Clean and Green; January 2006; Scientific American Magazine; by Rebecca Renner; 2 Page(s)
Stain repellents confer easy-to-clean convenience to carpets and clothing thanks to substances called fluorosurfactants. Yet this benefit comes at a price: the processes used to make these surfactants--which are also used to improve paints and polishes--generate chemicals that have become pervasive in the environment. Of particular concern is perfluorooctanoic acid (PFOA), one of the most common fluorosurfactant breakdown products. Last July the science advisory board of the Environmental Protection Agency recommended that the EPA classify it as a "likely" human carcinogen. Canada has already banned some compounds that have the potential to break down to PFOA in the environment. Chemists, however, are now changing the structure of fluorosurfactants so that they do the job but are safer and do not accumulate in the environment.
Fluorosurfactants basically consist of chains of carbon atoms surrounded by fluorine. Long rigid chains work best because they get many carbon-fluorine molecules to the surface, where they can do their jobs, and keep a large part of the chain embedded in a substrate. In stain repellents (the more demanding application), they pack tightly together so that their tips form an invisible protective armor. But chain length is also at the root of the environmental problem. Long-chain fluorosurfactants, based on a lineup of eight carbon atoms (C8), enter the body more readily than shorter analogues, and they can break down to form PFOA. PFOA and other related long-chain fluorochemicals stick to blood proteins and masquerade as digestive acids. Consequently, they are difficult to eliminate, says environmental toxicologist Jonathan Martin of the University of Alberta in Edmonton.