Compensatory release of per- and polyfluoroalkyl substances at the soil-water interface in paddy fields under...

Per- and polyfluoroalkyl substance (PFAS) accumulation and increasing drought events pose threats to agricultural ecosystem safety. However, the mechanisms by which post-drought rehydration (PDR) modulates compensatory PFAS migration at the soil-water interface remain unclear. To address this, this study investigated PFAS translocation across overlying water (OW), soil solution, soil microbe-adsorbed fraction (SM), and other soil fractions (OF) in paddy soils under PDR conditions. The results revealed significant releases of short-chain PFASs into OW under PDR, with migration rates ranging from 2.69 to 11.07 μg/L/day. Drought further accelerated the distribution of short-chain PFASs in OW after rehydration (β = 0.51) and inhibited their retention in SM (β = -0.43) and OF (β = -0.74). The compensatory migration of short-chain PFASs was regulated by both abiotic and biotic factors. In contrast, the compensatory migration of long-chain PFASs was mainly driven by biotic factors, including soil bacteria and protozoa. Soil untargeted metabolomics identified 7-chloro-L-tryptophan (associated with oxidative stress response) and N-acetyl-L-phenylalanine (associated with amino acid metabolism) as key metabolites involved in PFAS migration (p < 0.05). Verification experiments further confirmed that these two metabolites significantly altered PFAS release at the soil-water interface (p < 0.001). These findings provide new insights into PFAS pollution control in drought-affected paddy fields and highlight the need for targeted management strategies to ensure agricultural safety under dynamic climate conditions.