Influence of cadmium on decomposition of sewage sludge and microbial activities in Soils

Investigations were conducted to evaluate the influence of cadmium (Cd) on the decomposition of sewage sludge, microflora and enzyme activities in soils.Cadmium and sewage sludge were mixed with 5 different types of soil at levels of 0-30 ,umol/g and 20 mgl g, respectively.During 8 weeks of soil incubation at 28T, the mineralization of C was periodically measured.At the end of the incubation period.the soils were also analyzed to determine the amount of N mineralized, the numbers of bacteria, actinomycetes and fungi, the activities of p-glucosidase and proteinase, and the amount of Cd extracted with water, CH 3 COONH., Na.P 2 0 7 , and HC!.The amount of CO 2 evolved which decreased markedly with the addition of higher amounts of Cd, varied with the soils used.When the soil Cd concentration was based on the water-soluble form, the critical level for CO 2 evolution appeared to be identical.about I pg/g, for all soils.When the concentration was more than I pg/g, the amount of CO 2 evolved decreased in proportion to the log concentration of water-soluble Cd irrespective of soil type.Similar trends were observed for N mineralization, and numbers of bacteria and actinomycetes.In contrast, the number of fungi and the p-glucosidase activity tended to increase with the level of Cd.Proteinase was less active when the concentration of Cd increased.Since the concentration of water-soluble Cd in agricultural land of Japan is less than I pg/g soil, the influence of Cd in the soils on soil microorganisms and their activities is limited.