New research challenges assumptions about popular flame retardant

This week, the main U.S. manufacturer of two widely used flame retardants announced that it was going to discontinue their use as part of a voluntary agreement with the U.S. EPA. The agreement was “based on potential concerns associated with the continued use of the chemicals,” according to a joint statement. However, a paper published in ES&T this week provides the first definitive evidence that a third popular brominated flame retardant could be the source of some of the persistent, bioaccumulative, and potentially toxic chemicals in the environment that are associated with the discontinuation of the other two retardants.

The EPA agreement with the Great Lakes Chemical Corp. of West Lafayette, Ind., covered two widely used polybrominated diphenyl ether (PBDE) flame retardants known as the Penta and Octa formulations. The research posted to ES&T’s ASAP website this week deals with the Deca flame retardant, which is the most widely used PBDE flame retardant in the world.

Until quite recently, most researchers believed that—unlike their long-embattled cousins the Penta and Octa—the Deca PBDE chemicals added to consumer products to increase their safety posed relatively little risk to the environment. But the new ES&T research is just part of a growing body of data showing that Deca can be both toxic and persistent. Some researchers contend that the weight of evidence is now tipping the scales.

“It’s time for people to agree that Deca is not totally inert…that it can be taken up and that it can be broken down,” says Linda Birnbaum, director of the Experimental Toxicology Division of EPA’s National Health and Environmental Effects Research Laboratory.

The evidence comes from a number of fronts. The ES&T research by Heather Stapleton and Joel Baker of the University of Maryland’s (UMD) Center for Environmental Science and their colleagues provides persuasive evidence that fish exposed to Deca can metabolize it into the lighter brominated compounds associated with the Penta and Octa flame retardant formulations, which have also been banned in Europe. Deca could also be breaking down into substances that are much more toxic, including hydroxylated compounds or fully debrominated diphenyl ethers, Stapleton and Baker say.

Deca can cause developmental neurotoxic effects, too, according to research published in Toxocological Sciences (DOI 10.1093/toxsci/kfg210). Researchers from Stockholm University and Uppsala University (both in Sweden) exposed neonatal mice to bromodiphenyl ether (BDE) 209, the main compound in the Deca formulation, on their third day of life. Those mice exhibit altered behavioral patterns that worsen with age, they say. The researchers have reported similar altered behaviors in mice exposed to BDE-99, a compound in the Penta flame retardant formulation.

This paper is the first to show that Deca can have these effects, Birnbaum says. “It surprises us. But they did have to dose the animals on day three; the reason is because it took time for the chemicals to migrate,” she says. The researchers suggest that the effects they observed from BDE-209 could be the result of a metabolite, because they mirror developmental disturbances usually seen when the mice were dosed with PCBs or BDE-99 on day 10. Birnbaum notes that the data shown in the paper might appear even stronger if the statistics were compiled in a different way. “Clearly, we’d like to see the results repeated,” she adds.

The new research points to “somewhat of a different paradigm,” according to Baker. While concerns about accumulation of PCBs and dioxins are based on the chemicals themselves, the metabolites are the issue with BDE-209, he says.

Researchers are also finding more evidence of Deca in the environment, says Mark La Guardia of the Virginia Institute of Marine Sciences (VIMS). La Guardia will be presenting research at the Society of Toxicology and Environmental Chemistry meeting next week showing that minnows in a Virginia stream are taking up BDE-209.

The stream contained 50 parts per billion (ppb) of Deca, which La Guardia says he believes are the highest numbers yet reported. “This value surpasses the water solubility of 209 and likely reflects association with particulates,” says Rob Hale, La Guardia’s research adviser at VIMS.

The Deca flame retardant formulation is used in electrical and electronic equipment, as well as automotive equipment, construction materials, and textiles. In 2001, 56,100 metric tons of Deca were used, making it the second most heavily used brominated flame retardant in the world, according to the Bromine Science and Environmental Forum (BSEF).

All of the PBDE flame retardant formulations take their names from the number of bromine atoms in their major constituents. Deca has 10, although the commercial Deca formulation also contains compounds of different sizes; the same is also the case with the Penta and Octa formulations. In addition to being very large, the Deca molecules are extremely hydrophobic.

“The significance of this work from a fate and transport perspective is that Deca-BDE is itself quite involatile and less prone to atmospheric transport. However, the lighter congeners are more readily transported—we see them in the Arctic,” says Tom Harner, a research scientist for Environment Canada, the country’s environmental protection agency.

