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Dual Effects of PVC Microplastics on Cd Mobility in Red Soil: Enhanced Aqueous Concentration Versus Reduced Soil Bioavailability
Summary
Microplastics in farmland soils don't just stay put — they can change how toxic metals like cadmium move through the soil and into groundwater. This study found that PVC microplastics dramatically altered cadmium's behavior in red clay soils, doubling the amount of cadmium leaching into soil water while reducing the form available for plant uptake — a paradoxical finding that means lower risk to crops but higher risk of cadmium reaching streams and wells. The results underscore that microplastic pollution and heavy metal contamination in agricultural soils must be assessed together, not in isolation.
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 HNO 3 ‐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.