Cadmium distribution in plant residues amended calcareous soils as a function of incubation time.

摘要

Soluble organic compounds present in organic matter may increase heavy metal mobility. There is little knowledge of the effect of added cadmium (Cd) with and without organic amendments on Cd distribution in different soil fractions in contaminated calcareous soils. This study was conducted to investigate the effect of the application of plant residues and incubation time on Cd fractionation in three metal-amended calcareous soils of Iran. Four amended treatments with plant residues (helianthus, potato, rape, and wheat) were established at the rate of 2% and incubated for four weeks at 25 degrees C and constant moisture. Cadmium was added to amended-soils at the rate of 20 mg kg-1 as chloride. A control without amendments but with Cd (control) was also set up. The soil samples were incubated for 0.125, 3, 7, 14, 28, 42, and 56 days at 25 degrees C and constant moisture. After incubation, the soils were sequentially fractionated into water-soluble plus exchangeable (EXCH), organically bound (OM), inorganically bound (CARB), and residual (RES) forms. There were changes in the proportional distribution of Cd in all three studied soils during 56 days of incubation with spiked Cd. Organic residues affected the Cd transfer between different soil phases. In general, the proportions of Cd associated with the most weakly bound fraction (EXCH) tended to decrease, with corresponding increases in the other three more strongly binding fractions during the incubation. The higher proportions of EXCH fraction of calcareous spiked soils indicates its higher potential of downward leaching and runoff transport, especially at the early stage of pollution. Application of all plant residues increased significantly Cd in EXCH and OM fractions and decreased CARB fraction. The information on Cd relocation and transformation, due to the application of organic residues within these calcareous soils, is useful for assessing the short- and long-term environmental consequences.