Hydrodynamic and anthropogenic drivers of microplastic distribution in Labuan Bay, Banten

Microplastic pollution has become a critical environmental issue in coastal and estuarine ecosystems due to its persistence and potential impact on marine biota. This study aims to quantify the abundance and characterise the morphology, size, and colour of microplastics in both the surface water and sediment of Labuan Bay, while analyzing the influence of hydrodynamic factors on their distribution. Data collection was conducted at 9 sites representing riverine, estuarine, and marine zones. Surface water samples were collected using a plankton net, while sediment samples were collected using a Van Veen grab. Microplastic identification was conducted visually using a stereomicroscope. The results showed a mean microplastic abundance of 2.25 ± 0.99 particles/L in water and 1,566.67 ± 859.19 particles/kg in sediment. Fibres were the most prevalent morphology in the water (46.39%), whereas fragments dominated the sediment samples. Smaller particles (<200 µm) were more abundant in the sediment, while the 200–500 µm size range dominated the water column. PCA results (explaining 63.02% of the total variance) indicated that high current velocities trigger a flushing effect that reduces local abundance, whereas calm areas facilitate the deposition of denser particles. The findings suggest that Labuan Bay serves as a significant sink for microplastics, driven by domestic waste discharge and fishing activities. The study underscores the critical role of hydrodynamics and particle density in governing the transport and fate of microplastics in estuarine environments.