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.