Rice plant nutritional and human nutritional characteristics role in human Cd toxicity

Abstract

To test the role of malnutrition induced by subsistence rice diets, rats were fed with diets containing marginal or adequate levels of Fe, Zn and Ca in a factorial design for both roasted sunflower kernels (SFK) and polished rice grain using crop labelled with 109Cd at about 0.6 mg Cd/kg dry grain. Rats were preconditioned to the grain diets for 35 days before the 109Cd-labelled diets were fed for 24 h. Non-labelled diets were then fed for 16 more days. Most of the Cd in the 109Cd test meal was absorbed into intestinal cells and the excretion was markedly delayed by marginal Fe, Zn or Ca diets. At the end of the feeding test, kidney, liver and other organs were analysed. Most of the Cd remained in the intestine at the end of the feeding test. 109Cd absorption by liver and kidney was 2.7% of the Cd diet in marginal Zn-Fe-Ca rice diets or as low as 0.35% with adequate minerals. For SFK, marginal Zn-Fe-Ca diets caused 0.78% of 109Cd dose to reach the kidney+liver while animals with adequate diets retained only 0.22% of the 109Cd test meal. These results explain the high incidence of Cd disease in subsistence rice consumers. When other major food crops are grown on Cd+Zn contaminated soils, Zn is not excluded from the grain. Thus, rice allows soil Cd to harm humans much more than other crops, supporting epidemiological data. Tobacco offers similar high movement of soil Cd to the kidney of smokers.