Quantification and characterization of microplastics input from runoff water in Kamo and Takano Rivers, Kyoto, Japan.

Microplastic particles can be found everywhere in the world and sources, transport processes and impact on the environment and human health is yet to be well understood. The goal of this work is to quantify and characterize the impact of non-point source microplastic pollution in urban areas transported through runoffs. Here, we present the result of a survey performed during spring 2020 in the watersheds of Kamo and Takano rivers in Kyoto, Japan. The focus of the survey is to monitor microplastic particles in the range of 10 to 300 μm in river water during urban runoff occurring conditions. 26 samples and three blanks were collected during three different surveys under both sunny and rainy conditions. Samples were analyzed through micro Fourier Transform InfraRed spectroscopy (μ-FTIR) and a database of more than 1,300 particles was built from the analysis. Microplastic concentration was estimated on average at 7,212 items/m3 and 700 μg/m3 under sunny conditions. Microplastic concentration increased up to 605,000 items/m3 and showed strong variations under rainy conditions. For each rain event, the total load of microplastics per unit of urban area was calculated and was in the range of 2.37106 to 1.02107 items/ha and 188 to 731 mg/ha. It was showed that microplastic particles are on average significantly smaller under rainy conditions and that some polymer types have a significantly different size on average.