Microplastics in Marine Sediments in Eastern Guangdong in the South China Sea: Factors Influencing the Seasonal and Spatial Variations

Little is known about the comprehensive factors influencing temporal changes in microplastic abundance in marine ecosystems. We investigated seasonal variations in the microplastic distribution in marine sediments in multiple-used zones of Eastern Guangdong in the South China Sea. The top 10 cm sediments from 26 sites were collected by grab sampling in the spring, summer, and winter of 2021. Marine sediments had the lowest microplastic abundance in summer, significantly lower than in other seasons. The size of microplastics varied from 22.5 to 4363.3 µm but the 50–200 µm range was the most abundant. Transparent and fragmented microplastics were the most frequently observed composition. Microplastic abundance negatively correlated to distance to the coast. However, seaweed ecosystems impacted microplastic abundance by changing the microenvironment and/or direct contact and entrapment. Microplastic abundance is closely related to coastal mariculture and local residential and industrial activities. Polypropylene, polypropylene-polyethylene copolymer, polyethylene terephthalate, and polyethylene were the most frequently detected compositions, probably from packaging materials, textiles, and electronic/electrical/building industries. This work helps to understand the role of multiple-used zones and their influence on microplastic distributions in marine ecosystems. Appropriate management of the use and disposal of plastic waste on land was recommended to alleviate microplastic pollution in the marine environment.