Distribution of Microplastics in the Beach Indicating Anthropogenic Sediments: Case Study in Can Gio HCM City, Vietnam

Research on characteristics, composition, size, shape (fragment, fiber, granular), distribution, and content of microplastics in coastal sediments was conducted through boreholes and excavations on identified cross-sections. Field surveys were conducted in the rainy and dry seasons, drilling (2m/borehole) and excavations (1.0 x 0.8 x 1.0) to collect samples at low tide. Changes in sediment environment and microplastics in the 2m borehole column, and seasonal changes in sediment structure and microplastics were studied in the excavations. Changes in microplastic content in the sediment sample column (borehole, excavation) and sediment OSL age were also determined. Synthesizing documents on the cross-sections will determine the distribution characteristics of microplastics in coastal alluvial sediments in the study area. Coastal sedimentary environments are determined based on analysis of grain size, sediment structure and diatoms in borehole and excavation samples. In addition, geomorphology and coastal sediments play an important role in determining sedimentary environments such as intertidal, subtidal, beach, sand bar, etc. The presence of microplastics with varying composition and content in borehole sedimentary environments of geological cross-sections is the basis for studying the distribution and source of microplastics. The research results show that the microplastic content is medium to very low, about 0-300 microplastics / 1000 g of dry sediment sample, often found in fine, medium and silty sand in the upper intertidal sediments (0 to -0.6 m) with an age of about 30 years ago (OSL age), and does not appear in the lower part of the drill core (from -0.7 m to -2 m). In addition, microplastics do not appear in clay-silt and clay-silt-sand. Two areas with quite concentrated microplastic content are the intertidal flats of Soai Rap and Dong Tranh rivers in Dong Hai commune and the Long Tau river mouth area in Can Thanh town; the intertidal flats in the middle of Long Hoa commune has a non-concentrated microplastic content.