Potential role of polycyclic aromatic hydrocarbons (PAHs) oxidation by fungal laccase in the remediation of an aged contaminated soil

The transformation of PAHs by fungal laccases has been reported but there are no published studies on the direct application of free laccase in the remediation of PAHs-contaminated soil. Here we report a study in which the transformation of PAHs by a fungal laccase was studied both in reaction mixtures and in soil. Anthracene and benzo(a)pyrene were the most degradable of the 15 US Environmental Protection Agency (EPA) priority PAHs tested. Use of a redox mediator greatly enhanced the oxidation of several PAHs in reaction mixtures and the main intermediates were identified as anthraquinone for anthracene and benzo(a)pyrenyl acetate for benzo(a)pyrene as determined by GC–MS analysis. No significant correlation was found between oxidation and ionization potentials of individual PAHs. Soil microcosms were set up to test the potential of laccase to remediate an aged PAHs-contaminated soil. The laccase transformed the PAHs immediately after it was added to the soil and significant dissimilation of benzo(a)pyrene and toxic-equivalent concentration based on benzo(a)pyrene was observed after incubation for 14 days, indicating the potential of laccase to detoxify the soil. Moreover, extractable laccase activity was completely lost and the biomass of the indigenous microorganisms remained constant in the microcosms at the end of the incubation period, suggesting that the enzyme may have potential as an agent for the efficient and safe cleanup of soil contaminated with PAHs.