Field Experiment on the Stabilization of Cd in Soil Using Fe/Mn/S-Co-Doped Nanosilica and Its Effect on Cd Accumulation in Wheat Seedlings

A field experiment was conducted to investigate the stabilization effect of newly synthesized Fe/Mn/S-co-doped nanosilica (FMS-nanosilica) on cadmium (Cd) in soil and its potential effects on soil properties and wheat seedlings. The results showed that as the application rate of FMS-nanosilica increased from 0% to 1%, the soil pH, available potassium, available phosphorus (AP), and alkali-hydro-nitrogen decreased from 7.59 to 7.35, 276.66 to 251.99 mg/kg, 22.33 to 10.14 mg/kg, and 110.42 to 85.76 mg/kg, respectively. However, the soil organic matter content increased from 25.04 to 32.18 g/kg. After application of FMS-nanosilica, the available Cd (DTPA-Cd) and leachable Cd content were reduced by 57.8% and 43.4%, respectively. The acid-soluble and reducible Cd fractions were transformed into oxidizable and residue fractions, which increased by 26.3% and 8.1%, respectively. Furthermore, FMS-nanosilica significantly increased catalase and urease activities, and reduced alkaline phosphatase activity (p<0.05), but the change in invertase activity was nonsignificant (p>0.05). Correlation analysis indicated that DTPA-Cd, soil pH, and AP were the most important factors influencing these enzymes. In addition, FMS-nanosilica promoted the growth of wheat shoots, but its influence on wheat roots was variable. The total length, surface area, and average diameter of wheat roots decreased significantly when FMS-nanosilica application rate was 1.0%. Most importantly, FMS-nanosilica decreased Cd accumulation in wheat shoots and roots by 42.98% and 48.39%, respectively. These results indicate that FMS-nanosilica is a promising amendment for stabilizing Cd in contaminated soils.