Evaluation of the validity of a perfluorooctane sulfonic acid exposure reconstruction using a measured serum concentration among workers with a wide range of exposure.

Background: Studies among workers with a wide range of exposure to perfluoroalkyl substances inform risk assessments. Perfluorooctane sulfonate (PFOS), a ubiquitous environmental contaminant, was recently examined in relation to mortality and cancer incidence in an occupationally exposed population by Alexander et al. in 2024. In that study, cumulative occupational exposure (mg/m3 PFOS-equivalents in air) was reconstructed using a job-exposure matrix and individual work history. While the exposure reconstruction had good face validity, an assessment of its performance in relation to serum PFOS levels would allow improved interpretation of the occupational epidemiology findings.

Objective: The objective of this study was to assess the validity of the exposure reconstruction used by Alexander et al. (2024).

Methods: A previous study by Olsen et al. (2003) measured serum PFOS levels in 1998 for 260 workers and because these workers were included in the epidemiologic study by Alexander et al. (2024), the study reported herein compared serum PFOS levels to those predicted using a simple compartmental pharmacokinetic model.

Results: The Pearson correlation coefficient between the observed and pharmacokinetic model-predicted serum PFOS concentration was 0.80 (95% confidence interval, 0.75 to 0.84). The median ratio of predicted to observed serum concentrations was 12 (i.e. actual exposure was significantly less than predicted). The predicted serum PFOS concentrations were not sensitive to the parameters used in the pharmacokinetic model other than exposure concentration or absorption.

Conclusions: The model did not predict absolute exposure well, probably because of personal protective equipment use not being accounted for and absorption of PFOS or precursors being lower than modeled. On the other hand, the model did a reasonably good job of ranking the workers' exposure, thus classification of workers according to relative amount of cumulative PFOS-equivalents was reasonably accurate in the study by Alexander et al. (2024) when validated using the measured serum PFOS data.