Distribution Characteristics and Risk Assessment of Microplastics in Farmland Soil in Guyuan

Abstract

The farmland ecosystem faces the emerging risk of microplastic pollution. To investigate the distribution characteristics of microplastics in agricultural soils in Guyuan City, the abundance, type, color, size, and shape of microplastics in Guyuan City agricultural soils were analyzed using field survey, microscopic observation, and Fourier transform infrared spectroscopy. In addition, the risk of microplastic pollution was assessed using the pollution load index method (PLI). The results showed that the microplastic abundance of agricultural soils (0-20 cm) in Guyuan City ranged from 186.32 to 1286.24 n·kg-1, and the microplastic abundance of soils in facility agriculture increased significantly by 35.56% and 228.91% compared with those in non-facility agriculture with and without film, respectively, and the microplastic abundance in the arable layer was 0.31 times higher than that in the plough pan layer. PE (26.42% to 62.83%) and PP (27.64% to 42.62%) were the main microplastic polymer types, and the number of soil polymer species was significantly greater in facility agriculture than that in non-facility agriculture. Microplastics <100 μm accounted for 32.21%-42.52%, whereas >1000 μm accounted for only 0.28%-12.31%. The particle size of microplastics in the arable layer was 47.39% higher than that in the plough pan layer, and the particle size of microplastics was the largest in facility agriculture and the smallest in non-facility film-free planting. Microplastics were mostly in the form of films, fibers, fragments, and microbeads, with the greatest abundance in the form of fibers and the second largest in the form of films. A total of seven colors of microplastics were monitored, mainly white and black. The overall risk of contamination in the study area was low, and the highest risk of microplastic contamination was found in the soil of facility agriculture. The results of the study will provide data reference for the assessment of microplastic contamination in agricultural soils and microplastic soil environmental behavior in China.