ASSESSMENT OF THE METALLIC CONTAMINATION OF VEGETABLES CULTIVATED IN A SOIL ADJACENT TO KEHA RIVER IN GONDAR CITY, ETHIOPIA

Abstract

ABSTRACT It is a common practice to grow vegetables along banks of rivers passing through urban centers. Water of such rivers has been reported polluted by heavy metals as a result of urbanization and increasing anthropogenic activities. The study was conducted to assess the metallic contamination of vegetables cultivated in a soil adjacent to Keha River in Gondar city, Ethiopia, 2018. Concentrations of Cu, Mn, Zn, Cr, Cd, Ni and Pb metals were investigated in vegetable, soil and water samples using flame atomic absorption spectrometry. Purposive sampling method and composite sampling technique was employed to collect samples from the Keha (mariyam sefer) irrigation site in Gondar city, Ethiopia. The collected samples were processed in the laboratory and then digested using dry acid digestion method HNO3/HCl/HClO4 (5:5:3; v/v/v) for vegetable and water samples, additionally HF (5/5/3/2; v/v/v/v) was used for digestion of soil sample. Descriptive statistical analysis was computed using Microsoft excels and non parametric Kruskal - wallis test were employed to compare means. The mean concentrations of Cr, Mn, Cu, Zn, Cd, Ni and Pb in the vegetable samples range 5.83 –13.33, 0.91–76.67, 1.61– 11.29, 19.16–88.31, 0.23–6.25, 7.41-51.85 and 0–9.52 in mg/kg respectively. Obviously, the vegetables grown with Keha River were highly contaminated with Pb, Cd and Cr which are found to be above the permissible limits. The mean concentration of soil samples were within the range of Pb 138.09-259.24, Cd 4.63-20.37, Cr 30-48.33, Cu 28.06-138.71, Zn 191.95-355.94, Ni 85.18-259.26 and Mn 676.36-932.73 in mg/kg respectively. Pb, Cd and Ni in all the soil samples were above the FAO/WHO safe limit. The mean concentrations of Pb, Cd, Cr, Cu, Zn, Ni and Mn in the river water were 0.26, 0.046, 0.5, 1.80, 0.87, 0.17 and 0.48 mg/L respectively. The values of Cr, Cd, Mn and Cu detected in water samples were above the recommended limit set by US EPA (2004). From the present study we can conclude that the river water, soil and vegetables were contaminated with metals and the results show that vegetables grown in this area are unsafe for consumption. Therefore there is a need to conduct research work and further monitoring to identify whether these vegetables pose human health risk and taking measures. Keywords: Vegetables, Wastewater irrigation, Heavy metal, Safe limit