Characterization of Microplastic Pollution in Surface Waters of Agus River, Mindanao, Philippines

Abstract Rivers are considered the principal conduits of plastic pollution, transporting plastic waste from terrestrial environments to the ocean, where it contributes to the formation of microplastics by fragmentation. The riverine microplastic [MP] studies in the Philippines, conversely, focus solely on urban environments. The current study investigated the presence of microplastics in the surface waters of Agus River, Mindanao, Philippines, a tributary of the only ancient lake in the country. Collection of samples were conducted in 3 sampling sites, coinciding with the upstream, midstream, and downstream levels of the river. Microscopy and Fourier Transform Infrared Spectroscopy [FTIR] were utilized to identify and confirm 84 total microplastic pieces with an average density of 0.46MP/L, indicating that microplastics were pervasive in the region. Kruskal Wallis test also reveal that presence of pollutants and level of contamination significantly differ (P < 0.05) among the sites, predominated by brown-colored microplastics (34.5%). Morphological analysis reveals that the river is polluted with filament (39.2%), fragment (26.19%), and fiber (22.6%) microplastics. Notably, no common polymers were identified across the said sites. The results of this study serve as foundation for macroplastic reflux research and the exploration of additional environmental mediums, such as biota, to assess the magnitude of microplastic pollution in the ecosystem.