Scientists are perplexed by how quickly PBDEs are bioaccumulating in the frozen north.
K E L LY N S . B E T T S
FlameProofing the
A rctic?
T
he polybrominated diphenyl ether (PBDE) chemicals that
are used as flame retardants in consumer products appear to be contaminating pristine sections of the Arctic more
quickly than either polychlorinated biphenyls (PCBs) or dioxins, according to an article published in the research section of this issue (1). Other recent ES&T research provides insight into the mechanism that
allows the PBDEs to take such a quick trip to the Arctic (2) and reveals
BRYAN AND CHERRY ALEXANDER PHOTOGRAPHY
that some young children have significantly higher levels of PBDEs in their blood than older people (3). Åke Bergman, professor of chemistry at Sweden’s Stockholm University and one of the world’s foremost PBDE researchers, calls the new ES&T papers a “really important” part of an avalanche of data on PBDEs now entering the research literature.
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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 in polyurethane foam in North America (5). All nine of the congeners found in Ikonomou’s samples are known to be contained in the Penta formulation, Hardy says. In fact, because Penta is the only one of the three PBDE commercial flame retardant formulations (Penta, Octa, and Deca) containing congeners that tend to persist and bioaccumulate in the environment, Hardy objects to the use of the general term PBDEs to describe the chemicals of concern, although this practice has been established in the scientific literature. Hardy acknowledges that Penta is indeed composed of PBDEs, but she argues that the general use of the term PBDEs in the scientific literature to discuss effects associated with Penta unfairly stigmatizes the other two formulations. The Deca formulation represents 80% of the worldwide volume of PBDE-based flame retardants and tends to be very stable, she stresses. Because the European Union has banned the Penta formulation (6), it is now used primarily in North America, particularly in the United States, Rising PBDE levels which has some of the world’s most stringent firesafety requirements. 6000 10 Levels in Arctic ringed seals The Penta congeners are most likely to get into the Levels in human milk (Sweden) environment because they are added to polyurethane 8 Worldwide penta-BDE production foam padding material used in products like seat 4000 cushions, which tend to crumble with age (7 ), Hardy 6 says. Because the foam has an open-cell structure that air or water can move into, there is more surface 4 area that can be exposed, which allows the Penta fire 2000 retardant embedded in the foam to escape into the 2 environment, she says. Testing of the commercial PBDE mixtures shows 0 0 them to have low aquatic toxicity, but they are sus1980 1990 2000 pected to be endocrine disrupters. A new study also that developmental exposure to PBDEs can PBDEs appear to be traveling more quickly shows to the Arctic perturb thyroid function (8). than PCBs or dioxins, according to the first temporal analysis of brominated flame retardant levels in Arctic Pattern matching animals. If current PBDE usage rates continue, researchers Some researchers suspect that more testing may be predict that the levels of PBDEs in the Arctic will surpass in order because the patterns of congeners in the mixthose of PCBs by 2050. tures that have been tested don’t match with the ocSource: Environ. Sci. Technol. 2002, 36, 1886–1982. currence of congeners found in wildlife. “The data really suggest that the Penta source is North America, This is the first peer-reviewed research showing [but] what we’re finding in the environment doesn’t PBDE accumulation in animals living above the Arctic look like commercial products,” explains Linda Circle, Ikonomou says. Other studies have reported Birnbaum, director of the Experimental Toxicology high levels of PBDEs in fish in Virginia rivers (4) and division at the U.S. EPA’s National Health and Great Lakes fish, and scientists have presented data Environmental Effects Research Laboratory. “It’s reat a research conference showing exponential rates of ally interesting that BDE-47 is the most common conaccumulation of PBDEs in beluga whales further gener they’re finding out there in wildlife and in south in the St. Lawrence Seaway. people, and BDE-47 is not the major congener in any of the commercial products. The BDE-99 is much BDE-47 predominates more prevalent than BDE-47, even in the Penta forIkonomou’s team also looked at PBDEs in crabs, sole, mulation, and its levels are, in some of these samand marine mammals from the coastal waters of ples, very low compared to BDE-47.” British Columbia and found that all of the animal Hardy counters that the testing done to date prepg/g
PBDEs are accumulating in Arctic ringed seals 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 adviser to Albemarle Corp., a manufacturer of flame retardants. 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.
dicts 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, Ikonomou says. “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 in the Arctic may come from [the] 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 (9). 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.
