Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 1, 2001
Publication Date: July 26, 2001
Research has found human Cd disease (renal proximal tubular dysfunction) from soil Cd only in locations where subsistence rice farmers grew their diets on fields with Zn-Pb-Cu mining or smelter contamination. In flooded rice, Cd is rapidly transported to grain while grain-Zn is not increased. Rice is unique among crops in accumulating Cd without Zn from such contaminated fields. Besides being a poor source of Zn for humans, rice fails to provide adequate Fe and Ca for life, and Fe and Zn malnourishment are common in subsistence rice consumers. Further, Fe, Zn, and Ca malnutrition of humans promotes Cd absorption, as much as 20-fold compared to well nourished persons. To test the role of malnutrition induced by subsistence rice diets, rats were fed diets with marginal or adequate levels of Fe, Zn, and Ca in a factorial design with roasted sunflower kernels or polished rice grain, using crop labeled with 109Cd at about 0.6 mg Cd/kg dry grain. Rats were preconditioned to the diet for 21 days befor the 109Cd-labeled grain was fed for 24 hr; then the non-labeled grain diets were fed for 16 more days. Most of the Cd in the 109Cd test meal was absorbed into intestinal cells and turned over repeatedly over weeks after the feeding period. Animals with adequate levels of Fe, Zn, and Ca excreted unabsorbed 109Cd much sooner than animals which had marginal Zn, Fe and/or Ca. 109Cd absorption to liver and kidney reached as high as 2.7% of rice diet Cd in the low Zn, low Fe, low Ca diets, or as little as 0.35% with adequate minerals. For sunflower kernels, low Zn-low Fe-low Ca diets caused 0.78% of 109Cd dose to reach the kidney + liver, while animals with adequate diets retained only 0.22%. We believe these results explain the remarkable ability of rice to move soil Cd into human kidney.