The Effect of Land Use on the Distribution of Chemical Forms of Copper and Cobalt, and their Biological Risk Assessment in Soils of Zanjan Province

This study aimed to determine the chemical forms of cobalt and copper in soil under rain fed and irrigated cultivation and their biological risk assessment in Zanjan province. For this purpose, 120 samples (96 rain fed soil samples and 24 soil samples irrigated) were taken and after determination concentration of all the elements, 36 samples with maximum variation were selected for laboratory analysis. The results showed that the concentrations of total and DTPA-extractable cobalt under rain fed and irrigated land uses for Co were 25.6, 0.35 and 24.3 and 0.39 and for Cu were 29.8, 2.1 and 62.3, 5.2 mg/kg respectively. Copper distribution in the rain fed soil included residual fraction (74.2%), oxide fraction (10.5%), organic matter fraction (8.4%), carbonate fraction (4.6%) and soluble笗Ⅺ砞榹 fraction (4/2%) and in irrigated soil included residual fraction (70%), organic matter (13.1%), oxide (10.1%), carbonate (4.4%) and soluble笗Ⅺ砞榹 (2.3%). Chemical distribution of cobalt in soils showed no significant difference in the proportion of each fraction in order of residual fraction>oxidized>carbonate>soluble笗Ⅺ砞榹>organic fraction achieved. The highest correlation coefficient was found between bound to organic matter fraction of Cu with organic matter (r=0.731). Individual contamination factors (ICF) for copper and cobalt in rain fed and irrigated conditions were 0.35 and 1.11 and 0.50 and 1.28 respectively. Global contamination factor (GCF), under rain fed and irrigated were 1.46 and 1.78 respectively. Risk assessment code (RAC) for copper and cobalt was 6.9 and 27.24% respectively.