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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Adaptive Cropping Systems Laboratory » Research » Publications at this Location » Publication #313764
Title: How does contamination of rice soils with Cd and Zn cause high incidence of human Cd disease in subsistence rice farmers?

Author
item Chaney, Rufus

Submitted to: Current Pollution Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/7/2015
Publication Date: 4/14/2015
Citation: Chaney, R.L. 2015. How does contamination of rice soils with Cd and Zn cause high incidence of human Cd disease in subsistence rice farmers? Current Pollution Reports. 1:16-22. doi: 10.1007/s40726-015-0002-4.

Interpretive Summary: This manuscript re-interprets previous scientific research on cadmium contamination of rice soils which has caused widespread human disease in subsistence rice farmers, while higher cadmium contamination of soils for other crops has not harmed humans. New understanding shows that rice root transport protein accumulates very low cadmium in flooded soils and higher after fields are drained. Other crop species accumulate cadmium on a zinc transporter protein which strongly inhibits cadmium uptake. Rice grain is very low in zinc. Because of low zinc status in humans, absorption of dietary cadmium increases, particularly in polished rice. This new soil-plant-human model for cadmium in agriculture explains how soil cadmium harms subsistence rice farmers much better than previous models, and may provide support for improved standards for allowable cadmium in crops and identification of soils where remediation is required to improve food safety.

Technical Abstract: Rice (Oryza sativa L.) grown on Zn mine waste contaminated soils has caused unequivocal Cd effects on kidney and occasional bone disease (itai-itai) in subsistence rice farmers, but high intake of Cd from other foods has not caused similar effects. Research has clarified two important topics about how Cd from mine wastes-contaminated rice soils have caused Cd-disease: 1) bioaccumulation of soil Cd into rice grain without corresponding increase in Zn; and 2) subsistence rice diets potentiate Cd absorption/bioavailability and risk to farm families. Absorption of Cd by rice roots occurs on the NRAMP5 Mn2+-transporter. Although other transporters can influence Cd uptake-transport to shoots and grain, making NRAMP5 null greatly reduced grain Cd. Zn2+ has little ability to inhibit Cd2+ transfer in rice but clearly inhibits Cd uptake in other plant species. The bioavailability of dietary Cd is increased for subsistence rice diets. Research has identified that low levels and bioavailability of Zn and Fe in polished rice grain cause up-regulation of Cd absorption on the Fe2+-transporter of duodenum cells (DMT1). Added Zn can also inhibit intestinal Cd absorption somewhat. Nutritional stress (Fe, Zn deficiency) in humans consuming subsistence rice diets thus promotes Cd accumulation and adverse effects. No other dietary (crop) Cd exposure has caused unequivocal Cd induced renal proximal tubular dysfunction (the first adverse Cd-effect) in humans. Recognition of the very unusual nature of Cd risk from rice compared to other crops should be taken into account in setting international limits of Cd in rice and other foods.