HEAVY METALS IN ROADSIDE SOILS AND PLANTS ALONG THE MAJOR CONNECTING ROADS IN AKURE, ONDO STATE. NIGERIA

Abstract

The indication provided by roadside has great significance in ecological terms particularly when environmental pollution is a matter of concern. Soil and plant (Chromolena.odorata and Pennisetum. purpureum) samples from the major connecting roads inAkure, Ondo State were analysed for Pb, Cu, Zn, Cd, Cr, and Ni. Soil and plants samples were collected at 5m, 50 m and 100m away from the road edges. To further determine the effects of soil depth on the concentration of heavy metals, soil samples were taken at the surface 0-15 cm and subsurface (15-30 cm)levels.The soil physico– chemical properties (soil organic matter, soil texture and pH) were determined using standard methods.Heavy metal concentrations in soil samples were quantified after micro-wave oven extraction using inductively coupled plasma -emission spectroscopy (ICP-AES), while metal concentrations in plant samples were determined by Atomic Absorption spectroscopy (unicum solar 32 data station V7) after acid digestion. The data obtained were subjected to statistical analysis using One Way Anova and mean were separated using the New Duncan Mutiple Range Test. The results of the physico-chemical parameters of the soil show the pH ranging from 4.21- 9.06; the soil organic matter was in the range of 0.33-3.0% and the soil samples are characterized as, loamy, sand, clay and sandy loam. Heavy metal concentration in soils across the various roads ranged as follows: Pb 1.24-24.30; Cu 1.80-27.80; Zn 0.16-25.20;Cr 0.25-19.33; Ni 0.40-17.0 and Cd 1.70-58.0, while in the plant samples the following ranges were observed: Pb 0.01-1.50; Cu 15.70-30.0; Zn 42.60-49.60; Cr 13.60-28.90; Ni 0.86-12.32 and Cd 0.15-2.30 for C. Odorata and 0.01-0.09; 0.56-15.70; 6.43-49.30; 0.20-9.04; 0.20-1.15 and 0.00-0.15 for P.purpureum respectively. The enrichment factor (EF) ratios suggested that all metals were significantly enriched (EF>5) except Pb and Cu along Akure –Ado road which were moderately enriched(EF < 5). Ni along Idanre road was deficient of any enrichment (EF< 2). The geo-accumulation index values showed that the roadsides ranged from uncontaminated to moderately contaminated (0-1). The contamination factor (CF) was greater than six CF>6 for all the metals except nickel along Akure-Idanre road (CF <1). The pollution load index (PLI) for the six metals studied at the various zones showed that the overall degree of contamination by the six metals is of the order: Akure Ilesha>Akure – Ado>Akure-Ondo>Akure-Owo>Akure-Idanre road. The results from the analysis of the two plant species C.odorate and pennisetumpurpureum showed that the concentrations of Pb, Zn, Cu, Cr, Ni, and Cd were high especially at 5M distances. Generally, both plant species have the ability to bio- accumulate these metals.From the pollution pattern observed, the major source of these metals in the roadside soil is as a result of automobile emission since a decreases in metal concentration was observed with increasing distance from the roadside.