Spatial distribution and potential ecological risk assessment of heavy metals in agricultural soils of Northeastern Iran

Abstract

Illustrating the spatial distribution and potential sources of soil properties, and heavy metals, viz., Fe, Zn, Mn, and Cu, are the vital prerequisites for decreasing their pollution. The 68 composite agricultural soil samples in triplicates were collected by employing grid method to evaluate the concentration of pH, sand, silt, clay, organic carbon, P, K, and heavy metals. Multivariate techniques (Pearson’s correlation, heatmap, principal component analysis, and nonmetric multidimensional scaling), geostatistcal techniques, and contamination indices were employed. The contents of Fe, Zn, Mn, and Cu were lower than the limits for Iran EPA guidelines and Earth’s crust. The results of contamination factor and potential ecological risk index (RI) showed that agricultural soils have less contamination and low ecological risks. The enrichment factor (EF), geoaccumulation index (Igeo) and modified ecological risk index (MRI) indicated that 99%, 86.7% and 52.4% agricultural soil samples showed very high enrichment and ecological risks of heavy metals. Both anthropogenic activities and natural factors were responsible for heavy metal contents. The results of geostatistcal analysis revealed that Zn is accumulated more in Central regions, whereas Cu and Mn accumulated more in South and Northeastern regions of the studied area for EF, Igeo, and modified potential ecological RI.

Keywords

• agricultural soils
• multivariate techniques
• heatmap
• kriging
• ecological risk assessment