Quantitative analysis and risk assessment to full-size microplastics pollution in the coastal marine waters of Hong Kong

Given the potential risk to the ecosystem, attention has increased in recent decades to the contamination of the aquatic environment by microplastics (MPs). Due to the limitations of conventional analysis methods of MPs, little is known about the size distribution and abundance of a full-size MPs from 1 μm to 5 mm. The present study quantified MPs with size ranges of 50 μm - 5 mm and 1-50 μm in the coastal marine waters from twelve locations in Hong Kong using fluorescence microscopy and flow cytometry respectively, during the end of wet (September 2021) and dry (March 2022) seasons. The average abundance of MPs with size ranges of 50 μm - 5 mm and 1-50 μm from twelve sampling locations marine surface waters were found ranging from 27 to 104 particles L and 43,675-387,901 particles L in the wet season respectively, and 13-36 particles L and 23,178-338,604 particles L in the dry season respectively. Significant temporal and spatial variations of small MPs abundance might be observed at the sampling locations, which were contributed by the influences of the estuary of Pearl River, sewage discharge points, land structure, and other anthropogenic activities. Based on the MPs abundance information, ecological risk assessment was conducted and revealed that the small MPs (< 10 μm) in coastal marine surface waters may pose potential health risks to aquatic organisms. Additional risk assessments are needed in order to determine whether or not the MPs exposure would cause health risks to the public.