Zero-valent iron reduces cadmium and arsenic accumulation in spinach (<i>Spinacia oleracea</i> L.)

Cadmium (Cd) and arsenic (As) soil contamination poses significant problems for crop production worldwide. Zero-valent iron (Fe0) is a reactive material with reducing power capable of stabilizing toxic elements, including heavy metals and metalloids. In this study, we examined the effect of Fe0 application on Cd and As accumulation in spinach (Spinacia oleracea L.) grown in Cd- or As-contaminated soil. Fe0 soil application reduced Cd and As concentrations in spinach shoots and/or roots, and decreased their availability in soil, which may have affected their accumulation in spinach. Additionally, we examined the forms of soil Cd and As using the sequential extraction method. The potential availability of Cd and As forms in soils for plant root is: exchangeable > iron-manganese-oxide-bound > organic-matter-bound > free-oxide-occluded > residual. Fe0 application increased Cd and As distribution in the free-oxide-occluded fraction. Additionally, Fe0 application decreased As distribution in the iron-manganese-oxide-bound fraction while tended to decrease Cd in the organic-matter-bound fraction and increase it in the iron-manganese-oxide-bound fraction. Thus, Fe0 application can be effective in reducing Cd and As availability in their contaminated soils. Meanwhile, this study showed that Fe0 application inhibited the growth of spinach in Cd-contaminated soil. The unfavorable alterations caused by Fe0 in the contaminated soil should also be investigated in the future.