Effects of Different Combined Passivators on Cadmium Availability in Contaminated Soils and Uptake by Pakchoi (<i>Brassica chinensis</i> L.)

Abstract

To solve the problem of excessive heavy metals in farmland soil, there is a pressing need for research effort to screen for the soil passivator materials. The effects of combined passivators on cadmium (Cd) availability in soils and uptake by pakchoi have been investigated based on the passivator screening and pot experiment. The results indicated that sepiolite, calcined lime and polyacrylamide (PAM) could significantly decrease the available Cd content in soils among eight kinds of inorganic and organic passivators, which were declined by 28.64%, 40.06% and 74.55%, respectively. Therefore, sepiolite, calcined lime and PAM were identified as the components of the combined passivators to grow pakchoi. The pakchoi planting experiment results of combined passivators showed that the combination of "calcined lime+PAM+sepiolite" was the most effective in decreasing the available Cd content in soils, which can reduce it by 39.83% (P<0.05). Meanwhile, the increases in ratio of weak organic bound or iron and manganese oxidation fractions in soils were responsible for the transformation of soil available Cd to the more stabilized fraction after applying of combined passivators. The positive passivation responses of "calcined lime+PAM+sepiolite" for Cd transfer to the aboveground of pakchoi and "calcined lime+PAM" for Cd absorption by pakchoi root demonstrated that these combined passivators could reduce Cd uptake by pakchoi. Thus, application of combined passivator of "calcined lime+PAM+sepiolite" can effectively reduce the Cd availability and Cd uptake by pakchoi in this study. Based on the results of the present research would provide a useful reference to remediate Cd contaminated soils.