Red mud causes dynamic changes in the soil microbial community and cadmium fractions in a slightly cadmium-contaminated paddy soil

Authors: YAN, JIALI - Chuzhou University; LI, XUWEI - Nanjing Institute Of Environmental Sciences; PAN, ZHENGGUO - Chuzhou University; LIN, XIAOCHEN - Nanjing Institute Of Environmental Sciences; ZUO, QINGLIN - Anhui University Of Chinese Medicine; ZHOU, JIANKANG - Henan Agricultural University; ZHOU, SHIQI - Chuzhou University; SUI, FUQING - Henan Agricultural University; ZHANG, LEI - Chuzhou University; Fischel, Matthew

Submitted to: Journal of Hazardous Materials
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/18/2025
Publication Date: 4/20/2025
Citation: Yan, J., Li, X., Zuo, Q., Zhou, J., Fischel, M.H., Zhou, S., Lin, X., Sui, F., Zhang, L. 2025. Red mud causes dynamic changes in the soil microbial community and cadmium fractions in a slightly cadmium-contaminated paddy soil. Journal of Hazardous Materials. 493. Article 138349. https://doi.org/10.1016/j.jhazmat.2025.138349.
DOI: https://doi.org/10.1016/j.jhazmat.2025.138349

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. To reduce cadmium uptake into rice grain, it has been proposed that an industrial byproduct called red mud be added to rice fields to absorb and bind cadmium. Soil quality is significantly affected by the many types of microbes that live in it. Therefore, it was important to determine how the application of red mud to rice fields would affect the microbial community. The experiments showed that after applying red mud, the soil bacterial communities responsible for iron oxidation became more abundant and produced iron oxides capable of binding cadmium and preventing plant uptake of the cadmium, adding to the effect of the red mud. These results aid policymakers in deciding how to regulate safe levels of cadmium in rice paddy soils, as well as farmers, extension agents, crop advisors, and other scientists who are working to reduce the cadmium levels in rice grain to reduce human exposure and protect human health.

Technical Abstract: Red mud is a highly alkaline industrial by-product rich in iron oxides with great potential for soil cadmium remediation. Although the stabilization of Cd by red mud is well reported in rice potted and field experiments, the influence of red mud on microbial communities in paddy soil and the contribution of soil microbial communities subjected to red mud in Cd stabilization remain unknown. This study used high-throughput sequencing and bioinformatics, combined with a sequential extraction procedure, to determine the microbiological mechanisms of rice Cd reduction by red mud and information on the corresponding soil Cd fraction. The results showed that red mud significantly increased the soil pH and iron and manganese oxide-bound Cd fractions. Red mud application influenced the microbial beta diversity rather than the alpha diversity, especially for bacteria. Unique taxa associated with iron reduction (e.g., phylum Firmicutes and genus Anaeromyxobacter) were enriched at the rice-filling stage, which may contribute to the stabilization of Cd. Red mud application caused little difference in the fungal communities. A 2'% red mud amendment successfully decreased the grain Cd content in a high Cd-accumulating rice cultivar by 72'%. Red mud effectively reduces Cd accumulation in the short-term and demonstrates potential for remedial applications. This study provides microbiological evidence for stabilizing Cd in red mud, but its long-term environmental impact and field applicability require further research.