Assessment of heavy metal concentrations in soil at selected sites in urban west Unguja by energy dispersive x-ray fluorescence s pectrometry

The objective of this study was to assess the concentration of heavy metals V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Cd, Pb and Hg in the Spinach (amaranth) farm soil at selected site in Urban West of Unguja. Thirty six (36) samples of soil were collected from four selected areas where spinach (amaranth) was cultivated in Urban West of Unguja i.e. Chukwani (Ch), Mwera (Mw), Dimani (D), and Migombani (M). The samples were analyzed by using EDXRF Spectrometer of Tanzania Atomic Energy Commission (TAEC) in Arusha. Five samples of the soils of the nearby area far from the farms as Control soil also were collected and analyzed. The results were compared with the Control soil and the International Standards. The concentrations of V,Cr, Coand Hg were below the detection limits in all sites except V in Dimani area in which its concentration was below the permissible international limit of 0.04 mg/kg. The concentration of Cadmium Cd in the soil ranged between 6.1-11.4mg/kg, which was higher than the permissible limit of Cd in the soil according to the Dutch standards of 0.8 mg/kg. Cadmium was not detected with EDXRF at Migombani (M) site. The concentration of lead at Ch, Mw, D were within the permissible limit but in M and Control soils were high compared to the Dutch standard limits. The concentration of Cu in soil ranged between 8.1-43.8 mg/kg where as the permissible limit is 36mg/kg according to Dutch standards. The concentrations of Ch, Mw, M and Control soils areas were within the permissible limit but in area D the concentration was higher than the Dutch standard limits. Nickel concentrations in the analyzed soils were below the Netherlands standard limit which is 35 mg/kg except in D area which has high concentration compared to that Netherlands standard limit so there is a need of remediation. Therefore, farming in selected sites of Urban West of Unguja is introducing heavy metals in the food chain.