Annual Variability of Total and Leachable Heavy Metal Content in Street Sweeping Waste from a Medium Sized City

Street sweeping waste (SSW) represents a heterogeneous urban material rich in road-deposited particles and associated contaminants, including heavy metals. Although SSW is generated systematically in all cities and constitutes a relevant indicator of diffuse urban pollution, research addressing its chemical composition, especially its temporal dynamics, remains limited. This study investigates the annual variability of total and leachable concentrations of heavy metals (Zn, Cu, Pb, Ni, Cr, and Cd) in SSW collected monthly over a one-year period in a medium-sized city. Total metal content was determined using aqua regia digestion, while leachability was assessed through standardized extraction tests. Statistical evaluation included correlation analysis, variability indices and assessment of metal mobility. Results confirm that both total and leachable metal concentrations exhibit distinct seasonal patterns, strongly influenced by traffic intensity, winter maintenance practices, and fluctuations in particle size distribution. Several metals demonstrated a high mobility factor, highlighting the potential environmental risk associated with their transport to urban soils and stormwater systems. The findings emphasize the necessity of incorporating temporal dynamics into SSW management strategies and demonstrate the importance of monitoring mobile metal fractions rather than relying solely on total concentrations. Due to the scarcity of annual-scale studies on SSW contamination, this research contributes novel insights into the environmental behavior of heavy metals in urban settings.