Environmental effects of biodegradable microplastics in cadmium-contaminated soil and their regulation on cadmium bioavailability.

Biodegradable microplastics (BMPs) residues in soil are becoming increasingly prevalent; however, their effects on cadmium (Cd) bioavailability and toxicity in contaminated soils remain poorly understood. A pot experiment was conducted to investigate the effects of four typical BMPs-polylactic acid (PLA), poly(butylene adipate-co-terephthalate) (PBAT), polybutylene succinate (PBS), and polycaprolactone (PCL) on soil physicochemical properties, Cd speciation, pak choi growth, antioxidant responses, and rhizobacterial community structure in Cd-contaminated acidic soil. Results demonstrated that BMPs regulated Cd behavior through dual abiotic (pH, zeta potential, electrical conductivity) and biotic (microbial community restructuring) pathways, with effects highly dependent on BMPs type. PBAT elevated soil pH, increased negative zeta potential, reduced shoot Cd accumulation, alleviated oxidative stress, and enhanced bacterial diversity with enrichment of Cd-immobilising taxa. Conversely, PLA, PBS, and PCL decreased soil pH, increased Cd availability and plant Cd uptake, aggravated lipid peroxidation and leaf tissue damage, and inhibited antioxidant enzyme activity. PLA broadly suppressed soil enzyme activity, whereas PCL reduced bacterial richness and enriched Cd-mobilising taxa. These findings demonstrate that BMPs exert species-specific regulation on Cd fate through combined modifications of soil physicochemical properties and reshaping of functional microbial communities, highlighting the need for risk differentiation when introducing biodegradable plastics into metal-contaminated farmlands.