Microplastic acts as a carrier for pollutants and its potential risks in inland rivers focusing on China

Due to the massive production and consumption in modern society, plastic products can be delivered into the aquatic environment, where they will break down into innumerable small plastic fragments with a size less than 5 mm, namely microplastics (MPs). Most of the available literature over the last two decades mainly focused on MPs in the ocean, while recent studies have revealed that MPs are also widely distributed in the freshwater environment, particularly in developing countries. This study reviewed the occurrence of MPs in inland rivers of China. The primary direct sources of MPs in the inland rivers include effluents, plastic waste, personal care products, synthetic textiles, and agricultural materials. We further discussed the multiple carrier roles of MPs in aquatic ecosystems. MPs possess huge specific surface areas and decent hydrophobic properties and can concentrate organic pollutants (e.g., plasticizers, fire retardants, antibacterial agents, dyes, and other chemical components) in the aquatic environment. These organic pollutants will be released with the degradation of plastic and migrate with the flow of MPs, posing a potential environmental risk. In addition, the MPs surface can be readily covered by biofilm, providing an ideal habitat for insects to lay eggs as well as bacteria and algae to colonize.