A Combined Remediation Strategy of Arsenic and Cadmium in the Paddy Soil of Polymetallic Mining Areas

Dynamic Effect of Organic Fertilizer Application on Rice Growth, Soil Physicochemical Properties and Cd Activity Exposed to Excess Cd

To investigate the dynamic effects of organic fertilizer application on the agronomic traits of rice (Oryza sativa L.), soil physicochemical properties and soil Cd activity under excess cadmium (Cd) exposure, this study was conducted to simulate a paddy system under different organic fertilizer application rates using exogenous spiked Cd soil as the test soil and conducting a rice pot experiment. The obtained results showed that the application of organic fertilizer increased the number of rice tillers, rice plant height, total grain number and total grain weight at maturity in all treated soils, while it decreased the concentration of Cd in brown rice. The application of organic fertilizer increased the organic matter (OM), redox potential and electrical conductivity of all treated soils but decreased the pH and TCLP-extractable Cd of all treated soils. There was a significant or highly significant negative correlation (p < 0.05 or p < 0.01) between soil TCLP-extractable Cd and soil OM throughout the experimental period, implying that soil OM may be an important factor influencing the changes in Cd activity in soil. In addition, our experiment also examined in detail the dynamic change process of the abovementioned indicators throughout the experimental period and observed that the dynamic change process of soil Cd activity could be described as a trend of first decreasing and then gradually increasing throughout the rice reproductive period.

Effects of Red Mud on Cadmium Uptake and Accumulation by Rice and Chemical Changes in Rhizospheres by Rhizobox Method

Red mud (RM), a byproduct of aluminum production, is used as amendments to increase the pH and reduce the available Cd in soil, but the effects of RM treatments on rice and rhizosphere chemistry changes at different radial-oxygen-loss (ROL) rates and developmental stages remain unclear. To address this concern, a rhizobox trial was conducted to investigate the effect of 0%, 0.5%, and 1.0% RM, on Cd accumulation by rice cultivars differing in ROL rate (‘Zheyou12’ (ZY12), ‘Qianyou1’ (QY1), and ‘Chunjiangnuo2’ (CJN2)) at two growth stages (tillering and bolting). The results showed that mobility factors of Cd in the soil were decreased significantly at both stages. The Cd mobility factor (MF) of CJN2 was decreased by 33.01% under 1% RM treatment at bolting stage. The pH value was increased by 0.39–0.53 units at two stages. RM contains large amounts of metals, which can increase soil iron (Fe) and manganese (Mn) concentrations, reduce redox potential, and transform the available Cd into Fe/Mn oxide-bound Cd. In addition, the Fe plaque further increased to inhibit the transformation of Cd. These changes reduced the available Cd in the soil and further decreased Cd absorption by rice. With the increase in RM concentration, the shoot and root biomass increased, and Cd accumulation in the plant significantly decreased. Compared with that under 0% RM treatment, the shoot Cd concentrations of ZY12, QY1, and CJN2 under 1% RM treatment at the bolting stage decreased by 27.59%, 36.00%, and 46.03%, respectively. The relative Cd accumulation ability of the three rice cultivars was CJN2 < QY1 < ZY12. The ROL promotes Fe plaque formation on the root surface. The Fe plaque is an obstacle or buffer between Cd and rice, which can immobilize Cd in Fe plaque and further reduce Cd absorption by rice. The addition of RM, in combination with a high-ROL rice cultivar, is a potential strategy for the safe production of rice on Cd-contaminated soils.