Biochar mitigates the interactive effects of microplastics and cadmium pollution on soil characteristics and Pak choi (Brassica rapa chinensis L) growth

Heavy metals and microplastics (MPs) are persistent co-contaminants in agricultural soils, posing serious threats to agricultural sustainability. Biochar (BC) amendments have demonstrated potential for soil remediation and health improvement, but their efficacy in soils co-contaminated with heavy metals and MPs remains unclear. A factorial pot experiment evaluated four biochars derived from Solidago canadensis L. (SBU-BC), corn straw (CoB), rice straw (RoB), and peach twigs (PoB) in soils contaminated with cadmium (Cd) and polyethylene microplastics (PE-MPs), applied individually or together. After a growth cycle of Pak choi (Brassica rapa chinensis L.), soil properties and plant physiological indices (e.g., antioxidant enzymes) were assessed. Co-contamination of Cd and MPs synergistically exacerbated oxidative stress in plants, elevating leaf superoxide dismutase activity by 32% relative to single-stress conditions. Among the BC treatments, SBU-BC proved most effective, alleviating stress, increasing Pak choi biomass by 15.5%, reducing Cd accumulation in shoots and roots by nearly 20%, and enhancing soil nutrient availability (e.g., cation exchange capacity, nitrate). These findings suggest that SBU-BC may contribute to better soil conditions and increased crop resilience under Cd and MPs co-contaminated soils, however, further field-scale trials are required to validate its effectiveness under real agricultural conditions.