Characterization of microplastic distribution, sources and potential ecological risk assessment of domestic sewage from ships

Shipboard domestic sewage, encompassing both black water and gray water, has the potential to transport significant quantities of environmentally harmful microplastics, a concern that has garnered increasing global attention. In this study, Fourier infrared (FTIR) detection was used to detect microplastics in marine domestic wastewater. The primary objective was to evaluate the abundance and characteristics of microplastics present in ship domestic sewage, investigate potential sources and influencing factors, and assess the ecological risks associated with ship sewage through analyses of microplastic abundance and hazard indices. The findings revealed that the mean abundance of microplastics in ship domestic sewage are 50.82 particles per liter(n/L), with gray water exhibiting significantly higher levels at 167 n/L compared to black water at 36.96 n/L and mixed sewage at 46.57 n/L. Fiber microplastics constituted a predominant 95% of all samples collected from ships, followed by film microplastics. In terms of color distribution, transparent and blue microplastics were the most prevalent, with the majority measuring between 100 and 1000 μm in size. Polyethylene terephthalate (PET) emerged as the most common polymer type, followed by polypropylene (PP). The risk assessment highlighted that microplastics in domestic wastewater pose significant ecological risks to aquatic organisms, with pollution load indices consistently reaching Class IV levels. Correlation analyses between microplastic abundance and the physicochemical properties of sewage demonstrated a significant relationship between microplastic levels and the concentration of suspended solids in ship sewage. This study provides essential data to inform the development of regulatory policies aimed at managing the discharge of black water and gray water discharges from both domestic and international vessels.