Soil samples and cassava tubers and leaves collected from farmlands along Agbor-Asaba expressway were analysed for their heavy metal levels in order to assess their levels of contamination on the environment as a result of traffic activities. Physicochemical properties of the soil samples were also determined. The soil pH had a mean value of 5.15+ 0.48 indicating that the soils were moderately acidic. Total Organic Carbon and Total Nitrogen mean values were 1.20 + 0.13% and 0.09 + 0.80% respectively showing presence of some organic matters. Electrical conductivity of the soil samples had the mean value of 5.94 + 1.32µscm -1 indicating significant presence of ionisable materials in the soils. Particle size was dominated by sand size fractions followed by clay and then silt which revealed that the soils were coarse and have low supply of nutrients and moisture. The mean levels of heavy metals in the soil samples were (mgkg For both the soil and plant samples, the heavy metal levels were significantly higher than the levels obtained in the control sites confirming some heavy metal enrichments in the soils studied. The plant concentration factor values were in the order Cr > Pb > Fe > Ni showing that chromium was the easiest to migrate among all the metals studied and that all the metals fall into the category showing medium accumulation except for Nickel which fell into the category of elements lacking accumulation. The overall results show that there is some metal enrichments on the soils and cassava plants as a result of automobile emission on the highway.© JASEM http://dx.doi.org/10.4314/jasem.v19i4.18

ABSTRACT:The geochemical forms of some heavy metals in soils around selected petrol filling stations were studied in order to assess the mobility and bioavailability of the metals and hence their potential environmental risk. Water soluble fraction (F 1 ) contained an average of 0.97% iron, 1.40% zinc, 2.37% chromium, 2.08% lead and 41.96% nickel with the abundance trend of Ni > Cr > Pb > Zn > Fe. Metal bound to exchangeable phase followed the same abundance trend with an average of 6.46% nickel, 5.48% chromium, 2.64% lead, 2.55% zinc and 0.62% iron. Lead was predominantly associated with carbonate fraction with an average of 52.32% followed by iron with an average of 15.41%. Other metal average levels in the carbonate fractions were 9.66% for nickel, 8.78% for chromium, and 8.73% for zinc giving the abundance trend of Pb > Fe > Ni > Cr > Zn. The most important metal in iron-manganese oxide phase was zinc with an average of 42.49%, followed by iron with an average of 32.82%. The averages of the other metals bound to this phase were 30.39%, 13.24% and 6.46% for chromium, lead and nickel respectively. The organic bound metals were in the abundance trend of Fe > Zn > Cr > Pb > Ni with average of 39.48% for iron, 30.87% for zinc, 23.03% for chromium, 8.54% for lead and 4.94% for nickel. Nickel with an average of 51.58% was predominantly associated with the residual fraction. The other metals bound to this phase in order of their importance to the fraction had the average of 22.75% for chromium, 13.96% for zinc, 12.24% for lead and 10.97% for iron. The mobility factor values of the metals were moderately high with the abundance trend of Pb > Ni > Cr > Fe > Zn. The generally low levels of the metals in the residual fraction coupled with the mobility factor trend suggest potential risk for the metals. ©JASEM