While the liver is considered the major repository in the body for perfluorinated sulfonate (PFSA) and carboxylate (PFCA) contaminants, research by Environment Canada scientist Dr. Robert Letcher and his team has shown that both PFCAs and PFSAs cross the blood-brain barrier in polar bears and that they concentrate in specific regions of the brain.

Concentrations of highly persistent PFSAs such as perfluorooctane sulfonate (PFOS) and other PFCAs have been reported in the liver of polar bears, however no study to date has investigated levels of any PFASs in other tissues or body compartments. Given the high PFSA and PFCA exposures in polar bears and the concern for possible effects in the brain, Dr. Letcher and his team investigated the comparative accumulation of PFCAs and PFSAs as well as selected precursors including perfluorooctane sulfonamide perfluoroalkyl acids (PFAAs) in eight brain regions of polar bears collected in 2006 from Scoresby Sound, East Greenland.

On a wet-weight basis, blood-brain barrier transport of PFAAs occurred for all brain regions, although inner regions of the brain closer to incoming blood flow (pons/medulla, thalamus, and hypothalamus) contained consistently higher PFAA concentrations compared to outer brain regions (cerebellum, striatum, and frontal, occipital, and temporal cortices). For pons/medulla, thalamus, and hypothalamus, the most concentrated PFAA was PFOS. However, PFOS and the longer-chain PFCAs were highly correlated with lipid content for all brain regions.

A.K. Greaves, R.J. Letcher, C. Sonne, R. Dietz. 2013. Brain region distribution and patterns of bioaccumulative perfluoroalkyl carboxylic and sulfonic acids in highly exposed East Greenland polar bears (Ursus maritimus). Environmental Toxicology and Chemistry 32:713-722.

Contact: Dr. Robert Letcher, 613-998-6696, Ecotoxicology and Wildlife Health Division, Wildlife and Landscape Science Directorate