Manufacturing leftovers may help explain the puzzling presence of perfluorinated compounds
Chemicals left over from the manufacture of stain repellents and other products could be a major source of the perfluorinated compounds detected in humans and in the environment.
Chemicals left over from the manufacturing of stain repellents and other products could be a major source of the perfluorinated compounds present in people and in the environment, according to a new study published today (10.1021/es051619+).
University of Toronto chemists Mary Joyce Dinglasan-Panlilio and Scott Mabury are publishing the first systematic evaluation of the loose, unbound fluorinated alcohols in seven materials, including industrial paint and polish additives, consumer carpet-protector sprays, and windshield washer fluid. The perfluorinated compounds are residuals, unwanted chemicals left over from the manufacturing processes by which fluorinated alcohols are incorporated into and used to create the fluorinated surfactants and polymers that are active ingredients in these consumer and industrial products. The residuals are found in the commercial and industrial products because the processes used to synthesize the surfactants and polymers do not always incorporate all of the fluorinated alcohols. However, these unbound residuals remain associated with the active ingredients.
PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate), the most common perfluorinated chemicals, have been detected at low levels in human blood samples worldwide. These chemicals are even found in the remote Arctic, far from any possible sources. This is a puzzle for environmental scientists and government regulators. As a percentage of total annual production, the concentrations of residual fluorinated alcohols reported in this new paper (0.04–4%) would yield annual fluorinated alcohol emissions at atmospheric concentrations that have been measured, the authors say.
“Because [PFOS, PFOA, and similar] compounds are not directly used as commercial or industrial products, the question has always been, ‘Where do they come from?’” explains Dinglasan-Panlilio. “This is the first systematic study that directly identifies a point source for [the fluorinated chemicals that we believe are] precursor compounds,” she adds.
Mabury, Ford Motor Co. chemist Tim Wallington, and their colleagues had previously theorized that these volatile alcohols were the precursors to chemicals such as PFOS and PFOA. However, until now there were only data on industrial emissions of fluorotelomer alcohols. The new analyses are the first in the peer-reviewed literature to indicate that products themselves, not just manufacturing or application processes, are sources.
“We call perfluorinated chemicals ‘domestic persistent organic pollutants’ because we think that there are many sources in the home, although they have not been identified,” says Environment Canada research scientist Tom Harner. “It is good to see that more attention is being given to the question of sources and emissions of perfluorinated compounds,” he adds. Other scientists contacted for this story echoed his views.
Fluorinated alcohols include fluorotelomer alcohols, which are volatile chainlike compounds made up of primarily carbon, fluorine, and hydrogen atoms. Two numbers are often used to denote fluorotelomer alcohols: the number of carbons bonded to fluorine, and the number of carbons bonded to hydrogen. So, C8F17CH2CH2OH is 8:2 FTOH, or 8:2 fluorotelomer alcohol.
The residuals in the industrial coating additives and the windshield washer fluid that the Toronto scientists analyzed were dominated by 6:2 fluorotelomer alcohol. In contrast, residuals in the spray-on carpet-protector products were dominated by longer-chain alcohols. “These different signatures might eventually provide a way to track sources,” says Harner.
To measure the unbound fluorinated alcohols, Dinglasan-Panlilio dispersed the fluorinated material in water. This process forced the volatile alcohols into the air, where they were trapped for analysis via gas chromatography combined with mass spectrometry. Most of the unbound fluorinated alcohols escaped from the products in about 2 days. The industrial coating additives had the highest percentage of residuals; those of spray-on carpet protectors and windshield washer fluid were lower (see figure). The scientists report the concentrations as percentages of fluorinated alcohol to dry mass of the material.
The authors note that according to industry estimates, 11–14 million kilograms (kg) of telomer alcohols are produced annually. If unbound residuals constituted just a few percent of this amount, their emissions would be at least 100,000 kg annually.
“Based on our data, it appears that residuals are a significant source,” says Dinglasan-Panlilio. “Hence, removing them would make a significant impact on the environment,” she adds. However, Harner and other experts caution that these assumptions are uncertain and that further data are necessary to determine whether telomer alcohol residuals indeed account for the amount that Dinglasan-Panlilio estimates.
According to chemical engineers familiar with fluorochemical polymers and other plastics, it is likely to be feasible, but perhaps expensive, to remove these residuals. In February 2005, U.S. fluorotelomer polymer manufacturer DuPont pledged that it would remove residuals from its products by February 2006. The Environmental Protection Agency on Wednesday (January 25) asked DuPont and seven other chemical companies with operations in the US to work to eliminate residuals in their products. DuPont immediately accepted EPA’s challenge.
