Combined toxicity and ecological impacts of soil microplastics and heavy metals in rhizosphere microenvironments: a comprehensive review

This review systematically evaluates the combined effects of microplastics (MPs) and heavy metals (HMs) on rhizosphere soil–plant systems, with a focus on their synergistic impacts on soil physicochemical properties, microbial ecology, plant physiology, and the adaptive response mechanisms of the soil-plant continuum. The study aims to unravel the mechanistic interplay between MPs and HMs while highlighting implications for ecosystem resilience and remediation strategies. We analyzed approximately 109 peer-reviewed studies (2015–2025) from databases such as Web of Science, Elsevier ScienceDirect, and Google Scholar. The selected studies focused on experimental investigations of MP-HM interactions in rhizosphere environments, emphasizing dose-response relationships, soil structural changes, enzymatic activity shifts, and plant physiological responses. The co-contamination of rhizosphere soils with MPs and HMs drives non-linear alterations in physicochemical and biological properties, shaped by synergistic interactions among contaminant concentrations, polymer types, metal species, soil mechanical characteristics, and microbial community dynamics. These findings underscore the necessity for context-specific risk assessments in managing MP-HM co-contamination. The combined toxicity of MPs and HMs in rhizosphere soils exert both direct and indirect impacts on the soil-plant system. These synergistic effects are long-lasting and persistent, fundamentally altering soil health through multifaceted mechanisms. Future research should prioritize investigating the dynamic interactions between MPs and HMs, employing advanced analytical techniques for comprehensive ecosystem assessment. Additionally, innovative remediation strategies should be explored to mitigate the adverse effects of these contaminants on soil health and sustainability.