Indoor and outdoor air concentrations and phase partitioning of perfluoroalkyl sulfonamides and polybrominated
Mahiba Shoeib1, Tom Harner, Michael Ikonomou
1Meteorological Service of Canada, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada M3H 5T4.
Abstract:
Perfluoroalkyls (PFAs) and polybrominated diphenyl ethers (PBDEs) are two classes of emerging persistent organic pollutants (POPs) that are widely used in domestic and workplace products. These compounds also occur in remote locations such as the Arctic where they are accumulated in the food chain. This study makes connections between indoor sources of these chemicals and the potential and mode for their transport in air. In the case of the PFAs, three perfluoralkyl sulfonamides (PFASs) were investigated--N-methyl perfluorooctane sulfonamidoethanol (MeFOSE), N-ethyl perfluorooctane sulfonamidoethanol (EtFOSE), and N-methyl perfluorooctane sulfonamidethylacrylate (MeFOSEA). These are believed to act as precursors that eventually degrade to perfluorooctane sulfonate (PFOS), which is detected in samples from remote regions. High-volume samples were collected for indoor and outdoor air to investigate the source signature and strength. Mean indoor air concentrations (pg/m3) were 2590 (MeFOSE), 770 (EtFOSE), and 630 (sigmaPBDE). The ratios of concentration between indoor and outdoor air were 110 for MeFOSE, 85 for EtFOSE, and 15 for sigmaPBDE. The gas and particle phases were collected separately to investigate the partitioning characteristics of these chemicals. Measured particulate percentages were compared to predicted values determined using models based on the octanol-air partition coefficient (K(OA)) and supercooled liquid vapor pressure (pL(o)); these models were previously developed for nonpolar, hydrophobic chemicals. To make this comparison for the three PFASs, it was necessary to measure their K(OA) and vapor pressure. K(OA) values were measured as a function of temperature (0 to +20 degrees C). Values of log K(OA) at 20 degrees C were 7.70, 7.78, and 7.87 for MeFOSE, EtFOSE, and MeFOSEA, respectively. Partitioning to octanol increased at colder temperatures, and the enthalpies associated with octanol-air transfer (deltaH(OA), kJ/mol) were 68-73 and consistent with previous measurements for nonpolar hydrophobic chemicals. Solid-phase vapor pressures (pS(o)) were measured at room temperature (23 degrees C) by the gas saturation method. Values of pS(o) (Pa) were 4.0 x 10(-4), 1.7 x 10(-3), and 4.1 x 10(-4), respectively. These were converted to pL(o) for describing particle-gas exchange. Both the pL(o)-based model and the K(OA) model worked well for the PBDEs but were not valid for the PFASs, greatly underpredicting particulate percentages. These results suggest that existing K(OA)- and pL(o)-based models of partitioning will need to be recalibrated for PFASs.
