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The world was caught off-guard in thespring of 2000, when St. Paul, Minn.-

based 3M Corp. announced that it wouldphase out Scotchgard and its flourishing$300 million fluorochemical business afterresearchers had unexpectedly discovered apersistent fluorochemical in the blood ofhumans and animals in pristine areas faraway from any apparent source.

The compound they found was per-fluorooctane sulfonate, or PFOS, a break-down product of other 3M fluorochemi-cals. PFOS turned out to be so ubiquitousthat 3M even found it in the unadulterat-ed chow fed to lab rats. But how thisnonvolatile compound was traveling theworld and where it was coming fromwere mysteries.

The mystery actually dates back to1976, when University of Rochesterphysician Donald Taves made an unex-pected discovery while he was investigat-ing water fluoridation. Using NMR spec-troscopy, he identified organic fluorine ina sample of his own blood and speculatedthat “widespread contamination of humantissues with trace amounts of organic fluo-rocompounds derived from commercialproducts” could occur. The mystery re-mained dormant until the late 1990s,when improved analytical methods, suchas LC/MS/MS, furnished the necessarytools for 3M and others to go out andfind Taves’s “organic fluorocompounds”and identify them.

A new kind of POPThe PFOS discovery shed light on a newkind of persistent organic pollutant (POP),

according to University of Michigan tox-icologist John Giesy, who, along withKannan Kurunthachalam, first foundPFOS in hundreds of animal samples.Before the discovery of PFOS, researchon POPs focused principally on chlori-nated compounds, even though otherhalogenated compounds, including fluo-rinated compounds, had been found tobe persistent and bioaccumulative inthe environment. Because most perfluo-rinated compounds are incorporatedinto polymers, scientists and regulatorsassumed they would not travel in theenvironment and accumulate in livingorganisms.

But this assumption has proved false:Scientists continue to find PFOS andother perfluorinated chemicals practi-cally everywhere they look. After 3M’svoluntary ban on PFOS products, at-tention turned to another family of cur-rently manufactured compounds withsimilar uses—the perfluorocarboxylates.Perfluorooctanoic acid (PFOA) is thebest-known chemical in this group be-cause it is used to make Teflon, whichis found in many common items, in-cluding nonstick frying pans, utensils,stove hoods, stainproofed carpets, fur-niture, and clothes. The U.S. Environ-mental Protection Agency (EPA) is in-vestigating the health effects of PFOA,and a risk assessment is due out soon.PFOA, although not as abundant orwidespread as PFOS, has turned up inthe blood of 96% of children tested in23 U.S. states, river otters in Oregon,and polar bears in the Canadian Arctic.

Follow the volatilesUniversity of Toronto chemist ScottMabury has a theory for how perfluoro-chemicals, in particular the perfluorocar-boxylates, have become ubiquitous in theenvironment. Atmospheric degradationof the fluorotelomer alcohols, volatileprecursors to the perfluorocarboxylatesthat are used to protect carpets and fab-rics from stains, can explain the presenceof long-chain perfluorocarboxylic acids,including PFOA in Arctic animals. In aseries of papers published in the journalEnvironmental Science & Technology overthe past two years, Mabury and his col-leagues have reported data supportingeach hypothesis in this theory.

University of Toronto chemist NaomiStock and colleagues in the Mabury groupfound point sources of fluorotelomer alco-hols in their survey of air collected fromsix U.S. and Canadian cities in November2001, before the 3M phaseout. Sulfon-amides, which are PFOS precursors, andPFOA-precursor telomer alcohols werefound at all sampling locations. Levelswere highest in urban areas, particularlyin Griffin, Ga., a center for carpet manu-facturing. This led Stock to conclude thatfactories associated with the carpet indus-try are a source of the volatile precursorsfound in the atmosphere.

In collaboration with Ford Motor Co.,chemist Tim Wallington and colleagues inMabury’s group have conducted smog-chamber experiments to determine the at-mospheric lifetime of the telomer alcoholsand to see whether their atmosphericdegradation could result in the formation

Piecing together the perfluorinated puzzleResearchers have found persistent fluorochemicalsin unexpected places, but how they got there andwhere they came from remain elusive.

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of perfluorocarboxylates. Their smog-chamber results, described in a paper byEllis et al. (Environ. Sci. Technol. 2003,37, 3816–3820), determined that telomeralcohols could persist in the atmospherefor ~20 days, long enough to undergolong-range transport. Smog-chamberexperiments have also shown that suchdegradation can occur in remote locationssuch as the Arctic, where the concentra-tion of nitrogen oxides (NOx) is low.

