Safety of selected vegetables grown in urban areas; Case of heavy metals in Dar Es Salaam City

A Dissertation 2019

A study was carried out to assess the safety of selected vegetables grown in urban areas, focusing on a case of heavy metals in Dar es salaam, Tanzania. The study investigated the concentration of three heavy metals, namely Lead (Pb), Cadmium (Cd) and Copper (Cu) in the edible portions of selected leafy vegetables, and the effect of blanching on the possible reduction of heavy metals concentration. The study also compared the levels of metal in selected matured leafy vegetables across their sampling sites and their associated uptake rates of the metals from soil. The selected leafy vegetables were Chinese cabbage (Brassica rapa), Spinach (Spinacia oleracea), Amaranthus (Amaranthus spp), and Pumpkin leaves (Curcubita moschata). The heavy metals concentration was measured using an Atomic Absorption Spectrophotometer. The results showed that, Pb and Cd in dry weight (mg/kg) ranged from 4.46 to 10.09 and 0.49 to 0.79 respectively. The concentrations were higher than the permissible levels as per WHO, FAO and TBS for green leafy vegetables. Except for Pb, blanching had no significant reduction effect (p>0.05) in the heavy metals concentration in the vegetables. The mean concentration of Pb varied across sites and vegetables (p< 0.05), the mean concentration of Cd did not vary across sites but varied across vegetables (p>0.05), where the difference was observed between Chinese cabbage and Spinach. The mean concentration of Cu varied across sites and vegetables (p<0.05) where the difference was observed between Chinese cabbage and Amaranthus, Pumpkin leaves and Spinach. The uptake of Pb, Cd and Cu concentrations among vegetable varieties was not significantly different (p>0.05). This showed that all selected vegetable varieties up took the metals at a similar rate.