Distribution of microplastics in surface water and sediments of Qin river in Beibu Gulf, China

As a series of pollutants, microplastics have recently attracted widespread attention worldwide. In this study, different surface water and sediment samples were collected at 12 sampling sites along the urban section of Qin River in Guangxi Province, China. Water samples were collected using plankton nets with two different pore sizes (75 μm and 300 μm) and Teflon pump system with 25 μm mesh screen. The results showed that there was no significant difference in the abundance, particle size, and type of microplastics (F = 0.302, P = 0.588) between the two plankton nets, but the microplastic abundance in the samples collected by the Teflon pump was significantly higher (F = 9.12, P = 0.001), especially for microplastic fibers (F = 9.525, P = 0.001). Compared with the plankton net sampling method, the Teflon pump sampling had a smaller sample volume, resulting in a higher estimate of microplastic abundance in the water column. The microplastic abundance in the sediments was 0-97 items·kg dry weight. PE and PP were the main types of microplastics in Qin River, accounting for 67.2% and 72.3% in the water column and sediments, respectively. The microplastics in the water column and sediments were dominated by large-sized particles in the range of 1-5 mm. The sources of microplastic pollution in Qin River may be affected by many factors, including population density, industrial structure, and aquaculture activities. However, aquaculture activities were generally the main source of microplastic pollution in Qin River estuary. Wastewater treatment plants (WWTPs) could effectively decrease the microplastic abundance in urban sewage, reducing the impact of urban sewage discharge on microplastic accumulation in Qin River.