Country-specific riverine contributions to marine plastic pollution.

Marine plastic debris are mainly derived from land-based sources, and the transport of plastics via global rivers is of great concern. Ample efforts have been made in estimating the land-based contributions of plastic to the global oceans, but quantifying country-specific (and per capita) riverine outflows is an important step toward the development of a globally integrated framework to mitigate marine plastic pollution. To estimate the country-specific riverine contributions to global marine plastic pollution, we built a River-to-Ocean model framework. In 2016, the median annual country-specific riverine plastic outflows and related per capita values for 161 countries varied between 0.76 and 103,000 metric tons (MT) and 0.83-248 g, respectively. India, China, and Indonesia were the top three contributors to riverine plastic outflows, whereas Guatemala, Philippines, and Colombia had the highest per capita riverine plastic outflows. The total riverine plastic outflow from 161 countries was in the range of 0.15-0.53 million MT annually, accounting for 0.4 %-1.3 % of the 40 million MT plastic waste generated yearly by more than seven billion humans. Population, plastic waste generation, and Human Development Index are the dominant factors influencing riverine plastic outflows to global oceans from individual countries. Our findings provide an important basis for launching effective plastic pollution management and control measures in global countries.