Heavy Metal Levels in Soil, Tomatoes and Selected Vegetables from Morogoro Region, Tanzania

The concentrations of heavy metals of Cd, Cu, Cr, Pb and Zn were determined in cauliflower (Brassica oleracea L. var. butrytis L.), carrot root (Daucus carota L.), tomato fruit (Lycopersicon esculenta Mill.), onion bulb (Allium cepa L.) and leafy cabbage (Brassica oleracea var. capital capitata L.), and the respective soils from Morogoro region, Tanzania. The accumulated heavy metals were quantified and levels compared to FAO/WHO (2003) and TZS (2007) safety limits for such produce. The methodology involved random sampling, extraction of the metals from the tomatoes, vegetables and soil and determination of heavy metals by using ICP-OEC and GFAAS. The results showed that levels of Cd, Cu, Cr, Pb and Zn at 90% of the sites in vegetables and tomatoes were above the FAO/WHO limit. The mean concentrations of Cd, Cr, Pb and Zn in all vegetables and tomatoes except Cu were also found to be above this limit therefore advocating a health risk for consumers. Levels of heavy metals in the soils were below the limits of the Tanzanian standard (TZS 972: 2007) and were lower than levels found in vegetables. The bioconcentration factor for Cu recorded 1 for tomatoes and cabbage at Towelo and below 1 for tomatoes and cauliflowers from Mgeta. Cd in onions at Mgeta as well recorded below 1. However, the bioconcentration factor for these heavy metals in vegetables and tomatoes in all other sites were found to be above 1 in all heavy metals an indication of high uptake of heavy metals in the vegetables and tomatoes from the soil. These results suggest that such vegetables and tomatoes might place the consumers at health risk; therefore they are not safe for consumption in their raw state.