The impact of plastic debris on the aquatic environment is increasing with the use of plastic products by humans. The issue of plastic pollution in aquatic ecosystems has received significant attention from the public, policymakers, and the scientific community. Microplastic is one of the important branches of research, but only a very limited number of studies on microplastic consider all relevant processes, such as fragmentation, biofouling, aggregation, sedimentation, and burial. Therefore, this Ph.D. program tends to construct probabilistic models of microplastic transport and risks across scales. It will quantify the changes in the content of microplastics in the aquatic environment over a certain time scale and clarify the risks of microplastic all over the world. This study will also provide environmentally relevant guidance to policymakers and researchers.