Science News

Why do peoples' PBDE levels vary widely?
by Kellyn Betts

Researchers suspect that old furniture may be responsible for some people’s high levels of PBDEs.

It is becoming increasingly clear that North American women are taking up high levels of a relatively new persistent organic pollutant (POP), polybrominated diphenyl ethers (PBDEs), and new data out of the United Kingdom show that women there are accumulating more than their peers on the continent. As the evidence grows, many scientists studying the issue are observing that some people are taking up far more of the flame retardant chemicals than others.

The latest data come from England and three different areas of the United States: California, Indiana, and Texas. Arnold Schecter, a professor of environmental sciences at the University of Texas at Houston’s School of Public Health, revealed one of the largest collections of U.S. data amassed to date at the Society of Toxicology meeting in March.

The PBDE levels Schecter found are “strikingly high compared to Europe,” he says. He analyzed 47 samples of milk from women in Texas and looked for 13 different PBDE compounds, or congeners. The samples contained anywhere from 6.2 to 419 parts per billion (ppb) of the PBDEs per gram of milk fat. In comparison, Bert van Bavel of Örebro University in Sweden reports that the lowest level in Schecter’s sample is equal to the highest levels reported in Europe for workers in electronics recycling facilities.

However, the PBDE levels recorded in the milk of 67 British women by a team led by Kevin Jones of the University of Lancaster ranged from less than 1 ppb to 69 ppb. More than half of the women in the study, which has yet to be published, had levels of 6 ppb or above.

The PBDE levels of North Americans are 10 times higher than the (non-U.K.) European levels, and some North Americans have levels 10 times higher than their peers, summarizes Linda Birnbaum, director of the Experimental Toxicology Division of the U.S. EPA’s National Health and Environmental Effects Research Laboratory, who says that the range of the data that Schecter collected is roughly comparable to all of the data she has seen showing levels in North Americans (Environ. Sci. Technol. 2002, 36, 50A–52A).

The European data also show that some individuals have significantly higher levels than their peers, van Bavel says. He routinely finds higher levels in 5% of the samples he analyzes from Sweden.

The North American PBDE levels are notable for being orders of magnitude higher than human levels of dioxins, in the parts-per-billion, rather than the parts-per-trillion levels, says Schecter, who has studied human exposure to dioxins. However, PBDE levels are generally an order of magnitude lower than those for polychlorinated biphenyls (PCBs), stresses Robert Hale, a professor in the Virginia Institute of Marine Science’s Department of Environmental & Aquatic Animal Health. Still, Birnbaum notes that the highest PBDE levels may be similar to PCB levels.

The data on health effects from PBDEs are far from complete, but the chemicals are suspected endocrine disrupters, Birnbaum says. Rodent studies show that PBDEs may impair neurological functioning, and they appear to have additive effects with PCBs, she says. Although most of the data are for women, exposures to PBDEs—like all POPs—should be gender-blind, adds Myrto Petreas, one of the California researchers who reported new data in March.

A new study out of Indiana University suggests that mothers may be transferring PBDEs to their babies in utero (Environ Health Perspect. DOI 10.1289/ehp.6146). The researchers measured six different PBDE congeners in the blood of 12 mothers and found that their levels ranged from 15 to 580 ppb per gram of fat, and the levels in their babies’ umbilical cords ranged from 14 to 460 ppb. Although researchers were looking for impacts on the thyroid, no such correlation between the PBDE levels and the infants’ thyroid levels was found. However, they say that their study shows that U.S. babies may be exposed to relatively high levels of PBDEs.

Some PBDEs have been banned in Europe, and levels in countries where their use was already discontinued are dropping, which hints that the same could hold true in North America if the substances were banned, Schecter says.

“Although the U.K. is subject to the same EU bans, the U.K.’s fire regulations on the need for retardant treatments in furnishings, etc., were particularly stringent,” Jones notes. “The U.K. has also been a major manufacturer of PBDEs. Hence, the amounts 'present in the U.K.' are likely to be high, relative to other European countries.” He says that researchers in his lab have compared the level of PBDEs in the air with data collected by a group led by Ron Hites at Indiana University, and the levels are “very similar.”

One of the continuing mysteries surrounding the widely varying levels in humans is how these chemicals are taken up. Petreas speculates that diet cannot be the only source of PBDEs.

A number of scientists suspect indoor dust. Previous reports have shown that levels of PBDEs in dust can be strikingly high, up to the parts-per-million level (Environ. Sci. Technol. 2001, 35, 274A–275A). The sources of PBDEs in dust include the “Deca” formulation of flame retardants used in electronics products and the “Penta” contained in some of the polyurethane foam used as cushioning, Hale says.

When the polyurethane foam in an old piece of furniture is exposed to the environment, it tends to crumble, Hale explains; this releases the PBDEs embedded within the foam. Because PBDEs are used in percent by weight concentrations in flame retardant-treated foam, modest deterioration of such products could release and expose people to significant amounts of the Penta formulation that has to date been shown to have a great tendency to bioaccumulate, he says. For this reason, a small amt of PBDE-containing ‘foam dust’ could contribute significantly to the amount of the contaminant in household dust, he adds.

“Some people have nice, new furniture,” Hale points out. “Others are sitting on couches that are falling apart. When they vacuum, it re-suspends the material. If [someone is] chronically exposed to that, you can predict a spike in the[ir] blood level,” he says.