Microplastic Accumulation in Hong Kong’s Marine Sediment: Spatial Pattern and Potential Sources

Marine microplastic (MP) contamination has become a global issue due to its ubiquity, persistence, and potential ecological risks. Marine sediment is recognized as the final sink for marine microplastics and has therefore received increasing scientific attention. Currently, limited research has focused on microplastic pollution in the marine sediments of Hong Kong, China. In this study, we conducted a comprehensive investigation across Hong Kong to assess the abundance, polymer composition, and morphological characteristics of microplastics in marine sediments. Spatial pattern, risk assessment, and potential source analysis were further performed based on the field data. Our findings reveal that microplastics were unevenly distributed in Hong Kong's marine sediment with abundance ranging from 402.12 to 1507.96 items/kg (dry weight). The spatial pattern indicates higher microplastic accumulation in the western waters, with three hotspots at Deep Bay, Tai O, and Victoria Harbour. The dominant shapes of the observed microplastics were fibers and fragments. The major polymer types identified include polypropylene (PP), chlorinated polyethylene (CPE), and polyethylene (PE). The overall pollution load index (PLI) and pollution hazard index (PHI) were found to be at moderate levels. Notably, green PP was observed at 70% of sampling sites and accumulated in fishing farming areas and Victoria Harbor. It may be associated with regional intensive fishing and diverse anthropogenic activities. This research enhances our understanding of the health of Hong Kong's marine ecosystem and aids in the development of effective measures to mitigate marine microplastic pollution.