Characterizing microplastics in urban runoff: A multi-land use assessment with a focus on 1-125 m size particles

Urban areas play a significant role in generating microplastics (MPs) through increased vehicular and human activities, making urban runoff a key source of MP pollution in receiving waterways. The composition of MPs is anticipated to vary with land use; hence, identifying the hotspots of contamination within urban areas is imperative for the targeted interventions to reduce MPs at their sources. This study collected one-liter stormwater runoffs from three different land uses as sheet flow during two storm events to quantify the MPs and identify the polymers transported from land-based sources. The analytical method included a combination of Fourier transform infrared spectrometer, Raman microscope, and Nile red staining techniques. This study analyzed the broad spectrum of MPs, i.e., 1 mu m-5 mm, and tire wear and bitumen particles, considered the two major research gaps in stormwater studies. The MP concentrations were 67.7 +/- 11.3 pL(-1 )in commercial, 23 +/- 10.3 pL(-1) in residential, and 168.7 +/- 37.1 pL(-1 )in highways. The trend of MP concentrations followed an order of highway > commercial > residential with an exclusive presence of polymethylmethacrylate and ethylene-vinyl acetate in highways; cellophane, methylcellulose, polystyrene, polyamide, and polytetrafluorethylene in commercial; and high-density polyethylene in residential areas. The dominant MP morphology consisted of fragments, accounting for 89 % of the identified MPs, followed by 10 % fibers and 1 % films. This study observed a prevalence of MPs sizes <125 mu m constituting 49 % of the total composition. These findings underscore the vital role of land use patterns in shaping MP abundance and reinforce the urgency of implementing effective man-agement strategies to mitigate MP pollution in stormwater runoff.