Occurrence and distribution of monocyclic aromatic hydrocarbons (BTEX) and the impact on macrobenthic community structure in Lagos lagoon, Nigeria.

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. The impacts and distribution of major toxic components (benzene, toluene, ethylbenzene, and xylene (BTEX)) of petroleum products in water and sediment samples collected from sampling stations in the Lagos lagoon was investigated over a 2-year period (February 2009-July 2010). The distribution of benthic communities in the different sampling stations of the Lagos lagoon was assessed. 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 2.03 to 31.38 mg/l and 4.04 to 22.89 mg/l, respectively. The highest value of total BTEX in the lagoon sediment was also recorded in the Apapa station (450.53 µg/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. The levels of hydrocarbon observed in the aquatic environment showed that there is widespread contamination as a result of petroleum product importation, storage, and distribution. The assessment of the monocyclic aromatic hydrocarbon and benthic community will therefore provide important tools for early detection, diagnosis, and management of hydrocarbon pollution in the Lagos lagoon.

Histopathological alterations, biochemical responses and acetylcholinesterase levels in Clarias gariepinus as biomarkers of exposure to organophosphates pesticides.

Organophosphate pesticides, commonly used in large scale farming, have been found to be major contaminants in aquatic environment. Clarias gariepinus was exposed to acute and sublethal concentrations of phostoxin and DD Force to evaluate single and joint action toxicity of the organophosphates. Effects of phostoxin and DD force on antioxidant enzymes, fish organs and acetylcholinesterase levels in fingerlings and juveniles of C. gariepinus were also investigated. The lethal concentrations (96 h LC50) for phostoxin and DD Force were 0.631 and 1.759 mg/l, respectively. The results obtained from the bioassay showed that phostoxin was 2.8× more toxic than DD Force after exposure of C. gariepinus. Joint action toxicity evaluations of phostoxin and DD Force showed that the interaction between the chemicals was synergistic (RTU >1). The biochemical responses in the exposed fish differed significantly (P < 0.05) from the control fish. The result of acetylcholinesterase study revealed significant difference between acetylcholinesterase levels in the exposed fish and control, with reduction in the acetylcholineterase level in fish exposed to sublethal concentrations of phostoxin and DD Force. Haematological studies revealed an increase in WBC, RBC, PCV and platelets in the exposed fish. Histopathology of the gills showed shortened primary lamellae, loss of secondary lamellae and loss of ceratobrachial bones. In the acute toxicity studies, respiratory stress, erratic swimming and instant death of fish were observed in the exposed fish. This study reveals that changes in histopathology and acetylcholinesterase level are good biomarkers and can be successfully used to detect exposure to organophosphates pesticides in fish.