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

摘要

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 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.