Pollution Assessment and Source of Selected Heavy Metals in Agricultural Soils, Southern Sabzevar, Northeastern Iran

Heavy metals enter naturally in the soil environment from the pedogenic processes during weathering of parent materials or through a variety of human activities. Determining the source of heavy metal in agricultural soil is necessary to management the soil pollution. This study aimed to investigate soil pollution by selected heavy metals and determine their sources in agricultural soils in Southern Sabzevar.

The study area is located in the piedmont of ophiolotic belt in the South of Sabzevar city, Northeastern Iran. Surface soil samples from 0 to 20 cm depth of cultivated lands were regularly collected up to 2 km from the main road. Also, three profiles were studied at a distance of 1 km intervals. Five samples were taken from the depths of 0-20, 20-40, 40-60, 60-80, 80-100 cm. The total concentrations of Al, Fe, Mn, Ni, Cr, Zn, Cu, Pb, and Cd were measured by Inductively Coupled Plasma (ICP-OES). In this study, Pollution indices were calculated for the studied heavy metals. Multivariate statistical techniques were also applied to assess the sources of the heavy metals using SPSS software V 24.

Mean concentrations of Ni, Cr, Mn, Cu, and Zn were 306.2, 217.5, 781.4, 268.3, and 302.2 mg kg-1 was found to be higher than EU, WHO, and USEPA standards. Cadmium with an average concentration of 2.7 mg kg-1 was higher than WHO and USEPA standards and Pb with an average concentration of 18.8 mg kg-1 was higher than USEPA standards. Based on Pearson correlation coefficients, statistically-significant positive correlations (P < 0.01) were found between Ni and Cr, Cu and Zn (P < 0.01), and also between Pb and Cd (P < 0.05). In addition, based on principal component analysis (PCA), three components accounting for 76.97% of the total variance explained. The first component contained Fe, Mn, Cr, and Ni, the second and third components included Pb, Cd and Cu, Zn, respectively. According to the pollution indices (enrichment factor and geoacumulation index), Cd, Cu, and Ni are important pollutants, with the highest EF and Igeo index among the analyzed elements. Potential ecological risk factor (Er) also showed that Cd, Cu, and Ni are important pollutants responsible for ecological threats.

According to the results of correlation and multivariate statistical analyses the heavy metals were classified in three groups of (Mn, Cr, Ni), (Cu, Zn) and (Pb, Cd), which indicates their similar sources. Elevated amounts of Cd and Ni in the soil, based on EF, Igeo, and Er, were attributed to the long-term and extended applications of the chemical fertilizers and traffic emission for Cd and ophiolitic parent material for Ni. In comparison, the elevated amount of indexes for Cu were associated with both anthropogenic and geogenic sources. Hence, control of elements from geogenic and anthropogenic sources into the soil seems necessary. In case of non-observing environmental considerations such as excreting proper management in the region, The environmental cycle will face irreparable damage in the long-term; therefore, it seems necessary to make decisions to reduce these pollutants and, if possible to eliminate them.