Decomposition of organic matter with previews cadmium adsorption in soils

Decomposition of organic matter with previous Cd adsorption (thereafter referred to as OMACd) in soils and in water was studied in order to clarify the mechanism of Cd-induced inhibition of organic matter decomposition in soil. Two types of organic materials (sludge, rice straw) with or without previous Cd adsorption were mixed with a Gley soil or a Light-colored Andosol in a proportion of 1%. In the soils amended with the Cd-free organic materials, a CdCl2 solution was added to the soils. The decomposition of the organic matter was examined by measuring the CO2 evolution for 4 weeks at 28 degrees C. Although the same amount of Cd was added to the soils, the decomposition of OMACd was inhibited to a greater extent than that in the soils to which a CdCl2 solution had been added. Furthermore the decomposition of sludge with previous Cd adsorption (thereafter referred to as SACd) in water after inoculation of soil microorganisms was investigated. Although the control sludge without Cd was markedly decomposed at 30 degrees C during 4 weeks, SACd was not appreciably decomposed. These results suggest that OMACd cannot be readily decomposed by microorganisms.