Distribution of different fractions of Iron, Zinc, Chromium, lead and Nickel in Soils around Petrol filling stations in selected Areas of Delta State, Nigeria

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 (F1) 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.

Keywords: Soil pollution, speciation, petrol filling stations, heavy metals, Delta State