Submitted to: Molecular Mechanisms of Metal Toxicity Conference
Publication Type: Abstract Only
Publication Acceptance Date: September 8, 2002
Publication Date: September 8, 2002
A fuller understanding of soil-plant-human transfer of Cd has been reached in the last decade that should modify risk assessment for human exposure to environmental Cd. For individuals in a non-industrial environment, nearly all Cd exposure comes from food and tobacco. There is no question that subsistence rice consumers in Japan and China suffered renal tubular dysfunction, and a small fraction of those suffered osteomalacia. These individuals consumed home grown rice, which was grown on flooded soils that were contaminated by Zn-Pb-Cu mining and smelting wastes. However, farm families and gardeners in UK, Germany, USA, The Netherlands, Belgium, etc., who consumed other foods grown on more highly contaminated soils did not experience renal tubular dysfunction. At several of these locations, soils contained 10-times higher Cd and Zn than in the usual contaminated fields in Japan and China. Our investigations have shown that several properties of rice caused the subsistence farm families to be much more highly susceptible to soil and dietary Cd than other persons. Compared to other crops, paddy rice excludes Zn from grain and is inherently deficient in Fe, Zn and Ca for human life. Because leafy vegetables that are known to be relatively high accumulators of Cd also accumulate Zn at the ratio present in the soil phytoavailable pools, Zn is about 100-fold higher than Cd in the edible crop. Also, Zn in the edible crop both prevents Zn deficiency in the consumer and inhibits Cd absorption into the intestine. No other crop is so remarkable in exclusion of Zn from edible tissues (e.g., grain). And, no other major staple food is so deficient in Fe and Zn for human diets as rice.