Microplastic is a fine plastic of 0.3 to 5.0 mm.It is characterized by floating at a low concentration in the marine environment and adsorbing hydrophobic persistent organic pollutants at a high concentration.MPs that adsorb high concentrations of harmful substances may be incorporated into the food chain and contaminate marine ecosystems.On the other hand, the waters around Japan are called "MP hotspots" where MPs are highly accumulated at a concentration 27 times higher than the world average.Since plastic is consumed in the land area, it is assumed that MP generated in the land area flows out to the ocean through rivers, but the actual state of MP pollution in domestic rivers was unknown.

　In this study, MPs were collected from bridges by simply dropping a simple plankton net at 29 survey points in 36 rivers in Japan.As a result, MP was found at 86 survey points in 26 rivers, which is 31% of the total.The average MP concentration at this survey point was 1.6 / m3, which was about half of the sea area around Japan (average MP concentration 3.74 / m3). The MP concentration was 1 / m12, which was the highest in the Ohori River pouring into Teganuma, Chiba Prefecture, which was once the worst lake water quality.It was also found that the MP concentration is higher in rivers that are urbanized and have a high population density, that is, rivers with active human activity.

　From the results of this research, the importance of MP and plastic waste reduction measures in the land area, which is the source of MP pollution, has been shown again in order to solve the problem of MP pollution in the ocean.Since the research is limited to measuring the MP concentration, he wants to clarify the amount of MP transported from domestic rivers to the ocean in the future.

Paper information:[Environmental Pollution] Assessment of the sources and inflow processes of microplastics in the river environments of Japan