Microplastic abundance in the surface water of tropical estuarine fronts

Estuarine fronts are formed due to sharp density discontinuities resulting from the convergence of different water masses. This study, conducted in May and August of 2022 during the southwest monsoon season, focuses on assessing the role of estuarine fronts at Kuala Terengganu estuary in the accumulation of microplastics in surface seawater. The Terengganu River basin area covers approximately 4600 km² and consists of two main tributaries that drain into the Kuala Terengganu estuary. Microplastic samples were collected from three areas, the plume, front, and shelf, utilizing two methods: manta net (> 350 µm) and bucket-water sampling (> 20 µm). Results indicate that the estuarine front consistently exhibited higher microplastic concentrations than the plume and shelf regions throughout the study period, with bucket-water sampling contributing significantly to the abundance. Specifically, peak concentrations occurred during the ebb tide at the frontal region in both months, reaching 5761.703 particles m⁻³ and 12,687.437 particles m⁻³, respectively. The microplastics, predominantly transparent fibers smaller than 1000 µm, mostly showed signs of oxidative and mechanical weathering through SEM–EDS analysis, providing insights into their fate in estuarine surface waters. FTIR spectroscopy revealed polypropylene, polyethylene, and polyamide as the dominant polymers. These findings establish a baseline for microplastic abundance at the estuarine front of the Kuala Terengganu estuary and may inform future strategies for mitigating and recovering microplastic contamination in aquatic environments.