Effects of multiple environmental factors and land use patterns on microplastic distribution in the topsoil of the Qinghai and Sichuan provinces of China

Abstract

The ubiquity of microplastics (MPs) in the environment has raised wide concern; however, the distribution of MPs in the soils of remote areas at the Tibetan Plateau is poorly understood. In this study, 28 soil samples were collected from various land-use soil environments in the eastern part of the Tibetan Plateau, and MPs were isolated from soils by density separation and organic matter oxidation. The MP abundance identified in the samples ranged from 0 to 160 items/kg soil, and the majority shapes of MPs was film. μ-Raman spectroscopy was used to identify the MP composition and showed that polyethylene was the principal polymer. Moreover, MP concentrations decrease as the elevation increases, which most likely explains for the lack of plastic wastes produced from agricultural activities at high altitude areas. Furthermore, the MP composition among different terrain conditions at the Tibetan Plateau was presented, and the flat condition may be conducive to the accumulation of MPs compared with the slope condition. Most MP inputs in the study area were in the farmland soils (mainly plastic covering), and atmospheric deposition may have an important effect on MP distribution in grassland, especially in slope grasslands. This study provides evidence of MP distribution associated with environmental factors in the east area of the Tibetan Plateau, which promote the understanding of MPs driven by land-use patterns and topographic conditions in the plateau soil environment.