Occurrence of microplastic fragments in the Pasig River

Abstract Microplastics are plastic fragments with dimensions of less than 5 mm. These materials are formed within bodies of water by the forces shearing on the large plastics. Ultraviolet light from sunlight also degrades plastic materials causing discoloration and disintegration into smaller, micro- or even nano-sized particles. This study reports the isolation of microplastic fragments from the Pasig River within the vicinity of the Polytechnic University of the Philippines. The collection of floating particulates was done by sieving the river water (flow rate = 0.31 m s−1) through a 0.35 mm mesh for 10 minutes. Through this method, 25.7 m3 of river water was sieved over three samplings. Microplastics were isolated through a series of peroxide oxidation and sedimentation methods. All microplastic fragments were viewed and photographed under a compound microscope (40–100× magnification). A total of 34 microplastic fragments with lengths ranging from 0.56 to 4.58 mm were categorized. Microplastic fragments were categorized into two categories: small (1.16 ± 0.42 mm) and large (4.13 ± 0.37 mm), based on the size distribution. The microplastic fragments isolated were partially rounded and some showed signs of discoloration indicating mechanical and photo-degradation. The presence of microplastic fragments in Pasig River indicates persistent plastic pollution from the river source (Laguna de Bay), its tributaries, as well as the communities and industries situated along the river. Programs on solid waste management especially on plastic wastes could mitigate the production of microplastics in the river.