PFAS contamination in the Western Seto Inland Sea of Japan: Substitution lag and TFA risk alert

The western Seto Inland Sea (WSIS) is surrounded by major industrial zones in Japan and receives substantial inputs of pollutants. However, per - and polyfluoroalkyl substances (PFAS) contamination in the WSIS remains poorly characterized. In this study, we investigated the occurrence and potential sources of PFAS in seawater samples from the WSIS, and conducted a preliminary ecological risk assessment. A total of 24 PFAS were identified and quantified, with total concentrations (Σ 24 PFAS) ranging from 519 to 916 ng/L. Trifluoroacetic acid (TFA) was the predominant compound (mean: 680 ± 156 ng/L), accounting for 96.9% of Σ 24 PFAS. After excluding TFA, perfluoroalkyl sulfonic acids (PFSAs) accounted for more than half of the remaining PFAS. Except for TFA, the remaining PFAS generally exhibited a spatial pattern suggestive of localized point-source inputs, with higher concentrations nearshore waters than in offshore waters. Principal component analysis-multiple linear regression (PCA-MLR) suggested that non-TFA PFAS were mainly associated with electroplating-related and surfactant-related sources, whereas correlation patterns and spatial distributions suggested that TFA was primarily associated with the atmospheric degradation of hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs). The results further suggest that the transition from legacy PFAS to emerging alternatives remains incomplete. Ecological risk assessment based on risk quotients (RQs) indicated that the estimated risk posed by TFA varied substantially depending on the toxicity data used. Under the worst-case scenario, TFA posed a high risk (RQ > 1), whereas perfluorooctane sulfonate (PFOS) exhibited a low risk (RQ < 0.01). These findings underscore the need for multi-compartment and seasonal monitoring in the WSIS, inclusion of TFA monitoring programs across other marine regions, and expanded toxicity testing in marine organisms.