A new record for PBDEs in people
The newest data on polybrominated diphenyl ether (PBDE) flame retardants in U.S. residents, which was posted to ES&T’s Research ASAP website this week (es050399x), include the highest concentrations yet reported in humans. The data reveal some disturbing trends, experts agree.
Kurunthachalam Kannan of the New York State Department of Health and his colleagues collected data that set records on two fronts, says Linda Birnbaum, director of experimental toxicology for the U.S. EPA’s National Health and Environmental Effects Research Laboratory. The group of 52 people whose tissue Kannan collected and analyzed harbors the highest individual PBDE concentrations yet reported—9630 nanograms of PBDEs per gram of lipid fat (ng/g) in a 32-year-old man and 4060 ng/g in a 23-year-old woman. These levels are 4 to 9.5 times higher than any reported previously. Taken as a whole, the group also has the highest median (77.3 ng/g, which equals 77.3 parts per billion [ppb]) and mean (399 ppb) levels, she says. Learning that some people have PBDE levels this high was a “big shock,” Birnbaum says.
Scientists have known that people are taking up increasing concentrations of PBDEs for seven years, particularly in North America (Environ. Sci. Technol. 2001, 35, 274A–275A), but these data are higher than what extrapolating from previous trends would predict, Birnbaum says. Most PBDE researchers “are seeing levels between 4 and 400 ppb in [human] blood and milk,” explains Arnold Schecter, a public-health physician at the University of Texas Health Science Center in Dallas. He says that he has recently collected data from New York City men that show levels much lower than those Kannan’s team is reporting.
Although researchers have not seen human health effects associated with high PBDE body burdens, animal studies have shown that the chemicals can cause liver toxicity, disrupt thyroid hormone levels, and lead to developmental neurotoxicity and reproductive toxicity (Environ. Sci. Technol. 2004, 38, 386A–387A). The PBDE levels in the two people with exceedingly high concentrations in Kannan’s study are on a par with levels that have been shown to cause effects in animals in some of these studies, Birnbaum says. “There really is no margin [of safety] for some of these highly exposed people,” she says.
“The health effects that have been shown in animals have been a little bit subtle, so they might not be readily apparent in people,” says Schecter, who recommended that the people with very high levels be monitored. “There has been virtually no epidemiology done of people looking for effects of PBDE exposure,” adds Tom Webster, an environmental epidemiologist at the Boston University School of Public Health. Because most of what scientists do know points to infants and toddlers as the most vulnerable population, the fact that one of the people with the highest levels reported in Kannan’s study is a 23-year-old woman is “a concern,” he adds. There is a growing body of evidence showing that dust is a major source of exposure to people, especially children, in addition to food and indoor air.
More than half of the people in the study also had higher amounts of PBDEs than PCBs in their fat, a U.S. trend that many scientists have noted as both significant and troubling. The PBDE concentrations in the two people with the highest overall levels were more than 100 times higher than their PCB concentrations. The fact that PBDE concentrations in some individuals can rise so much higher than those of the majority of the population sets these flame retardants apart from most other persistent organic pollutants (POPs), Birnbaum says.
Even if the study’s two outliers are excluded—and Birnbaum stresses that there is no reason to believe they should be—the mean level for the remaining 50 people is 141 ppb. This is “strikingly high,” especially because the data from Kannan’s team do not include the larger and heavier PBDE compounds, or congeners, associated with the Deca formulation used in electronics products, Birnbaum explains.
Although two of the PBDE formulations that are known to result in human exposure, Penta and Octa, were banned in Europe last year and discontinued in the United States this year, the researchers interviewed for this article say that it will take years, perhaps even decades, for these actions to be reflected in decreasing human body burdens. This is partly because people tend to keep potential sources of the Penta and Octa formulations, such as furniture and mattresses, for extended periods. However, these products also may continue to contribute PBDEs to the environment at the end of their lifespans, says Myrto Petreas, an environmental scientist at the California EPA. Petreas says that she and her colleagues have been finding high levels of PBDEs in discarded electronics (e-waste) and auto shredder waste that may end up in landfills.
