Transformation of cadmium in soils treated with Cd-enriched sewage sludge and cadmium chloride under field capacity and flooding moisture regimes

摘要

A laboratory incubation study was conducted to examine the long-term (16 m) dynamics of transformation of Cd in soils polluted by Cd-enriched sewage sludge or cadmium chloride under field capacity (1/3 bar) and flooding moisture regimes. Cadmium transformation was investigated by determining: (i) different operationally defined chemical fractions of Cd ; (ii) DTPA extractable and (iii) 1M CaCl_2 extractable Cd. Under field capacity moisture regime, Cd added through cadmium chloride transformed into NaOAc extractable and residual Cd fractions while Cd added through Cd-enriched sludge was transformed from water soluble + exchangeable fraction into the NaOAc extractable, and organically bound, fractions in all soils and also into the residual fraction in neutral soil. Under a flooding moisture regime, Cd added through cadmium chloride transformed from water soluble + exchangeable Cd fraction into the residual fraction in acidic soil and into NaOAc extractable, and residual, fractions in alkaline soil. However, in neutral soil, residual Cd fraction underwent a small decrease to cause a minor increase in the water soluble + exchangeable, and organically bound, Cd fractions. With Cd-enriched sludge as the Cd source under a flooding moisture regime, water soluble + exchangeable Cd transformed into NaOAc extractable fraction in acidic and alkaline soils but into an organically bound fraction in neutral soil. Flooding decreased DTPA, and 1M CaCl_2 extractable, Cd in soils polluted through cadmium chloride or Cd-enriched sewage sludge as compared to the field capacity moisture regime.