Assessment of the Combination of Aspergillus niger and Fluorapatite for Cadmium Immobilization in Soil and Its Effect on Soil Biological Properties

This study evaluated the effects of combining Aspergillus niger and fluorapatite (FAp) as a remediation strategy on cadmium (Cd) immobilization in contaminated soil. Soil Cd speciation, immobilization efficiency, soil microbial abundance, and soil enzyme activities were used as parameters to evaluate the effectiveness of the amendment. European community Bureau of reference (BCR) sequential extraction was used to determine fractions or speciation of the heavy metal in the soil. At 50 mg/kg Cd contamination level, the concentration of acid-soluble species was significantly the lowest at 19.54 mg/kg under the combination amendment. The concentrations (mg/kg) of acid-soluble species under separate applications of FAp and the fungus were 22.05 and 25.34, respectively. At 50 mg/kg contamination, residual fraction or species immobilized under the combination amendment was 5.74 mg/kg, while that immobilized under applications of FAp and the fungus separately were 2.79 mg/kg and 1.46 mg/kg, respectively. At 25 mg/kg contamination level, the residual fraction immobilized under the combination amendment was 8.42 mg/kg, while that of applications of FAp and the fungus separately were 4.28 mg/kg and 1.27 mg/kg, respectively. The higher populations of soil microorganisms and the improved enzyme activities observed under the combination amendment also indicate that combining the fungus with FAp reduced Cd bioavailability and toxicity effectively, and restored soil biological activities.