Perfluorooctane sulfonate precursors as indirect sources of internal exposure to perfluorooctane sulfonate (PFOS)

Perfluorooctane sulfonate (PFOS) is a pertluoroalkyl substance with extensive historical use. Its persistence, bioaccumulation, toxicity and health concerns led to its incorporation in the Stockholm Convention as a persistent organic pollutant in 2009. Direct exposure to PFOS has been reported in different environmental and biological samples, and recent human biomonitoring studies indicate that levels are in decline. However. certain uncertainties remain when estimating its body burdens: indirect exposure to so called PFOS-precursor compounds - such as perfluorooctane sulfonamides and petfluorooctane sulfonamidoethanols - , followed by in vivo metabolism could contribute to the current levels of PFOS in human biological samples. To evaluate the direct and the indirect contribution to PFOS exposure, sample preparation and instrumental HPLC-MS/MS methods for the analysis of PFOS - linear and sum of branched isomers - and PFOS precursors - three FOSAs, two FOSEs and three FOSAAs - in dust, food and serum samples were developed and validated. Daily intakes for total PFOS and PFOS precursors via dust and food ingestion were estimated under different scenarios, and compared with reported internal exposure levels of PFOS. Finally. for a better understanding of the link between external and internal exposure, a qualitative study of the in vitro metabolism of two PFOS precursors was conducted.