Distribution Characteristics of Microplastic Pollution in the Surface Sediments of the Laoshan Coastal Area of Qingdao

Owing to the extensive production and utilization of plastic products, a substantial volume of plastic waste is inevitably generated, comprising plastic particles < 5 mm in size, which are categorized as microplastics. Microplastics emanating from diverse sources can be classified as primary and secondary. Primary microplastics encompass plastic particles with a diameter < 5 mm that are synthetically produced in industrial processes, such as plastic microbeads found in exfoliating scrubs, toothpaste, and facial cleansers. Secondary microplastics result from mechanical abrasion, ultraviolet radiation, biological fragmentation, and other processes acting on larger plastic items. Surveys have revealed the global distribution of microplastics, aptly termed the "PM2.5 of the ocean." Microplastics are a prominent environmental issue, paralleling challenges posed by climate change, ozone depletion, and ocean acidification as an emerging global concern. Consequently, their pollution characteristics and associated ecological and environmental risks have become focal points of global research. Marine microplastics originate predominantly from atmospheric deposition, land-based inputs, coastal tourism, maritime shipping, and fishery production. Seabed sediments serve as a significant reservoir or "sink" for microplastics in oceans. Disparities in microplastic abundance are evident in nearshore beaches, offshore sediments, and deep ocean sediments. The pollution status of microplastics in sediments may be exacerbated in urban nearshore areas owing to intense human activities. However, the status and distribution characteristics of microplastics in urban nearshore sediments remain unclear. Qingdao is a typical coastal and marine city. In this study, we investigated the abundance, morphology, polymer types, and color of microplastics in the surface sediments of the Laoshan coastal area of Qingdao. Microplastics were isolated from surface sediment samples and examined under a stereomicroscope equipped with a camera. Fourier-transform infrared spectroscopy was employed to identify the polymer types of microplastics. The results revealed that the abundance of microplastics in the surface sediments of the Laoshan coastal area of Qingdao ranged from 9.06–34.48 ind./kg with an average of (21.97±8.32) ind./kg. Microplastics with particle sizes < 0.5 mm constituted 76% of the total microplastic count. Fiber, granule, and film shapes were predominant, accounting for 53%, 33%, and 14%, respectively. Transparent microplastics were more prevalent than other colors, accounting for 66% of the total. Four polymer types of microplastics were identified: Polypropylene (PP), polystyrene (PS), cellulose, and polyethylene. PP was the dominant polymer type, representing 45%, followed by PS (22%). The microplastic pollution levels in the surface sediments of the Laoshan coastal area of Qingdao were found to be comparatively lower than those in other domestic sea sediments. Considering the heightened human activity in coastal cities, further investigation of the microplastic pollution status and distribution characteristics in coastal areas is warranted. These findings contribute to an enhanced understanding of the environmental risks posed by microplastics to marine ecosystems and provide a scientific foundation for the assessment and management of microplastic pollution in coastal regions.