This happens because reactions withOH in the atmosphere set off a cascadeof reactions in which the perfluorinatedmolecule “unzips” by sequential elimina-tion of carbonyl fluoride units. This cas-cade is well known and does not directlyproduce long-chain perfluorocarboxyl-ates. But intermediates generated in eachunzipping cycle may undergo reactionswith peroxy radicals to yield the corre-sponding perfluorocarboxylate acids.

These reactions can only occur in airwith low levels of NOx, because higherlevels in urban areas facilitate the unzip-ping of the chain. This means that telo-mer alcohols are unlikely to degrade tocarboxylic acids in city air. But in re-mote areas such as the Arctic or over theopen ocean, concentrations of peroxyradicals are high enough to turn telomeralcohols into carboxylic acids.

Send in the polar bearsThe scientists also believe they can differ-entiate between the now abandoned man-ufacturing process of 3M and the telomerprocess used by current manufacturers.To do this they had to find a way to mea-sure the isomer profiles of perfluorinatedchemicals in polar-bear livers. Polar bearsare sentinel species impacted by chemicalsable to undergo long-range transport,because they are at the top of the Arcticfood chain and their livers contain thehighest levels of these compounds.

3M is the only known major manufac-turer to have used an electrochemicalfluorination process that produces bothbranched and straight-chain isomers. Allof the other major known manufactur-ers—DuPont (U.S.), Adolfina (France),Clariant (Germany), Asihi Glass (Japan),and Daikin (Japan)—use the telomeriza-tion process, which makes fluorochemicalsby reacting tetrafluoroethylene with other

fluorine-bearing chemicals. The processyields only straight-chain products.

Amila DeSilva and Mabury developeda method to identify the isomer profilesof perfluorocarboxylates in environmen-tal samples and applied it to livers ofpolar bears from the Canadian Arcticand Greenland. Although LC/MS/MS istypically used for perfluorocarboxylate de-termination, they developed a GC-basedmethod because it has greater potentialfor resolving the isomers and is less sus-ceptible to contamination. Although sub-tle differences existed between samplesfrom the two locations, most were domi-nated by the linear isoforms. This pointsto a telomer process as the principalsource of the long-chain carboxylate inthe northern polar region (Environ. Sci.Technol. 2004, doi 10.1021/es049296p).

The Mabury theory is gaining accept-ance. “It’s not a question of if this hap-pens. Now it’s a question of how much,”says Mabury. Wallington, along with theMabury group and others, is currentlyusing models, source estimates, and otherdata to determine whether this theory canexplain the quantities of perfluorinatedchemicals in the Arctic and in the bloodof people who live in remote areas.

Closer to homeOther investigators are finding evidenceof dispersed sources closer to home. Thelevels of some of the volatile precursorsto PFOS inside homes are ~100� higherthan outdoor levels, according to mea-

surements made in a limited number ofbuildings (four houses and two labs) byEnvironment Canada chemist MahibaShoeib and colleagues. They speculatethat the precursors are residual com-pounds that haven’t been incorporatedinto the polymer and/or compoundsreleased from degradation of the poly-mer. The researchers haven’t looked fortelomer alcohols yet.

Perfluorinated compounds are also get-ting into wastewater, according to OregonState University chemist Melissa Schultz,in Jennifer Field’s group. In an exten-sive survey of U.S. wastewater treatmentplants, Schulz has found perfluorinatedcompounds in influents and effluents.Concentrations are sometimes higher inthe effluent; this suggests possible forma-tion during treatment. Because filtrationremoves many perfluorinated compounds,Field’s group adopted a simple samplepreparation method. They centrifuge thesample and draw off the liquid. Then theyuse a high-volume sample loop to, in ef-fect, concentrate the sample. “This way,you let the autosampler act as a concen-tration step, and the machine does thework,” says Field.

Despite the 2000 withdrawal, Scotch-gard is back on the market after refor-mulation to what the company and EPAsay is a more environmentally benignfluorine-based chemistry. 3M accom-plished this, in part, by reducing thelength of the carbon–fluorine chainso that the new compound does notbioaccumulate. Mabury, for one, be-lieves that this approach may hold prom-ise for perfluorinated surface treatmentsin general. “Instead of banning thesechemicals, we should use what we knowabout their chemistry and occurrenceto solve the problem,” he says. Becausethere’s evidence that surface-treatmentresiduals are a source of perfluorinatedcompounds in the home and the envi-ronment, manufacturers should figureout a way to remove these residuals.They should also follow 3M’s lead andconsider shorter-chain-length chem-istry, and they should look for ways tostrengthen the polymer linkages so thatdegradation doesn’t release them, hesays. a

—Rebecca Renner

The answer lies inside. Isomers of perfluori-nated compounds in polar-bear livers candifferentiate between industrial sources.

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