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Piecing together the perfluorinated puzzle Researchers have found persistent fluorochemicals in unexpected places, but how they got there and where they came from remain elusive.
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he world was caught off-guard in the spring of 2000, when St. Paul, Minn.based 3M Corp. announced that it would phase out Scotchgard and its flourishing $300 million fluorochemical business after researchers had unexpectedly discovered a persistent fluorochemical in the blood of humans and animals in pristine areas far away from any apparent source. The compound they found was perfluorooctane sulfonate, or PFOS, a breakdown product of other 3M fluorochemicals. PFOS turned out to be so ubiquitous that 3M even found it in the unadulterated chow fed to lab rats. But how this nonvolatile compound was traveling the world and where it was coming from were mysteries. The mystery actually dates back to 1976, when University of Rochester physician Donald Taves made an unexpected discovery while he was investigating water fluoridation. Using NMR spectroscopy, he identified organic fluorine in a sample of his own blood and speculated that “widespread contamination of human tissues with trace amounts of organic fluorocompounds derived from commercial products” could occur. The mystery remained dormant until the late 1990s, when improved analytical methods, such as LC/MS/MS, furnished the necessary tools for 3M and others to go out and find Taves’s “organic fluorocompounds” and identify them.
A new kind of POP The PFOS discovery shed light on a new kind of persistent organic pollutant (POP), © 2005 AMERICAN CHEMICAL SOCIETY
according to University of Michigan toxicologist John Giesy, who, along with Kannan Kurunthachalam, first found PFOS in hundreds of animal samples. Before the discovery of PFOS, research on POPs focused principally on chlorinated compounds, even though other halogenated compounds, including fluorinated compounds, had been found to be persistent and bioaccumulative in the environment. Because most perfluorinated compounds are incorporated into polymers, scientists and regulators assumed they would not travel in the environment and accumulate in living organisms. But this assumption has proved false: Scientists continue to find PFOS and other perfluorinated chemicals practically everywhere they look. After 3M’s voluntary ban on PFOS products, attention turned to another family of currently manufactured compounds with similar uses—the perfluorocarboxylates. Perfluorooctanoic acid (PFOA) is the best-known chemical in this group because it is used to make Teflon, which is found in many common items, including nonstick frying pans, utensils, stove hoods, stainproofed carpets, furniture, and clothes. The U.S. Environmental Protection Agency (EPA) is investigating the health effects of PFOA, and a risk assessment is due out soon. PFOA, although not as abundant or widespread as PFOS, has turned up in the blood of 96% of children tested in 23 U.S. states, river otters in Oregon, and polar bears in the Canadian Arctic.
Follow the volatiles University of Toronto chemist Scott Mabury has a theory for how perfluorochemicals, in particular the perfluorocarboxylates, have become ubiquitous in the environment. Atmospheric degradation of the fluorotelomer alcohols, volatile precursors to the perfluorocarboxylates that are used to protect carpets and fabrics from stains, can explain the presence of long-chain perfluorocarboxylic acids, including PFOA in Arctic animals. In a series of papers published in the journal Environmental Science & Technology over the past two years, Mabury and his colleagues have reported data supporting each hypothesis in this theory. University of Toronto chemist Naomi Stock and colleagues in the Mabury group found point sources of fluorotelomer alcohols in their survey of air collected from six U.S. and Canadian cities in November 2001, before the 3M phaseout. Sulfonamides, which are PFOS precursors, and PFOA-precursor telomer alcohols were found at all sampling locations. Levels were highest in urban areas, particularly in Griffin, Ga., a center for carpet manufacturing. This led Stock to conclude that factories associated with the carpet industry are a source of the volatile precursors found in the atmosphere. In collaboration with Ford Motor Co., chemist Tim Wallington and colleagues in Mabury’s group have conducted smogchamber experiments to determine the atmospheric lifetime of the telomer alcohols and to see whether their atmospheric degradation could result in the formation
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of perfluorocarboxylates. Their smogchamber results, described in a paper by Ellis et al. (Environ. Sci. Technol. 2003, 37, 3816–3820), determined that telomer alcohols could persist in the atmosphere for ~20 days, long enough to undergo long-range transport. Smog-chamber experiments have also shown that such degradation can occur in remote locations such as the Arctic, where the concentration of nitrogen oxides (NOx) is low. This happens because reactions with OH in the atmosphere set off a cascade of reactions in which the perfluorinated molecule “unzips” by sequential elimination of carbonyl fluoride units. This cascade is well known and does not directly produce long-chain perfluorocarboxylates. But intermediates generated in each unzipping cycle may undergo reactions with peroxy radicals to yield the corresponding perfluorocarboxylate acids. These reactions can only occur in air with low levels of NOx, because higher levels in urban areas facilitate the unzipping of the chain. This means that telomer alcohols are unlikely to degrade to carboxylic acids in city air. But in remote areas such as the Arctic or over the open ocean, concentrations of peroxy radicals are high enough to turn telomer alcohols into carboxylic acids.
