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Polar bears and their fellow Arctic top predators accumulate perfluorooctanoic acid (PFOA) and other perfluorochemicals that industry uses in consumer products such as non-stick pans, stain repellants, and fast-food wrappers. Scientists have two theories for how the persistent pollutants make their way from industrialized countries to the bears’ isolated habitat. Now an analytical technique that can detect different perfluorochemical isomers might help resolve this debate (Environ. Sci. Technol., DOI: 10.1021/es102582x).
The debate boils down to a matter of timing, manufacturing method, and transportation route (Environ. Sci. Technol., 2007, 41, 4497). The legacy oceanic theory holds that the perfluorochemicals in the Arctic originated from a now-defunct manufacturing process by 3M. The company abandoned it 10 years ago after scientists raised concerns about perfluorochemicals' persistence and toxicity. According to the legacy theory these pollutants settled into the ocean, migrated via currents to high latitudes, and now linger in Arctic waters.
The current use atmospheric theory holds that the most significant source is fluorotelomer alcohols (FTOHs), the volatile precursors of chemicals currently used to coat commercial products. FTOHs escape into the atmosphere from factories or consumer products and travel by wind currents to the Arctic, where they break down to PFOA and other perfluorochemicals, and then adsorb into the ocean.
Fortunately, the two routes to PFOA and other perfluorochemicals leave behind different chemical signatures. 3M's old manufacturing process produced a specific ratio of branched to linear PFOA isomers. Meanwhile, the process used by fluorotelomer alcohol manufacturers, including DuPont, leads to only linear PFOA isomers.
So environmental chemists Jonathan Martin and Jonathan Benskin of the University of Alberta and colleagues in Japan and China developed a technique using liquid chromatography and tandem mass spectrometry to isolate the two types of isomers and measure their levels. By comparing current isomer profiles to the historic profile created by the 3M process, the scientists can calculate the relative contributions from the two manufacturing processes.
To test their technique, the researchers analyzed samples from rivers, canals, and oceans near manufacturing regions in North America, Asia, and Europe and estimated that more than 80% of the PFOA in these waters came from the legacy process. The result was what the researchers had expected, Benskin says: "The branched isomer discharges into the water were high in these areas and this legacy signature helped us to validate the method."
The scientists have now turned their attention to Arctic waters. Ocean samples will provide better clues to resolve the perfluorochemical debate than will samples from animals, Benskin says, because previous studies have shown that biological processes can change isomer ratios.
"Isomer profiling will be a useful way to look at perfluorochemical sources," says environmental chemist Scott Mabury of the University of Toronto. But he cautions that physical processes, such as how the chemicals interact with sediments, also could alter the isomer ratios from their original state.
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