Occurrence, fate, and ecological impacts of microplastics in soil: a comparative analysis of conventional, biodegradable microplastics, and tire wear particles

As plastic waste continues to build up in soil, the issue of microplastics (MPs) has become a global concern. However, there is much less information available on soil-associated MPs compared to aquatic MPs. Most of our knowledge about MPs is primarily based on research on conventional microplastics (CMPs), which may not apply to biodegradable microplastics (BMPs) and tire wear particles (TWPs). Unlike previous reviews that largely focused on CMPs in aquatic systems, this review integrates bibliometric and thematic analyses to comparatively examine CMPs, BMPs, and TWPs in soils, offering a new framework that highlights type-specific behaviors, ecological risks, and critical knowledge gaps. Bibliometric analysis reveals a shift from early emphasis on occurrence and identification toward growing concerns over ecological impacts and contaminant interactions. Thematic analysis summarizes published data about the occurrence, aging processes, and impacts on soil properties and biota, with a focus on the differences between the three types of MPs. Compared to CMPs, BMPs degrade more rapidly and destabilize soil elemental cycles, while TWPs release highly toxic leachates such as carcinogens and heavy metals, which will persist in fauna. The risks posed by BMPs and TWPs may be underestimated, and more research is needed to understand their environmental behavior and impacts. Persistent gaps remain in standardized monitoring, comparative ecotoxicological studies, and long-term field assessments, underscoring the urgent need for integrated, system-level risk evaluation of different types of soil MPs.