Potential impact of urbanization on heavy metals accumulation in surface soils of rapidly urbanizing cities

BACKGROUND AND OBJECTIVES: Rapid urbanization significantly alters soil quality by influencing its chemical properties and accelerating the accumulation of toxic metals. Moreover, despite the extensive studies on vehicular emissions and their impact on metals like lead, zinc, and copper, limited studies have comprehensively examined how various human activities interact to shape heavy metal contamination across different urban gradients. This study addresses this critical knowledge gap by integrating high-resolution spatial analysis, multivariate statistical modeling, and ecological risk assessment to unravel the combined effects of transportation density, construction intensity, and industrial expansion on soil contamination.METHODS: Ninety geo-referenced topsoil samples were collected from residential, industrial, recreational, and roadside areas. Ten priority toxic metals, including cadmium, lead, chromium, copper, zinc, nickel, cobalt, manganese, arsenic, and mercury, were analyzed using high-resolution mass spectrometry. To assess concentration patterns and identify possible sources of pollution, spatial interpolation and multivariate statistical analyses were employed. Additionally, human health and ecological risk assessments were conducted to evaluate potential hazards associated with soil contamination.FINDINGS: Concentrations of metals revealed notable spatial differences across diverse urban land-use classifications. High-resolution inductively coupled plasma mass spectrometry detected high lead concentrations reaching 375 milligrams per kilogram and zinc up to 492.7 milligrams per kilogram. Cadmium concentrations, although lower in absolute terms, peaked at 2.1 milligrams per kilogram but contributed disproportionately to ecological risks. Mercury concentrations were relatively low, peaking at 0.9 milligrams per kilogram, whereas chromium, copper, and nickel levels were recorded at 142.6, 160.3, and 89.5 milligrams per kilogram, respectively, suggesting possible contributions from multiple sources beyond just vehicle emissions. Principal component analysis explained 78.3 percent of total variability and revealed three dominant components, with the first (34.7 percent) strongly influenced by lead, zinc, and copper, confirming traffic-related inputs.CONCLUSION: The study underscores the notable effect of fast-paced urban development on soil contamination and delivers crucial information regarding the spatial distribution, sources, and risks associated with toxic metals in urban soils. These findings are essential for guiding land-use planning, environmental management, and the development of targeted mitigation strategies in rapidly expanding cities.