Abstract:
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.
