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

Abstract

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 CaCl2 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 CaCl2 extractable, Cd in soils polluted through cadmium chloride or Cd-enriched sewage sludge as compared to the field capacity moisture regime.