Potential explanation for fluorinated compounds’ persistence

The first assessment of the atmospheric lifetime of an important class of fluorinated chemicals, fluorotelomer alcohols (FTOHs), indicates that they persist for 20 days before breaking down, according to a team of scientists from the Ford Motor Co. and the University of Toronto. In research posted to ES&T’s Research ASAP Web site this week (DOI: 10.1021/es034136j ), the group concludes that FTOHs merit further study as a potential source of the persistent, bioaccumulative, and potentially toxic perfluorocarboxylic acids (PFCAs) that are being discovered worldwide.

“By most international [regulatory] conventions, 20 days is a long time in the troposphere,” explains Scott Mabury, chair of the University of Toronto’s chemistry department, a paper co-author who is well known for his research into PFCAs such as perfluorooctanoic acid (PFOA), which is used in Teflon and causes reproductive toxicity in rats. “In the Canadian context, if it lasts longer than 2 days, you have to call it persistent,” he adds, stressing that FTOH lasts long enough in the atmosphere to be transported to remote locations. Mabury is leading a team looking for the FTOH in the Arctic, but the data is still being processed.

FTOHs are under increasing scrutiny because of their suspected connection with PFOA. The U.S. EPA is already pursuing enforceable consent agreements with telomer manufacturers through the Telomer Research Program, an industry group that represents the major FTOH producers, which include AGA Chemicals, Inc., Clariant GmbH, Daikin America, Inc., and E. I. du Pont de Nemours & Co. EPA “has identified potential human health concerns from exposure to perfluorooctanoic acid (PFOA) and its salts, although there remains considerable scientific uncertainty regarding potential risks,” according to a Federal Register notice published on April 14, 2003.

The Telomer Research Program estimates that 5 million kilograms of FTOHs are used annually as intermediates in a wide variety of products, including paints, coatings, polymers, adhesives, waxes, polishes, metals, electronics, and caulks. However, Mabury indicates this figure may not represent the total quantity of FTOH-based material in current use.

Scientists had previously estimated the lifetime of FTOHs on the basis of structure–activity relationships, but such estimates can be off by up to a factor of 5 and are therefore not good enough, given current concerns about them, says Tim Wallington, an atmospheric chemist at Ford Motor Co.’s Scientific Research Laboratories and the ES&T paper’s lead author.

Because of PFCA’s chemical characteristics, some activists have taken to comparing the group of perfluorochemicals (PFCs) of which they are part to polychlorinated biphenyls, dubbing them the “PCBs of the 21st century.” “We think that the whole family of perfluorinated compounds [is] highly toxic, and we think the science more than justifies phasing out the telomers,” says Kris Thayer, senior scientist at the Environmental Working Group (EWG), an environmental nonprofit association that has researched PFCs extensively.

While Mabury doesn’t necessarily agree with all of EWG’s contentions, he says that the FTOHs last longer than some PCB compounds. However, other PCBs persist for far longer, up to 45 days, he says.

“This work was driven by a desire to understand where the PFCAs identified in the environment have been coming from…they’ve been identified all over the place, and particularly interestingly, at remote locations, places way up in the Canadian north Arctic,” Wallington says. Because the molecules are fairly large, with a molecular weight between 350 and 550 atomic mass units, it is surprising that they persist for so long in the atmosphere, Mabury adds.

“We don’t know a lot about the environmental fate of larger fluorinated organic compounds,” Mabury says. “They’re relatively persistent because the carbon–fluorine bond is so stable. And when you polyfluorinate something, it tends to be far more volatile on a mass basis than a heavy molecule that doesn’t have fluorine.” Thayer says the fact that PFOA is found in rainwater in remote locations hints that it is an atmospheric breakdown product of some as-yet unidentified precursor, perhaps FTOH.

The experiments described in the paper were conducted at Ford’s research laboratories, where the scientists studied how the atmospheric gas phase of three generic FTOH molecules, F(CF₂CF₂)₂CH₂CH₂OH, F(CF₂CF₂)₃CH₂CH₂OH, and F(CF₂CF₂)₄CH₂CH₂OH, reacted when exposed to chlorine atoms and OH radicals. They used a smog chamber to simulate atmospheric conditions and analyzed their results with a Fourier transform infrared (FTIR) spectrometer. The experiments showed that, as is the case with other PFCAs, the “fluorinated tail” of the FTOH molecules makes them less susceptible to attack by both OH radicals and chlorine atoms than other compounds, according to the authors.

Wallington says that the new paper indicates that FTOHs survive in the atmosphere long enough to reach the remote locations where PFCAs are being found. For example, PFOA has been discovered at the Sand Island Wildlife Refuge in Midway Atoll in the middle of the Pacific Ocean.

Wallington and Mabury are currently conducting experiments to determine how the FTOHs behave in the environment. They are focusing on both abiotic and biological factors that could degrade the chemicals. “There is some literature to suggest that FTOH will biologically oxidize to perfluorinated acids in rats,” Mabury says. “It is clear that at least some FTOHs break down,” Thayer adds, noting that DuPont has shown that telomer 82 degrades to PFOA.

Mabury is also involved in an effort to monitor the atmospheric concentrations of a number of fluorinated compounds. His group is waiting to see if the levels of the compounds plummet in response to 3M’s retraction of their PFOS product (Environ. Sci. Technol. 2000, 34, 371A). If the levels don’t drop as expected, it suggests that these materials are slowly being evolved and released from consumer products, he explains.

The undertaking is challenging because “the vast majority [80%] of the FTOHs…are incorporated into polymeric materials, and we have no data on whether those polymeric materials break down, and if so, under what conditions or how fast,” Mabury says. “We hypothesize that the polymers are degrading because people often have to reapply their coatings, on carpets, for example. That seems to suggest that they don’t last forever,” he continues, stressing that he and his fellow researchers are testing these hypotheses.
It’s too early for companies like Ford to consider removing FTOHs from use in their products or supply chains, Wallington says. “Clearly, we need to understand the environmental impacts of our products and processes, and that’s what we’re trying our best to do,” he adds. “If we have a complete understanding of what these compounds do in the atmosphere and why they do it, we can perhaps make suggestions as to how one might alter the structure of these compounds such that they would be more environmentally friendly. That’s the goal.” —KELLYN S. BETTS