Occurrence and Composition of Microplastics in the Seabed Sediments of the Coral Communities in Proximity of a Metropolitan Area

In marine environments, microplastics have become a focus in scientific research in the last decade due to the global threat this pollutant poses to the marine environment. Corals in Hong Kong are under threat due to the degradation of the marine environment caused by human activities. This study investigated the occurrence, abundance and composition of microplastic debris (0.3–5 mm) in seabed sediments adjacent to coral communities in Hong Kong. Twenty-four benthic sediment samples were collected from four study sites located along the northeastern and eastern shores of Hong Kong. Microplastic concentrations ranged from 169 ± 48 to 221 ± 45 items/kg, and the mean concentration of microplastics in the seabed sediments was 189 ± 50 items/kg, which was comparable to similar studies in other regions. Microplastics accounted for 95.4% of particles extracted from benthic sediment samples using 40× light microscopy. ATR-FTIR spectroscopy analysis showed that polyethylene (PE) and polyethylene terephthalate (PET) comprised the majority of polymer types, contributing 45.3% and 29.3%, respectively. The proportion of microplastics made from PE and PET in seabed sediments was significantly higher than that observed in local beach sediments. The proportion of microplastics made from PE and low-density polyethylene (LDPE) and polypropylene (PP) together in the seabed sediments was much higher than that of PET and polyvinyl chloride (PVC). The results have provided information with reference to environmental concentrations of microplastics for fringe reef habitat close to urban areas, which can be applied in studies concerning ecotoxicity of microplastics.