Distribution, sources and multi-dimensional environmental risk assessment of microplastics in soils and groundwater along the middle and lower reaches of the Yellow river.

A novel assessment approach for multi-dimensional microplastic particles (Multi-MPs), grounded in the objective weighting method, is applied to the soil and groundwater alongside the middle and lower reaches of the Yellow River. The results showed that MPs concentration ranged from 426 to 3011 n∙kg in soil layer (0-15 cm). Dominant soil MPs exhibited sizes ranging from 25 to 150 μm (61.4 % - 88.3 %), with fibrous (51.3 % - 71.1 %), and transparent (26.2 % - 60.4 %) constituents, respectively. The polymer types mainly included polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). The abundance of MPs in groundwater ranged from 2.28 to 20.5 n∙L. The main characteristics of MPs in groundwater were sizes of 25-150 μm (90.2 % - 97.1 %), with fibrous (17.7 % - 74.0 %), and transparent (26.1 % - 60.3 %) constituents, and PE/PP/PET polymer composition. Land-use type was the main factor determining the distribution of MPs in soil, and the community composition of MPs in soil and groundwater varied accordingly. The Multi-MP risk assessment index revealed that soil risks were predominantly ranked at Class Ⅲ (medium), while 23.1 % of groundwater samples reached Class Ⅳ (high-risk). These findings highlight the critical need to prioritize groundwater microplastic pollution in environmental management. This study aims to develop a holistic approach incorporating multidimensional indicators to enhance the risk assessment framework for MPs. Future studies should focus on long-term ecological impacts of MPs and the development of standardized protocols for multi-dimensional risk assessment to guide targeted mitigation strategies.