Characterization and Quantification of Surficial Sediment Microplastics and Its Correlation with Heavy Metals, Soil Texture, and Flow Velocity

AbstractInvestigating the presence of microplastics in the Pasig River, the highest plastic-emitting river in the Philippines and one of the ocean's leading contributors of these materials, is highly relevant. In this study, surficial sediments in eight stations along the main channel of the Pasig River were analyzed for microplastic content, heavy metals, and soil texture. The microplastics were categorized according to shape, color, and size. The polymer type was determined using infrared spectroscopy. The number of microplastics was correlated with heavy metals, soil texture, and flow velocity. The results show that the dominant shape, color, size, and polymer type were fragment, color white, size range from 0 to 500 μm, and polyvinyl alcohol, respectively. Downstream stations 5 and 8 had the highest microplastic concentration. The number of microplastics showed a positive moderate correlation with percent sand (r = 0.40) and clay (r = 0.42), and a negative high correlation with percent silt (r=-0.80). For microplastics and heavy metals, a positive moderate correlation was observed for iron (r = 0.52) and zinc (r = 0.58), while a negative weak correlation was present for lead (r=-0.06). Microplastics and flow velocity showed weak correlations demonstrating that the accumulation in the bottom river sediment may be based on the proximity of the plastic source rather than on the flowing water with plastic sources. Results reflect the diverse influences on the Pasig River which is surrounded by informal settlements, manufacturing industries, urban offices, and residential areas. More plastic management initiatives and better implementation of existing laws should be done by the government.Keywords: Heavy metalsmicroplasticsPasig Riverpolymersediment Disclosure statementThe authors declare that they have no known competing financial interests or personal relationships that influenced the results reported in this article.Additional informationFundingThis article was produced from the project entitled "Characterization and quantification of microplastics and heavy metals with correlation to surficial sediments in Pasig River" funded by the Office of the Vice-Chancellor for Research and Extension (OVCRE), UPLB, Basic Research Program. This work was also funded by the UP System Enhanced Creative Work and Research Grant (ECWRG-202201-8RG047). The authors would like to express their gratitude to the Pasig River Coordinating and Management Office for the provision of the annual water quality reports and to the Pasig River Ferry Service Office for the ferry boat and support during the conduct of the field works. The authors would like to acknowledge the reviewers for their scientific suggestions and constructive comments which led to significant improvements to the manuscript.