Distribution characteristics of microplastics in the seawater and sediment: A case study in Jiaozhou Bay, China

As a newly identified form of pollutant in the ocean, microplastics are receiving more and more attention from researchers. In order to evaluate the potential impact of microplastics, it is important to have comprehensive knowledge of the current microplastic situation. This study analyzed the abundance, polymer type, size, shape and color of microplastics in the seawater and sediments of Jiaozhou Bay, China, a semi-enclosed bay highly affected by surrounding human activities. Qualitative and quantitative analysis of microplastics were carried out using stereo microscope and attenuated total reflection micro-Fourier transform infrared spectrometer (ATR-μ-FT-IR). The abundance of microplastics in the bay seawater samples ranged between 20 items/m and 120 items/m. The abundance of microplastics in sediment samples in the bay were between 7 items/kg d.w. and 25 items/kg d.w. The microplastics were mainly in black and blue colors with fiber being the dominant shape in all samples. All microplastics identified were smaller than 4 mm in this study. Polyethylene terephthalate (PET) was the main type of microplastics, followed by polypropylene (PP) and polyethylene (PE). Both the abundance and types of microplastics show positive correlations between the seawater and sediment samples. Microplastic polymer types in the bay showed close match to the polymer types in the estuaries. Relatively higher abundance of microplastics tended to be found in the area where there were residual currents and sediment transport trends. Our study showed riverine input is an important contributor to the microplastics in the bay and physical factors such as residual currents would greatly affect the aggregation of microplastics.