Depth-wise Distribution of Microplastics Around Teluk Lerong Intake, the Mahakam River: Implications for Water Treatment Processes

The Mahakam River is an essential raw water source for the Water Treatment Plant (WTP) in the Regional Drinking Water Company of Samarinda City. This means its quality is crucial, specifically due to several activities usually conducted in the river and the density of the surrounding community. One of the most critical issues related to surface water quality is microplastics. This study aimed to assess the abundance, size, and types of microplastics present in the water column of rivers at various depth levels. Samples were collected from the intake using a composite sampling method. The samples were processed by first filtering with 180 µm nylon, removing organic substances with H2O2, separating by density, conducting a second filtration with different nylon sieves, and then performing microscopic observation. The identification of polymers was carried out using FTIR. The results indicated the presence of microplastics in all tested samples. The highest abundance of microplastics, 25.4 particles per liter, was in the size range of 180-250 µm at a depth of 0.5 meters. The abundance of microplastics decreased as the depth of the river increased. The most common types of microplastics detected were fibers, fragments, and films. It is crucial to map the distribution of microplastics, mitigate their occurrence, and reduce degradation and fragmentation to increase WTP performance.