High levels in children The new ES&T research showing that infants and children under the age of four in Norway have levels of PBDEs in their blood that are 1.6−3.5 times higher than older people is yet another reason for concern about PBDEs, Bergman argues. The research, which was conducted by researchers from the University of Oslo and Norway’s National Institute of Public Health, “is showing dramatic increases over time,” Birnbaum says. “The fact that young children are the ones with the highest levels, several times that of adults is very important…. It’s further documentation of the dramatic increases in MAY 1, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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[PBDEs] in another human population (10),” she says. That said, Bergman notes that the levels in Norway are very low compared to what is being seen in the United States. However, because the United States is not following the precautionary principle that guides decision making about chemicals in the European Union, more dataincluding toxicological datawill probably be necessary to persuade North American legislators to take action on PBDEs. To collect the data that will be used to determine whether the compounds represent a problem, North American scientists are following a different approach than the one pioneered by their European colleagues, Ikonomou says. Instead of focusing on three or four different congeners, the North American scientists have been taking a more holistic approach by evaluating all detectable PBDEs, he explains, noting that some Europeans are now beginning to follow suit. This holistic approach “will allow us to look at patterns in a more detailed way and try to understand the transport mechanisms and fate of these compounds in the environment,” he says. It will also allow us to evaluate the overall toxicity of these compounds, as some of the congeners found in low concentrations may prove to be more potent than the congeners found in higher concentrations, as is the case with PCBs, he adds. Although exactly how the PBDEs are being transported up to the Arctic is not yet clear, Ikonomou says he expects that PBDEs are governed by a mechanism similar to one that sends pesticides to the far north, which has been documented in previous research by scientists from Fisheries and Oceans Canada (11), although the vapor pressure and solubility of PBDEs and pesticides differ somewhat.
The grasshopper effect Further insight into the mechanism by which the PBDEs may be traveling to the Arctic comes from new ES&T research by scientists at Trent University in Canada and Lancaster University in the United Kingdom. Conducted by a group led by Todd Gouin and Doug Mackay of Trent University’s Canadian Environmental Modelling Centre, the research reports “surprisingly” high levels of PBDEs in air samplesthe total PBDE concentrations reached 1250 picograms/cubic meter (pg/m3), a level more than double the total concentration of PCBstaken from a rural site in southern Ontario. Their analysis shows that the PBDEs, like PCBs, tend to oscillate back and forth between being airborne and adhering to surfaces such as vegetation, a mode of atmospheric transport known as the “grasshopper” effect that tends to move chemicals efficiently and rapidly. The researchers believe they observed an “early spring pulse” transporting the PBDEs and PCBs from the surface into the atmosphere as it warmed. Gouin and Mackay’s findings are in accord with yet more new research into the physical and chemical properties of PBDEs as a function of temperature (12), says Tom Harner, a research scientist with Environment Canada, a governmental organization. “Our findings show that PBDEs are special in that most of 192 A
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the dominant congeners (BDE-47, BDE-99, BDE-100, BDE-153, etc.) exist in two states in the atmospheresplit between the gas phase and partitioned onto aerosols. The temperature dependence of this particle−gas partitioning is such that at warmer temperatures, the partitioning favors the gas-phase (more transportable) and at colder temperatures, it favors partitioning onto aerosols (i.e., deposition).” However, Harner says it is still unclear why this transport occurs more efficiently for PBDEs than for PCBs, dioxins, or furans, all of which have similar partitioning behavior to the PBDEs. He says the Gouin paper should lead to “some interesting debate however and ultimately more process-related research to investigate the role of surface–air interactions and ground cover type on ambient concentrations and atmospheric transport of PBDEs.” In any case, it is clear that PBDEs are making it up to Arctic and moving up the food chain in record time, Ikonomou says. 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.
References (1) Ikonomou, M.; Rayne; S.; Addison, R. Exponential increases of brominated flame retardants, polybrominated diphenyl ethers, in the Canadian Arctic from 1981 to 2000. Environ. Sci. Technol. 2002, 36, 1886–1892. (2) Gouin, T., Thomas, G. O.; Cousins, I.; Barber, J.; Mackay, D.; Jones, K. C. Air−surface exchange of polybrominated diphenyl ethers and polychlorinated biphenyls. Environ. Sci. Technol. 2002, 36, 1426–1434. (3) Thomsen, C.; Lundanes, E.; Becher, G. Brominated flame retardants in archived serum samples from Norway: A study on temporal trends and the role of age. Environ. Sci. Technol. 2002, 36, 1414–1418. (4) Renner, R. Flame retardant levels in Virginia fish are among the highest found. Environ. Sci. Technol. 2000, 34, 163A. (5) Polybrominated diphenyl ethers—Environmental contaminants of concern. The Standard 1999, 4, 2. (6) Renner, R. At odds over PBDEs. Environ. Sci. Technol. 2002, 36, 11A. (7) Betts, K. Mounting concern over brominated flame retardants Environ. Sci. Technol. 2001, 35, 274A–275A. (8) Zhou, T.; Taylor, M.; DeVito, M.J.; Crofton, K. M. Developmental exposure to brominated diphenyl ethers results in thyroid hormone disruption. Toxicological Sciences 2002, 66, 105−116. (9) Hardy, M. L. The toxicology of the three commercial polybrominated flame retardants. Chemosphere 2002, 46, 757−777. (10) Betts, K. Rapidly rising PBDE levels in North America. Environ. Sci. Technol. 2002, 36, 50A−52A. (11) Macdonald, R. W.; Bewers, J. M. Contaminants in the arctic marine environment: Priorities for protection. Ices J. Mar. Sci. 1996, 53, 537−563. (12) Harner, T.; Shoeib, M. Measurements of Octanol–air partition coefficients (KOA) for polybrominated diphenyl ethers (PBDEs): Predicting partitioning in the environment. J. Chem. Eng. Data 2002, 47, 228−232.
