Spatial Distribution and Source Analysis of Microplastics in Surface Sediments of Dianchi Lake

PurposeTo study the spatial distribution and sources of microplastics in surface sediments of Dianchi Lake.

MethodsA total of 14 surface sediment samples were collected from Dianchi Lake using Peterson grabs in April 2019 and September 2021. The microplastics in the surface sediments of Dianchi Lake were separated using the density flotation method, and microscopic examination and identification were conducted using microscopes and Raman spectroscopy instruments. Correlation analysis was carried out to determine the relationship between microplastic abundance and water depth.

ResultsMicroplastics abundance in surface sediments ranged from 344.6 to 1171.8 items/kg (dry weight), with an average abundance of (609.6±206.1) items/kg that was indicative of high pollution levels. Fibrous microplastics constituted the majority (83.49%) of all microplastics, while fragments, particles, and films each accounted for about 5%. Blue and transparent microplastics were the most commonly observed color types, making up 46.43% and 34.92% of the total, respectively. The proportion of red, black, and green microplastics decreased by degress. The number of microplastics with particle sizes <1 mm, 1-3 mm and >3-5 mm accounted for 69.74%, 27.62% and 2.64%, respectively. The most common types of polymers found in the microplastics were polyethylene terephthalate (38.12%), colored plastics (36.77%), and polypropylene (12.56%).

ConclusionMicroplastics in Dianchi Lake’s surface sediments are concentrated in the lake center in northern part and outlet areas in southern part, with a distribution pattern that decreases from north to south. Based on the physical and chemical features of the microplastics and the surrounding human activities, it is inferred that the main sources of microplastics are fishing nets and textiles.