Although freshwater and estuary systems are recognized as origins and transport pathways of plastics to
the oceans, there is a lack of comparison of microplastics in different water bodies or river networks. In
the present study, the spatial distribution of microplastics was compared across different water bodies,
including city creeks (Shanghai), rivers (Suzhou River and Huangpu River), an estuary (Yangtze Estuary)
and coastal waters (East China Sea) in the Yangtze Delta area. Significant spatial differences of microplastic
abundances were revealed across the sampling areas. The results showed that the abundance of
microplastics was higher (1.8e2.4 items/L) in freshwater bodies than that in estuarine and coastal water
(0.9 items/L). In the Suzhou River and the Huangpu River, microplastics showed trends of increasing
abundance downstream, where the peak of microplastic pollution is closer to the city center and the
estuary. In respect of abundance, microplastics are likely to be transported from pollution sources to sink
areas via river networks. The proportion of fibers was the highest in city creeks (88%), followed by the
Suzhou River (85%), the Huangpu River (81%), the Yangtze Estuary (66%) and the East China Sea (37%).
Similarly, polyesters dominated in city creeks and rivers. The results suggest that both the abundance and
properties of microplastic pollution varies across different water bodies. Microplastic pollution in small
freshwater bodies is more serious than in estuarine and coastal waters. Therefore, we support prioritization
of water monitoring for microplastics within entire river networks, instead of single water body
surveys.