Initial Indication of Microplastics in the Water and Sediment of the Tukad Badung River in Bali, Indonesia

Abstract Microplastics are plastic fragments smaller than 5 mm that pose greater harm than larger plastic pollution. The ocean harbor substantial quantities of tiny particles, and their presence is significantly impacting marine species. The ingestion of microplastics by smaller aquatic species, who mistake them for food and their subsequent incorporation into the food chain is a matter of considerable concern. Rivers serves as primary conduits for transporting these materials from terrestrial environment to the oceans. This study aimed to examine the concentration of microplastics in water and sediment from the Denpasar River Basin, Indonesia. Under rigorous selection process designed to guarantee a representative sample, five districts and 10 specimens were identified. The results showed that all samples exhibited microplastics, with abundance of microplastics in the water samples ranged from 48.5 ± 1.5 to 105.4 ± 1.3 particles/L, and in the sediment, ranged from 225.33 ± 48 to 589.33 ± 12 particles/kg. Station 5 exhibited the highest occurrence of microplastics. The study indicated that microplastic fragments constituted the majority of samples obtained from water and sediment, accounting for 39.48%. Furthermore, the quantity of particles measuring under 1000 µm was notably elevated, constituting over half of the total microplastics, with their proportion calculated to be approximately 50.12%. Black and blue were predominant colors, constituting almost 80% of microplastics. Two types of polymers were detected by FTIR spectroscopy, polyethylene and polystyrene. This research provides vital insights into the distribution, properties and polymer composition of microplastic in the Denpasar River Basin.