Studies on hydrocarbon pollution in the upstream and downstream areas in the Niger delta region of Nigeria

Abstract

The Niger Delta region of Nigeria over the years have been ravaged with series of hydrocarbon contamination/pollution due to various anthropogenic activities related to oil and gas industries. The main aim of this research work was to investigate the total petroleum hydrocarbon (TPH) concentrations in various environmental matrix in the study area, and the efficacy of some alternative analytical techniques for the determination of hydrocarbon concentration in surface water, sediment, soil and subsoil samples. For surface water, a total of ninety (90) surface water samples were collected and analysed from six (6) sampling locations, inclusive of the control location. The results indicated that the concentration of TPH varies in surface water samples which ranged from 0.033 to 10.32 mg/L. The surface water average TPH of 3.49±2.64 mg/L for the five monitoring locations was above both the Nigerian Standard for Drinking Water Quality (NSDQW) and Environmental Guidelines and Standards for Petroleum Industry in Nigeria (EGASPIN) standard of 0.003 and 0.05 mg/L for drinking water and sources of drinking water respectively. For soil, a total of fifty (50) soil samples were collected and analysed from five (5) sampling locations. The results indicated that the presence of TPH concentration varies in soil samples which ranged from 55.34 to 2,520 mg/kg. The average TPH of 786.3±612.7 mg/kg was above the EGASPIN target value of 50 mg/kg for a functional and sustainable soil. While all of the analysed soil samples were below the EGASPIN intervention value of 5,000 mg/kg, but were above the 50 mg/kg target value. For sediment, a total of ninety (90) sediment samples were collected and analysed from six (6) sampling locations. The results indicated the presence of TPH concentration at various degree in sediment samples which ranged from 93.7 to 1672 mg/kg. The TPH mean of 447.8±262.4 mg/kg of sediment sample was above the EGASPIN target value of 50 mg/kg. While majority of the analysed sediment samples were below the EGASPIN intervention value of 5,000 mg/kg, most of the sample TPH concentration were far above the 50 mg/kg target value. Hence, surface water from the various locations are polluted with hydrocarbons and fall below the EGASPIN regulatory standard, soils in upstream farm lands are contaminated with hydrocarbons, and river sediments are contaminated with hydrocarbons in the study area. Enzyme-Linked Immunosorbent Assay (ELISA) demonstrated to be a good analytical technique for the determination of TPH in various environmental matrix. The level of accuracy and reproducibility of ELISA for determination of TPH in environmental matrix were reported. The presence of hydrocarbon plumes was determined with the application of Electrical Resistivity Tomography (ERT) as an indirect non-destructive monitoring technique on farm lands with previous record of hydrocarbon contamination/pollution and a control site in the research. The results from the four (4) ERT tomograms at the three hydrocarbon contaminated sites indicated the presence of hydrocarbon plumes in the soil at various depth and horizontal spread. ERT demonstrated applicability in environmental monitoring relating to hydrocarbon contaminants in sub-surface soil and has demonstrated its ability of identification and imaging of subsurface hydrocarbon contaminants in soil.