For the first time, a group of perfluorochemicals used on food wrappers has been identified in human blood at low part-per-billion concentrations. The chemicals, known as polyfluoroalkyl phosphoric acid diesters (diPAPs), also were found at concentrations about 100 times higher in sewage sludge. These findings, published in ES&T (DOI 10.1021/es900100d) by chemistry graduate student Jessica D’eon at the University of Toronto and colleagues, provide new clues about people’s exposure to perfluorochemicals but further complicate investigations into the fate and transport of these compounds, say academic scientists.
The ubiquitous presence of perfluorochemicals, most notably perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA), and concerns about their potential toxicity in humans and in wildlife have raised numerous questions about exposure to and sources of these chemicals. Determining the sources of this exposure has been complicated because these chemicals are usually not sold as commercial products; they are breakdown products or processing aids used to make other commercial chemicals.
Because diPAPs are commercial products themselves, it will be easier to trace back exposures and sources, says D’eon. “There is a much clearer link between food packaging and the presence of these diPAPs in blood,” she says. Environmental engineer Keri Hornbuckle at the University of Iowa agrees: “Finding these chemicals in paper products gives us a link from the product side to human blood. Then finding them in sewage sludge gives us a link on the other end, and that is crucial if you want to reduce exposure,” she says.
Ongoing U.S. Food and Drug Administration (FDA) studies indicate that diPAPs and other perfluorinated chemicals used to make food wrappers grease-proof can migrate into some foods at levels up to several hundred times higher than current FDA-approved guidelines; this suggests an overlooked and potentially important source of human exposure (Food Addit. Contam., Part A 2008, 25, 384?390).
Similar to other perfluorinated chemicals, diPAPS are fluorinated surfactants that contain a long fluorinated carbon tail attached to an acidic head group. Unlike PFOA and PFOS, though, the fluorinated tail and acidic head in diPAPs are joined by a phosphate ester linkage, which makes the ester linkage vulnerable to degradation via enzymes that are prevalent in nature, D’eon notes.
D’eon previously showed in lab experiments with male rats that, once ingested, diPAPs are bioavailable and can be metabolized to PFOA and other perfluorinated carboxylic acids. “DiPAPs are also contributing to the PFOA burden in humans because we know they form PFOA and other perfluorocarboxylates when they break down,” notes coauthor Scott Mabury, also of the University of Toronto.
The cascade of breakdown products from diPAPs to PFOA and other carboxylates includes fluorotelomer alcohols. The toxicity of fluorotelomers to liver cells has recently been demonstrated by biochemist Jonathan Martin at the University of Alberta (Canada).
However, the new findings are likely to complicate attempts to understand PFOA’s fate in the human body and the environment, notes coauthor Laurence Libelo, a senior environmental engineer with the U.S. EPA. This is because efforts to track PFOA in the human body or in the environment will now have to consider diPAPs. “This finding makes it clear that we cannot just look at one single chemical or class and understand perfluorinated chemicals in the environment and in humans,” he says.
D’eon and her colleagues used pooled blood samples collected across the midwestern U.S. from donors of both sexes who ranged from 19 to 70 years old and had various blood types. Each pooled sample consisted of at least 10 blood donors. Ten pooled samples were collected in 2004 and 2005, and another 10 were collected in 2008. The team also analyzed extracts from six sewage sludge samples collected from wastewater treatment plants in Ontario, Canada, in 2002.
“The diPAPs occur at levels in human blood that are comparable to PFOA. We know diPAPs don’t last long in the body, so this suggests an important and fairly constant source,” says Mabury.
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