Vallisneria natans drives pesticide removal from agricultural waters: The role of bioaccumulation and epiphytic bacteria

Pesticide mixtures are prevalent in aquatic systems within agricultural regions, but their transport and removal mechanisms in the presence of submerged macrophytes remain unclear. This study investigated changes in water quality, plant physiology, epiphytic microbial communities, and pesticide distribution in wetland substrates during 56 days of repeated exposure to a mixture of 12 pesticides at environmental (0.5 and 1 μg/L) and high (5 and 10 μg/L) concentrations. The average removal rates of total pesticides ranged from 58.61% to 75.52% and decreased with increasing pesticide addition and exposure time. Bioconcentration factors in plants were significantly higher than sediment-water partition coefficients for all pesticides. Notably, triazole pesticides (paclobutrazol, tebuconazole and hexaconazole) tended to accumulate in the system compared to neonicotinoid insecticides (dinotefuran, imidacloprid, and thiamethoxam). Pesticide addition reduced nutrient removal efficiency and induced oxidative damage in V. natans leaves. A total of 3, 14, and 17 biomarkers were identified in Con, PG1, and PG10, respectively, suggesting that PG1 and PG10 disturbed the epiphytic bacterial community. Co-occurrence network analysis revealed potential associations between pesticide residues and epiphytic bacterial taxa in PG10. PICRUSt2-based functional prediction indicated that compared to control, the predicted potential for xenobiotics biodegradation and metabolism was higher in PG1, whereas predicted genes related to starch and hemicellulose decomposition increased and denitrification-related predicted genes decreased in PG10. These data highlight that V. natans can accumulate pesticides and survive repeated pesticide exposure during the 56-day experiment, although high concentration pesticides had adverse effects on V. natans -epiphytic bacterial community.