BINDING OF ENDOGENOUS AND EXOGENOUS CADMIUM TO GLUTELIN IN RICE GRAINS AS STUDIED BY HPLC ICP-MS WITH USE OF A STABLE-ISOTOPE/

Cadmium (Cd) in polished rice grains was extracted under various condi tions and the chemical forms of the metal in soluble fractions were de termined together with copper, zinc and other metals by HPLC with on-l ine detection by inductively coupled argon plasma (ICP)-mass spectrome try (MS). Cd (753 ng/g) in rice grains grown in Cd-contaminated rice f ields was mostly bound to glutelin in soluble fractions. Binding of Cd in vitro to constituents in rice grains was examined by incubating Cd Cl2 enriched with Cd-113 (96.3 % enrichment) in a suspension of powder ed rice grains. Distribution of exogenous Cd-113 in the soluble fracti on of Cd-contaminated rice grains was identical with that of endogenou s Cd on a size-exclusion column, and the metal was shown to bind to gl utelin up to 5.0 mu g/g in the control rice grains, indicating that ex ogenous Cd can be bound to glutelin up to this capacity. Simultaneous speciation of exogenous Cd-113 and endogenous Cd-111 was demonstrated to be highly effective for comparing the binding of Cd of natural and artificial origins.