Detection and quantification of nanoparticles in runoff from a highly trafficked urban motorway

Urban rainfall and runoff are major transport vectors for pollutants into the aquatic environment. In this context, road traffic is a significant factor in the contamination of the urban environment in general, and runoff in particular. Some metals, such as Cu, Zn, Fe, and Ti, have been found in dissolved fraction (< 0.45 μm) in such water. The present study focuses on characterizing the number concentration and mass distribution of nanoparticles (NPs) containing Ti, Fe, Zn, and Cu in runoff from a heavily trafficked urban motorway (≈ 100,000 vehicles/day) in Nantes, western France. Seven runoff samples were taken between July 2023 and March 2024. A rainfall sample was also taken in the same proximity for comparative purposes, providing knowledge of atmospheric wet deposition levels. Using two sample preparation methods, filtration, and ultra-filtration, single particle ICP-MS (sp-ICP-MS) analysis confirmed the existence of the targeted elements in nanoparticulate fraction. Ti was found to be the most abundant element, followed by Fe, while Zn and Cu were less prevalent, with average number concentrations of 4.83 x 10^8, 1.68 x 10^8, 7.78 x 10^7 and 9.04 x 10^7 particles/L, respectively. Except for Fe, runoff samples exhibited higher concentrations of Ti, Zn, and Cu nanoparticles compared to the rainfall sample, with a larger average equivalent diameter indicating a likely anthropogenic origin. Comparisons between sample preparation methods demonstrates that the effectiveness of ultrafiltration is element dependent.