Isomers of perfluorooctanesulfonate and perfluorooctanoate and total perfluoroalkyl acids in human serum from two cities in North China

Abstract

The sources and pathways of human exposure to perfluoroalkyl acids (PFAAs) are not well characterized, particularly in China where many perfluorinated substances are now manufactured. Here, isomer-specific PFAA analysis was used for the first time to evaluate exposure sources for Chinese people, by applying the method to 129 serum samples collected in two typical cities (Shijiazhuang and Handan) in North China. Among all samples, total perfluorooctanesulfonate (∑PFOS, mean 33.3 ng/ml) was the predominant PFAA followed by perfluorohexanesulfonate (2.95 ng/ml), total perfluorooctanoate (∑PFOA, 2.38 ng/ml), and perfluorononanoate (0.51 ng/ml). The level of ∑PFOS was higher than in people from North America in recent years. The mean concentrations of ΣPFAAs in the participants living in urban Shijiazhuang (59.0 ng/ml) and urban Handan (35.6 ng/ml) were significantly higher (p<0.001 and p=0.041, respectively) than those living in the rural district of Shijiazhuang (24.3 ng/ml). The young female sub-population had the lowest ΣPFAA concentrations compared with older females and all males. On average, the proportion of linear PFOS (n-PFOS) was only 48.1% of ∑PFOS, which is much lower than what was present in technical PFOS from the major historical manufacturer (ca. 70% linear), and which is also lower than data reported from any other countries. Moreover, the proportion of n-PFOS decreased significantly with increasing ∑PFOS concentration in the serum samples (r=-0.694, p<0.001). Taken together, the data lend weight to previous suggestions that i) high branched PFOS content in serum is a biomarker of exposure to PFOS-precursors, and ii) that people with the highest ∑PFOS concentrations are exposed disproportionately to high concentrations of PFOS-precursors. On average, linear PFOA (n-PFOA) contributed 96.1% of ∑PFOA, significantly higher than in technical PFOA (ca. 75-80% linear), but lower than in Americans, suggesting higher exposure to electrochemically fluorinated PFOA than in other countries, including the United States.