Most of the people in the new study had uptake patterns for individual PBDE compounds that match what researchers have come to expect. But 14% of the individuals in the study, including those with the highest overall PBDE levels, had elevated concentrations of brominated diphenyl ether–153 (BDE–153), according to Kannan and his colleagues. This is noteworthy because BDE–153 makes up only about 4% of the commercial Penta and Octa PBDE formulations. This pattern has previously been seen in electronics recycling workers and people from the Faroe Islands, who have been the subject of numerous studies because their traditional diet includes whale meat, which increases their uptake of POPs, says Åke Bergman of Stockholm University (Sweden), who has studied occupational exposures.
Kannan and his colleagues suggest that occupational exposure may account for some of the high BDE–153 levels, but the manuscript musters little evidence to support this contention. Petreas debates the hypothesis and suggests that environmental exposures are a better explanation. “BDE–153 is more persistent, in terms of its half-life, compared to the other PBDEs,” she explains. Petreas predicts that BDE–153 will ultimately become the dominant compound in North Americans and perhaps in people worldwide, just as PCB–153 became the dominant PCB compound worldwide because of its greater persistence. BDE–153 is currently bioaccumulating more than other PBDE congeners in top carnivores such as wild peregrine falcons (Environ. Sci. Technol. 2004, 38, 9A).
PCB–153 and BDE–153 are so very persistent because of the way that the chlorine and bromine are attached to the molecular backbone, Bergman explains. “The structure is making the compound less available for metabolism,” he adds.
In addition to the small amounts of BDE–153 found in the Penta and Octa formulations, Deca is a potential source of the compound, Bergman and Birnbaum agree. “The elevated levels of BDE–153, together with the unidentified PBDE compounds [discussed in the manuscript that do no originate from a known commercial formulation], are an indication of debromination,” Bergman says. Researchers have shown that fish can metabolically break down Deca, and other studies show that PBDEs in soil and sediment can be broken down by the environment (Environ. Sci. Technol. 2004, 38, 8A–9A), Birnbaum says. If it is proven to be the source of PBDEs that people take up, Deca—which is the most widely used flame retardant in the world—would risk becoming subject to regulation.
Kannan’s findings are similar to what other researchers have seen in North Americans: People’s PBDE levels—unlike those of other POPs like PCBs—do not correlate with their age. This points to other sources besides diet, says Petreas, who is also studying PBDE levels in people. “We all find these extremes. . . . 5–10% of the people are way higher than anyone else, and 1% is very high,” she says.
The research is noteworthy for using human adipose tissue, or stored fat, which Kannan and his colleagues argue is more representative than the samples of human blood or breast milk that are the basis of most of the reports of PBDEs in humans to date. “The levels of lipids in blood and breast milk can vary every day, depending upon what you eat,” Kannan says. However, Birnbaum, Schecter, and Petreas say that the use of the adipose tissue would not be expected to result in numbers substantially higher than those found in human blood and milk.
The tissue that Kannan and his colleagues analyzed was donated by David Rapaport, a New York City-based cosmetic surgeon who performs liposuction to remove people’s excess fat. The data broaden the information on PBDE levels in men, experts agree, because most of the human samples analyzed to date have been collected from women. Kannan and his colleagues say that they found no significant difference between the PBDE levels in the men and women.
Although the people who supplied the tissue cannot be considered representative of the U.S. population, especially since most of the donors resided in New York City, neither can most of the other data collected on PBDE levels in the country, Petreas points out. For that reason, researchers throughout the world are awaiting the data on PBDE levels in blood lipids that are being collected by the U.S. Centers for Disease Control and Prevention (CDC). However, the earliest that the PBDEs could be included in CDC’s National Report on Human Exposure to Environmental Chemicals is in 2007, according to an agency spokesperson.
Scientists disagree as to whether the levels of contaminants such as PBDEs would be lower or higher in liposuction patients than in the general public. “We know that the higher [the] amount of body fat a person has, the longer the apparent half-life,” Birnbaum says.
“If we see these concentrations diluted in a lot of lipids, we may actually see people with less fat having higher concentrations than presented here,” Bergman says. Dieting—which patients who resort to liposuction might presumably try before spending thousands of dollars to have their fat surgically vacuumed away—has been shown to increase the concentrations of fat-soluble contaminants, Webster says.
