Fungal enzyme production and biodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans in contaminated sawmill soil

• Using non-sterile soil from historically contaminated sawmill area in experiments.
• Measuring enzyme activities directly from soil.
• PCDD/F degradation (64% of WHO-TEQ value) by fungi.
• No degradation with cell free MnP preparation.
• Results support earlier findings of involvement of P450 in biodegradation of PCDD/F.

The current treatment method for PCDD/F-contaminated soil, which fulfils the requirements for POP soils, is incineration at high temperature. In this study, we investigated if bioaugmentation with fungal inoculum or treatment with manganese peroxidase (MnP) enzyme preparation could be used instead. The main source of PCDD/F contamination in Finland has been the national production and use of a chlorophenol containing wood preservative, which contained PCDD/Fs as impurities. Therefore, historically contaminated soils from three sawmill sites were used in the experiments. In bioaugmentation experiments with living fungal mycelia, enzyme production, CO2 production and degradation of chlorinated dioxins were measured. When cell free MnP preparation was added to the soil, it was likewise important to follow how enzyme activity was maintained in the soil. As a result of this study, we showed that fungi were able to efficiently degrade PCDD/F, but surprisingly the addition of MnP preparation did not have any effect to the PCDD/F concentration. However, substantial amounts of MnP activity were found in the soil still after 10 d of incubation. Treatment with either Stropharia rugosoannulata or Phanerochaete velutina resulted in 62–64% decrease in WHO-TEQ value in 3 months. One critical factor for efficient biodegradation was strong growth of fungal mycelia in non-sterile contaminated soil.

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