Influencing factors on transfer and bioaccumulation of soil cadmium and assessment of its environmental risk in a typical karst area, China

Cadmium has become the foremost inorganic pollutant in farmland in China. It is widely accumulated in karst areas in southwest China, especially in Guangxi Province. In this study, vertical soil profiles, rice grains and corresponding root-soil samples were collected in Guangxi. The Cd contents of soil and rice grain samples and several soil properties, including organic matter, Fe2O3, Al2O3, CaO, MgO, SiO2 contents and pH were tested. Meanwhile, sequential extraction procedure were used to analysis the chemical fractions of Cd in root-soil samples. Based on the measured data, influencing factors on bioaccumulation of Cd and its contamination risk in study area were discussed. The results indicate that the bioaccumulation and mobility of Cd from soil to rice grain are restrained by high soil pH, high contents of organic matter, clay mineral and carbonate. Guangxi has strong development of karst landform, with the continuous process of soil formation, the activity of Cd in the soils in such areas will gradually become stable. In general, the environmental risk of soil cadmium contamination in karst areas of Guangxi is relatively low. But preventing soil acidification is the significant measure to prevent the environmental risk of it.