Microplastic contamination of the surface waters of Japanese rivers
Abstract
Contamination of the geosphere by microplastics (plastic particles < 5 mm in diameter) is currently a major environmental problem. However, regardless of the main sources of plastics in the oceans, the progress of microplastic contamination of rivers is hardly understood. Thus, quantifying microplastic contamination is essential to understand its progress and develop effective countermeasures. In this study, the surface waters at 85 sites in non-tidal areas of 67 Japanese rivers were sampled for microplastics using a plankton net. Sampling was conducted from August 2015 to January 2019. Microplastics were found in the water from 84 of the sites, indicating that almost all Japanese rivers are contaminated with microplastics. As expected, polyethylene and polypropylene, whose densities are lower than that of freshwater, are the predominant plastic materials (73% and 79% by number and mass, respectively). The numerical concentration (NC) and mass concentration (MC) were quantified by measuring the number and mass of microplastics per unit volume of freshwater, respectively, based on field surveys. The geometric means of NC and MC are 1.9 particles/m3, within a range of 0.030 -75 particles/m3, and 0.17 mg/m3, within a range of 0.000077 -16 mg/m3, respectively. Both NC and MC were statistically significantly regressed with urbanization and population density (p < 0.05), indicating that a greater concentration of microplastics was generated due to urbanization and population growth. Further, when focusing on the longitudinal distribution of microplastic contamination in the Ara River (length: 173 km, catchment area: 2940 km2) and Tsurumi River (length: 42 km, catchment area: 235 km2), the local maxima of both NC and MC were found in the middle basin of the two rivers, even though they showed high temporal fluctuation. Our results indicate that microplastic contamination has already progressed in Japanese rivers. Therefore, the continual monitoring of microplastic contamination in freshwater away from the oceans is necessary to understand microplastic contamination in rivers and develop effective countermeasures.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H43O2286K
- Keywords:
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- 1803 Anthropogenic effects;
- HYDROLOGY;
- 1834 Human impacts;
- HYDROLOGY;
- 1871 Surface water quality;
- HYDROLOGY;
- 1879 Watershed;
- HYDROLOGY