Antioxidant Enzymes and Histopathological Biomarkers of Exposure to Monocyclic Aromatic Hydrocarbons in Clarias Gariepinus (Catfish) and Eudrilus Eugeniae (Earthworm).
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos.
The widespread distribution of petroleum products arising from the rapid growth of the petroleum industry in Nigeria has resulted in the pollution of the environment through oil spills involving leakages from tankers, pipelines, tank farms and dumping of waste petroleum products. This study was aimed at identifying histopathological alterations and antioxidants defence systems in Clarias gariepinus (catfish) and Eudrilus eugeniae (earthworm) that can be used as a good battery of biomarkers for early detection of pollution associated with petroleum hydrocarbon and that can be used in monitoring programmes in Nigeria. The impacts and distribution of major toxic components (BTEX - Benzene, Toluene, Ethylbenzene and Xylene) of petroleum products in water and sediment samples collected from sampling stations in the Lagos lagoon and in groundwater and soil around hydrocarbon impacted areas in Ijegun, Lagos, following a pipeline explosion in May 2008 was investigated over a two- year period (February, 2009 – July, 2010). The distribution of benthic communities in the different sampling stations of the Lagos lagoon was assessed. The toxicological evaluations of BTEX were carried out against juvenile stages of C. gariepinus and E. eugeniae. The effect of BTEX on antioxidant enzyme system, lipid peroxidation formation and different organs was investigated in C. gariepinus, Tilapia zillii, Chrysichthys nigrodigitatus and E. eugeniae. The determination of hydrocarbon levels in the samples showed that the levels of Total Hydrocarbon Content (THC) in the water samples around the Atlas cove and Apapa were high with values ranging from 2.03mg/l - 31.38 mg/l and 4.04mg/l - 22.89mg/l, respectively. The highest value of total BTEX in the lagoon sediment was also recorded in the Apapa station (450.53µg/kg) where oil depots and tank farm facilities are located. The study of the macrobenthic community structure showed that the species richness ranged from 1.57 to 2.02 in the reference station, Unilag while in the Atlas Cove, Iddo and Apapa stations, it ranged from 1.80 to 2.89, 1.95 to 3.03 and 1.86 to 2.95 respectively. The highest number of organisms (183) was recorded in the reference stations while the least number (46) was recorded in Apapa. The main hydrocarbon pollution indicator species identified in the impacted aquatic stations were Nais eliguis and Heteromastus filiformis. Results showed elevated THC levels (2.00mg/l–689.12mg/l) in groundwater compared to the World Health Organization maximum permissible value of 0.1 mg/l. Higher values of THC in the soil ranging from 2.16 to 401.41mg/kg were also observed around the impacted area of Ijegun in comparison with 7.03 to 44.61mg/kg observed in the control station. The level of BTEX in the groundwater sampled within the 100m and 150m buffer zones ranged from 1.19 to 4964.33 μg/l compared to the safe limit of 0.2 μg/l set for BTEX compounds in the Environmental Guidelines and Standards for Petroleum Industry in Nigeria (EGASPIN). Toxicological evaluations of the monocyclic aromatic components (BTEX) on Clarias gariepinus showed that ethylbenzene (0.479ml/l) was the most toxic compound tested followed by xylene (0.519ml/l), benzene (0.666ml/l) and toluene (1.190ml/l). Toxicity evaluations against Eudrilus eugeniae showed that xylene (1.212 mg/kg) was the most toxic compound followed by toluene (1.335mg/kg), ethylbenzene (1.366mg/kg) and benzene (1.896mg/kg). The biomarker study revealed an increase in malondialdehyde level and inhibition of the activities of Superoxide dismutase (SOD), Catalase (CAT), Glutathione (GSH) and Glutathione-S-Transferase (GST) in the liver and gills of Clarias gariepinus, Tilapia zillii and Chrysichthys nigrodigitatus, which can serve as good biomarkers for early detection of BTEX and related hydrocarbon pollution. Similar results of consistent increase in MDA levels and inhibition of SOD, CAT, GSH and GST activities in Eudrilus eugeniae exposed to sublethal concentrations of BTEX and petroleum hydrocarbon were observed, therefore confirming the relevance of these antioxidant enzymes as good general biomarkers of hydrocarbon related stress. The histological study identified necrosis and deformation of the gills, inflammations in the liver, wrinkling of the oocyte membrane in the gonads of fish, and endothelial degeneration in earthworms as good histopathological biomarkers of hydrocarbon related stressors. The levels of hydrocarbon observed in the aquatic and terrestrial environment showed that there is widespread contamination as a result of petroleum product importation, storage and distribution. The combination of chemical analysis with these identified biomarkers will therefore provide important tools for early detection, diagnosis and management of hydrocarbon pollution.