Bioavailability and speciation of potentially toxic elements in agricultural soils neighboring an industrial complex in northwest Isfahan, Iran

The mobility and bioavailability of trace elements in the agricultural soils are extremely important in assessing the risk of toxicity to the growing plants. A five step sequential extraction procedure (SEP) has been employed to study the speciation of As, Sb, Cr, Cu, Cd, Pb, Zn, Ni, Fe and Mn in 18 soil samples neighboring an industrial complex in Isfahan, central Iran. Enrichment factor (EF) calculation shows that in the soils studied, Cd and Fe are the most and the least enriched elements, respectively. Sequential extraction results indicate that although the total concentration of Ni, Sb, As, Cr and Cu is high, their concentration in the exchangeable plus carbonate fractions is rather low. This suggests that these elements are not easily transferred from soil to the plants. The high proportions of Cr, Cu and Fe in both organic matter and residual fractions, reduces the phytoavailability and the toxicity of these metals. On the other hand, Zn, Pb and Cd are strongly associated with exchangeable plus carbonate fractions, much more bioavailable than other studied elements. Good correlation between total contents and concentration of elements in each fraction indicates that the studied elements, excluding Fe, are mainly derived from the anthropogenic sources. Remediation measures and soil amendment practices are therefore recommended for the study site.