Folks with higher socioeconomic status can take these measures, but as usual, low socioeconomic folks, with potentially crumbling old furniture [and so on], can't take these measures easily."