Analysis of microplastics in soils on the high-altitude area of the Tibetan Plateau: Multiple environmental factors

Microplastics (MPs), a class of emerging contaminants, are ubiquitous in the environment, but limited information is known about them in remote terrestrial environment at high-altitude areas with inconvenient traffic and sparsely populated. In this study, 54 soil samples were collected from various land use patterns (greenhouse, ordinary farmland, grassland, and bare land) in western area of the Tibetan Plateau to determine the influence of land use type, altitude, meteorological parameters, and distance from the road edge on MP distribution. The MP abundance ranged from 0 (not detected) to 190 items/kg, with an average number of 64.8 items/kg. The concentration of MPs was slightly negatively correlated with altitude because of less human activities in high-altitude areas (especially agricultural activities). The random forest (RF) models showed that altitude was the most important driving factor that affected the MP distribution. Small-sized MPs were more abundant at higher altitudes than at low ones, and the special natural environment of the high-altitude areas (tall vegetation scarcely, UV, and strong wind speed) may be conducive to the degradation of MPs in surface soils. The special source of MPs in non-agricultural soils was associated with traffic behavior: parking and rest behavior beside roads at high altitude areas, which filled an important source of MPs in the plateau area. This study emphasized the need to investigate the effects of traffic activities on MPs in remote areas at high altitudes.