Increased zinc supply does not inhibit cadmium accumulation by rice (Oryza sativa L.)

Abstract

ABSTRACTRice (Oryza sativa L.) grown on cadmium (Cd)-contaminated soils has caused health problems in Asian subsistence rice farmers. For other crops, normal co-contaminant zinc (Zn) inhibits the increased uptake of Cd. We used a multi-chelator-buffered nutrient solution to characterize the interaction of Zn and Cd in uptake-translocation of Cd in “Lemont” rice. The activity of free Zn2+ varied from 10−7.6 to 10−5.2 M, while free Cd2+ held constant at 10−10.7 M. Zinc activity 10−5.6 M and higher was phytotoxic to rice, resulting in severe chlorosis, reduced growth, and increased Cd transport to shoots. In contrast to previous studies with wheat, lettuce, and spinach, free Zn2+ maintained at adequate to sub-phytotoxic levels (10−7.6 to 10−6.1) did not inhibit Cd uptake by rice. The inability of Zn to inhibit Cd uptake by rice is a key factor in Cd risk from zinc-lead mine waste contaminated soil compared with other crops.