Biochar-induced changes in soil microbial affect species of antimony in contaminated soils

Antimony (Sb) is a highly toxic heavy metal, and the amount of Sb in the soil is increasing due to anthropogenic activities. Recently, biochar (BC) has been used for remediation of Sb-contaminated soil, therefore, understanding the effect of BC-induced changes in soil microbial on the change of Sb speciation will help to elucidate the mechanism of BC in immobilization/mobilization of Sb in contaminated soils. Sb-contaminated soil with 10 wt % of Wheat straw-derived BC (SBC) and fruit (apple) tree-derived BC (FBC) and control was incubated for 130 days. Changes of soil bacterial community composition and Sb oxidation gene induced by BC were explored during the incubation. Dynamic change of Sb speciation was assessed by the citric acid extraction. The redundancy analysis (RDA) and spearman analysis (PCA) was used to analyze the relationship between Sb immobilization/mobilization and change of soil bacterial community induced by BC. The soil properties change induced by BC affected soil bacterial community composition, and Sb mobilization was strongly related to the change of soil bacterial community composition. The relative abundance of Sb oxidation gene increased in the soil amended by BC, which proved that oxidation of Sb(III) after 20 d incubation with SBC and 50 d incubation with FBC incubation. It is noteworthy that the application of BC has a potential mobilizing risk for Sb and both the change of soil bacteria and soil chemical properties play an important role in Sb mobilization. The possible risks induced by BC should be considered before applying the BC to Sb contaminated soil.