Iron promotes cadmium binding to citrate

Ironcadmium interactions are important in cadmium toxicity. Dietary iron supplements may decrease cadmium retention after oral cadmium exposure but the underlying mechanism is not known. Using a CdS/AgS ion selective electrode to measure Cd²⁺] in physiological saline solution at pH 7.4, we show that Fe²⁺ promotes Cd²⁺ binding to citrate thereby decreasing the availability of free Cd²⁺. This suggests the formation of high molecular weight Cd²⁺Fe²⁺citrate complexes. We confirm this suggestion by showing that ¹⁰⁹Cd²⁺ is retained by 1 kDa cut off filters when present with total 50 M Fe²⁺ plus 1 mM citrate but not when present with citrate alone. The formation of high molecular weight complexes may prevent Cd²⁺ absorption. As citrate is part of the diet, we suggest that these ironcadmium interactions may contribute to the protective effect of iron against cadmium toxicity.