Iron promotes cadmium binding to citrate

Iron‐cadmium 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 μM 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 iron‐cadmium interactions may contribute to the protective effect of iron against cadmium toxicity.