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Open AccessArticle

High-Resolution Mapping of Japanese Microplastic and Macroplastic Emissions from the Land into the Sea

1
Department of Civil Engineering, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan
2
Business Planning and Development Division, Yachiyo Engineering Co., Ltd., Tokyo 111-8648, Japan
*
Author to whom correspondence should be addressed.
Water 2020, 12(4), 951; https://doi.org/10.3390/w12040951
Received: 22 February 2020 / Revised: 24 March 2020 / Accepted: 25 March 2020 / Published: 27 March 2020
(This article belongs to the Section Aquatic Systems—Quality and Contamination)
Plastic debris presents a serious hazard to marine ecosystems worldwide. In this study, we developed a method to evaluate high-resolution maps of plastic emissions from the land into the sea offshore of Japan without using mismanaged plastic waste. Plastics were divided into microplastics (MicPs) and macroplastics (MacPs), and correlations between the observed MicP concentrations in rivers and basin characteristics, such as the urban area ratio and population density, were used to evaluate nationwide MicP concentration maps. A simple water balance analysis was used to calculate the annual outflow for each 1 km mesh to obtain the final MicP emissions, and the MacP input was evaluated based on the MicP emissions and the ratio of MacP/MicP obtained according to previous studies. Concentration data revealed that the MicP concentrations and basin characteristics were significantly and positively correlated. Water balance analyses demonstrated that our methods performed well for evaluating the annual flow rate, while reducing the computational load. The total plastic input (MicP + MacP) was widely distributed from 210–4776 t/yr and a map showed that plastic emissions were high for densely populated and highly urbanized areas in the Tokyo metropolitan area, as well as other large urban areas, especially Nagoya and Osaka. These results provide important insights that may be used to develop countermeasures against plastic pollution and the methods employed herein can also be used to evaluate plastic emissions in other regions. View Full-Text
Keywords: microplastic; macroplastic; river; plastic pollution; marine debris microplastic; macroplastic; river; plastic pollution; marine debris
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MDPI and ACS Style

Nihei, Y.; Yoshida, T.; Kataoka, T.; Ogata, R. High-Resolution Mapping of Japanese Microplastic and Macroplastic Emissions from the Land into the Sea. Water 2020, 12, 951.

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