Geochemical characteristics of rice uptake of cadmium and its main controlling factors: A case study of the Suxichang (Suzhou-Wuxi-Changzhou) typical area

Abstract: On the basis of collecting and testing about 416 couples of rice seeds and the cultivated soil samples from Suxichang typical area of Jiangsu Province, a series of geochemical data related to Cd distribution and other relative elements concentrations since 2011 was obtained. By studying and analyzing these data, the authors confirmed that rice uptake of Cd from soil is mainly controlled by such geochemical factors as cadmium, zinc, selenium, pH, organic matter (OM) and cation exchange capacity (CEC) within the cultivated soil. Some conclusions have been reached: 1) When the pH is lower than 7.0 in soil and BCF (Bioconcentration Factor) is larger than 10% in milled rice, there exists obvious positive correlative relationship between Cd concentration of milled rice and Cd and Zn content within soil, and their correlation coefficients are above 0.67; bioactivity of cadmium in farmland soils is higher in most cases; there exists more significant correlative relationship between Cd of rice and bioavailable Cd of soil than total Cd within soil if cadmium content from the cultivated soil reflects only exchangeable and weak acid-soluble fraction, with the correlation coefficient larger than 0.7; 2) Se, OM and CEC could inhibit the rice uptake of Cd from the cultivated soil, and there exists a significant negative correlation between Cd concentration of milled rice and Se, OM and CEC concentrations within the soil under some limited conditions, with the correlation coefficients being less than -0.5; 3) Soil acidification could stimulate the increase of Cd content in the milled rice, when Cd concentration of milled rice is larger than 0.2mg/kg and its OM is equal to 2.5%~6.5%, and there yet exists significant negative correlation between Cd concentration of milled rice and pH in the cultivated soil, with the correlation coefficient smaller than -0.6; 4) the Cd distribution in different rice organs is not uniform, from the roots to the upper rice organs, the Cd content in rice gradually reduced, and it is obvious that root rice organs could play a greater role in absorption of Cd from the cultivated soil during the rice growth.