Oxidation of polycyclic aromatic hydrocarbons by fungal isolates from an oil contaminated refinery soil.

Indigenous soil microorganisms are used for the biodegradation of petroleum hydrocarbons in oily waste residues from the petroleum refining industry. The objective of this investigation was to determine the potential of indigenous strains of fungi in soil contaminated with petroleum hydrocarbons to biodegrade polycyclic aromatic hydrocarbons (PAH). Twenty one fungal strains were isolated from a soil used for land-farming of oily waste residues from the petrochemical refining industry in Singapore and identified to genus level using laboratory culture and morphological techniques. Isolates were incubated in the presence of 30 mg/L of phenanthrene over a period of 28 days at 30 degrees C. The most effective strain was further evaluated to determine its ability to oxidise a wider range of PAH compounds of various molecular weight i.e acenaphthene, fluorene, fluoranthene, chrysene, benzo(a)pyrene and dibenz(ah)anthracene After 28 days of incubation, 18 of the 21 fungal cultures were capable of oxidising over 50% of the phenanthrene present in culture medium, relative to abiotic controls. Fungal isolate, Penicillium sp. 06, was able to oxidise 89% of the phenanthrene present. This isolate could also oxidise more than 75% of the acenaphthene, fluorene and fluoranthene after 30 days of incubation. However, the oxidation of high molecular weight PAH i.e. chrysene, benzo(a)pyrene and dibenz(ah)anthracene by the Penicillium sp. 06 isolate was limited, where the extent of oxidation was inversely proportional to PAH molecular weight. Fungal isolate, Penicillium sp. 06, was effective at oxidising a range of PAH in petroleum contaminated soils, but higher molecular weight PAH were more recalcitrant. There is potential for the re-application of this fungal strain to soil for bioremediation purposes.