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ADSORPTION OF CADMIUM ON BIOSOLIDS-AMENDED SOILS
Citation:
Li**, Z., J A. Ryan*, J. L. Chen**, AND S R. AlAbed*. ADSORPTION OF CADMIUM ON BIOSOLIDS-AMENDED SOILS. Dick, W.A. (ed.), ENVIRONMENTAL QUALITY. ASA, CSSA, SSSA, Madison, WI, 30(3):903-911, (2001).
Description:
A considerable controversy exists over the biosolid phase (organic or inorganic) responsible for the reduction in phytoavailable Cd in soils amended with biosolids as compared to soils amended with inorganic salts. To test the importance of these two phases, 2 biosolids, 15 biosolids-amended soils and their 5 companion controls were collected from 5 experimental sites with an extensive history of biosolids application that had been terminated 5-15 years ago. Portions of these soil samples were treated with 0.7 M NaClO to remove organic carbon. Cadmium nitrate was quantitatively added to both moist soil samples and their soil inorganic fractions (SIF) in a 0.01 M Ca(NO3)2 solution at three pH levels (6.5, 5.5, and 4.5), and equilibrated at 22 +/- 1C for at least 48 hrs. Isotherms of Cd adsorption on biosolids-amended soils were intermediate between control soils and biosolids with higher biosolids rates resulting in greater Cd adsorption on soils. Reduction of pH to 4.5 did not remove the difference between thes groups although adsorption of Cd decreased with decreasing pH level. Removal of organic matter reduced Cd adsorption on all soils but had little influence on the observed difference between biosolids-amended soils and controls. The increased adsorption associated with biosolids application was not limited to the organic matter addition from biosolids, rather the biosolids application also altered the adsorptive properties of the inorganic fraction. Therefore the alteration of adsorption capability in biosolids-amended soils would not vanish with the degradation of organic matter. The great affinity of Cd on biosolids and the inorganic fraction of biosolids suggests that biosolids amendment in soils increases retention of Cd on soils is of a persistent nature. It can be concluded that, even when the organic carbon added by biosolids is gone, the soils which hs received biosolids will have a great capability to retain Cd from solution.