Polyethylene microplastics interfere with MICP-based cadmium remediation: A dual-system evaluation of microbial performance and environmental response

Microbially induced calcite precipitation (MICP) is a sustainable and effective approach for immobilizing heavy metals such as cadmium (Cd) in contaminated environments. However, the influence of coexisting microplastics (MPs), particularly polyethylene microplastics (PE-MPs), on MICP performance remains unclear. This study systematically investigated the effects of 1 μm and 50 μm PE-MPs on MICP-mediated Cd remediation in both liquid cultures and soil systems. In aqueous systems, PE-MPs imposed oxidative stress on Stenotrophomonas maltophila Z-6 (with CAT and SOD activities increased by 15.83-59.44 % and 37.41-149.81 %, respectively), inhibited bacterial growth (OD₆₀₀ decreased by 0.20-8.43 %), and delayed Cd²⁺ immobilization. Notably, low-to-moderate concentrations of 1 μm PE-MPs exerted greater inhibitory effects. SEM and XRD analyses showed a transformation of mineral products from metastable spherical vaterite to stable stacked calcite, enhancing Cd fixation, especially at low concentrations of 1 μm PE-MPs. In soil, PE-MPs altered MICP-induced pH (decreased 0.075-0.096 units), EC (decreased 4.52-10.73 %), enzymatic activities, and microbial community structure, yet promoted overall mineralization and reduced Cd mobility and bioavailability (1.98-2.79 %). These findings highlight the complex effects of PE-MPs on MICP performance and microbial ecological stability, underscoring the need to account for emerging pollutants in MICP-based remediation strategies.