Selenium-carrageenan mediates dual regulation of arsenic mobilization and cadmium immobilization during the simulated gastric phase.

Arsenic (As) and cadmium (Cd) co-contamination in environments poses threats to human health, yet the mechanisms underlying their synergistic toxicity and modulation by selenium (Se) supplementation remain poorly understood. This study investigated the dual regulatory role of selenated carrageenan (Se-car), an organoselenium compound, in modulating the bioaccessibility of As and Cd during the simulated gastric phase. The in vitro bioassays demonstrate that Se-car enhances As mobilization by competitively displacing As from ferrihydrite surfaces and promoting reductive dissolution of iron minerals, while simultaneously suppressing Cd release via ternary complexation with Fe and organic matter. Notably, Se-car shifted As speciation toward the more toxic As(III) and stabilized Cd through Fe-Se-Cd interfacial interactions. These findings reveal paradoxical "double-edged sword" effect of Se-car in the gastric phase, where it increases As mobilization but mitigating Cd toxicity. This study provides mechanistic insights into Se-As-Cd interactions and inform targeted strategies to manage health in co-contaminated environments.