Bioremediation of soil microplastics: the role of microbial and earthworm activity

Microplastics in soil transform through interacting abiotic, microbial, and faunal processes that collectively determine their persistence and ecological impact. To establish a mechanistic understanding of these complex interactions, we systematically reviewed 150 studies following PRISMA 2020 guidelines, synthesizing qualitative evidence on contamination patterns (n = 128) and quantitative data on microplastic occurrence, degradation mechanisms, and bioremediation potential (n = 22) across diverse terrestrial ecosystems. Principal component analysis of polymer distribution patterns identified polymer composition, residence time, soil physicochemical properties, and ecological risk factors as key determinants of microplastic fate in terrestrial systems. The study reveals that microplastic degradation in soils occurs through a sequential, multi-agent pathway. The process initiates with abiotic weathering that creates surface irregularities and functional groups, facilitating subsequent plastisphere development. Within these biofilm microenvironments, microbial communities accumulate oxidative and hydrolytic enzymes that drive enzymatic depolymerization, resulting in polymer fragmentation and partial to complete mineralization. Across studies, polyethylene, polypropylene, and polystyrene emerged as the most persistent polymers, while biodegradable alternatives exhibited accelerated transformation under favourable soil conditions. Earthworms critically amplify degradation through mechanical fragmentation, gut redox modification, and enrichment of degradative microbial communities, achieving upto 60% low-density polyethylene mass reduction. Their burrowing activity further extends degradation by improving soil aeration, moisture distribution, and microbial dispersal. These findings demonstrate that effective bioremediation requires coordinated interactions among polymer properties, soil conditions, microbial diversity, and earthworm activity, providing a mechanistic framework for developing soil-specific strategies to mitigate terrestrial microplastic pollution.