Abundance and variation of microplastics between seasons in a tropical estuary: The case of Can Gio estuary, Vietnam

Every year, millions of tons of plastic waste are dumped into the ocean from estuaries. The process of accumulating and converting plastic into microplastics (MPs) in this dynamic system has not received as much attention compared to the open-ocean region. Therefore, this study aimed at evaluating the seasonal variation in microplastic (MP) content at the Can Gio estuary, Vietnam, during the rainy and dry seasons of 2021 and 2022. Water, sediment, and biological samples were collected at four sites. MP contents ranged from 0.00134 ± 0.00043 to 0.00095 ± 0.00014 items/L in water surface samples, from 4.22 ± 0.46 to 2.44 ± 0.46 items/L in water column samples, and from 200 ± 13.68 to 90 ± 13.68 items/kg in sediment samples. There was an interactive effect of seasonal fluctuation and the complex flow regime on the MP content. MP bioaccumulation in Saccostrea and Periophthalmodon schlosseri was 1.5 – 1.8 and 0.2 – 0.52 items/individual, respectively. The main MP shapes were fibers and fragments. The composition mainly consisted of polypropylene (45.45%), polyethylene (18.18%), polystyrene (9.09%) and other plastics (27.28%). The source of MPs can be projected from the macro-plastic stream accumulated at the sampling sites. This study found the presence of MPs in both seasons of the year, and the accumulation of MPs in this dynamic region is closely correlated with hydrological properties of the estuary.