Plastic trade-off: Impact of export and import of waste plastic on plastic dynamics in Asian region

Environmental contamination by plastics has been receiving considerable attention from scientists, policy makers and the public, and waste plastic trade has become a major social issue in recent years. In this study, the authors applied eco-hydrology model coupled with plastic debris model in Asian regions by including effect of waste plastic trade in order to clarify this research gap. Result showed settling and resuspension of plastic particles have great impact on mobilisation of plastic and its high intra-annual variability, and that the plastic transport becomes drastically higher during the flood periods accounting for most of the annual flux. In particular, the model simulated the size distribution of plastics in the water and riverbed sediment of the global major rivers and showed that the coarser particles are more distributed in the riverbed than those in the water. Further, the authors evaluated impact of waste plastic trade on change in riverine plastic transport by newly including effect of plastic trade on Mismanaged plastic waste (MPW) in the extension of previous studies. They newly modified to calculate municipal plastic waste by including these effects of plastic trade and disposal, and revised MPW assuming that the import of plastics is treated as the same as the export of plastics as the first approximation, which is the innovation of this study. The modified MPW became smaller than the original one in the exporting countries and vice versa in the importing countries. Further, this analysis clarified waste plastic trade has promoted decrease of riverine plastic transport in Japanese rivers, its slight increase in Yangtze, Yellow, and Ganges Rivers, and almost its constant in Mekong, Indus, Irrawaddy, and Brahmaputra Rivers. Recently, there is a growing progress in compiling existing research results and setting policy making in various countries under the umbrella of an intergovernmental negotiating committee (INC) on plastic pollution. The present results help to quantify plastic trade-off about impact of export and import of waste plastic on plastic dynamics in regional scale and to support the achievement of sustainable development goals (SGDs).