The restriction on legacy perfluoroalkyl
substances (PFASs) has
led to increasing application and contamination of their precursors
and novel alternatives. However, the indirect contribution from precursors
has not been well characterized. In this study, 24 PFASs were measured
in the paired human blood and urine from general volunteers (n = 20), as well as their corresponding exposure matrices
(7 day duplicate diet, drinking water and dust). Perfluorooctanoic
acid (PFOA) was predominant, followed by 6:2 chlorinated polyfluoroalkyl
ether sulfonate (6:2 Cl-PFESA), contributing 21.6–47.0 and
6.6–20.0% of the total concentrations, respectively. Total
oxidable precursor (TOP) assay and isomeric analysis coupled with
a toxicokinetic model suggested that around 19% of perfluorooctane
sulfonate (PFOS) in human was contributed by its precursors. The strong
correlation between the estimated daily intake (EDI) and human blood
concentration for 6:2 Cl-PFESA suggested that it was mainly contributed
by direct exposure. The bioavailability of 6:2 Cl-PFESA in the food
matrices was estimated as 18.6% by comparing the estimated and measured
blood concentrations, implying that human exposure might be overestimated
if the bioavailability of PFASs in food was not considered. Assuming
that they had a similar bioavailability, it was estimated that ca.
20% of PFOS body burden was from indirect exposure to its precursors,
which was supported by TOP assay.