Dual Effects of PVC Microplastics on Cd Mobility in Red Soil: Enhanced Aqueous Concentration Versus Reduced Soil Bioavailability

Abstract

Microplastic and cadmium (Cd) co‐contamination affects Cd fate in soil‐water systems. However, it remains unclear whether soil type regulates the microplastic‐induced changes in Cd bioavailability. Moreover, the effects of microplastics on Cd leaching behavior are also poorly understood. To fill the above gaps, this study employed column leaching experiments to systematically investigate the impact of polyvinyl chloride (PVC) microplastics on Cd dynamics in two typical soils: cinnamon soil and red soil. The results showed PVC disrupted the Cd solid–liquid equilibrium in a soil‐type‐dependent manner. PVC had a stronger effect on Cd fate in red soil than in cinnamon soil, increasing Cd in aqueous phases (porewater and leachate) while decreasing Cd bioavailability in solid phases, including HNO3‐extractable fractions, exchangeable fractions, and reducible fractions. In high‐polluted red soil, PVC increased porewater Cd by 2.35 times and leached Cd by 2 times. Meanwhile, PVC induced a decrease in pH (0.14 units) and an increase in Eh (65 mV), regulating phosphatase activity and available phosphorus levels, thereby influencing Cd mobility. These changes intensified Cd migration risk in clay mineral‐rich soil, whereas the effect was weaker in lower‐organic‐matter, larger‐grained cinnamon soil. These findings underscore the need to incorporate aqueous‐phase Cd dynamics into pollution risk assessments, while recognizing microplastics as a critical factor in farmland pollution control to support differentiated soil management and source reduction strategies.