Microplastic Pollution in Waters and Sediments in a Lentic System: A Case Study in a Tropical Wet Urban Lake of Samarinda, Indonesia

The widespread use of plastic materials globally has sparked concerns regarding microplastic (MP) pollution, which is prevalent in water bodies worldwide and poses threats to aquatic life. Despite this, there remain uncertainties regarding the quantity, types and chemical makeup of MP, particularly in tropical urban lakes. This study aimed to examine the presence, distribution, types and chemical composition of MP in both the surface water and sediment of Air Hitam Lake, located in Samarinda City, East Kalimantan, Indonesia. Field sampling was conducted in February 2023 at 10 sites within the lake. The average concentration of MP in water was measured at 0.91 particles per litre, while sediment concentrations reached 375 particles per kilogram of dried sediment. Higher concentrations were observed near the lake inlet. Fibres were the most commonly observed type of MP in both surface water (79%) and sediment (76%) samples, followed by fragments and films. There was no significant correlation between MP concentrations in water and sediment. Fourier Transform Infrared (FTIR) analysis revealed the presence of polyester, polypropylene, nylon fibres, polyethylene, polystyrene polyvinylchloride in the samples, with polyethylene being the predominant compound, accounting for 46% of all surface water and sediment samples. The presence of MP derived from the degradation of larger plastic debris originating from visitors and the local community who dispose of plastic trash improperly highlights the importance of implementing effective plastic waste management strategies in communities surrounding the lake. This is crucial for preserving the ecosystem benefits provided by the lake. This study contributes to addressing knowledge gaps regarding MP pollution in tropical urban lakes and lays the groundwork for further research into inland freshwater environments.