Heavy metal tolerance of rice plants (Oryza sativa L.) to some metal oxides at the critical levels.

The toxicity of metal oxides (CdO, ZnO, PbO) were compared with each other and the critical levels of metal uptake by rice plants were determined. The order of metal toxicity to rice plants is CdO greater than ZnO greater than PbO. The highest concentration obtained for unpolished rice was 4.97 micrograms/g at the Cd 10,000 ppm in soil. This values is higher than every other we have seen in the reports for treatment with CdO. We are able to find out that the concentration of 10,000 ppm Cd in the form of CdO in the critical one towards rice plant. By contrast, such damage was not observed at even higher levels of ZnO and PbO were considered to have low toxicity toward rice plant. Also, a negative correlation between Zn or Cu accumulation in rice plants and Cd concentration in soil was found.