Migration characteristics and bioaccessibility of selenium in soil-crop-human system depending on parent rocks and soil types

Soil formation characteristics substantially influence selenium (Se) transfer to food crops and its subsequent bioaccessibility to humans. This study investigated how parent materials and resulting soil properties affect Se‑cadmium (Cd) interactions and Se bioaccessibility in rice by analyzing paired soil-rice samples from agricultural areas in Guangxi, China. Total Se content in soil varied considerably (3.98–19.0 μg g⁻¹) across parent materials, with clasolite-derived soils exhibiting the highest Se levels (13.84 μg g⁻¹). Soil physicochemical analysis revealed pronounced Se–Cd co-occurrence, with pH emerging as a critical factor controlling their accumulation, antagonistic interactions, and mobility. Rice grain Se content ranged from 0.005 to 0.37 μg g⁻¹, strongly influenced by soil Cd levels and pH conditions. In vitro digestion assays demonstrated distinct patterns of Se bioaccessibility between gastric (42.5 % average, range: 10.7 %–72.8 %) and intestinal phases (80.2 % average, range: 50.3 %–92.8 %), primarily governed by soil Cd content, pH, and grain phytic acid. Risk assessment indicated that daily Se intake through rice consumption (14.0–136 μg d⁻¹ for adults, 10.1–97.0 μg d⁻¹ for children) remained within safe limits but below optimal levels for nutritional benefits. Results suggest that targeted agricultural zoning based on parent materials could provide a sustainable alternative to conventional Se fertilization programs, while integrated soil pH management may simultaneously address Se deficiency and Cd contamination risks. The study highlights pedological constraints to Se nutrition in rice-based diets.