Chemicals that prevent grease from seeping through food packaging transform in rats into a suspected carcinogenic compound. This conversion could help explain why that compound—perfluorooctanoic acid (PFOA)—shows up so widely in people’s blood, say researchers.
PFOA, used to manufacture nonstick cookware and rain gear, turns up in blood samples worldwide, reaching concentrations of 30 nanograms per milliliter or more. The chemical doesn’t degrade, and people excrete it slowly. An advisory group to the Environmental Protection Agency has recommended classifying PFOA as a rodent carcinogen that may harm people.
But scientists don’t know the primary route by which PFOA gets into people (see Nonstick Pollution Sticks in People). Environmental chemists Scott A. Mabury and Jessica C. D’eon of the University of Toronto tested a pathway that begins with related chemicals called polyfluoroalkyl phosphate surfactants (PAPS), substances used to coat oil- and water-repellent food wrappers. A study in 2005 showed that similar compounds used in these applications can leach from microwave-popcorn packaging into the food.
That finding left two issues unresolved, says Mabury. Can PAPS reach the bloodstream from the gut, and if so, will they break down to PFOA in the body?
Mabury and D’eon synthesized two PAPS and administered one or the other directly into rats’ stomachs in single doses of 200 milligrams per kilogram of body weight. Over the following 15 days, they monitored the rats’ blood for PFOA and both PAPS. The highest background concentration among the rats, including animals that weren’t dosed with a PAPS, was 2 nanograms of PFOA per gram (ng/g).
Exposure to either PAPS elevated the amount of PFOA in a rat’s blood. One of the surfactants, monoPAPS, boosted PFOA concentrations to 34 ng/g. The other, diPAPS, produced a smaller jump to 3.8 ng/g. The researchers report their findings in the July 1 Environmental Science & Technology.
Not only can the body absorb PAPS, but the chemicals degrade into a potentially toxic compound “widely observed in the bloodstream,” concludes Mabury.
The study identifies a source of PFOA contamination, says Kurunthachalam Kannan, an environmental chemist at the New York State Department of Health in Albany. With growing concern over how PFOA affects people, there is a need to identify additional sources of exposure, Kannan says. “There may be many more unknown sources out there,” he says.
If PFOA is in people’s blood because they make it inside their bodies, says Mabury, then the behavior of the intermediate chemicals in this exposure pathway becomes important as well. Some of these intermediates “have the potential to be far more toxic than PFOA,” he says.
Mabury’s group is now assessing the toxicity of the intermediates. The team also plans to study how widespread PAPS are in the environment.
