Depletion of bioavailable As/Cd with rice plant from paddy soils of high contamination risk.

Co-uptake and high accumulation of As and Cd by rice is an outstanding issue threatening public health. From the viewpoint of soil cleanup, however, efficient As/Cd extraction by this paddy-adapted plant, followed by biomass removal, could provide a major pathway depleting As/Cd accumulation in paddy soils and thus inhibiting their transfer in food chain. Here a field trial was performed to identify the significance of As/Cd cleanup from paddy soil by rice. 88 % and 51 % of total extracted As and Cd were retained in root. To eliminate specifically rice-available As/Cd pool and obstruct their cycling back to soil, one crop of rice root was removed, leading to the depletion of 46 % and 69 % of plant available As (soluble & exchangeable) and Cd (exchangeable & carbonate-bound), respectively. In the following cultivation on the post-cleanup field, polished rice As fell from 0.23 mg kg to 0.12 mg kg, markedly lower than the Chinese (WHO) limit (0.2 mg kg). Meanwhile, white rice Cd decreased by 24 %. This field work identified that As/Cd co-extraction by paddy-adapted rice plant, followed by root removal, as a primary step toward rice safety in areas with high contamination risk but little reserved paddy resources.