a b s t r a c tThere is an environmental risk of Sb becoming a major pollutant due to the quick increase in the production of Sb industry. However, there have been few investigations on interactions between Sb and microorganisms and bioremediation of Sb this paper presents an investigation on bioleaching of Sb from contaminated sediment which is collected in the vicinity of a Sb processing plant using the iron-oxidizer, Acidithiobacillus ferrooxidans. The bioleaching of Cr, Cu, Mn, Ni, and Zn in the sediment was also investigated to compare with that of sb. Duplicated batch-type experiments based on different incubation time, on the presence or absence of Fe 2+ and/ or Ag + , were conducted to compare the efficiency of metal extraction. After bioleaching, 97.4% of Ni, 95.2% of Mn, 65.8% of Cr, 36.2% of Cu, 34.8% of Zn, and 2.2% of Sb were extracted from sediments. The extraction efficiency of Sb was the lowest in comparison to those of Cr, Cu, Mn, Ni, and Zn. This result indicated that Sb is difficult to solubilize by bacterial leaching. The catalytic effect of Ag + was not observed, which could be due to the inhibition of Ag + on the activity of A. ferrooxidans and formation of Ag jarosite precipitation on the surface of sediment particles. Though the extraction of Sb was not efficient, this study demonstrates the potential for Sb to be bioleached and a feasible technique in remediation of Sb.

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Soil stabilization is a remedial technique that reduces the exposure of the soil environment to soil contaminants. Its efficacy can be assessed by determining whether the environmental availability of a contaminant decreases following treatment. We evaluated several chemical leaching treatments by assessing both contaminant leachability and bioaccumulation in the earthworm Eisenia fetida, and determined the most effective treatment for achieving soil stabilization. Soil samples contaminated with As, Cd, Cu, Pb, and/or Zn were collected from abandoned mine areas and stabilized by adding limestone and steel slag (5% and 2% w/w, respectively). All leaching and earthworm tests were conducted using both contaminated and stabilized soils. In addition to bioaccumulation in earthworms, several toxicity parameters (number of cocoons, growth changes, and survival rates) were also assessed to determine the effects of the treatments on the earthworms. The study showed that treatment of soil with EDTA-NHOAc resulted in a significant decrease in contaminant leachability following soil stabilization. There was an increase in survival and growth of earthworms exposed to the stabilized soil compared with those exposed to the non-stabilized soil. Bioaccumulation in earthworms was found to be statistically correlated with the leachability of As by EDTA-NHOAc. We conclude that limestone and steel slag effectively decreased the availability of heavy metals in the soil and reduced the toxicity to earthworms. Leaching with EDTA-NHOAc has the potential to be predictive in estimating the bioavailability of As in soils, but further studies are needed if it is to be proposed as a standard method.

Applicability of bioleaching of Cu, Pb, and As from paddy soil in the vicinity of a refinery site was experimentally examined using a sulfur-oxidizing bacterium, Acidithiobacillus thiooxidans. As a result of aqua regia digestion, the concentrations of Cu (187 mg/kg), Pb (380 mg/kg), and As (107 mg/kg) in the studied soil exceeded the environmental criteria regulated by the Korean government. Batch experiments were performed to investigate the removal efficiency of the heavy metals according to various sulfur supply (0%, 0.1%, 0.5%, and 1%). All microbial experimental sets amended with sulfur showed the enhanced amount of heavy metals extracted, which showed the extraction processes require sulfur addition for proper metabolism of the bacterium. Among various amounts of sulfur addition, 1% (w/v) sulfur addition to the soil inoculated with bacterium led to the removal efficiencies of 67.6%, 25.8%, and 53.3% for Cu, Pb, and As, respectively. The relatively low removal efficiency of Pb resulted from formation of insoluble PbSO 4 precipitate. As a result of sequential extraction for the treated soil, most metals were found to exist as a highly stable fraction which is recalcitrant against change of the surrounding environment.

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