Ecological risk potential assessment of heavy metal contaminated soils in Ophiolitic formations

Abstract

The purpose of this study is to generate maps of contamination risk for cadmium (Cd), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) in soils of a large alluvial fan located in Neyriz, Iran and to investigate their possible entry into the food chain. To this aim, the concentrations of the heavy metals of the soils are measured. The Geo-accumulation index (I_geo), Muller index, and potential ecological risk index are then used to evaluate soil contamination. The spatial distribution map of elements is also prepared using the kriging method. The results show that the Cd concentration in soils (mean 23 mg/kg) is 10-40 times higher than the global standard threshold (0.30-0.70 mg/kg), the Ni concentration (mean 13 mg/kg) is lower than the threshold (34 -12 mg/kg), the Cu concentration (mean 19.39 mg/kg) is below the threshold (24-13 mg/kg), the Zn concentration (mean 14.11 mg/kg) is also below the threshold (45-100 mg/kg), and the Pb concentration (mean 93.78 mg/kg) is higher than the threshold (44-22 mg/kg). The accumulation index values for Pb and Cd are 1.61 and 5.3, respectively, which decrease from the top to bottom of the study area. The enrichment factor values for Cu, Zn, Pb, Cd, and Ni are 0.43, 0.14, 4.60, 62.57, and 0.27, respectively, which also decrease from top to bottom. The accumulation index values in the soils confirm the occurrence of contamination and further indicate that the elements in the soils originated from local materials and Ophiolitic formations masses in the area. Overall, this research for the first time investigates the effect of natural factors (geological formation) on the soil and plant pollution in the study area and shows that, in addition to pollution by human activity, natural factors such as type of formation can lead to soil and plant pollution.

Keywords: Alluvial fan; Heavy metal concentration; Ophiolitic formations; Potential risk of pollution; Soil pollution.