Response of Soil Microbial Characteristics to Soil Properties and Metal(Loid) Pollution in a Typical Antimony Mining Site

Mining, smelting and tailing deposition activities can cause metal(loid) contamination in surrounding soils, threatening ecosystems and human health. Microbial indicators have a crucial role in evaluating soil quality. Selecting the Xikuangshan antimony mine in China as the research area, the purposes of this study were to explore the effects of long-term mining activities on soil quality and to reveal the internal relationship of microbial characteristics with soil properties and metal(loid) pollution. The assessment of the single pollution index (Pi) and Nemerow synthetic pollution index (PN) showed that the soils were mainly polluted by Sb, As and Cd, in which sampling site S1 had a moderate pollution level and the other sampling sites reached a heavily polluted level. There were significant differences in the microbial indicators among the sampling sites, especially for fluorescein diacetate (FDA) hydrolase, urease and acid phosphatase. A correlation analysis indicated that FDA hydrolase, potential nitrification rate (PNR) and microbial biomass carbon (MBC) were negatively correlated with extractable Sb, total As and PN, respectively; that dehydrogenase was positively correlated with pH; and that PNR and the abundance of ammonia oxidizing bacteria (AOB) and ammonia oxidizing archaea (AOA) were negatively correlated with NH4+-N and positively correlated with NO3--N. The results of the correlation analysis showed that the microbial indicators were affected by metal(loid) contamination and soil properties. In addition, the microbial parameters urease, PNR, AOB and AOA related to nitrogen cycle processes had significant positive relationships, demonstrating their inherent connections in soil N transformation. Our results have significance for establishing microbial indicator systems for ecological risk assessments of contaminated soil.