Investigation of Cadmium and Zinc Interactions in Soils using Desorption Isotherms

Abstract

Investigation of Cd and Zn availability in four different soils as affected by the interactions of these two heavy metals was conducted using the metal desorption quantity-intensity (Q/I) isotherms. The soils were artificially contaminated with proper concentrations of Cd and Zn as <TEX>$CdSO_4\;and\;ZnSO_4$</TEX> solutions. DTPA (diethylene triamine pentaacetic acid) - extractable and water-extiactable Cd or Zn from the soils were used as <TEX>$Q_{Cd}\;or\;Q_{Zn}\;and\;I_{Cd}\;or\;I_{Zn}$</TEX> factors, respectively. The coefficient of determination for Cd and Zn desorption Q/I linear regression in the soils ranged from 0.947 to 0.999, which indicated that Q and I factors were closely correlated. The buffering capacity of Cd, <TEX>$BC_{Cd}$</TEX>, in the soils decreased with increasing Zn treatments, and the <TEX>$BC_{Cd}$</TEX> values were ranged between 205.8 and 2255.6. The decreases of <TEX>$BC_{Cd}$</TEX> values were mainly dependent upon the increases of <TEX>$I_{Cd}$</TEX> factors. However, Zn buffering capacity. <TEX>$BC_{Zn}$</TEX> decreased with increasing Cd treatments in acidic soils, and increased in neutral and calcareous alkaline soils. The <TEX>$BC_{Cd}$</TEX> values were ranged from 143.2 to 6158.0. The values of <TEX>$BC_{Zn}$</TEX> as influenced by the treatments of Cd were also controlled by the solubility of water-extractable Zn, <TEX>$I_{Zn}$</TEX> factor. The solubility of water-extractable Cd and Zn was significantly dependent upon the changes of soil pH that were impacted by the treatment of Zn and Cd, respectively. Also, the availability of Cd was higher than Zn availability in the acidic and neutral soils, but Zn was higher than Cd in the calcareous alkaline soil.