Impact of rice residue decomposition on the diffusion of perfluoroalkyl substances in drainage and waterlogged paddy fields

The mobility of perfluoroalkyl substances (PFASs) at the soil–water interface in paddy soils directly influences their availability to crops. However, the mechanisms by which rice residue decomposition affects PFAS diffusion under different hydrological conditions remain unclear. To address this, this study investigated PFAS diffusion across overlying water (OW), pore water (PW), soil solution, soil microbe-adsorbed fractions, and other soil compartments in drainage and waterlogged soils during rice residue decomposition. The results revealed that PW ( β  = 0.74) and OW ( β  = 0.97) served as crucial sinks for PFAS diffusion in drainage and waterlogged soils, respectively. Mass distribution analysis indicated that residue input reduced the content of perfluorocarboxylic acids by 5.33% in PW and 6.67% in OW. In contrast, perfluorinated sulfonic acids increased by 18.43% in PW but decreased by 12.49% in OW. At the molecular level, aggregated boosted tree modeling identified cacodylic acid (36.3%–38.2%) and deoxycorticosterone 21-glucoside (56.2%–59.3%) as key regulators of PFAS distribution in drainage and waterlogged soils, respectively. These findings provide valuable insights into PFAS migration in paddy soils during residue decomposition and highlight the need to control PFASs under both drainage and waterlogged hydrological conditions.