Effective agronomic biofortification of rice with selenium: Ensuring dietary intake through relative bioavailability...

Despite advances in large-scale selenium (Se) biofortification, a critical knowledge gap persists regarding precise safety assessments for Se-enriched rice by incorporating Se speciation, bioaccessibility (raw and cooked), and relative bioavailability (RBA) into dietary intake and risk evaluations in different age groups. This study lies in its multifactorial approach, combining field data with bioaccessible Se metrics to refine dietary intake standards across demographic strata. Biofortification through soil and foliar Se applications significantly increased rice grain Se content (0.007-0.85 mg/kg), meeting established standards. Soil application maximized Se bioconcentration (BCF) in roots, while foliar application did so in leaves, indicating limited Se mobility to rice grains (0.12-0.97). Speciation analysis revealed a significant increase in organic Se (notably selenomethionine [SeMet]; P < 0.05), with no corresponding rise in inorganic Se in rice grains. The study demonstrated that Se intake from CK was not enough to meet the daily need of recommended daily intake (RDI). Moreover, Se-enriched rice containing 0.63-0.91 mg/kg Se remained below the tolerable upper intake level (TUL) of 400 μg day^-1 while meeting the RDI of 55-350 μg day^-1 for individuals aged 2-70 years. Based on Se-RBA, intake ranged from 28.27 to 117.63 μg day^-1, with corresponding THQ < 1 for RDI and TUL. Bioaccessibility-based values for raw rice and boiled rice likewise satisfied RDI thresholds and yielded THQ < 1 for RDI and TUL, respectively. Moreover, this study incorporates RBA and bioaccessibility, revealed estimated dietary intake (EDI) values declining from total Se to bioaccessible Se, with RBA-adjusted estimates minimal. Furthermore, ecological risk assessments (ecological risk factor < 40) confirmed no Se soil pollution with organic Se application. This work uniquely integrates total Se, bioaccessible Se, and Se-RBA into dietary Se risk evaluation, advancing agricultural and food chemistry by molecularly correlating Se absorption-utilization dynamics with population-specific intake and hazard assessment for consumption of Se-enriched crops, thereby enabling precision biofortification strategies in staple crops.