Burning your bacon may have more serious consequences than a spoilt breakfast, suggests Canadian research on chemicals used in non-stick frying-pans. Heat breaks this and similar compounds down to persistent and potentially toxic chemicals whose long-term environmental effects are unknown1.

Replacement gases for ozone-eating chlorofluorocarbons (CFCs) bring their own problems: they degrade in the atmosphere to trifluoracetic acid (TFA), which lingers in the environment. But levels of TFA in rainwater are far higher than these fluorine-based coolants can account for.

Scott Mabury and his University of Toronto team point the finger at 'fluoropolymers', like Teflon and its chemical cousins. Increasingly used in high-temperature applications - ovens, cookware and engines - these 'fluoropolymers' are a likely source of TFA.

At high temperatures the compounds give off TFA, the team confirm. They heated commercial products - such as motor oil, frying-pans and surgical needles - and pure polymers to 360-500°C, similar temperatures to those used to burn domestic waste. They then analysed the products.

Degrading fluoropolymers are a major source of TFA in Toronto rainwater, the team suggests, using modelling to predict environmental levels. Being highly unreactive, TFA loiters almost indefinitely in soil and water.

"We're using compounds that persist in the environment for very long periods of time," says Mabury. "The issue for society is: is this something we need to deal with?"

Some experts think not. Although TFA might be mildly noxious to plants, a 1999 risk assessment found no threat to humans and the environment, says Archie McCulloch, an environmental consultant in Northwich, England, who worked on the assessment.

Intriguingly, the oceans hold huge amounts of TFA, points out McCulloch, for which modern sources cannot be blamed. The large accumulation suggests a pre-industrial origin. "All in all, burning frying-pans in Toronto may add to the environmental burden of TFA but it's hardly significant," says McCulloch.

The discovery that the CFC replacements hydrochlorofluorocarbons and hydrofluorocarbons degrade into TFA prompted initial concern. Unlike CFCs, which slowly attack ozone in the high stratosphere, these fluorocarbons break down rapidly in the lower troposphere.

Besides TFA, fluoropolymer degradation releases other possible toxins, including long-chain perfluorocarboxylates, Mabury's team also found. One major source of such chemicals, waterproofing materials such as Scotchguard, were pulled off the market last year by their manufacturer 3M, based on evidence that they build up in human tissues. Again, long-term effects are unknown.

If CFCs taught us anything, it's to be careful about what we assume to be benign: "Any replacement is a potential pollutant," says Alan Brisdon, who studies such compounds at the University of Manchester, England. But he is cautious about incriminating fluoropolymers: "Compared to what's already in the atmosphere it probably has a negligible effect."