Ecological risk assessment and source apportionment of heavy metal contamination in urban soils in Shiraz, Southwest Iran

Soil quality in urban areas is deteriorating globally due to diverse anthropogenic activities. This study assessed urban soils from Shiraz (SW Iran), a city with heterogeneous industrial activity and anthropogenic emissions. The objectives of this study were to (1) determine soil properties and concentrations of cobalt, chromium, iron and nickel and (2) assess the geoaccumulation index (Igeo), enrichment factor and pollution indices of the studied metals and their adverse impacts on environmental quality and human health. A total of 143 soil samples (0–20-cm depth) were collected from the study area, and multivariate analysis, including spatial mapping, was performed. The average concentrations of chromium and nickel exceeded the limits for residential/parkland/industrial soils according to Canadian guidelines, whereas the average cobalt concentration was less than that specified by Swedish and Canadian guidelines. A multivariate analysis (cluster analysis, Pearson correlation and principal component analysis) confirmed that the heavy metals had the same origin and that anthropogenic activities had a significant effect on the heavy metal contamination of the soil. Furthermore, the contamination factor and enrichment factor indicated that the soil samples were moderately to highly contaminated by nickel, chromium and cobalt, whereas Igeo indicated very high contamination in all soil samples tested. The potential ecological risk index and modified potential ecological risk index also indicated moderate to high ecological risk from the heavy metals in the urban soil samples.