Flame-Proofing the Arctic?

Research published in ES&T today shows that the polybrominated diphenyl ether (PBDE) chemicals used as flame retardants in consumer products appear to be contaminating pristine sections of the Arctic more quickly than either PCBs or dioxins did.

Over the last two decades the concentrations of PBDE flame retardants taken up by Arctic ringed seals, the chief prey of polar bears, have increased exponentially.

PBDEs are accumulating in the Arctic ringed seal at an unprecedented rate, according to Michael Ikonomou, a research scientist at Canada’s Institute of Ocean Sciences and the lead author of the paper published today. Ikonomou and a group of researchers from Fisheries and Oceans Canada, a government agency, analyzed archived tissue samples taken from Arctic ringed seals caught during Inuit subsistence hunts on Holman Island in the Canadian Arctic between 1981 and 2000 for PBDEs, dioxins, furans, and PCBs. The oldest samples were taken just a few years after PBDEs began to be used widely in both North America and Europe, says Marcia Hardy, senior toxicology advisor to Albemarle Corp., a manufacturer of flame retardants.

PBDEs appear to be traveling more quickly to the Arctic than PCBs or dioxins, according to the first temporal analysis of brominated flame retardant levels in Arctic animals. If current PBDE usage rates continue, researchers predict that the levels of PBDEs in the Arctic will surpass those of PCBs by 2050. Source: Environ Sci. Technol. 2002; doi# es011401x

The samples show that the concentrations of PBDEs in the ringed seals, which are the most common seals in the Arctic and the main prey of polar bears, have been doubling every 4-5 years, Ikonomou says. The finding is particularly notable because, while PBDE levels have been increasing exponentially over the past two decades, the levels of dioxins, furans, and PCBs in Arctic animals have been stable or declining, he says. PCBs have been banned for years, and regulations governing dioxin and furan emissions have tightened in recent years, he explains.

This is the first peer-reviewed research showing PBDE accumulation in animals living above the Arctic circle, Ikonomou says. Other studies have reported high levels of PBDEs in fish in Virginia rivers and Great Lakes fish, and scientists have presented data at a research conference showing exponential rates of accumulation of PBDEs in beluga whales further south in the St. Lawrence Seaway.

BDE-47 predominates
Ikonomou’s team also looked at PBDEs in crabs, sole, and marine mammals from the coastal waters of British Columbia and found that all of the animal samples they tested had significantly elevated levels of one specific PBDE molecule, or congener, BDE-47. Although BDE-47 has only four bromine atoms, it is commonly found in the commercial Penta formulation (which is not pure, but, as its name implies, mainly contains BDEs with five bromine atoms) used with polyurethane foam in North America (232KB PDF). All nine of the congeners found in Ikonomou’s samples are actually from the Penta formulation, Hardy says.

Because the European Union has banned the Penta formulation, it is now used primarily in North America, particularly in the United States, which has some of the world’s most stringent fire-safety requirements.

The Penta congeners are most likely to get into the environment because they are added to polyurethane foam padding material used in products like seat cushions, which tend to crumble with age, Hardy says. Because the foam has an open-cell structure that air or water can move into, so there is more surface area that can be exposed, allowing the Penta fire retardant embedded in the foam to escape into the environment, she says.

Testing of the commercial PBDE mixtures shows them to have low aquatic toxicity, but they are suspected to be endocrine disrupters. A new study also shows that developmental exposure to PBDEs can perturb thyroid function.

Pattern matching
Some researchers suspect that more testing may be in order because the patterns of congeners in the mixtures that have been tested don’t match with the occurrence of congeners found in wildlife. “The data really suggest that the Penta source is North America, [but] what we’re finding in the environment doesn’t look like commercial products,” explains Linda Birnbaum, director of the Experimental Toxicology division at the U.S. EPA’s National Health and Environmental Effects Research Laboratory. “It’s really interesting that BDE-47 is the most common congener they’re finding out there in wildlife and in people, and BDE-47 is not the major congener in any of the commercial products. The BDE-99 is much more prevalent than BDE-47, even in the Penta formulation, and its levels are, in some of these samples, very low compared to BDE-47.”

Hardy counters that the testing done to date predicts these results. BDE-47 typically makes up about 70% of the “total PBDEs” detected in biological specimens collected in the environment, she says. “If you look at a fish bioconcentration study done using the Penta, you’ll find that the [BDE-47 does] bioaccumulate extensively. That’s probably related to its uptake and how it’s handled by the body,” she explains. The main reason that BDE-99 does not bioconcentrate as readily as BDE-47 is because BDE-99 is slightly less water-soluble, she says. Additionally, she says, metabolism studies in rats and mice show that BDE-47 is excreted very slowly.

