Microplastics pollution in the soils of various land-use types along Sheshui River basin of Central China

Very little information is now available about the occurrence of microplastics in the soils of various land-use types. In this study, 18 sampling sites with two soil layers were investigated for four different land-use types (grassland, dry land, paddy field, and plastic greenhouses) in Sheshui River basin of central China. The results demonstrated that the total abundance of microplastics in all sites lied within the range of 875 ± 229-6075 ± 865 n kg^-1, and had an average value of 2522 ± 1276 n kg^-1 ('n' being the number of microplastics). The abundance of microplastics in dry land had the highest value, whereas the greenhouse had the lowest value. There were no significant differences in the number of microplastics among the four land-use types. Except for four sites, no significant difference was observed in the abundance of microplastics between 0-10 cm and 10-20 cm layers. Fiber and fragment were the leading shapes of the microplastics along with brown color and the size of less than 1 mm. Combined with the site survey, the potential sources of microplastics in the studied region were mainly the wastewater irrigation, application of organic fertilizer, and plastic mulching film. Multivariate analysis and principal component analysis demonstrated that the carbon and nitrogen in soil samples were positively correlated with the abundance of microplastics, whereas a significantly negative correlation was observed between the soil δ¹³C and the abundance of microplastics. It was inferred that the transformation and degradation of aging microplastics were primarily associated with the turnover of soil's carbon and nitrogen. The results of the current study contribute towards an in-depth understanding of the level of microplastics pollution for various land-use types and corresponding policy-making regarding the management of microplastics.