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Environmental Geosciences

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Concentrations of heavy metals and hydrocarbons in groundwater near petrol stations and mechanic workshops in Calabar metropolis, southeastern Nigeria

¹ Department of Geology, University of Calabar, PMB 1115, Nigeria; ntonzi{at}yahoo.com
² Department of Geology, University of Calabar, PMB 1115, Nigeria
³ Department of Geology, University of Calabar, PMB 1115, Nigeria

Therese Nganje received her B.Sc. degree in geology, her M.Sc. degree, and her Ph.D. in 2003 from the University of Calabar, Nigeria. Nganje also holds a certificate in Geochim–United Nations Educational, Scientific, and Cultural Organization postgraduate training course on "Geochemical Exploration Methods and their Environmental Applications" from the Czech Geological Survey. She is currently a lecturer at the University of Calabar. Nganje is a recipient of the European Association of Organic Geochemists Travel Award.

Aniekan Edet received his B.Sc. in geology from the University of Calabar, Nigeria, his M.Sc. degree and his Ph.D. from the Universities of Ibadan and Calabar. Edet also holds a certificate in hydrogeology from the University of Tübingen in Germany. He is currently a professor at the University of Calabar. Edet is a recipient of awards from the Nigerian Mining and Geosciences Society, the German Academic Exchange Service, the Alexander von Humboldt (AvH) and the Commonwealth Fellowship.

S. J. Ekwere received his B.Sc. and his M.Phi., degrees and his Ph.D in geology from the University of Ibadan. He is currently a professor of geochemistry and economic geology in the University of Calabar.

Groundwater and soil samples from 16 locations near petrol stations (PS) and mechanic workshops (MW) around Calabar, Nigeria, were analyzed for heavy metals and hydrocarbons to determine their concentrations and assess the impact of the PS and MW on groundwater in the area. Results show that mean concentrations of arsenic, cadmium, chromium, copper, iron, mercury, manganese, nickel, lead, and zinc in groundwater are higher than the reference data (maximum admissible concentration, baseline value, and control site value). The mean concentration of total organic content in soil is low (4.03%), but the mean concentrations of total petroleum hydrocarbons (46.87 mg kg^–1) and naphthalene (340.00 µg g^–1) in the soil are high in comparison to the reference data. The mean concentrations of parameters in soil and groundwater are higher where PS and MW are located near each other (PS/MW). The mean total hydrocarbon content (0.66 mg L^–1) and total polycyclic aromatic hydrocarbon (PAH) (66.64 µg L^–1) in groundwater are higher than the maximum admissible concentration of 0.1 mg L^–1 and 0.2 µg L^–1, respectively. The concentration of PAH compounds with mean concentrations greater than 1 µg L^–1 are of the order phenanthrene > anthracene > fluorene > benzo(b)fluoranthene-benzo(k)fluoranthene pyrene > naphthalene. The ratios of phenanthrene/anthracene, fluoranthene/pyrene, and benzo(a)anthracene/chrysene and factor analysis indicate several sources for the PAH. The most important sources include anthropogenic (petrogenic, pyrolytic) and natural.