The BDE-47 congener’s light weight helps explain its abundance in the Arctic environment, Ikonomous says. because “The atmosphere is distilling the most volatile congeners among those present in the commercial flame retardant mixtures,” he explains, noting that the situation in the Arctic is particularly complicated because PBDEs from both North America and Europe are transported there.

Although all of these factors help explain why the uptake of the PBDE congeners does not match what researchers would expect to be in the environment, Ikonomou says the evidence nonetheless points to some process that removes bromine atoms. The compounds may be metabolized as they go through the food chain, or they may break down via photolytic degradation in the presence of light, according to Ikonomou’s paper, which discusses some potential debromination pathways.

Debromination conundrum
“We believe that some of the BDE-47 may come from higher brominated compounds present in commercial mixtures such as the Penta, Octa, and Deca” Ikonomou says, stressing that he does not yet have enough evidence to support the hypothesis. But he says he intends to observe the deposition patterns in the Arctic over the next five years because the Arctic is the final resting place for PBDEs from both Europe and North America. If BDE-47 remains the predominant congener in the Arctic, even though Europeans have dramatically scaled back use of the compound, it will certainly strengthen the case for debromination, he says.

Hardy says that it is far-fetched to speculate that the Deca product is degrading to lower-brominated congeners, although she did not address the issue of whether Penta or Octa congeners may degrade. To evaluate Deca’s potential for debromination, the Brominated Flame Retardants Industry Panel (BFRIP), an industry group, has conducted studies of anaerobic sediment biodegradation and photolytic degradation, Hardy says. Neither BFRIP nor Swedish researchers have found evidence of anaerobic biodegradation of the Deca product in sediments, she says, but she acknowledged that Deca will photodegrade into lower PBDE congeners in an organic solvent. “However, we don’t typically see that combination of events in the environment,” she says. “If we look at [Deca’s] potential to degrade into lower BDEs in a more environmentally realistic matrix, we don’t find good evidence for that.” Hardy adds that the levels of the PBDEs observed to date are too low to be cause for concern.

Researchers are nonetheless continuing to investigate whether photolytic degradation can debrominate PBDE molecules, according to Birnbaum, Ikonomou, and Bergman. If evidence of debromination comes to light, it should force the industry to begin testing to find whether there are health effects from the patterns of congeners found in the environment, in addition to the commercial formulations that have been tested to date, Birnbaum says.

“As stuff goes through the environment and through biotic systems, we are definitely getting changes,” Birnbaum explains. “We need to look at the effects of the chemicals that we’re actually being exposed to... . The real question, it seems to me, is what are the potential health effects from the chemicals we’re finding in wildlife as well as people, and at what doses?” Because PBDEs are usually found in combination with dioxins and PCBs and together these compounds may act synergistically (or antagonistically), Ikonomou says that the compounds should be evaluated as mixtures.

The toxicology studies conducted to date show that the Octa mixture includes developmental toxicity in rats and that the no-observable-effect level for Penta is 1 milligram/kilogram (mg/kg), according to a recent article by Hardy.

Ikonomou and other scientists interviewed for this article nonetheless argue that there is a pressing need for more toxicology data on PBDE compounds. Chris Metcalfe at Trent University and Nigel Bunce of University of Guelph, both in Canada, and Abraham Brouwer of the Institute for Environmental Studies in the Netherlands are among the few researchers investigating PBDE toxicology, Ikonomou says.

Bergman argues that scientists already have enough evidence. “Bioaccumulation and persistency is really enough. You do not need a lot of toxicological data. We do have some toxicological data that indicate the PBDEs are as toxic as PCBs. They will cause a problem sooner or later; sooner, if we let the levels increase,” he says. In that sense, what North America does affects the entire world, he adds.

If PBDEs continue to be used at the same levels currently found in North America, Ikonomou predicts that they will surpass PCBs as the most prevalent organohalogen compound in the Arctic environment by 2050. Hardy declined to comment on that prediction, but she acknowledges that the industry is keeping its options open by investigating new flame retardants that can play the same role as the Penta formulation with polyurethane foam. “Polyurethane foam needs to be flame retarded,” she says. —KELLYN S. BETTS