Biomonitoring of per- and polyfluoroalkyl substances (PFAS) exposure in firefighters: Study design and lessons learned from stakeholder and participant engagement

Apparent Half-Lives of Chlorinated-Perfluorooctane Sulfonate and Perfluorooctane Sulfonate Isomers in Aviation Firefighters

Elevated levels of perfluorooctane sulfonate (PFOS) and elevated detection frequency of chloro-substituted PFOS have been reported in Australian firefighters with historical exposure to aqueous-film forming foam (AFFF). The aim of this study is to estimate the apparent half-lives of Cl-PFOS and PFOS isomers in firefighters following the end of exposure to 3M-AFFF. Paired serum samples from 120 firefighters, collected approximately five years apart, were analyzed for 8-Cl-PFOS (8-chloroperfluoro-1-octanesulfonic acid) and PFOS isomers via targeted LC-MS/MS. Apparent half-life was estimated by assuming a first order-elimination model. Cl-PFOS was detected in 93% of all initial serum samples (<LOQ-1.09 ng/mL). The average half-life of Cl-PFOS among the firefighters was 5.0 years. Branched PFOS isomers made up 55% of the total isomer concentration at the initial sampling timepoint. Five years later, the proportion of branched PFOS isomers was greater (65%). The longest average half-life (11.5 years) was estimated for "1m-PFOS". Other isomers had average half-lives ranging from 4.0 to 7.5 years. Marked differences in half-lives between PFOS isomers suggest that the elimination rate of "total PFOS" (sum of all PFOS isomers) is non-linear. This is the first study to report the serum concentrations and apparent half-life of Cl-PFOS in humans.

Associations between serum perfluoroalkyl acid (PFAA) concentrations and health related biomarkers in firefighters

Firefighters who used aqueous film forming foam in the past have experienced elevated exposures to perfluoroalkyl acids (PFAAs). The objective of this study was to examine the associations between clinical chemistry endpoints and serum concentrations of perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS), perfluoroheptane sulfonate (PFHpS) and perfluorooctane sulfonate (PFOS) in firefighters. Multiple linear regression was used to assess relationships between PFAA serum concentrations and biochemical markers for cardiovascular disease, kidney-, liver- and thyroid function, in a cross-sectional survey of 783 firefighters with elevated levels of PFHxS, PFHpS and PFOS in relation to the most recently reported levels in the general Australian population. Linear logistic regression was used to assess the odds ratios for selected self-reported health outcomes. Repeated measures linear mixed models were further used to assess relationships between PFAAs and biomarkers for cardiovascular disease and kidney function longitudinally in a subset of the firefighters (n = 130) where serum measurements were available from two timepoints, five years apart. In the cross-sectional analysis, higher levels of all PFAAs were significantly associated with higher levels of biomarkers for cardiovascular disease (total-cholesterol, and LDL-cholesterol). For example, doubling in PFOS serum concentration were associated with increases in total cholesterol (β:0.111, 95% confidence interval (95%CI): 0.026, 0.195 mmol/L) and LDL-cholesterol (β: 0.104, 95%CI:0.03, 0.178 mmol/L). Doubling in PFOA concentration, despite not being elevated in the study population, were additionally positively associated with kidney function marker urate (e.g., β: 0.010, 95%CI; 0.004, 0.016 mmol/L) and thyroid function marker TSH (e.g., β: 0.087, 95%CI: 0.014, 0.161 mIU/L). PFAAs were not associated with any assessed self-reported health conditions. No significant relationships were observed in the longitudinal analysis. Findings support previous studies, particularly on the association between PFAAs and serum lipids.

Serum concentration trends and apparent half-lives of per- and polyfluoroalkyl substances (PFAS) in Australian firefighters

BACKGROUND

Per- and polyfluoroalkyl substances (PFASs) are persistent manmade compounds used in aqueous film forming foam (AFFF). The extensive use of AFFF has led to widespread environmental PFAS contamination and exposures of firefighters.

OBJECTIVES

To determine PFAS blood serum concentration trends and apparent serum half-lives in firefighters after the replacement of AFFF.

METHODS

Current and former employees of an Australian corporation providing firefighting services, where AFFF formulations had been used since the 1980s up until 2010, were recruited in 2018-2019 to participate in this study. Special focus was put on re-recruiting participants who had provided blood samples five years prior (2013-2014). Participants were asked to provide a blood sample and fill in a questionnaire. Serum samples were analysed for 40 different PFASs using HP LC-MS/MS.

RESULTS

A total of 799 participants provided blood samples in 2018-2019. Of these, 130 previously provided blood serum in 2013-2014. In 2018-2019, mean (arithmetic) serum concentrations of perfluorooctane sulfonate (PFOS, 27 ng/mL), perfluoroheptane sulfonate (PFHpS, 1.7 ng/mL) and perfluorohexane sulfonate (PFHxS, 14 ng/mL) were higher than the levels in the general Australian population. Serum concentrations were associated with the use of PFOS/PFHxS based AFFF. Participants who commenced service after the replacement of this foam had serum concentrations similar to those in the general population. Mean (arithmetic) individual apparent half-lives were estimated to be 5.0 years (perfluorooctanoic acid (PFOA)), 7.8 years (PFHxS), 7.4 years (PFHpS) and 6.5 years (PFOS).

CONCLUSION

This study shows how workplace interventions such as replacement of AFFF can benefit employees at risk of occupational exposure.