G.R. Wibisono, K.A.F. Annisa, K.S. Kristianti, M. Maudina
Microplastics are increasingly acknowledged as emerging pollutants in freshwater environments; however, their seasonal variations in terms of abundance and characteristics remain poorly understood, especially in tropical urban rivers. This study explores the seasonal dynamics of microplastic contamination in the Kasin River, Malang, Indonesia, by comparing conditions during the dry season (August 2024) and the rainy season (April 2025). Surface water samples (3 liter each with 3 repetitions) from six sites were treated with the Wet Peroxide Oxidation (WPO) method to digest organic matter. This was followed by density separation and microscopic examination to assess microplastic abundance, as well as their shapes, sizes, and colors. Polymer types were identified using Fourier Transform Infrared Spectroscopy (FTIR). Concurrently, in situ water quality parameters were measured (in situ): pH, temperature, dissolved oxygen (DO), electrical conductivity (EC), salinity, total dissolved solids (TDS), turbidity, and oxidation-reduction potential (ORP). Microplastic concentrations ranged from 190 to 390 particles per liter during the rainy season and from 100 to 590 particles per liter in the dry season, with higher average levels recorded during the dry season. This increase is likely due to surface runoff and elevated human activity. Fiber was the dominant type of microplastic in both seasons, while FTIR analysis revealed the presence of polymers such as polyvinyl chloride (PVC) and acrylonitrile butadiene styrene (ABS). These findings offer crucial baseline data on microplastic trends in tropical urban rivers and highlight the urgency of enhancing monitoring efforts and plastic waste management, particularly during periods of increased water flow. © 2026 Published under licence by IOP Publishing Ltd.
Department of Water Resources Engineering, Universitas Brawijaya, Malang, Indonesia
