Assessment of soil contamination with monocyclic aromatic hydrocarbons and heavy metals in residential areas sited close to fuel filling stations in Ibadan metropolis

Abstract

The study aimed to assess soil contamination with mono-cyclic aromatic hydrocarbons and heavy metals in residential areas situated close to (1-20m range) fuel filling stations in Ibadan metropolis, Nigeria. The study involved a laboratory based analysis of soil samples collected in the neighbourhood of five fuel filling stations systematically selected during the study. Two local government areas were randomly selected for the study, they were split into five natural clusters and soil samples were purposively collected from the neighbourhood of one fueling station per cluster. Topsoil (0 – 15cm deep) and subsoil (15 – 30cm deep) samples were collected at 5m, 10m, and 20m intervals away from the fuel filling stations. Samples were analyzed for benzene, toluene, ethylbenzene, xylene, lead, and chromium using standard methods. Results were compared with Canadian and United Kingdom standards. Results were analyzed using descriptive statistics and were compared with the Canadian (monocyclic aromatic hydrocarbon) soil quality guideline limit for human health and the UK heavy metal guideline limit for soil in residential areas. Apart from xylene, the mean concentration of benzene, toluene, and ethyl-benzene were approximately 600 times higher than the Canadian limit both for topsoil and subsoil. Fortunately, mean concentrations of lead and chromium in all soil samples were insignificant compared with the UK limit. The study showed that there is contamination of the soil in the study area with some monocyclic aromatic hydrocarbons namely benzene, toluene, and ethyl-benzene while there are no potential threats with regards to heavy metal contamination.