Abundance, morphology, spatial-temporal distribution and sources of microplastics in Shilaoren Beach, Qingdao, China

Located in the transitional zone between the ocean and land, beaches are the main site for the accumulation of microplastics and the main source of microplastics in coastal area. However, most studies focusd on the difference in microplastics abundance on the surface layer of different beaches, ignoring the spatial and seasonal variation characteristics of microplastics and their influence mechanisms in the same beach. In this study, high-resolution sampling was conducted at Shilaoren Beach in October 2022 and March 2023 respectively, to reveal the spatial and seasonal variation of microplastics and their influencing factors in the same beach, and to speculate the potential sources of microplastics. The results showed that the abundance of microplastics was higher in autumn than in spring, the average abundance of microplastics was 452.2 +/- 176.5 n/kg and 748.5 +/- 395.5 n/kg in spring and autumn respectively. The abundance of microplastics was higher in the central area of the beach where tourist activities were concentrated, and the abundance of microplastics near the sewage outlets and the high tide line was generally higher than that in other areas. The shape of microplastics was mainly fibers/lines (>90 %), and other shapes such as fragments, pellets, and films were less common. The abundance of microplastics decreased with their own increasing particle size. The color of microplastics was mainly transparent, followed by black and blue. The polymer types of microplastics included PA, PET, PE and PS. Beach tourism activities and sewage discharge would be the main factors affecting the spatial and seasonal distribution of beach microplastics.