MINERALIZATION AND CONVERSION OF PENTACHLOROPHENOL (PCP) IN SOIL INOCULATED WITH THE WHITE-ROT FUNGUS Trametes versicolor

MARJA TUOMELA*, MERJA LYYTIKÄINEN**, PEKKA OIVANEN*

and ANNELE HATAKKA*

*Department of Applied Chemistry Microbiology, P.O. Box 56,

Biocenter 1, FIN-00014 University of Helsinki, Finland

**Department of Biology, University of Joensuu, P.O. Box 111, 80100 Joensuu, Finland

Pentachlorophenol (PCP) is a toxic chemical which has been used in saw mills against sapstaining and bluestaining fungi. Although the use of PCP has been prohibited in Finland in 1988, there are still PCP polluted areas. PCP degradation by white-rot fungi has been studied intensively and already some full scale experiments have been carried out for treating PCP polluted soil with white-rot fungi.

In this study we have investigated the fate and distribution of PCP, degraded and transformed by the white-rot fungus Trametes versicolor in autoclaved soil supplemented with straw. We used ¹⁴C-labelled PCP to monitor the distribution of ¹⁴C-label into different fractions and non-labelled PCP to monitor the degradation and transformation products of PCP by gas chromatography. The flasks inoculated with T. versicolor were incubated for 42 days, and control flasks to monitor abiotic PCP degradation were incubated for 28 days. During incubation mineralization and volatilization of PCP and its transformation products were measured by radiorespirometry. After incubation soil was successively extracted with water, dioxane, alkali (KOH-methanol) and the residue was combusted. PCP was analyzed from all extracts and its transformation products were analyzed from both water and dioxane fractions.

During 42 days of cultivation of T. versicolor with PCP, the total PCP amount decreased rapidly and mineralization was ongoing, reaching 29%. The original PCP was found mostly in the dioxane fraction and the amount of ¹⁴C label in the dioxane fraction decreased along with PCP levels throughout the experiment. The concentration of non-labelled PCP decreased to 4% of its original value during the incubation period. After 42 days 7.0% of ¹⁴C-labelled compounds were in the water extract, 6.6% in the dioxane extract, 12.4% in the alkali extract and 4.9% in the soil residue calculated from the total ¹⁴C-PCP. Part of the ¹⁴C-label was alkali-extractable, indicating that it was bound to humic substances, but this part was apparently later attacked and mineralized by the fungus. Mineralization in non-inoculated flasks was only 0.1% of the total ¹⁴C-PCP in 28 days and ¹⁴C label in dioxane fraction remained constant. Only trace amounts of anisoles such as pentachloroanisole (PCA) and 2,3,4,6-tetrachloroanisole (2,3,4,6-TeCA) were formed during incubation but they represented less than 0.0001% of total PCP added. T. versicolor could tolerate higher PCP concentration than none other white-rot fungi studied. These results suggest that T. versicolor has an efficien mechanism for PCP mineralization and the treatment of PCP polluted soils with T. versicolor is a possibility.