Science News - September 15, 2004

PBDEs and the environmental intervention time lag

When the manufacturers of two of the world’s most widely used brominated flame retardants agreed to withdraw their products from the U.S. market last year after California and the European Union (EU) banned the products, environmental scientists around the globe heralded the action as a victory. But new evidence suggests that the decision may not go far enough to protect public health. Because the major sources of these chemicals are products in homes and workplaces, scientists are beginning to realize that the pathways to the health risks posed by the discontinued flame retardant formulations—as well as by others that are still used—may be very different from those of older persistent organic pollutants (POPs) such as dioxins and PCBs.

Kellyn Betts Researchers believe that the PBDEs found in house dust could put young children at risk.

Study after study shows that a class of flame-retarding polybrominated diphenyl ethers (PBDEs) are traveling throughout the globe instead of staying inside the consumer products they are meant to protect. The fat-soluble chemicals have been discovered in a wide array of animals, as well as in plants, air, algae, and sediments from the North to the South Poles. However, perhaps the biggest concern is the rapidly rising PBDE levels found in people living in North America, which are currently 10–70 times higher than the levels of people in Japan or Europe (Environ. Sci. Technol. 2002, 36, 50A–52A). Although scientists still haven’t pinpointed exactly where those PBDEs are coming from, a study posted to ES&T’s Research ASAP website this week (es049260x) provides strong new evidence that indoor air can be a significant source of PBDEs in North American homes. Another recent study (es0490830) suggests that U.S. food is widely contaminated with PBDEs.

Brominated flame retardants are concerns because of their potential for liver toxicity, disruption of thyroid hormone levels, developmental neurotoxicity, and reproductive toxicity based on animal studies, says Ken Moss, a policy analyst for the U.S. EPA’s Office of Pollution Prevention and Toxics. Although EPA is actively collecting toxicology data, there’s not enough evidence to support regulatory action via the Toxic Substances Control Act, he says. “We can’t act on the precautionary principle at this point, as much as some of us would like to,” he adds. Arnold Schecter, a public health physician at the University of Texas Health Science Center in Dallas, deems the lack of published human health studies very disturbing.

The fact that products found in almost every North American home—including upholstered couches, chairs, curtains, carpet padding, and mattresses—contain high levels of brominated flame retardants is one of the reasons that scientists like Schecter are so concerned. All 74 of the randomly selected homes in Ottawa, Canada, tested in the new study had detectable levels of PBDEs, and the mix of individual PBDE compounds, or congeners, found was consistent with the recently discontinued Penta formulation.

“The Penta formulation is added to polyurethane foams at such high levels—5–30%, by weight—essentially, it’s like having the pure chemical just sitting there, volatilizing to the air, all over the house. The house becomes like an equilibration chamber,” says Tom Harner, a research scientist with Environment Canada, the country’s environmental protection agency.

Harner is the corresponding author of the new ES&T research into PBDE levels in indoor air, which is the most extensive study conducted on the topic to date. In the paper, he and colleagues at Lancaster University and Health Canada also calculate the maximum daily human exposure likely to result from breathing in PBDEs at the levels they recorded. The median levels found in the tested homes correspond to relatively low inhalation levels of 1.9 nanograms per day (ng/day) for females and 2.0 ng/day for males. “The differing levels of uptake are due to inhalatation rates being higher for men than women,” says Bryony Wilford of Lancaster University, a co-author on the study. However, the situation is very different for the most contaminated homes, which harbor PBDE levels that are an order of magnitude higher. The women living in the most highly contaminated homes could be inhaling up to 66 ng of PBDEs each day, while the men might be taking up 71 ng/day, according to the study.

PBDE researchers consistently report that 5–10% of the people they test have significantly higher PBDE levels in their fat or blood than the rest of the population (Environ. Sci. Technol. 2003, 37, 164A–165A). By documenting that the air in some homes has PBDE levels that are more than 10 times higher than the median levels, Harner and his colleagues say that their findings may help explain why. Harner’s data are important for providing an unbiased source of the range of PBDE levels found inside North America homes and the associated uptake levels, says Heather Stapleton of the National Institute of Standards and Technology in Gaithersburg, Md., another researcher who is trying to determine the source of these PBDEs.

The fact that household goods may be a major source of people’s exposure is one way that PBDEs are significantly different from most other POPs, Schecter says. For POPs such as PCBs and dioxins, food accounts for more than 95% of human exposure, he explains.

Schecter is the lead author of the food survey, which is the first published “market basket” survey of PBDEs in U.S. food. Schecter and his colleagues analyzed 32 samples of food from 3 major supermarket chains in Dallas, Texas. They selected foods mainly of animal origin likely to represent the dietary sources of PBDEs for the women who participated in an earlier study that found that the levels of PBDEs in U.S. women’s breast milk are 10–100 times higher than numbers reported anywhere else. The researchers also analyzed soy infant formula.

The researchers found that the PBDE levels in the tested foods varied widely, but the highest levels, on average, were in fish: up to 3.1 ng per gram of tissue (ng/g, wet weight), followed by meat (up to 1.4 ng/g), and dairy products (up to 0.68 ng/g). The results for the tested fish are similar to the levels recorded in a much larger study of PBDEs in wild and farmed salmon (Environ. Sci. Technol. 2004, 38, 360A–361A).

The PBDE levels for U.S. food are 9–20 times higher than those reported for food from Spain or Japan, where lower amounts of PBDEs are used in commercial products. Schecter’s report is also notable for showing that congeners associated with the Deca flame-retardant formulation are found in U.S. food. This formulation is added to the plastics used home electronics such as televisions and computers, and it is the most heavily used brominated flame retardant in the world. To date, the Deca formulation has not been discontinued or banned anywhere.

