As an emerging pollutant, microplastics (particle size < 5mm) are easily ingested by aquatic organisms due to their small size and may also be carriers of other pollutants. In most previous microplastic studies, the research areas were mainly in the ocean, while inland water bodies were found to be nonnegligible sinks of microplastics in more and more studies, and rivers were considered to be an important source of marine microplastics.

Several modelling studies showed that the flux of microplastics transported from the Yangtze River to the ocean were all considered as the highest among all rivers in the world. However, these modelling studies lack the verification and support of actual data.

As one of the earliest research teams focusing on microplastic pollution of inland water bodies, the Research Group of Chemical Ecology at Institute of Hydrobiology (IHB) of Chinese Academy of Sciences, collaborating with IHB’s Research Group of Conservation Biology of Aquatic Animals, recently investigated the pollution condition of microplastics in the middle and lower reaches of the Yangtze River. The study was published in Science of the Total Environment. 

Microplastic samples in the water and sediments from 15 sites along the middle and lower reaches of the Yangtze River were collected by researchers.

They determined concentrations of microplastics in the samples and measured the morphology features and polymer types of microplastics from these sites. Besides, they initially identified the characteristics of microplastic pollution in the middle and lower reaches of the Yangtze River, and discussed the problems of the previous prediction models. 

The results revealed that the concentration of microplastics in the middle and lower reaches of the Yangtze River is moderately high compared to rivers sampled by similar methods worldwide. Megacities and large lakes might affect the concentration of microplastics in the Yangtze River. There was no increasing trend of microplastics concentration from upstream to downstream, and there were microplastics in the sediment of the Yangtze River.

The finding indicated that considerable microplastics were retained in the Yangtze River. 

This study implied that the previous modelling studies of microplastics flux from river to the ocean might exist bias. The retention should be considered in the model and the sampling site used to model should also be selected cautiously. What’s more, microplastics retained in the Yangtze River might leave the risk to ecological system and human health in the Yangtze River catchment.

The study provided scientific support for the management of microplastic pollution in the Yangtze River Basin and the protection of ecological environment of the Yangtze River, and more detailed investigations to sources, fates, and effects of microplastics in the Yangtze River are vital in the future.

Photos of microplastics from the Yangtze River under the microscope (Image by IHB)