Vertical distribution characteristics of pollutants in a typical soil profile in the tannery sludge landfill site
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Abstract:
To find out the pollution status of tannery sludge to the soil in the unsaturated zone, we investigated the soil samples at the depth of 0-200 cm in a typical soil profile, and identified the vertical distribution characteristics of the main pollutants, especially the different forms of nitrogen and chromium. High-throughput sequencing was further applied to reveal the bacterial community structures of the soils. The results showed that the tannery sludge contained a variety of high-concentration contaminants, such as high salinity (99000 mg/kg), total nitrogen (30900 mg/kg) and total chromium (30970 mg/kg), which had caused heavy contamination to the surface soil above 20 cm depth. The sludge leachate containing a large amount of organic matter and acid compounds caused a decrease in pH and an increase in TOC of the surface soil. The concentration of pollutants decreased obviously with the increase in soil depth. However, low-concentration organic nitrogen (723 mg/kg) and salinity (7070 mg/kg) were still detected in the soil at the depth of 200 cm. The alkaline soil in the study area had a distinct retardation effect on the transfer of chromium. When the soil depth was deeper than 40 cm, the concentrations of Cr(Ⅲ) and Cr(Ⅵ) decreased to less than 200 mg/kg and 2 mg/kg, respectively. High-salinity and high-chromium contamination can inhibit the growth of some microorganisms in the soil, and Proteobacteria, Firmicutes and Bacteroidetes will become the dominant microbial population in the contaminated soil.
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