Screen low-accumulation rice varieties, and identify soil safety utilization thresholds in Cd/Hg-contaminated paddy fields

Synchronous approaches for the safety utilization of paddy soils co-contaminated with cadmium (Cd) and mercury (Hg) remain limited, especially regarding the threshold of soil Hg concentration for safety production of rice. Meanwhile, little attention has been given to the stability of low-Cd/Hg-accumulation rice cultivars. Therefore, combined three-year, three-site field trials using 55 rice varieties with stability analysis and soil thresholds calculation, was conducted to screen low-Cd/Hg rice varieties, their stability, and explore the threshold of soil Cd/Hg concentration for safety production of rice using K -means clustering, genotype plus genotype-by-environment interaction (GGE) biplots, and species sensitivity distribution (SSD) modelling in Ningbo City, China. Results indicated that some rice varieties exceeded the 0.2 mg kg −1 national food safety standards limit of Cd in rice, while Hg concentrations generally remained within 0.02 mg kg −1 national food safety standards limit of Hg in rice (GB 2762–2025). Low-Hg/Cd rice (e.g., S7, S13, S19), low-Hg rice (e.g., S54, S55, S8), low-Cd rice (e.g., S6, S11, S4), and non-low-Hg/Cd rice (e.g., S24, S52, S42) were determined by clustering analysis. Japonica rice cultivars NanJing-46 (S13) and XiuShui-14 (S26), which combine low-Hg/Cd accumulation rice with high stability were identified by GGE analysis. The thresholds of soil Cd and Hg concentration for safety production of rice were estimated as 0.15 mg kg⁻¹ and 1.19 mg kg⁻¹ , respectively. These findings provide a scientific basis for screening low-Cd/Hg accumulation rice cultivars and offer an approach for controlling, treating and remedying Cd/Hg contaminated agricultural soils to make grains safe for human consumption.