Heavy Metals in Soils and Tomatoes Grown in Urban Fringe Environment in Asaba, Delta State, Nigeria

Abstract

Pb, Cu, Ni, Zn, Cr, Mn and Fe in soils and tomato leaves and fruits from peri-urban environments in Asaba, Delta State were determined after acid digestion by using atomic absorption spectrophotometry (AAS). The concentrations of metals in the soil samples were 10.14, 2.28, 3.96, 7.88, 0.15, 14.53 and 66.00 mg/kg site A; 7.01, 2.01, 2.03, 5.53, 0.16, 12.15, and 70.12 mg/kg site B, and 9.12, 2.24, 3.01, 4.35, 0.01, 11.52, and 61.22 mg/kg site C for Pb, Cu, Ni, Zn, Cr, Mn and Fe respectively. The concentrations of metals in the tomato leaves samples were 4.01, 1.91, 1.83, 4.89, 0.16, 4.51 and 7.13 mg/kg in site A; 3.84, 1.56, 2.07, 4.00, 0.41, 4.48 and 8.15mg/kg in site B, and 4.03, 1.75, 2.01, 4.52, 0.01, 4.42 and 8.11 mg/kg in site C for Pb, Cu, Ni, Zn, Cr, Mn and Fe respectively while in the tomato fruits, the concentrations of metals in mg/kg were 2.96, 0.41, 1.35, 3.33, 0.01, 3.83 and 6.38 mg/kg in site A; 3.01, 1.35, 1.88, 2.98, 0.15, 3.01 and 5.09 mg/kg in site B, and 3.92, 1.44, 1.82, 3.73, 0.01, 3.05 and 6.00 mg/kg in site C for Pb, Cu, Ni, Zn, Cr, Mn and Fe respectively. These values obtained in the soils for all sites were below the given values for naturally occurring metals in soil and Department of Petroleum Resources target and intervention values for metals in soil while the values recorded for tomatoes leaves and fruit are below the levels recommended by WHO/FAO and NAFDAC for metals in foods and vegetables but are within the normal range of metals in plants. There was positive correlation among metals except Pb/Cr, Cr/Mn and Cr/Fe. The values of transfer factor (tf) obtained for all the metals except Fe in leaves and fruits for all the sites were above 0.2 indicating anthropogenic contamination of the sites and also high take up and accumulation of the metals from the soil by the tomatoes thus the need for environmental monitoring of the area.

Key words: Heavy metals, tomato, anthropogenic, contamination, pollution