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TECHNICAL REPORTS

Bioremediation and Biodegradation

Pyrene Degradation in Forest Humus Microcosms with or without Pine and its Mycorrhizal Fungus

^a Department of Biosciences, Division of General Microbiology, P.O. Box 56 (Viikinkaari 9), FIN-00014 University of Helsinki, Finland
^b Department of Applied Chemistry and Microbiology, P.O. Box 56 (Viikinkaari 9), FIN-00014 University of Helsinki, Finland
^c Department of Ecological and Environmental Sciences, University of Helsinki, Niemenkatu 73, FIN-15140 Lahti, Finland
^d VTT Biotechnology, Tietotie 2, Espoo, P.O. Box 1500, FIN-02044 VTT, Finland

^* Corresponding author (romantsc{at}mappi.helsinki.fi).

Received for publication April 4, 2002. The mineralization potential of forest humus and the self-cleaning potential of a boreal coniferous forest environment for polycyclic aromatic hydrocarbon (PAH) compounds was studied using a model ecosystem of acid forest humus (pH = 3.6) and pyrene as the model compound. The matrix was natural humus or humus mixed with oil-polluted soil in the presence and absence of Scots pine (Pinus sylvestris L.) and its mycorrhizal fungus (Paxillus involutus). The rates of pyrene mineralization in the microcosms with humus implants (without pine) were initially insignificant but increased from Day 64 onward to 47 µg kg^–1 d^–1 and further to 144 µg kg^–1 d^–1 after Day 105. In the pine-planted humus microcosms the rate of mineralization also increased, reaching 28 µg kg^–1 d^–1 after Day 105. The ¹⁴CO₂ emission was already considerable in nonplanted microcosms containing oily soil at Day 21 and the pyrene mineralization continued throughout the study. The pyrene was converted to CO₂ at rates of 0.07 and 0.6 µg kg^–1 d^–1 in the oily-soil implanted microcosms with and without pine, respectively. When the probable assimilation of ¹⁴CO₂ by the pine and ground vegetation was taken into account the most efficient microcosm mineralized 20% of the 91.2 mg kg^–1 pyrene in 180 d. The presence of pine and its mycorrhizal fungus had no statistically significant effect on mineralization yields. The rates of pyrene mineralization observed in this study for forest humus exceeded the total annual deposition rate of PAHs in southern Finland. This indicates that accumulation in forest soil is not to be expected.

Abbreviations: PAH, polycyclic aromatic hydrocarbon