Heavy metal pollution in soil, water and vegetables in Dar es Salaam – Tanzania

Abstract

Heavy metals (Cu, Cr, Cd and Pb) in soil and vegetable leaves (Amaranthus blitum, Ipomea batata and Cucurbita maxima) were determined along Msimbazi River, in Dar es Salaam – Tanzania. Atomic Absorption Spectrophotometer was used to analyse all samples, and results obtained were compared with standard limits. Laboratory results showed that concentrations of heavy metals in soils were all below maximum limits. Vegetable samples had copper concentrations below standard limits. The concentrations of Cadmium, Lead and Chromium were between 0.309 ± 0.01 mg/Kg and 0.331 ± 0.01 mg/Kg, 2.526 ± 0.01 mg/Kg and 9.143 ± 0.11 mg/Kg, and 1.118 ± 0.01 mg/Kg and 13.981± 0.87 mg/Kg, respectively, that exceeded maximum standard limits of 0.02, 2 and 1.3 mg/kg, respectively. The presence of such elevated levels of dangerous heavy metals in edible vegetables indicates a potential health risk to urban consumers of vegetables grown along Msimbazi River, through long-term dietary intake. The trends for heavy metal concentrations in soil, water, and vegetables, for the past 20 years, for the same study site, were also established. The trend for average concentrations of heavy metals in soils and vegetables showed average increases from year 2000 to 2010 and decreases from 2010 to 2020. On the contrary, concentrations of heavy metals in water showed an increase from year 2000 through 2020, except for chromium that decreased from 2010 to 2014. This information is vital for policy makers and other concerned stakeholders in monitoring urban vegetable farming activities in major cities especially Dar es Salaam.