Biochar Offsets Microplastic-Induced Cadmium Mobilization and Plant Accumulation in Contaminated Soils

Abstract Co-occurrence of heavy metals and plastic-derived pollutants represents a novel challenge for agroecosystem sustainability, yet the mechanistic interplay between biochar (BC) amendments, microplastics (MPs) and cadmium (Cd) remains largely unresolved. A controlled greenhouse factorial experiment arranged in a completely randomized factorial design with six replicates per treatment was conducted to elucidate the BC-MPs-Cd interactions in a loamy slightly neutral soil cultivated with wheat ( Triticum aestivum L.). Treatments included two Cd levels (0, 10 mg kg −1 ), three MPs doses (0, 1, 2% w/w) and two BC rates (0, 1% w/w). BC application markedly increased soil pH (up to 8.11) and organic matter, while reducing DTPA-extractable Cd by up to 36% under Cd10MP2, indicative of pH-driven sorption and precipitation processes. MPs, in contrast, enhanced Cd mobility in a dose-dependent manner in BC-free soils. Elevated Cd bioavailability under Cd10 + MPs treatments resulted in substantial increases in shoot and grain Cd concentrations (20.2 and 4.00 mg kg −1 , respectively) and concomitant reductions in biomass and grain yield (15–26% decreases), whereas BC partially mitigated these effects by lowering tissue Cd accumulation (~ 12% reduction). Nitrogen dynamics remained largely unaffected, while Zn availability exhibited secondary yet significant shifts. PCA revealed distinct clustering along Cd mobility versus plant performance axes, reflecting the contrasting regulatory roles of BC and MPs. Overall, BC functioned as a robust chemical buffer against Cd stress even under MPs presence, whereas MPs exacerbated Cd bioavailability and phytotoxicity. These findings provide critical insights into multi-contaminant interactions and underscore the necessity of integrated remediation strategies in contaminated agricultural soils. Graphical Abstract