Histopathological and biochemical alterations in Eudrilus eugeniae (Kinberg 1867) as biomarkers of exposure to monocyclic aromatic hydrocarbons in oil impacted site

Background Monocyclic aromatic hydrocarbons are toxic compounds which are major components of petroleum products. This study was aimed at identifying histopathological alterations and changes in antioxidants defense systems in Eudrilus eugeniae (earthworm) that can be used as good battery of biomarkers for early detection of pollution associated with hydrocarbons. The toxicological evaluations of benzene, toluene, xylene, and ethylbenzene (BTEX) were carried out against E. eugeniae. Earthworm samples were collected around oil impacted and control sites. The effect of BTEX was investigated on oxidative stress markers of E. eugeniae . Results Results showed that xylene (1.2 mg/kg) was the most toxic compound, followed by toluene (1.3 mg/kg), ethylbenzene (1.4 mg/kg), and benzene (1.9 mg/kg). The biochemical responses revealed an increase in malondialdehyde level and decrease in the level of superoxide dismutase, catalase, glutathione, and glutathione- S -transferase in E. eugeniae collected around the oil impacted area of Ijegun. The results from the laboratory studies were confirmed in the field studies. Significant histopathological alterations in the whole organisms were observed in both field and laboratory studies. The pathological findings include cellular and epidermal degeneration, and presence of pigment and inclusion bodies. Conclusion The results reflect the biological effects of hydrocarbon pollution, thus confirming the relevance of histopathological and antioxidant enzymes as biomarkers for detection of hydrocarbon pollution during environmental monitoring programs.