Effects of electron donors on the degradation of hexachlorocyclohexane and microbial community in submerged soils

Abstract

PURPOSE: Hexachlorocyclohexane (HCH) is a pesticide that is persistent in aerobic but not in anaerobic conditions. The aim of this investigation was to elucidate the impacts of different electron donors on the degradation of hexachlorocyclohexane and their relationships with the microbial community in submerged soils. MATERIALS AND METHODS: Soil samples were collected from a pesticides-polluted site which was previously used for long-term storage of pesticides since the 1960s. Residual amounts of HCHs in submerged soils were assessed to evaluate the efficiency of the added electron donors after incubation. Changes in microbial community were monitored during incubation. RESULTS AND DISCUSSION: The efficiencies of removal of HCHs by Fe⁰, Fe⁰ + straw and glucose treatments were 63.8%, 40.3%, and 22.0%, compared with 5.4% by the control. Soil redox potential decreased rapidly following addition of Fe⁰ and became anaerobic, but there was no significant decrease in redox potential following the addition of glucose. Principal coordinates analysis (PCoA) confirms that the electron donors greatly affected the soil bacterial community. Furthermore, community composition analysis shows that Firmicutes was the dominant phylum after addition of carbon sources (straw and glucose) but Proteobacteria were dominant in the control and the Fe⁰ treatment. Prauserella, Actinobacteria, and Streptomyces showed highly significant increases in the Fe⁰ treatment and were positively correlated with total HCH residues. CONCLUSIONS: These findings indicate that the addition of organic materials (straw and glucose) had a gradual effect on the degradation of HCH while Fe⁰ acted rapidly. Elucidation of the relationships between electron donors and soil microbial communities will help in the bioremediation of HCH-contaminated sites.