Submitted to: Environmental Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2002
Publication Date: 6/1/2002
Citation: Reeves, P.G., Chaney, R.L. 2002. Nutritional status affects the absorption and whole-body and organ retention of cadmium in rats fed rice-based diets. Environmental Science and Technology. 36:2684-2692. Interpretive Summary: Cadmium is a trace element found in most foods. If we eat too much cadmium, we might develop problems with kidney function. Restrictions on the amount of cadmium in food are based primarily on the amount of cadmium in the food, and not on whether the cadmium can be absorbed into the body from the ingested food. Work in our laboratory suggests that low intakes of natural minerals such as iron, calcium, and zinc, could increase the absorption of cadmium. Some grains, such as polished rice does not contain high amounts of these minerals, but if grown in polluted paddies, it can have high amounts of cadmium. So, people who consume this rice as a staple food would more than likely absorb more cadmium unless they also consume adequate amounts of the other minerals. To determine if this were true, we fed female rats diets with 40% cooked, dried rice containing cadmium in amounts similar to that in rice grown in polluted paddies, but with normal amounts of calcium, iron, or zinc. The diets contained a low and a normal amount o calcium, iron, and zinc. After five weeks, we measured the amount of cadmium absorbed from the rice. Rats fed low dietary iron or calcium absorbed three times more cadmium than those fed normal amounts of the minerals. Rats fed low zinc diets also absorbed more cadmium, but much less than those fed low iron and/or calcium. The amounts of cadmium found in the small intestine, liver, and kidney were much higher when the rats ate diets with low iron and calcium than when they ate diets with normal amounts of these minerals. The results of this work suggest that food cadmium would be less toxic if the food or the diet contained ample amounts of calcium, iron, and or zinc.
Technical Abstract: Staple grains consumed by different societal groups differ greatly in their concentrations and bioavailability of the cadmium (Cd) antagonists, zinc (Zn), iron (Fe), and calcium (Ca). We hypothesized that the low nutritional status of consumers, which results from an inadequate supply of these minerals from rice, could contribute significantly to a higher apparent susceptibility to soil to rice Cd contamination than the higher nutritiona status of those who consume grains with high mineral content. To test this hypothesis, a 2x2x2 factorial study was conducted. Rats were fed diets with adequate or marginal amounts of dietary Zn, Fe, or Ca. The basal diets contained 40% unenriched, milled rice fortified with 0.62 mg Cd/kg (0.25 mg Cd/kg diet). Rat consumed the diets for 5 weeks and then were fed 1 g of similar diet containing 109**Cd-labeled rice. After 2 weeks, whole-body (WB) retention of 109**Cd was determineD. Rats then were killed and organs removed for total Cd determinations. Rats fed marginal concentrations of dietary Zn had slightly but significantly more WB retention of 109Cd than controls; however, rats fed marginal Fe or Ca had as much as 3-fold higher retention of the label. Rats fed marginal amounts of Zn, Fe, and Ca retained as much as 8 times more 109**Cd than rats fed adequate minerals. The effects on Cd concentrations in liver and kidney were similar to the effects on label retention. These results support the hypothesis that populations exposed to dietary sources of Cd and subsisting on marginal mineral intakes could be at greater risk than well-nourished populations exposed to similar amounts of dietary Cd. Thus, different food crops can cause unequal Cd risk at equal Cd concentration.