Dynamic production of hydroxy radicals affects the available Cadmium in paddy soils under microplastic contamination

The coexistence of microplastics (MPs) and Cadmium (Cd) in soil poses a critical yet understudied environmental and agricultural risk, particularly in redox-dynamic paddy systems. This study quantifies the mechanistic interplay between polyethylene (PE) MPs and available Cd under two water management regimes. Results demonstrate that MPs significantly amplify hydroxyl radical (•OH) production in paddy systems, with particle size, concentration, and hydrological regimes driving spatiotemporal dynamics. MPs further altered redox thresholds unpredictably. Pearson's positive correlation results revealed that photochemical activation of MPs-derived dissolved organic carbon (DOC) and Fe(II) governed •OH generation in the overlying water. Small, high-concentration MPs amplified Fe(II) turnover in soils under fluctuating hydrology, driving sustained •OH production, elevating soil available Cd contents by 4.5-fold higher than controls after 30 days (p < 0.05). This study establishes a critical link between MPs contamination and •OH-mediated Cd cycling in paddy ecosystems, highlighting MPs-induced redox dynamics as a linchpin controlling heavy metal availability under variable soil oxygenation. The findings advance predictive frameworks for co-mobility of MPs and metal contaminants, while establishing innovative paradigms for addressing the non-negligible role of •OH in agroecosystems.