Environment's stuck with nonstick coatings

Jessica Gorman

The family of nonstick materials that includes Teflon can degrade into pollutants that persist in the environment, new research suggests.

Known as fluoropolymers, these coatings get their tough and slippery traits from fluorine atoms strongly bonded to the materials' carbon backbones. Manufacturers use the materials in products ranging from frying pans and other kitchen items to engines and electrical insulation.

Scott A. Mabury of the University of Toronto and his colleagues heated a variety of fluoropolymers to 360°C and 500°C. In both cases, a version of nuclear magnetic resonance analysis tuned to detect fluorine showed that the materials broke down into several undesirable products. One of these, called trifluoroacetate (TFA), is toxic to plants, and there's no evidence that it degrades in the environment. Environmental concentrations are low now but could eventually build to troublesome levels, say the researchers.

Other breakdown products included long-lasting fluorine- and chlorine-rich carboxylic acids, which might have negative health and environmental effects because animal tissues absorb them, Mabury's group reports in the July 19 Nature. Moreover, Mabury says the team was surprised to find ozone-depleting chlorofluorocarbons (CFCs) and greenhouse gases known as fluorocarbons coming from the heated materials.

The researchers discovered the chemical cocktail while trying to solve a riddle, says Mabury. Several years ago, scientists realized that gases known as hydrochlorofluorocarbons and hydrofluorocarbons, which have replaced ozone-destroying CFCs in many products, break down in the atmosphere to form TFA. However, the amount of TFA measured in the environment is much higher than this process could supply.

Using environmental models depicting TFA's diffusion into Toronto rainwater, Mabury's group found evidence that the widespread heating of fluoropolymers could produce the missing TFA. Among the sources for such heat are engines and open burning of household trash, Mabury notes.

This is "a plausible explanation for the observed amounts of [TFA] in rainwater around and downwind of urban areas," comments Tim Wallington, an atmospheric chemist with the Ford Motor Co. in Dearborn, Mich. Even so, he says, the benefits of such coatings currently outweigh their risks.

Mabury agrees. "I'm not getting rid of my frying pans," he says.

Still, since TFA sticks around for so long, researchers ought to keep an eye on it, adds Thomas M. Cahill of Trent University in Peterborough, Ontario. "In order to do that, we need to know how the stuff is getting into the environment," he says. On that score, he says, Mabury and his colleagues have "plugged a fairly significant hole [in our knowledge base]."

"It fills a nice little gap, but it's not a big gap that it fills," comments Hartmut Frank of the University of Bayreuth in Germany. Significant sources of TFA in the environment, particularly in the oceans, are still missing, he says.

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References:

Ellis, D.A., S.A. Mabury, et al. 2001. Thermolysis of fluoropolymers as a potential source of halogenated organic acids in the environment. Nature 412(July 19):321.

Further Readings:

Berg, M., et al. 2000. Concentrations and mass fluxes of chloroacetic acid in rain and natural waters in Switzerland. Environemtnal Science & Technology 34:2675.

Cahill, T.M., et al. 2001. Accumulation of trifluoroacetate in seasonal wetlands in California. Environmental Science & Technology 35:820.

Cahill, T.M., and J.N. Sieber. 2000. Regional distribution oof trifluoroacetate in surface waters downwind of urban areas in Northern California, U.S.A. Environmental Science & Technology 34:2909.

Jordan, A., and H. Frank. 1999. Trifluoroacetate in the environment. Evidence for sources other than HFC/HCFCs. Environmental Science & Technology 33:522.

Wujcik, C.E., T.M. Cahill, and J.N. Seiber. 1999. Determination of trifluoroacetic acid in 1996–1997 precipitation and surface waters in California and Nevada. Environmental Science & Technology 33:1747.

Sources:

Thomas A. Cahill
Canadian Environmental Modelling Centre
Trent University
1600 West Bank Drive
Peterborough, ON K9J 7B8
Canada

Hartmut Frank
Environmental Chemistry and Ecotoxicology
University of Bayreuth
D-95440 Bayreuth
Germany

Scott A. Mabury
Department of Chemistry
80 St. George Street
University of Toronto
Toronto, ON M5S 3H6
Canada

Tim Wallington
Ford Motor Company
20000 Rotunda Drive
Mail Drop SRL-3083
Dearborn, MI 48121-2053

From Science News, Volume 160, No. 3, July 21, 2001, p. 36.