Origin, Occurrence and Threats of Microplastics in Agricultural Soils: A Comprehensive Review

Microplastics (MPs) enter terrestrial ecosystems through various pathways, including the use of plastic mulching films, treated sewage sludge, and chemical and organic fertilizers. Polypropylene (PP) and polyethylene (PE) are the dominant polymers found in both traditional and facility-based farmland soils. MPs negatively impact soil microbial communities and harm soil invertebrates such as earthworms, nematodes, and springtails. In plants, MPs can induce oxidative stress, damage cells and inhibit growth. Polystyrene (PS) is often identified as the most hazardous polymer, frequently linked to reduced plant growth, which is the most commonly reported effect of soil MP contamination. This review provides novel insights beyond those reported in the previous literature, revealing that greenhouse-based cultivation, vegetable crops, orchards, and vineyards are significant contributors to increased microplastic soil contamination. Furthermore, the findings underscore pronounced global heterogeneity in microplastic concentrations within paddy soils, with recorded levels varying widely from 16 to 10,300 items kg−1. Oxidative stress and additive leaching are the dominant mechanisms driving soil microplastic toxicity across exposed organisms. Quantitative studies of fungal-mediated microplastic biodegradation report mean degradation efficiencies of ~7.5% after 50 days, with mass losses of ~23.8% after 30 days and 35–38% after 90 days.