In effect, Stapleton and Baker’s work shows that Deca can be transformed into a persistent compound, says Åke Bergman of Stockholm University in Sweden, who coauthored a paper showing that Swedish recycling workers take up BDE-209 but that their levels drop rapidly during their vacations. Bergman likens Deca to DDT, which is readily transformed into a more persistent compound (4, 4' DDE) in the environment.

Not surprisingly, the BSEF views the findings a bit differently. The research “seems to counter the contention that Deca debrominates in fish to form BDE-47 (tetrabromo diphenyl ether) or BDE-99 (pentabromo diphenyl ether), the major species typically found in fish. Also, the findings are favorable in that the research seems to clearly support our extensive research demonstrating that Deca is not well absorbed and, with certainty, does not show signs of bioaccumulating,” according to a statement from the organization.

Stapleton and Baker used a BDE-209 standard from Cambridge Isotope Laboratories to overcome the issues raised by the Swedish researchers who first reported that a fish (in that case, a rainbow trout) was metabolically debrominating the Deca molecules by exposing the fish to the commercial Deca formulation. Amelie Kierkegaard and her colleagues at Stockholm University’s Institute of Applied Environmental Research could not rule out the impurities in that commercial mixture as the source of the lighter brominated compounds they reported.

The UMD researchers exposed their fish to the BDE-209 standard for 60 days and then fed them clean food for 40 days. Although the researchers found no BDE-209 in the fish during either the exposure or the subsequent “depuration” periods, they detected peaks associated with lower-brominated compounds. They used a cool on-column injection gas chromatography coupled with an electron capture detector—a technique they had devised to overcome known problems posed by gas chromatography with mass spectrometry.

The fact that the lower-brominated compounds were detected after the Deca was no longer being fed to the fish indicates that the fish were metabolically debrominating the Deca. The compounds found in the experimental group of fish, but not the control group, include BDE-154 and BDE-155, which are associated with both the Octa and Penta formulations. The researchers also identified compounds that were homologues of the Penta-, Hexa-, Hepta-, and Oocta-brominated molecules.

Stapleton and Baker found that the levels of a few of the debrominated molecules, particularly the Penta homologue, continued to increase after the fish were no longer exposed to the Deca in their food. Mehran Alaee, a paper coauthor from Environment Canada and a principal investigator for a study of PBDEs in the Canadian environment, confirmed the findings by gas chromatography combined with high-resolution mass spectrometry.

“We were just looking for PBDEs. It’s possible that other compounds could be formed in the carp that we can’t measure based on our extraction methods in the lab,” Stapleton stresses.

Stapleton even back-calculated to prove that the brominated compounds must have come from the deca. She showed that the levels they found were above the detection limits for the food fed to the fish, Alaee says.

Scientists have long suspected that the brominated flame retardants were undergoing some kind of metabolic transformation, because the amounts found in human and animal tissues do not match the percentages in the commercial formulations. “Some of the PBDE congeners were missing if you looked for them,” Baker explains. “That clues you in that there might be some metabolism going on.”

For example, the harbor seals in San Francisco Bay have a lot of BDE-153 and 154, Birnbaum says. “There’s a little bit of 153 and 154 in the commercial Penta mix, but not very much. So are [these congeners] coming from Octa, or are they coming from Deca breakdown?” she asks.

“In nature, opportunities for uptake of Deca may be limited due to its extremely low water solubility and large molecular volume. However, clearly [La Guardia’s] work and some of that examining 209 burdens in humans show that this opportunity does, in some cases, exist,” Hale points out. Carp appear to be particularly good at debrominating the PBDEs, he says, noting that the fish with the highest levels of PBDEs recorded to date, which was discovered by VIMS researchers, is also a carp. But he says it is extremely unlikely that carp are the only fish able to do it.

Researchers have a wealth of evidence that Deca is breaking down in other species and perhaps in the environment, Birnbaum says. “We have data demonstrating that Deca can be broken down in mammals,” she says. A Stockholm University metabolism study on Deca showed that rats transform the compound to Nona-BDEs and hydroxylated metabolites, Bergman points out.

“There’s lots of evidence from lab studies that UV light leads to rapid degradation, albiet in organic vehicles,” Birnbaum continues. “The Swedes [also] have some evidence that there may be some breakdown in sediments or sludge,” she says. Additional evidence that Deca is bioavailable comes from Arnold Schecter, who detected the compound in human milk for the first time (Environ. Health Perspect. 2003, 111, 1723–1729).

Stapleton and Baker say that they are planning to try to look for other, non-PBDE breakdown products, including hydroxylated compounds, in the next studies they conduct. —KELLYN S. BETTS