Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2011
Publication Date: 5/15/2011
Citation: Gu, H., Qui, H., Tian, T., Zhan, S., Deng, T., Chaney, R.L., Wang, S., Tang, Y., Morel, J., Qiu, R. 2011. Mitigation effects of silicon rich amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on multi-metal contaminated acidic soil. Chemosphere. 83:1234-1240. Interpretive Summary: Dispersal of mine wastes has contaminated large land areas in China with cadmium, zinc and lead has caused rice produced on the contaminated soils to exceed allowable cadmium levels. Different methods to prevent production of rice with excessive cadmium are being tested. One method is to add soil amendments which increase binding of cadmium by the amended soil, or reduce cadmium uptake and translocation to grain. Steel mill slag and fly ash are rich in alkalinity and silicate, both of which can increase soil pH of strongly acidic contaminated sols (due to pyrite in the mine wastes) to limit cadmium uptake, and iron oxides which increase cadmium binding by the soil. Experiments were conducted to test the effect of these amendments on grain and leaf cadmium of rice grown under flooded conditions which also reduces cadmium uptake by the plants. Amendments reduce grain cadmium by 71% when applied at practical rates. Using Diffusion Gradient T method, it was shown that the phytoavailability of soil cadmium was reduced about 84%. Interestingly, the amendments reduced the translocation of cadmium from shoots to grain (Cd in grain was reduced relative to Cd in shoots). For these soils with moderate soil contamination, amendment with steel slag and fly ash reduced grain cadmium to regulated levels. Thus soil amendments can contribute to reduction of soil cadmium risks to subsistence rice farmers, the population at greatest risk from soil cadmium contamination.
Technical Abstract: The mechanisms of stabilization by silicon-rich amendments of cadmium, zinc, copper and lead in a multi-metal contaminated acidic soil and the mitigation of metal accumulation in rice were investigated in this study. The results from a pot experiment indicated that the application of fly ash (20 and 40 g'kg-1) and steel slag (3 and 6 g'kg-1) increased soil pH from 3.99 to 5.01-6.37, decreased the phytoavailability of heavy metals at least 71%, and further suppressed metal uptake by rice. Diffusion gradient in thin-films measurement showed the heavy metal diffusion fluxes from soil solid to solution decreased by greater than 84% after remediation. X ray diffraction analysis indicated the mobile metals were mainly deposited as their silicates, phosphates and hydroxides in amended treatments. Moreover, it was found metal translocation from stem to leaf was dramatically restrained by adding amendments, which might due to the increase of silicon concentration and co-precipitation with heavy metals in stem. Finally, a field experiment showed the trace element concentrations in polished rice treated with amendments complied with the food safety standard of China. These results demonstrated fly ash and steel slag could be effective in mitigating heavy metal accumulation in rice grown on multi-metal contaminated acidic soils.