Iron plaque effects on selenium and cadmium stabilization in Cd-contaminated seleniferous rice seedlings

Dietary intake of selenium (Se)-enriched rice has benefit for avoiding Se-deficient disease, but there is a risk of excessive cadmium (Cd) intake. Through hydroponic culture and adsorption-desorption experiments, this paper focused on Se and Cd uptake in rice seedlings associated with the interactive effects of Se (Se⁴⁺ or Se⁶⁺), Cd, and iron (Fe) plaque. The formation of Fe plaque was promoted by Fe²⁺ and inhibited by Cd but not related with Se species. Shoot Se (Se⁴⁺ or Se⁶⁺) uptake was not affected by Fe plaque in most treatments, except that shoot Se concentrations were decreased by Fe plaque when Se⁴⁺ and Cd co-exposure. Shoot Cd concentrations were always inhibited by Fe plaque, regardless of Se species. Inhibiting Cd adsorption onto root surface (Se⁴⁺  + Cd) or increased Cd retention in Fe plaque (Se⁶⁺  + Cd) is an important mechanism for Fe plaque to reduce Cd uptake by rice. However, we found that DCB Cd concentrations (Cd adsorbed by Fe plaque) were not always positively correlated with Fe plaque amounts and always negatively correlated with the distribution ratios of Cd mass in root to that in Fe plaque (abbreviated as DRCMRF; r =  - 0.942^**); meanwhile, with the increase of DCB Fe concentration, the directions of variations of DCB Cd concentration and DRCMRF were affected by Se species. It indicated that the root system is also an important factor to affect DCB Cd concentration and inhibit Cd uptake, which is mediated by Se species. This paper provides a new understanding of Fe plaque-mediated interactive effect of Se and Cd uptakes in rice, which is beneficial for the remediation of Cd-contaminated and Cd-contaminated seleniferous areas.