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[Distribution Characteristics and Risk Assessment of Microplastics in Soil in Danjiangkou Reservoir Area of South-to-North Water Diversion Project].
Summary
This study characterized microplastic occurrence in four types of agricultural soil in the Danjiangkou Reservoir area of China — a critical water source for the South-to-North Water Diversion Project. Orchard soils had higher microplastic concentrations than paddy or dryland soils, driven by plastic mulch use and irrigation. Microplastic contamination of this major water supply raises concerns about downstream drinking water quality for millions of people.
To explore the occurrence characteristics and influencing factors of microplastics in soil in the Danjiangkou Reservoir area, this study collected soil samples from orchards, dryland, paddy fields, and wetland and identified microplastics in soil via density sorting, microscope observation, and Raman spectrometry. The results showed that microplastics were detected in 64 samples collected in the study area, and the abundance ranged from 645 to 15161 n·kg-1. The spatial distribution of microplastics in the bottom of the reservoir was higher than those in the middle and head of the reservoir, and the abundance of microplastics in the surface soil(0-20 cm) was significantly lower than that in the bottom soil(20-40 cm). The main types of microplastics were polypropylene(26.4%) and polyamide(20.2%), the particle size was mainly concentrated between 50-500 μm(75%), and the common shape was fragments(66.2%). Correlation analysis showed that soil microplastic abundance was closely related to land use, distance from water and housing, population density, and soil properties. From the perspective of microplastic pollution risk, 72.1% of the region's microplastic polymer risk index was at level Ⅲ and level Ⅳ, and there was a certain risk of microplastic pollution in the Danjiangkou Reservoir area. The results of this study can provide support for risk assessment of microplastics.