Groundwater contamination levels in residential areas having close proximity with fuel filling stations in two local government areas of Ibadan

Abstract

Levels of groundwater contamination with monocyclic aromatic hydrocarbons (Benzene, Toluene, Ethyl benzene, and Xylene) and some heavy metals (Lead and Chromium) were assessed in residential areas having close proximity (1-20m radius) with fuel filling stations in two Local Government Areas (LGAs) of Ibadan. The fueling stations in the study areas (Ibadan Southwest and Southeast LGAs) were grouped into five natural clusters and samples were collected from the neighbourhood of one fueling station in each cluster based on its proximity to residential dwelling. Groundwater samples were collected in amber coloured bottles (500 ml) from two groundwater sources, most of which were well water (10 – 17m deep) located within and/or around the fueling stations. Samples were transported to the laboratory and analysed (using spectrophotometric method) for possible contaminants which included Benzene, Toluene, Ethyl-benzene, Xylene, Lead, and Chromium. Results were analysed using descriptive statistics and were compared with the World Health Organisation (WHO) and the StandardsOrganization of Nigeria (SON) guideline limits. Mean concentrations of Benzene, Toluene, Ethyl-benzene, and Xylene (BTEX) in groundwater were 4.5±1.7, 4.5±1.7, 4.4±1.7, and 4.7±1.9 mg/l respectively. These were way beyond (about 400 times) the WHO permissible limits of 0.01, 0.7, 0.3, and 0.5 mg/l respectively. Also, the mean concentration of Lead was high (1.31 mg/l) compared with the WHO and SON permissible limits of 0.01 mg/l.This study showed that the quality of groundwater sources in residential areas around fuel filling stations of the selected study areas was grossly contaminated with hydrocarbons (BTEX) and lead, making it seriously compromised and unsafe, especially for drinking by neighbouring residents.