Rehabilitation of a historically contaminated soil by different laccases and laccase-mediator system

PurposeIn this study, the degradation of polyaromatic hydrocarbons (PAH) present in naturally contaminated soil by laccases was evaluated. For that purpose, laccase was produced by solid-state fermentation (SSF) on agroindustrial residues by Trametes versicolor and Agrocybe aegerita. At the same time, commercial laccases from T. versicolor and Aspergillus sp. (Novozym 51,003) were used.Material and methodsContaminated soil was collected at a dumping site in Lagos, Nigeria, 15–30 cm depth, with a total measurement of 74.87 mg kg−1 of PAH (UHPLC) and 235.26 mg kg−1 of metals (ICP). Soil rehabilitation was evaluated in amber bottles containing 20 g contaminated soil, 20 mL of 10 U g−1 of different laccases and 1 mM of mediators (ABTS, ferulic and coumaric acid) for 12 days.Results and discussionAfter 12 days of treatment with laccases and mediators, the total PAH in soil was reduced to 28.20 mg kg−1 and 33.40 mg kg−1 by the laccases from A. aegerita and T. versicolor strains studied in this work, respectively, and to 42.23 mg kg−1 and 39.46 mg kg−1 by the action of the commercial laccases from T. versicolor laccase and Aspergillus sp., respectively. Despite redox mediators such as 2,2′-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS), ferulic acid and coumaric acid were studied; it was observed that laccase alone could also achieve high degradation of the contaminants load. In general, ABTS and ferulic acid were the most effective mediators in PAH degradation.ConclusionsDespite the high price, laccases and laccase-mediator system (LMS) may degrade or transform different pollutants in real environment and work very efficiently in a first approach to the rehabilitation of soil.