Heavy metals concentration and availability of different soils in Sabzevar area, NE of Iran

Soils developed in the Sabzevar ophiolitic area originate from different bedrocks. All samples display similar physico-chemical properties, but heavy metal concentrations vary extremely in different soil samples. Serpentine soils have the highest total concentration of Cr, Ni and Co; while soils derived from mafic rocks (olivine basalts and hornblende gabbros) show the highest Cu (85.29-109.11 ppm) and Zn (46.88-86.60 ppm). The DTPA-extraction of soil samples indicates that the order of metal bioavailability was Cr3% of total Cr; >12% of total Co and >17% of total Zn). Oxide minerals (such as chromite and magnetite) in Sabzevar soils play as resistant minerals and impede the heavy metal availability; while forsterite, pyroxene, serpentine and talc are more labile and show higher DTPA-extractable of heavy metals.