SOURCE:

Faculty: Biosences
Department: Applied Microbiology And Brewing

CONTRIBUTORS:

Mbachu, A. Ebele
Chukwura E. I.

ABSTRACT:

The environmental impacts associated with exploration and exploitation of crude oil has been a major area of experimental research. Pollution caused by the refined products such as engine oil has not been given proper attention. Used engine oils (UEO) contain numerous toxic substances, including polycyclic aromatic hydrocarbons (PAHs) which are known to be carcinogenic and mutagenic. They also contain heavy metals which are toxic to hydrocarbon degrading microorganisms, humans, animals and plants, hence this study. The aim of this study is to investigate the impact of heavy metals on UEO degradation by fungi isolated from automobile workshops in Mgbuka-Nkpor, Nigeria. The objectives include to: determine the physicochemical parameters and heavy metal contents of the soil samples; isolate and identify fungi from UEO-polluted soil; assess the UEO, diesel and petrol biodegradation potentials of the isolates; determine the ability of the isolates to degrade the PAHs in UEO, diesel and petrol; and determine the effect of varying concentrations of heavy metals on UEO degradation by the isolates at different pH. Soil samples were randomly collected from UEO-polluted soil in 3 automobile workshops at Mgbuka-Nkpor, Nkpor, Nigeria. Uncontaminated soil samples were also randomly collected from a fallow plot of land about 100 m from the contaminated soil. The physicochemical parameters and heavy metal contents of the soil samples were determined using standard methods. Fungi were isolated from the soil samples polluted with UEO using vapour phase transfer method. The isolates were identified using the standard methods and confirmed using 18S rRNA gene sequence. The ability of the isolates to utilize UEO, diesel and petrol was assessed using spectrophotometric method. The ability of the isolates to degrade the PAH component of UEO, diesel and petrol was assessed using gas chromatography. The effect of varying concentrations of heavy metals on UEO degradation by the isolates at different pH levels was also determined. Data were analyzed using t-test and ANOVA at P=0.05. The total nitrogen, total organic carbon and moisture contents of the contaminated soil were (%) 2.688 ± 0.016, 0.174 ± 0.006 and 3.510 ± 0.015 respectively, while those of the uncontaminated soil were (%) 2.016 ± 0.115, 0.163 ± 0.002 and 6.790 ± 0.012 respectively. However, the potassium, magnesium, zinc (Zn), lead (Pb), cadmium (Cd) and copper (Cu) contents of the contaminated soil were (ppm): 18.885± 0.091, 21.046 ± 0.064, 8.628 ± 0.087, 0.960 ± 0.029, 1.762 ± 0.011 and 2.579 ± 0.008 respectively, while those of the uncontaminated soil were (ppm): 19.855 ± 0.152, 16.481 ± 0.029, 1.140 ± 0.10, 0.240 ± 0.010, 1.323 ± 0.010 and 0.318 ± 0.008 respectively. A total of 8 fungal isolates were identified in this study. Candida tropicalis and Aspergillus clavatus exhibited the highest extent of biodegradation of UEO, diesel and petrol, and thus were selected for further studies. High removal efficiency (> 70%) was recorded with both the pure and mixed cultures of the isolates during removal of PAHs in UEO, diesel and petrol. The mixed culture of the isolates recorded 4.9% stimulation in UEO degradation in the presence of 10mg/l Zn at pH 5.5. Highest stimulation (20%) of UEO degradation was achieved in the presence of 10mg/l Cu at pH 5.5, with A. clavatus. This study showed that the level of heavy metals in UEO contaminated soil do not have any negative impact on the ability of the isolates to degrade UEO, when adequate environmental conditions such as pH are maintained. Therefore fungi such as C. tropicalis and A. clavatus isolated from automobile workshops could be utilized in remediation of UEO-polluted soil.