Fronts converging microplastics in the Asia-Pacific river plumes

Convergent surface fronts are a common feature in river plumes, where they gather suspended materials and biota, playing an important role in the estuarine ecological processes. Yet, systematic observations of microplastics in plume fronts have been limited despite rivers being major conduits of plastic waste entering the global ocean. By collecting samples in front, plume and shelf waters, our research measured the distribution of microplastics in the Terengganu River, Malaysia and the Yellow River, China. Our findings indicate that the majority of ratios of microplastic abundances in fronts to non-frontal regions were greater than 1, with some ratios reaching up to 500. This confirms the significant microplastic accumulation in plume fronts. The wide range of plastic ratios observed within and between estuaries could be attributed to the dynamical nature of fronts, highlighting the need for fine-scale observation of frontal dynamics. By comparing our findings with previous observations of microplastics in plume fronts, we have identified inconsistencies in methods and propose recommendations for generating a more reliable dataset through field observations. An advanced understanding of the frontal processes that govern the transport of microplastics is critical for predicting and managing plastic pollution near its source, warranting further efforts.