Bioaccumulation of legacy and emerging per- and polyfluoroalkyl substances in hydroponic lettuce and risk assessment for human exposure

Abstract

Reclaimed water for irrigation or hydroponic cultivation provides exposure pathways for per- and polyfluoroalkyl substances (PFAS) to enter the human food chain. This study employed hydroponic methods to investigate the behavior of legacy PFAS and emerging chlorinated polyfluoroalkyl ether sulfonic acids (Cl-PFESAs) in lettuce grown under environment-related exposure levels and assessed the human exposure risks from consuming contaminated lettuce. Overall, PFAS in lettuce were concentration-dependent, with long-chain PFAS tending to accumulate in roots and short-chain PFAS accumulating more in shoots. The enrichment of PFAS in lettuce was jointly influenced by their chain length and polar functional groups. Specifically, the root concentration factors (RCFs) of PFAS generally increased with increasing chain length, and RCF values of most perfluoroalkanesulfonic acids (PFSAs) were significantly higher than those of perfluoroalkyl carboxylic acids (PFCAs) with the same chain length (p < 0.01), while the translocation factors (TFs) exhibited opposite trends. RCF values of perfluorooctane sulfonate (PFOS) and its alternatives, Cl-PFESAs, were ranked as follows: 8:2 Cl-PFESA (mean: 139) > 6:2 Cl-PFESA (28.6) > PFOS (25.7), which was attributed to the increased molecular size and hydrophobicity resulting from the insertion of ether bonds and additional CF₂ in 8:2 Cl-PFESA. Notably, TF value of 8:2 Cl-PFESA (mean: 0.007) was the smallest among all PFAS, indicating 8:2 Cl-PFESA was difficult to transfer to nutritional compartments. Adults and children would exceed the most conservative health-based reference dose (RfD) by consuming approximately 15.9–148 g and 7.92–74.0 g of contaminated lettuce per day, implying high health risks.