Transport mechanism of microplastics from a still water system to a dynamic estuarine system: A case study in Macao SAR.

Significant amount of microplastics (< 5 mm) were transported into the South China Sea via Pearl River Estuary. However, comprehensive studies on the occurrence and retention of microplastics in this estuarine system were still limited. To fill this gap, we investigated the distribution of microplastics in still-water ecosystems and running water ecosystems in the west bank of the Pearl River Estuary. Microplastics were found in both waterways and lakes. The results of the Manta trawl (330 μm mesh) yielded an average abundance of 0.66 ± 0.61 n/m3 in waterways and 5.66 ± 3.47 n/m3 in lakes. Polyethylene (PE) and polypropylene (PP) were the most abundant polymers in water bodies. The main source of microplastics in waterways was riverine inputs, and microplastics in lakes mainly originated from the surrounding terrestrial environment. Lakes, which were less mobile than rivers, tended to act as reservoirs for microplastic transport. This study highlights the diversity of riverine microplastics during transport and improves our knowledge of the sources and transport mechanisms of microplastics in estuarine waters.