The Migration and Pollution Risk of Microplastics in Water, Soil, Sediments, and Aquatic Organisms in the Caohai Watershed, Southwest China

The migration and driving factors of microplastics (MPs), as an emerging pollutant, have been reported in plateau lakes. However, whether MPs can accumulate to an extreme degree in the local aquatic organisms of plateau lakes remains unclear. Therefore, the present study mainly aims to investigate the MPs accumulated in tissues of grass carp as well as reveal their migration processes and driving factors in the Caohai watershed, a typical plateau lake in southwest China. Density flotation (saturated NaCl solution) and laser direct infrared imaging spectrometry were used to analyze the relative abundance and morphological characteristics of MPs, respectively. The results showed that the MPs’ abundance in soil, water, and sediments ranged from 1.20 × 103 to 1.87 × 104 n/kg, from 9 to 223 n/L, and from 5.00 × 102 to 1.02 × 104 n/kg, respectively. The contents and composition of MPs in forestland soils were more plentiful in comparison with cultivated land soils and marshy grassland soils. Polyethylene (PE), polyvinylchloride (PVC), PA from caprolactam (PA6), and PA from hexamethylene diamine and adipic acid (PA66) were detected in grass carp, and PE was detected in all organs of grass carp. MP concentrations in the stomach, intestines, tissue, skin, and gills of grass carp ranged from 54.94 to 178.59 mg/kg. MP pollution probably mainly originated from anthropogenic factors (road traffic, farming activities, the habits of residents scattered around the study area, etc.) due to the Caohai watershed’s considerable proximity to Weining city. In addition, wind, land runoff, rivers, and atmospheric deposition in the locality directly and indirectly promoted MP migration. Our results suggested that although there is moderate MP pollution in soil, water, sediment, and grass carp in comparison with other areas, it is necessary to pay attention to PE and PVC migration via the various environmental media and the risks associated with consuming the local grass carp. The local government can make several policies to reuse and recycle agricultural film to alleviate local PE and PVC pollution.