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Abstract

John Yang, Xi Tang. 2008. Microbial risk assessment of metal-contaminated soils using a bacteria-based assay. JEMREST 5:159-165.

Elevated metal contaminants in soil are well known a threat to human health and environment. However effective methodologies that allow to rapidly assess the impact of the contamination on soil microbial community are very limited. This study was conducted to evaluate a bacteria-based assay for a quick microbial-toxicity assessment of metal-contaminated soil and to assess the ecological risk reduction of the soil by in situ phosphate treatment. A bacteria-based toxicity assay that was developed for water quality assessment was evaluated with various extraction procedures. The variables included S/L ratio, filter pore size, and time of measurement. Soils containing ~4000 mg Pb kg-1 that had been treated with and without soluble phosphate were collected from the Jasper County Superfund Site, southwest Missouri. Surface waters in the treated plots were also sampled for quality control and comparison of the treatment effects with soil measurements. Results showed that measurements of the bacteria assay of the soils varied with the S/L ratio, filter pore size, and time of measurement. The procedures that used > 1:4 S/L ratio, 0.45 µm pore size, and measured >2 days after extraction would provide a stable and consistent result. Soil measurements were comparable with water assessments. Data also indicated that in situ phosphate treatment would significantly reduce the toxicological risk of the soil to microbial community through the immobilization reactions. This study illustrated that the modified bacteria-based assay is applicable and effective for soil micro-toxicological assessment and the soluble phosphate treatments resulted in reduced ecological risk of metal-contaminated soils.