AN ASSESSMENT OF HEAVY METAL CONTENT OF ROADSIDE VEGETATION ALONG TWO MAJOR HIGHWAYS IN THE SOUTHWESTERN NIGERIA

Abstract

Emission of pollutants from motor vehicles is a problem associated with road transportation. Plants and plant materials on roadsides are directly impacted by such emissions.  The level of impact needs to be established and related to vehicular traffic density. Vehicular counting and collection of samples from both roadside plants and plant materials being sun-dried were carried out on  two roads selected for this study; Ife/Ibadan road in Osun/Oyo Sates and Ogbomosho - Igbeti road  in Oyo State. The samples were collected at various distances along the roads, and analyzed for lead, zinc and cadmium in the laboratory using Atomic Absorption Spectrophotometer (AAS).  A combination of t-test, Pearson correlation and descriptive statistics (bar chart) were used in presenting the results at ( p< 0.005) . The result shows that there are more vehicles plying Ife-Ibadan road (7,732 vehicles per day) than Ogbomosho-Igbeti road (2941 vehicles per day).  The results confirmed the presence of lead, zinc and cadmium in varying amounts in the plant materials and cassava flour sampled along the two roads. The order of the metal concentrations on both roads is the same i.e. Pb > Cd> Zn. It also revealed that vehicle type is of great importance in emission from automobile exhaust.  When the heavy metal contents of the plant materials were compared with FAO/WHO guidelines for edible materials for man (plants and animals, it was established that roadsides vegetation were contaminated by heavy metals such as lead. The implication of this is that roadside farming and drying of plant materials by the roadside should be discouraged.