A Soil Cadmium Risk Index (SCRI) Framework for Cd Risk Assessment and Cultivar Selection in Cadmium-Contaminated Paddy Fields: A Case Study of Xiangtan County, China.

Soil cadmium (Cd) contamination threatens food security in China's rice-growing regions. Current risk assessment mainly relies on physicochemical indicators, overlooking microbial ecological responses. Here, 40 soil samples from a Cd-contaminated paddy field in Xiangtan, China, were analyzed for soil properties, Cd concentration, and bacterial communities using 16S rRNA sequencing. An eight-indicator minimum data set (MDS) was identified through principal component and correlation analyses to develop a soil Cd risk index (SCRI), which was further validated using 71 regional field samples with rice grain Cd and yield data. The MDS explained 75.33% of the total variance, and SCRI showed strong agreement with the full data set (R2 = 0.81). SCRI thresholds identified high- (≤0.28) and low-risk (≥0.30) areas, with grain Cd exceedance rates of 94.12% and 41.38%, respectively. SCRI provides a practical framework for Cd risk assessment, cultivar selection, and sustainable management of contaminated paddy soils.