Seasonal Variation Analysis of Microplastic Distribution in the Estuary of Brantas River

Every year, 0.48-1.29 million tonnes of plastic waste is estimated to enter the waters due to poor plastic waste management in Indonesia. Plastic waste has the potential to be degraded into smaller particles through ultraviolet (UV) radiation, weathering process, water currents, physical-mechanical and biodegradation. Plastics with particle sizes between >1 μm and <5 are categorized as microplastics (MP). Microplastic particles are mainly distributed in surface waters. Rivers are considered as the main route of plastic transportation from the land to the ocean. The Brantas River in Surabaya is the main downstream section of the Brantas River and plays an important role in providing clean water for Surabaya City, aquatic biota habitat, and irrigation. With extreme weather conditions such as long dry seasons and high rainfall in the rainy season distribution and abundance of microplastics in water bodies/rivers tend to vary. The study's goal is to determine the effect of seasonal water volume (dry and rainy) on the abundance and characteristics of microplastics in water and sediment samples from the downstream Brantas River (Surabaya city). Observations of the abundance of microplastics in water and sediment at three stations during the dry season revealed a trend of increasing abundance downstream. Microplastics were abundant in the water at sta 1 with an average of 0.8 particles/L, sta 2 with 1.25 particles/L, and sta 3 with 1.02 particles/L. The abundanceof microplastics in the sediment at sta 1 averaged 0.2 particles/gr, sta 2 0.51particles/gr, and sta3 0.25 particles/gr. Meanwhile, in the rainy season, the abundance of microplastics in water and sediment shows a higher abundancecompared to the dry season. Abundance of microplastics in the water at sta 1 with an average of 0.9 particles/L, sta 2 1.24 particles/L, and sta3 1.17 particles/L. The abundance of microplastics in the sediment at sta 1 averaged 0.55 particles/gr, sta 2 0.56 particles/gr, and sta3 0.60 particles/gr.