Microplastics in surface water and sediments of Chongming Island in the Yangtze Estuary, China

Abstract

Background

The Yangtze Estuary acts as gateways where microplastics transport from freshwater into marine environments, with one of the largest discharge volumes in the world. The occurrence of microplastics in surface water and sediments of the Yangtze Estuary has been reported. However, little is known about microplastics in and around Chongming Island in the estuary. In this study, the distribution of microplastics in surface water and sediments of Chongming Island was investigated and compared in different environmental medium.

Results

Abundances of microplastics in surface water and sediments were in the ranges of 0–259 items m ^{− 3} and 10–60 items kg ^{− 1} dry weight, respectively. Microplastics were more abundant in the surface water of the Yangtze River shores than in the inland rivers (p < 0.01). Proportions in fiber form in surface water and sediment were 33% and 67%; and those in fragment form were 39% and 24%. Most particles (> 72%) were < 1 mm in the longest dimension; 65% were white and 30% were transparent. Of the 11 compositions identified, polyethylene, polypropylene, and α-cellulose predominated in both phases.

Conclusion

This is the first study to focus on microplastics in inland watercourses on Chongming Island and along the Yangtze River’s shores in both phases. There were differences between the island and estuary in composition and density due to the distinct vertical mixing processes. The in situ filtration of surface water (100 L) sampling method was well employed in various freshwater environments and free of plastic materials in front of the filter, analysis results of which provided an important baseline reference for evaluating microplastic pollution in the Yangtze Estuary.