Integrated Assessment of Heavy Metal Accumulation in Urban Trees and Soils and Associated Non-carcinogenic Health Risks in Sabzevar, Iran.

Urban environments are increasingly affected by heavy metal pollution originating from traffic, industrial activities, and other anthropogenic sources, which can have adverse consequences for urban ecosystems and human health. This study investigated the concentrations of heavy metals, including cadmium (Cd), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn), in the leaves of three commonly occurring urban tree species-pine (Pinus sp.), mulberry (Morus sp.), and Chinaberry (Melia azedarach)-as well as in the corresponding surface soils in Sabzevar, Iran. To assess species-specific accumulation patterns, the bioaccumulation factor (BCF) and metal accumulation index (MAI) were calculated, and non-carcinogenic health risks from soil exposure were estimated using the hazard quotient (HQ) and hazard index (HI). The results indicated significant differences in metal concentrations among tree species, with Morus sp. exhibiting the highest accumulation of Fe, Mn, and Ni, whereas Pinus sp. displayed the highest MAI values. Soil analysis revealed considerable spatial heterogeneity, with the highest Pb and Zn concentrations observed in high-traffic urban areas. HQ and HI values for all metals and age groups were below critical thresholds, although children exhibited higher values than adults. These findings underscore the importance of selecting appropriate tree species for biomonitoring and managing heavy metal pollution in semi-arid urban environments.