Decrease of Cadmium Accumulation in Crops by Zero-valent Iron

Cadmium (Cd) contamination in soils is a serious problem for crop production in the world. Zero-valent iron (Fe(0)) is a reactive material with reducing power capable of stabilizing toxic elements, including heavy metals and metalloids, in a solution. In the present study, we examined the effect of Fe(0) application on Cd accumulation in rice (Oryza sativa L. cv. Kirara 397) and spinach (Pinacia oleracea L.) plants growing in Cd-contaminated soils under paddy and upland conditions, respectively. The Fe(0) application significantly reduced the Cd concentration in seeds and leaves of rice, and that in shoots of spinach. The forms of Cd in soil were determined by sequential extraction. The potential availability of Cd forms in soils for plant root is: exchangeable > Fe-Mn oxides bound > organic matter bound > free-oxides occluded > residual. In Cd-contaminated paddy soils where rice was grown, the Fe(0) application increased the free oxides occluded Cd content, and decreased the exchangeable and iron-manganese oxides bound Cd content. In Cd-contaminated upland soils where spinach was grown, the Fe(0) application increased the iron-manganese oxides bound and free-oxides occluded Cd content, and decreased the exchangeable and organic matter bound Cd content. Thus, this study clearly showed that the application of Fe(0) is a promising approach for remediation of Cd-contaminated soils under both paddy and upland conditions