Send in the polar bears The scientists also believe they can differentiate between the now abandoned manufacturing process of 3M and the telomer process used by current manufacturers. To do this they had to find a way to measure the isomer profiles of perfluorinated chemicals in polar-bear livers. Polar bears are sentinel species impacted by chemicals able to undergo long-range transport, because they are at the top of the Arctic food chain and their livers contain the highest levels of these compounds. 3M is the only known major manufacturer to have used an electrochemical fluorination process that produces both branched and straight-chain isomers. All of the other major known manufacturers—DuPont (U.S.), Adolfina (France), Clariant (Germany), Asihi Glass (Japan), and Daikin (Japan)—use the telomerization process, which makes fluorochemicals by reacting tetrafluoroethylene with other 16 A
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The answer lies inside. Isomers of perfluorinated compounds in polar-bear livers can differentiate between industrial sources.
fluorine-bearing chemicals. The process yields only straight-chain products. Amila DeSilva and Mabury developed a method to identify the isomer profiles of perfluorocarboxylates in environmental samples and applied it to livers of polar bears from the Canadian Arctic and Greenland. Although LC/MS/MS is typically used for perfluorocarboxylate determination, they developed a GC-based method because it has greater potential for resolving the isomers and is less susceptible to contamination. Although subtle differences existed between samples from the two locations, most were dominated by the linear isoforms. This points to a telomer process as the principal source of the long-chain carboxylate in the northern polar region (Environ. Sci. Technol. 2004, doi 10.1021/es049296p). The Mabury theory is gaining acceptance. “It’s not a question of if this happens. Now it’s a question of how much,” says Mabury. Wallington, along with the Mabury group and others, is currently using models, source estimates, and other data to determine whether this theory can explain the quantities of perfluorinated chemicals in the Arctic and in the blood of people who live in remote areas.
Closer to home Other investigators are finding evidence of dispersed sources closer to home. The levels of some of the volatile precursors to PFOS inside homes are ~100 higher than outdoor levels, according to mea-
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surements made in a limited number of buildings (four houses and two labs) by Environment Canada chemist Mahiba Shoeib and colleagues. They speculate that the precursors are residual compounds that haven’t been incorporated into the polymer and/or compounds released from degradation of the polymer. The researchers haven’t looked for telomer alcohols yet. Perfluorinated compounds are also getting into wastewater, according to Oregon State University chemist Melissa Schultz, in Jennifer Field’s group. In an extensive survey of U.S. wastewater treatment plants, Schulz has found perfluorinated compounds in influents and effluents. Concentrations are sometimes higher in the effluent; this suggests possible formation during treatment. Because filtration removes many perfluorinated compounds, Field’s group adopted a simple sample preparation method. They centrifuge the sample and draw off the liquid. Then they use a high-volume sample loop to, in effect, concentrate the sample. “This way, you let the autosampler act as a concentration step, and the machine does the work,” says Field. Despite the 2000 withdrawal, Scotchgard is back on the market after reformulation to what the company and EPA say is a more environmentally benign fluorine-based chemistry. 3M accomplished this, in part, by reducing the length of the carbon–fluorine chain so that the new compound does not bioaccumulate. Mabury, for one, believes that this approach may hold promise for perfluorinated surface treatments in general. “Instead of banning these chemicals, we should use what we know about their chemistry and occurrence to solve the problem,” he says. Because there’s evidence that surface-treatment residuals are a source of perfluorinated compounds in the home and the environment, manufacturers should figure out a way to remove these residuals. They should also follow 3M’s lead and consider shorter-chain-length chemistry, and they should look for ways to strengthen the polymer linkages so that degradation doesn’t release them, he says. a —Rebecca Renner
