Human exposure to PFAS and organofluorine compounds in northern Norway between 1986 and 2015: a fluorine mass-balance study in pooled human serum samples

Presentation at Dioxin 42nd International Symposium on Halogenated Persistent Organic Pollutants, New Orleans (October 2022)

Abstract:

Per- and polyfluoroalkyl substances (PFAS) are a class of over 4700 synthetic chemicals used in numerous industrial and consumer product applications¹. The widespread use of PFAS has led to human and wildlife exposure globally. Despite their discovery in the environment nearly 2 decades ago, current analytical methods only monitor ~1 % of known PFAS, raising concerns that human PFAS exposure may be underestimated². In this study, serum samples from the Tromsø study were pooled and analyzed for total fluorine (TF), extractable organic fluorine (EOF), total oxidizable precursors (TOP) and selected legacy PFAS. The aim was to evaluate concentrations of organofluorine compounds in blood collected between 1986 and 2015 in northern Norway estimating TF, EOF, portion of unidentified EOF and contribution of oxidizable precursors.

Serum from the Tromsø study was collected in 1986, 2007 and 2015 from men and women living in Tromsø, Norway. For the present work, these samples were pooled based on sampling year, sex, age and type 2-diabetes diagnosis. The pooled samples (46 pools, 8-15 individuals in each pool) were analyzed for TF, EOF, TOP and selected legacy PFAS. TF and EOF measurements were performed using combustion ion chromatography directly on 100 μl of pooled serum and on 450 μl acetonitrile extracts (225 μl of serum), respectively, using previously validated methods³. For the TOP assay, 150 μl of serum was extracted with acetonitrile and oxidized using an optimized protocol for human serum⁴. Compound-specific PFAS analyses were performed on 50 μl of the EOF extracts and on the TOP assay extracts before and after oxidation. Differences between the sampling years as well as the influence of sex and mean age on the different fluorine fractions were assessed using multiple linear regression.

TF (<25-1330 ng F/ml, mean: 126 ng F/ml in 1986, 79 ng F/ml in 2007, 73 ng F/ml in 2015) and EOF concentrations (12-45 ng F/ml, mean: 24 ng F/ml in 1986, 21 ng F/ml in 2007, 19 ng F/ml in 2015) showed no clear trends between 1986 and 2015 and no significant differences based on sex and age. In the EOF extracts, 10 legacy PFAS were detected (C₈-C₁₁ perfluorocarboxylic acids, C₆-C₈ perfluorosulfonic acids, 3 perfluorooctane sulfonamido acetates). These known PFAS constituted 24-100 % of the EOF. The unidentified EOF fraction was largest in 1986 (20–76 %; mean: 49 %), significantly declined in 2007 (0-40 %, mean: 14 %) and increased again in 2015 (0–56 %; mean: 27 %). Mean age was not a predictor for unidentified EOF, while women had significantly higher unidentified EOF than men. The TOP assay showed that oxidizable precursors of target PFAS only accounted for 0-3 % of the unidentified EOF fraction.

The relative contribution of known legacy PFAS and unidentified fluorine varied across time, but no clear changes were observed for the overall concentrations of organofluorine compounds in human serum in Northern Norway between 1986, 2007 and 2015. The blood in a northern Norwegian population contained unknown organofluorine compounds and interestingly, this fraction was larger for women than men. Oxidizable precursors accounted only for a small portion of unidentified EOF, meaning that additional analyses are required to characterize the yet unidentified organofluorine compounds in human serum.  

References:

1. Glüge J, Scheringer M, Cousins IT, et al. (2020) Environ Sci Process Impacts. 22: 2345-2373.

2. Sunderland EM, Hu XC, Dassuncao C, et al. (2019) J Expo Sci Environ Epidemiol. 29(2): 131-147.

3. Miaz LT, Plassmann MM, Gyllenhammar I, et al. (2020) Environ Sci Process Impacts. 22: 1071-1083.

4. Cioni L, Nikiforov V, Coêlho AC et al. (2022) ChemRxiv (preprint).