Spatial and seasonal variation of Microplastics in the Avoimitro Ghat and Kalurghat of the Karnaphuli River, Chattogram

Abstract The study investigated the Microplastics (MPs) abundance in the two distinct locations (Avoimitroghat and Kalurghat) of the Karnaphuli River, Chattogram, Bangladesh. Eight samples were collected monthly throughout the study period, with three transects covering a total area of 500 m at each site. MPs were collected using a 200 μm mesh size manta net, separated through a density separator, enumerated, and characterized using a microscope. Avoimitro Ghat (94861 ± 97126) had a higher mean abundance of MPs (particles per Km2) than Kalurghat (31343 ± 33183). Statistically significant variation was observed (p < 0.05) in the mean abundance of MPs per km2 between the rainy (76134 ± 89641) and dry (63101 ± 79174) seasons. Fragment group MPs had the highest mean abundance (117430 ± 105028 MPs/Km2), whereas pellets had the lowest (8264± 8637). MPs with an elongated shape were dominant at both stations and during all seasons. Blue MPs had the highest mean item value in Avoimitro Ghat and during the dry season, while brown-colored MPs were highest in Kalurghat and during the rainy season. Among the five different size groups, 1–2 mm MPs were abundant in both seasons and Avoimitro Ghat, whereas 500 µm to < 1 mm MPs were abundant at the Kalurghat stations. This study identified and quantified microplastics at the chosen sites, which will be helpful for stakeholders in mitigating microplastic pollution in the Karnaphuli River.