The Bromine Science and Environment Foundation (BSEF), an industry group, contends that the Deca formulation poses no threat to human health. The organization also maintains that the discontinued Penta and Octa formulations are not harmful. The benefits that all these chemicals provide far outweigh their risks, according to the organization’s website, which says “brominated flame retardants probably save more lives, by preventing and limiting fires, than most other chemical substances.”

In any case, “The levels in food really don’t account for the levels we’re seeing in people,” says Kim Hooper, who heads the Biomonitoring Group operated by the California EPA’s Hazardous Materials Laboratory in Berkeley, Calif. Instead, a growing number of researchers say that the Schecter and Harner reports confirm their suspicions that food and indoor air alone cannot fully account for human PBDE levels.

Harner says that he and his colleagues “expected the indoor air concentrations to be higher than what we found. The thing that limits the amount that builds up in the house is the ventilation system.” He adds that the results of the study are likely to apply across most of North America.

Home ventilation systems actually send the pollutants outside. “The indoors is polluting the outdoors, essentially. It’s kind of a twist,” Harner says. He is referring to another major difference between PBDEs and most other POPs: Contaminants such as dioxins and chlorinated pesticides like DDT are far more abundant in outdoor air. “Standard POPs are outdoor chemicals that come in,” Hooper adds.

Dust may prove to be the third major source of the PBDEs that people are taking up. Scientists have been reporting high levels of PBDEs in dust for some time (Environ. Sci. Technol. 2001, 35, 274A–275A), but a number of scientists interviewed for this story say persuasive evidence that dust plays a major role should soon be published. “The dust that we’re finding has pretty high levels of both the Penta and the Deca mixture,” Stapleton says, referring to data from unpublished studies.

While people of all ages may be taking up PBDEs from house dust, children under the age of 4 are disproportionately at risk because studies show that they tend to eat a lot more dust than older people. “I think that the children are of concern especially because of their developmental stages. They can get exposures from mother’s milk, from the air, and from the dust in the homes…. It’s just like the issues with lead in paint,” says Stapleton. Researchers have estimated that infants nursing on mother’s milk may be taking in up to 1700 ng/day of PBDEs, Stapleton says, characterizing this as “quite high”.

The presence of the PBDE congeners associated with the Deca formulation in house dust also raises questions about whether they could be the source of the lighter congeners that are more likely to volatilize into the air and be taken up by people. A growing number of published and unpublished studies are showing that Deca degrades fairly readily and breaks down in both sediments and sludge. Earlier this year, Gunilla Söderström of Sweden’s Umeå University published the strongest evidence yet that this breakdown can form some of the lighter PBDE congeners, including BDE-99, BDE-100, BDE-153, and BDE-154, being found in the environment—and in people (Environ. Sci. Technol. 2004, 38, 127–132).

Researchers have previously shown that carp and rats are able to break Deca down into smaller brominated compounds (Environ. Sci. Technol. 2004, 38, 8A–9A), but no one knows how many other animals can do this—or whether humans can.

However, emerging evidence presented at the Dioxin conference last week that people from The Netherlands, the Faroe Islands and Sweden have higher levels of BDE-153 than BDE-47—which has historically been the dominant congener in environmental samples collected from areas affected by general pollution—raises more new questions, says Åke Bergman of the environmental chemistry department at Sweden’s Stockholm University.

The BDE-153 congener is associated with the discontinued Penta and Octa formulations. The fact that people in parts of Europe have rising levels of BDE-153 is notable, because the levels of PBDEs in Swedish people’s blood have been decreasing since the use of brominated flame retardants was reduced in that country, Bergman explains.

The presence of the Deca in Schecter’s food study was a surprise, Schecter says. “It was present, and present in high amounts in some of our samples,” he says, noting that Deca could be a major contributor in some food supplies. “[The molecule] was previously thought to be too big to get into the cells of people and food,” he adds. “We definitely need to figure out how it’s getting into the food,” Stapleton says. However, the BSEF industry group says that the levels Schecter reported are “well within the levels identified as safe by national and international experts.”

But the biggest surprise was finding the Deca congener in the soy infant formula, Schecter stresses. He says that to the best of his knowledge, this is the first time that a POP has been found in a vegetable product. The Deca congener’s presence could be attributable to a route similar to the one by which dioxins enter cow’s milk through the grass on which the animals graze. Wilford suggests that another explanation for the presence of Deca BDE in infant soy milk may be because of contamination from processing or packaging materials.

Despite all the unanswered questions about PBDEs, researchers complain that U.S. funding has never been sufficient for this work and is growing scarcer. “Unlike dioxins and PCBs, which were funded very well… we’ve found it incredibly difficult to get funding for brominated flame retardants,” Schecter says. Hooper says that the brominated flame retardant industry has no incentive to fund work that could show that their products harm people, because such data could fuel lawsuits.

One area that is being funded is the search for alternatives. The EPA’s Design for the Environment program is working with the American Fire Safety Council and furniture manufacturers to develop environmentally preferable approaches for achieving fire-safety standards. In the meantime, regulatory agencies like EPA must carefully evaluate the substitutes the industry is proposing, which include other brominated substances as well as chlorinated compounds and non-halogenated phosphorous-based chemicals, says EPA’s Moss.

EPA’s efforts are particularly important because the U.S. Consumer Products Safety Commission is considering a new flame-retardant standard for residential upholstered furniture, which could lead to the use of more chemicals in furniture, Moss says. But he acknowledges that the contaminant could continue to be broadcast into the environment if countries where the Penta and Octa PBDEs have not been banned or discontinued, such as China and India, begin using the flame retardants in their products. —KELLYN BETTS