Red mud amendments reduce cadmium mobility in paddy soil and limit cadmium accumulation in rice grains: A mechanistic investigation

Authors: YAN, JIALI - Chuzhou University; LI, XUWEI - Nanjing Institute Of Environmental Sciences; LI, JINTAO - Chuzhou University; ZHOU, JIANKANG - Henan Agricultural University; SHI, JIAMIN - Chuzhou University; LIU, KANGFU - Chuzhou University; CHEN, XIN - Chuzhou University; ZHOU, SHIQI - Chuzhou University; SUN, WEIWEI - Chuzhou University; SUI, FUQING - Henan Agricultural University; LIN, XIAOCHEN - Nanjing Institute Of Environmental Sciences; ZHANG, LEI - Chuzhou University; Fischel, Matthew

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2025
Publication Date: 4/10/2025
Citation: Yan, J., Li, X., Li, J., Zhou, J., Shi, J., Liu, K., Chen, X., Fischel, M.H., Sun, W., Sui, F., Lin, X., Zhang, L. 2025. Red mud amendments reduce cadmium mobility in paddy soil and limit cadmium accumulation in rice grains: A mechanistic investigation. Plant and Soil. https://doi.org/10.1007/s11104-025-07403-9.
DOI: https://doi.org/10.1007/s11104-025-07403-9

Interpretive Summary: Cadmium is a carcinogen and toxin that impacts human health worldwide and dietary ingestion through grains like rice represents the major human exposure pathway. Red mud is an industrial byproduct from aluminum processing with a high sorption capacity and alkaline pH, which can be added to rice fields to reduce cadmium uptake into the rice grain. However, it is unknown how the rate of red mud application and the duration of flooding in rice paddies impact the grain cadmium uptake during the filling stage and the subsequent human exposure risk. This study investigated varying application rates of red mud and differing flooding regimes to determine the mechanisms of soil cadmium mobility under rice paddy conditions, which paired with a potted rice experiment to quantify the reduction in rice grain cadmium levels. The experiments showed after applying red mud, the rice grain cadmium levels dropped to safe amounts even in flooded conditions, where there were previously high levels of cadmium. These results aid policymakers in deciding how to regulate safe levels of cadmium in rice paddy soils and scientists and farmers working to reduce the cadmium levels in rice grain to reduce human exposure and protect human health.

Technical Abstract: Background and Aims Red mud, an alkaline byproduct of aluminum smelting, can serve as a soil amendment to mitigate soil cadmium contamination. Rice uptakes cadmium mainly during the grain-flling stage after soils are drained. During the fooding-drainage process, substantial fuctuations in redox potential occur, and the effectiveness of red mud amendment under these conditions remains unresolved. The aim is to test the effects of red mud on soil cadmium mobility after soil drainage and subsequent rice cadmium accumulation. Methods Soil cadmium fractions and release kinetics were assessed by sequential extraction and stirred-fow experiments followed by soil microcosm incubation with slightly cadmium-contaminated paddy soil (0.52 mg Cd kg-1), respectively. Rice cadmium accumulation was assessed in a potted rice experiment. Results Incorporating up to 2% red mud enhanced the proportions of cadmium bound to iron and manganese oxides from 12.5–28.1% to 25.1–44.0%, thus efectively reducing the mobility of cadmium in paddy soil after soil drainage. As a result, cadmium contents were decreased by 72.5–76.9% and 84.7–91.2% in the rice grains and straw, respectively. Conclusions Applying 2% red mud enhanced the soil iron and manganese oxide-cadmium proportions after soil drainage,decreasing the soil cadmium release maximum and rate, limiting cadmium uptake and subsequent accumulation into the rice grain to a level permissible for human ingestion. The stability of iron minerals impacts soil cadmium adsorption. These fndings provide a scientifc basis for using red mud in paddy soil cadmium remediation.