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.