Effects Of Bagasse Application On Chemical Fractions And Bioavailability Of Cadmium In Contaminated Soils

Cadmium (Cd) contamination has great potential threat to ecosystem, food safety and human health. It has been an important environmental problem widely concerned. There are abundant organic materials in China. Application of organic materials to reduce mobility of Cd not only adapts to national conditions of China but also consists with the demand of sustainable agriculture. Therefore, to investigate the effect of bagasse on speciation and bioavailability of Cd in agricultural soil, the unmodified and thiol-modified bagasse were used as soil ameliorants in pot experiments and soil culture experiments. The main findings were obtained as follows:(1) Soil pH was affected by the application of bagasse and thiol-modified bagasse, but no significant correlation was found between the chemical speciation of Cd and pH in the soil. The concentration of humic acid (HA) and fulvic acid (FA) in soils was found to correlate with that of Cd:the concentration of HA in the soil decreased with the incubation time, and the exchangeable Cd decreased, while the residual Cd increased in the soil.(2) Soil incubation experiments were conducted to study the effect of bagasse on changes of cadmium fractions in soils.During the whole incubation period of90days, exchangeable Cd decreased and other fractions increased when bagasse was applid. Exchangeable Cd in soils decreased significantly during the fist45days after the application of bagasse. This decreasing effect decreased with the incubation time and was not significant after incubation for60days. The content of residual Cd was increasing with the incubation time, and it increased significantly during the fist30days after the application of bagasse, and this increasing effect was not significant after incubation for45days. The effect of thiol-modified bagasse on changes of Cd fractions was more significant than that of unmodified bagasse.(3)In the pot experiments, Cd has obvious influence on the growth of Brassica Chinensis, biomass of Brassica Chinensis was decreased significantly by the addition of Cd compared with uncontaminated soil. The two amendments significantly improved biomass, and remarkably decreased Cd content in Brassica Chinensis and the content of DTPA extractable Cd in the Cd-contaminated soil, and the effect of thiol-modified bagasse was more remarkable than unmodified one.It was also found that the concentration of Cd in Brassica Chinensis has a significant negative correlation with the biomass, whereas it has a significant positive correlation with the content of DTPA extractable Cd.