Levels and composition of microplastics and microfibers in the South Saskatchewan River and stormwater retention ponds in the City of Saskatoon, Canada.

In recent decades, contamination of the environment with microplastics and microfibers has been recognized as a pervasive and ubiquitous issue of global concern. While much research in this field has been undertaken in marine environments, more recent studies have identified rivers as major conveyors of plastic pollution from terrestrial into marine systems. However, reports on the levels and composition of microplastic and microfiber contamination in rivers of the Canadian prairie region, specifically the South Saskatchewan River (SSR), are scarce, which leaves this vital source of water for societies and ecosystems in a vulnerable state. To fill this gap, we obtained samples from seven sites along the Saskatchewan portion of the SSR, as well as three stormwater retention ponds (SRP) in the city of Saskatoon during the spring, summer, and fall of 2020. We used optical and Raman microscopy to enumerate and characterize particles in these samples. Total levels of particles and fibers in all samples ranged from 32 to 116 particles m -3 . Most particles (approximately 77%) were natural fibers, while polymers accounted for the remaining 33%. Average microplastic levels were lower (3.18 ± 3 particles m -3 ) downstream of Lake Diefenbaker, a large reservoir on the SSR, compared to upstream (12.0 ± 9 particles m -3 ). Retention of microplastics in the reservoir could explain the lower mean microplastic concentration of 4.43 ± 3 particles m -3 recorded in the SSR compared to mean concentrations of 26.2 ± 18 particles m -3 reported in the North Saskatchewan River, which is not dammed. This study is among the first to describe microplastic and microfiber levels in the SSR and thereby helps improve our understanding of this pervasive environmental contaminant on the Canadian prairies.