The relative exclusion of zinc and iron from rice grain in relation to rice grain cadmium as compared to soybean: Implications for human health

During 2000–2002, diagnostic rice and soybean plant samples and concurrent soil samples were collected from cultivated fields within a geo-physically unique Zn/Cd co-contaminated location in Thailand. For the fields sampled, aqua regia-digested Zn and Cd concentrations ranged from 2.91–284 and 254–8036 mg kg^–1, respectively. In comparison, rice and soybean Cd concentrations ranged from 0.02–5.00 and 1.08–1.71 mg kg^–1, respectively. Further, the results indicate that grain Cd, Zn and Fe concentrations are in the order rice^Gr=soybean^Gr, soybean^Gr>rice^Gr, soybean^Gr>rice^Gr, respectively. However, and critically from a human health perspective, Cd:Zn and Cd:Fe ratios are in the order rice^Gr>soybean^Gr. In addition, the rice^Gr Cd:Fe ratio is an order of magnitude higher than that determined for soybean^Gr. The results of this study, clearly demonstrate that compared to rice stalk (rice^St) and rice leaf (rice^L), rice^Gr accumulates comparatively higher Cd than Zn and Fe thus resulting in the high rice^Gr Cd:Zn and Cd:Fe ratios. This is in direct contrast to the results observed for soybean.