Effects of Environmentally Relevant Microplastic and Nanoplastic Concentrations on Soil Hydro-Physical Properties: A Global Meta-Analysis

Aims Microplastics (MPx) and nanoplastics (NPx) are widely distributed in agricultural ecosystems, but their effects on soil physico-hydrological properties remain poorly understood. Methods To better constrain the role of MPx/NPx in soil processes and potential impacts, we conducted a meta-analysis on the effects of MPx/NPx on soil bulk density, porosity, water retention, hydraulic conductivity, and soil organic. Results This study indicates that MNPx decreased soil bulk density (2–6%) and significantly increased porosity (~ 23%), implying that soil compaction was potentially alleviated. The effects of MNPx on water-related properties (e.g., field capacity, hydraulic conductivity) were inconsistent and depended on the polymer types, concentration, and exposure time. MNP was found to be positively associated with soil organic carbon, suggesting that carbon cycling may be altered. The responses of evapotranspiration and aggregate stability to MPx/NPx were variable, indicating context-dependent effects on soil structure. Conclusion In conclusion, our study provided quantitative evidence for predicting the mechanistic effect pathways of MPx in altering soil physic-hydrological properties. Nonetheless, both experimental and modeling studies are required to reveal the ecological impacts of MPx under realistic environmental scenarios. This work also pointed out a significant knowledge gap regarding the long-term and field-scale effects of MPx on soil-water interactions and carbon cycling.