Microplastics, which are plastic debris with a particle diameter of less than 5 mm, have attracted growing
attention in recent years. Its widespread distributions in a variety of habitats have urged scientists to
understand deeper regarding their potential impact on the marine living resources. Most studies on
microplastics hitherto are focused on the marine environment, and research on risk assessment methodology
is still limited. To understand the distribution of microplastics in urban rivers, this study
investigated river sediments in Shanghai, the largest urban area in China. Seven sites were sampled to
ensure maximum coverage of the city's central districts, and a tidal flat was also included to compare
with river samples. Density separation, microscopic inspection and m-FT-IR analysis were conducted to
analyze the characteristics of microplastics and the type of polymers. The average abundance of
microplastics in six river sediment samples was 802 items per kilogram of dry weight. The abundance in
rivers was one to two orders of magnitude higher than in the tidal flat. White microplastic spheres were
most commonly distributed in river sediments. Seven types of microplastics were identified, of which
polypropylene was the most prevailing polymers presented. The study then conducted risk assessment of
microplastics in sediments based on the observed results, and proposed a framework of environmental
risk assessment. After reviewing waste disposal related legislation and regulations in China, this study
conclude that in situ data and legitimate estimations should be incorporated as part of the practice when
developing environmental policies aiming to tackle microplastic pollution.