Evaluation of contamination and spatial variations of Zn, Cu and Ni in arid-zone soils of the Route between Zabol and Zahedan

Heavy metals are one of the most important soil pollutants. The increased level of them in the environment with respect to their stability has led to researchers attraction in recent decades. Soil contamination produced by heavy metals released from vehicles is a serious environmental problem. Considering the importance of soil contamination, evaluation of soil contamination by various industries seems to be necessary. Characteristics of the spatial distribution of pollutants in contaminated soils are important factors to identify and eliminate pollution. This study aimed to investigate the spatial distribution of heavy metals such as Ni, Zn, and Cu at the roadside soils of Zabol - Zahedan route. 252 soil samples were collected from a depth of 0-20 cm, using a regular systematic sampling process. In addition to the total concentration of the metals in the soil, the soil’s properties including its pH, EC, organic matter, lime percentage and soil texture were measured. The contamination assessment of soil was done by using the enrichment factor and biological accumulation indicator. For heavy metals concentration maps of Cu and Zn, we used Ordinary Kriging and Exponential model and for Ni, we used Ordinary Kriging and Gaussian model. The method accuracies were compared by using mean absolute error (MAE) and root mean square error (RMSE), and the method with the highest accuracy was used to prepare the heavy metal maps. As the distance from the road increased, the concentration of heavy metals decreased. To prepare the map of nickel Gaussian model, and for the zinc and copper Exponential model has the highest precision. The average Zn, Cu and Ni concentration at 0, 50 and 100 meters intervals were 54.33, 52.75, 51.56, 9.67, 9.49, 9.03 and 10.26, 10.02, 9.76 mg kg-1. Zn, Cu and Ni concentrations in roadside roads in the study area were less than the WHO limit. The results of this study showed that the relationship between zinc, copper and nickel is positive and meaningful. In fact, the existence of correlations between different metals represents their common source. The results of spatial distribution of metals showed that these soils are uncontaminated to Zn, Cu and Ni. The concentration and distribution of these elements in the region are of geological and human origin. Zn, Cu and Ni are naturally occurring in the soil, but human activities, such as agricultural activities and the combustion of fossil fuels, have led to the accumulation of these metals in parts of the study area.