Waste Engine Oil Degrading Potentials of Indigenous Fungi Isolated From Auto-Mechanic Workshops: Impacts of Heavy Metals (Zn and Pb) Co-Contamination and pH

Abstract

Waste engine oil (WEO) constitutes a potential hazard to humans, animals and vegetation. Studies on the effects of metals on organic pollutant biodegradation demonstrate that metals have the potential to inhibit pollutant biodegradation. Fungi were isolated from soil samples contaminated with WEO using vapour phase transfer method. The ability of the isolates to utilize WEO was assessed using gravimetric method. The impact of Zn and Pb and the effect of pH (5.5, 7.0 and 8.5) on WEO biodegradation by the pure and consortium culture of the isolates were determined. A total of 8 fungal isolates were obtained in this study. 4 that showed high hydrocarbonoclastic potentials were confirmed as Candida tropicalis, Rhodosporidium toruloides, Fusarium oxysporium and Aspergillus clavatus using 18S r RNA gene sequence. C. tropicalis and A. clavatus exhibited the highest extent of biodegradation of WEO and were therefore selected for further studies. Although there was significant (P<0.05) increase in inhibition of WEO degradation at high concentration of the heavy metals with increase in pH, low concentration of the metals stimulated the degradation of used engine oil. Highest stimulation of 10.1% and 14.2% was recorded in the presence of 1.0 mg/L Zn and Pb at pH 5.5, with the consortium culture and A. clavatus, respectively. The results showed that the pure and consortium culture of the isolates (C. tropicalis and A. clavatus) have promising potential for effective bioremediation of waste engine oil polluted soil co-contaminated with low levels of Zn, and Pb at pH 5.5.