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

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. However, more and more studies have found that inland water bodies are also nonnegligible sinks of microplastics, and rivers are also considered to be an important source of marine microplastics. 

In several previous modelling studies, 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, collaborated with IHB’s Research Group of Conservation Biology of Aquatic Animals, has recently investigated the pollution condition of microplastics in the middle and lower reaches of the Yangtze River. 

The research team collected microplastic samples in the water and sediments from 15 sites along the middle and lower reaches of the Yangtze River. Concentrations of microplastics in the samples were determined. The morphology features and polymer types of microplastics from these sites were also been measured. The characteristics of microplastic pollution in the middle and lower reaches of the Yangtze River were initially identified, and the problems of the previous prediction models were also discussed. 

This study 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. It indicated that considerable microplastics were retained in the Yangtze River. 

The results of 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. This 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. More detailed investigations to sources, fates, and effects of microplastics in the Yangtze River are vital in the future.    

This study has been published on Science of the Total Environment entitled “Occurrence and fate of microplastic debris in middle and lower reaches of the Yangtze River - From inland to the sea”. The research group has also published their studies of microplastics in inland waterbodies of China, such as Three Gorges Reservoir, Qinghai Lake, and Tibetan lakes on “Environmental Science & Technology”, “Environmental Pollution”, and “Science of the Total Environment” previously. 

 
Figure: Abundance and shapes of plastic debris from sampling sites along the Yangtze River. a) Abundance of microplastics and the proportion of microplastic shapes. b) Abundance of mesoplastics and the proportion of mesoplastic shapes. c) Microplastic abundance of benthic sediment samples. d) representation of quantities of microplastics by multiplying the abundance of microplastics by river width. (Image by IHB)