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.

Levels of pesticides and trace metals in water, sediment, and fish of a large, agriculturally-dominated river.

Basin land-use interacts with hydrology to deliver chemical contaminants to riverine environments. These chemicals are eventually taken up by aquatic organisms, where they can cause harmful effects. However, knowledge gaps related to the connections between hydrological, chemical, and biological processes currently limit our ability to forecast potential future changes in contaminant concentrations accurately. In this study, concentrations of three pesticide classes (organochlorines, organophosphates, and herbicides) and a standard suite of trace metals were analyzed in the South Saskatchewan River, Canada in 2020 and 2021 in water, sediments, and fishes. Organochlorine pesticides have been banned in Canada since the 1970s, yet there were some detections for methoxychlor and lindane, predominantly in sediment and fish samples, which could be attributed to legacy contamination. Except for malathion and parathion, organophosphate pesticides were scarcely detected in both sampling years in all matrices, and neonicotinoids were below detection in all samples. Conversely, the herbicides 2,4-D and dicamba were detected consistently throughout all locations in water samples for both sampling years. Overall, concentrations were 3 times higher in 2020 when river discharge was ∼2 times higher, suggesting run-off from the surrounding catchment or disturbance of contaminated sediments. Analysis for trace metals revealed that Cu and Zn exceeded sediment quality guidelines in some locations. Mercury concentrations exceeded the guidelines for about 18% of the samples (water and sediment) analyzed. These findings fill gaps in monitoring datasets and highlight key links between hydrology and chemistry that can be further explored in computational models to predict future contaminant trends in freshwater systems.

Qualitative and quantitative analysis of microplastics and microfiber contamination in effluents of the City of Saskatoon wastewater treatment plant.

In recent years, contamination of the environment with microplastics has received increasing scientific and public attention. Wastewater treatment plants (WWTPs) are considered important emitters of microparticles into aquatic systems. Among these microparticles are microplastics from, e.g., cosmetic products, and microfibers that are released during laundry of textiles made from synthetic fibers. The purpose of this study was to qualitatively and quantitatively characterize microplastic and microfiber contamination in effluents of the City of Saskatoon WWTP, Saskatchewan, Canada. The WWTP discharges directly into the South Saskatchewan River, which is an important water resource of central economic and environmental importance to the Canadian Prairies. To achieve this goal, a reference dataset was developed by determining Raman and Fourier-transform infrared (FTIR) spectra of neat plastic standards. Subsequently, samples were obtained from the final effluent of the Saskatoon WWTP during winter, spring, and summer 2019 by use of fine-meshed plankton nets. Microplastics and microfibers were extracted using Fenton oxidation and filtration, counted, and their identity determined by comparing Raman and FTIR spectra of individual microplastics and microfibers with the previously developed reference dataset. The number concentrations of both microplastics and microfibers were relatively stable across seasons, and fibers accounted for 82% of the total number of synthetic microparticles. Although the average total number concentration of microplastics and microfibers was only 1.76 per liter of effluent, at an average daily discharge of 80 million liters, this would amount to the emission of 141 million particles into the river per day. While the environmental relevance of these findings remains to be demonstrated, these results are an important first step toward understanding the magnitude of microplastic contamination in the Canadian Prairies.