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Abstract
Soils contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) are commonly found in petroleum, gas-work and wood-impregnation sites. Interest in the biodegradation and environmental fate of PAHs is motivated by a worldwide ubiquitous distribution, low bioavailability and prolonged environmental persistence. PAHs are toxic and present both human and environmental health hazards; therefore they need to be mineralized to harmless products such as carbon dioxide (CO 2), methane (CH 4) and water (H 2O). Due to high hydrophobicity, however, PAHs tend to interact with solid phases that reduce their availability for microbial attack - the principal mechanism for mineralization. In this research, laborator y and greenhouse studies were conducted to determine the effectiveness of using natural organic compost amendments to increase the bioavailability, degradation rates, and PAH concentrations in c ontaminated soils. The results indicate that Organic Compost Tea , a mushroom compost extract (MCE) rich in dissolved organic carbon (DOC), is capable of increasing the solubility and bioavailability of PAHs. High microbial respiration rates, measured by CO 2 production, and greater microbial numbers in soils treated with MCE, which were > 4 orde rs of magnitude higher than in the no amendment controls,indicated enhanced microbial de gradation of PAHs. Biodegrada tion in MCE treated soils was confirmed by the identifica tion of key PAH metabolites such as carboxylic acid, 3,4-dihydroxybenzaldehyde, and 1-benzopyran-2-one. Fast er degradation rates, well described by first order kinetics, were also realized with the application of MCE. This was in contrast to the bi-phasic kinetic models determined in the cont rol soils representing initial rapid PAH loss due to sorption followed by a slow transformation phase. In greenhouse experiments, high PAH con centrations were decreased from 2100 mg/kg to <100 mg/kg within 6 weeks of MCE pre-treatment. This a llowed for successful plant establishment while residual PAH concentrations (> 200 mg/kg) in the controls were shown to be toxic to plants. This research indicates that MCE acts as a natural co-solvent to increase PAH solubility in soil matrices, increases microbial de gradation in contaminated soils, and decreases PAH concentrations. Highly contaminated sites can therefore be rapidly remediated by the application of compost extracts as pre-treatment with the po tential for phytoremediation as a polishing tool.