Screening of Stable Low-Cadmium Rice Cultivars and Derivation of Soil Cd Threshold Based on Bioconcentration Factor and Multi-Environment Analysis.

Cadmium (Cd) contamination in agricultural soils poses a significant threat to food safety and human health, especially in rice-consuming regions. This study aimed to identify rice cultivars with consistently low Cd accumulation and to establish a soil quality standard based on the bioconcentration factor (BCF) derived from field trials across 10 environments in central Taiwan. Fifteen rice cultivars were evaluated over four years (2020-2023), and BCF values were determined for each cultivar and environment. Genotypic and environmental effects on Cd accumulation were assessed using genotype plus genotype-by-environment (GGE) biplot analysis. The results indicated that environmental factors contributed the most to BCF variability (93.11%), followed by genotype-environment interaction (5.61%) and genotypic effect (1.28%). Several cultivars, including KH139 and TT30, exhibited stable and low BCF values across environments. Furthermore, the BCF values were used to construct a species sensitivity distribution (SSD) curve fitted with the Burr Type III distribution, and the HC5 value was estimated for the derivation of food safety and health-based Cd soil thresholds. The former's soil threshold was 0.7 mg/kg, while the latter's ranged from 4.5-6.0 mg/kg depending on gender. The results suggest that the soil Cd threshold can be maintained at the current Taiwan's soil pollution control standard of 5 mg/kg. These findings provide scientific evidence for the development of site-specific, risk-based soil management strategies and cultivar selection to mitigate Cd exposure from rice consumption.