The Shrinking Case For Fluorochemicals

Chemical & Engineering News

Stephen K. Ritter

This year marks the end of a program launched by the Environmental Protection Agency to eliminate the production and use of one of the chemical industry’s most important classes of compounds: perfluorooctanoic acid (PFOA), along with its precursors and analogs.

The program, launched in 2006, was prompted by years of pressure by environmental and consumer groups and regulatory scrutiny of the safety of the long-alkyl-chain fluorocarbons, which are used to treat the surfaces of metals, paper, carpet, and fabrics to impart water-, soil-, and oil-repellent properties. They are also used to make abrasion-, chemical-, and fire-resistant polymers and are found in products as diverse as nonstick cookware, grease-wicking pizza boxes, airplane hydraulic fluid, stain-resistant carpet, and breathable rain jackets.

Unfortunately, the properties that make the compounds so useful also make them persistent in the environment. The chemicals and their degradation products are now found in places ranging from pristine areas of the Arctic to sludge in municipal wastewater treatment plants. Low levels of the compounds have contaminated nearly every corner of the food chain, from herring to humans.

Research has shown that the compounds can cause cancer and disrupt sexual development in lab animals. Still-emerging epidemiological evidence suggests the compounds might cause or contribute to similar problems in people, prompting scientists to conclude that the risk of continuing to use the compounds is too great.

The industry is voluntarily doing away with the long-chain compounds and replacing them with short-chain analogs that are still persistent but that are much less bioaccumulative and therefore expected to be less toxic. Even so, now that the long-chain compounds are making their exit, some scientists and advocacy groups are issuing calls for the short-chain compounds to be discontinued. There remains disagreement, however, about whether the replacement compounds are safer than their predecessors.

Long-chain fluoroalkyl chemistry had its beginning more than 60 years ago. 3M’s Scotchgard brand of stain-protection products made with perfluoroalkyl sulfonamidoethanols was one of the first to hit the market. This family of compounds is identified by perfluorooctanesulfonic acid (PFOS), which is a sulfonamidoethanol degradation product.

PFOA was another of the early products. Its ammonium salt is used in small amounts as a surfactant to help solubilize fluorinated monomers during emulsion polymerization, which is used to make plastics such as DuPont’s Teflon brand of poly(tetrafluoroethylene). PFOA and related carboxylic acids are also degradation products of fluorotelomer alcohols, which are tetrafluoroethylene-based compounds used to attach fluoroalkyl groups to surfactants, polymers, and material surfaces.

Chemists attribute PFOS and PFOA’s armorlike properties to the eight carbons in their fluoroalkyl chains. Such chains have the rigidity and steric properties needed to optimize water and oil repellency.

When it became clear in the 1990s that PFOS was accumulating in people and might cause health problems, 3M accepted a deal with EPA to voluntarily terminate production of PFOS-related products. The firm unveiled a new version of Scotchgard, reformulated with shorter chain perfluorobutane-based chemistry.

Scientists had discovered a tipping point: Compounds with six or fewer fluorinated carbon atoms work nearly as well as the longer chain versions. However, their bioaccumulation potential is significantly reduced because shorter, less rigid chains boost their water solubility.

Federal government data show that PFOS and PFOA concentrations have been dropping in the blood of the general population. But even as the fluorochemicals industry is doing away with the long-chain compounds, some scientists and environmental groups are calling for the short-chain replacements to be gone, too.

Developing nonfluorinated alternatives is a tough nut to crack because of the fluorochemicals’ broad range of uses—replacements are easy in some applications, but not in others. For example, in textiles that require only water repellency, polyether/polyester fabrics work well. The fluorochemicals industry has been doing great to clean up its chemistry and by introducing the short-chain alternatives that are less bioaccumulative and are clearly better for reducing exposure to people and the environment.