Mercapto–palygorskite decreases the Cd uptake of wheat by changing Fe and Mn fraction in Cd contaminated alkaline soil

Abstract

Wheat is one of the major sources of dietary nutrition for human body, and excessive Cadmium (Cd) in wheat poses a serious risk to human health. Mercapto–palygorskite (MP) has been proven to efficiently reduce Cd stress in wheat, but the contribution of major soil oxides to the stability of soil Cd under MP treatment is unclear. Here, a wheat pot experiment was conducted to evaluate the effects of soil Fe and Mn oxides on the Cd fraction under MP treatment. The results showed that the application of MP decreased the diethylenetriaminepentaacetic acid (DTPA)–extractable Cd by 24.0–34.7 %, increased the Fe and Mn oxide-bound Cd (OX–Cd) by 5.0–12.0 % and significantly reduced the Cd content in wheat grains (17.9–69.5 %). It also decreased the soil’s free Fe and Mn oxides by 6.1–11.7 %and 6.9–12.4 %, respectively, and increased the amorphous Fe and Mn oxides by 19.3–32.5 % and 21.9–24.1 %, respectively. In addition, the application of MP increased the concentration of Fe and Cd in soil colloid by 19.3–33.3 % and 11.3–45.3 %, respectively. Correlation analysis indicated that the amorphous Fe, Mn oxides in soil had a significant positive correlation with the content of Fe and Mn bound Cd in soil (P < 0.01). Primary component analysis (PCA) analysis shows colloidal Fe and Mn on the soil available Cd had relatively high positively loadings. Meanwhile, soil colloidal Fe exhibited a significant positive correlation with colloidal Cd (P < 0.01) and amorphous Fe oxides (P < 0.01). These results indicated that MP remediated Cd-contaminated soil by promoting an increase in amorphous Fe, Mn oxides and their adsorption and precipitation of Cd on these oxides.