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Heavy metals concentrations in selected areas used for urban agriculture in Dar es Salaam, Tanzania

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This study was carried out to assess the concentration of heavy metals in selected areas used for urban agriculture in Dar es Salaam and compare them with permissible limit from the Tanzania Bureau of Standards (TBS) in order to establish risk levels. Samples were collected from six sites of Tazara mchichani, Ubungo darajani, Kigogo darajani, Temeke wailers, Tegeta and Bunju, which reflect frequently flooded and non-flooded areas and areas within the city and at the outskirts. The samples were analyzed for Zinc (Zn), Chromium (Cr), Cadmium (Cd), Lead (Pb) and Copper (Cu) as these are the common heavy metals in the city. The highest value of Cu (8.98 mg/kg), Zn (57.10 mg/kg) and Pb (33.70 mg/kg) were observed in Tazara Mchichani, which may reflect pollution from various manufacturing industries surrounding the areas including steel, iron, food processing and detergents. Bunju had the lowest Cu and Zn levels in the soil, averaging 1.92 mg/kg and 13.53 mg/kg, respectively, while Kigogo Darajani had the lowest Pb concentrations of 6.88 mg/kg. High and low values of Cr were observed in Tegeta and Temeke Wailes with the mean concentrations of 15.29 and 3.66 mg/kg respectively. The Cd level was high in Temeke Wailes, Kigogo Darajani and Tegeta with mean concentration of 0.26 mg/kg. The lowest Cadmium concentration (0.15 mg/kg) was observed at Tazara Mchichani. Heavy metal concentrations in the six sites were within the Tanzania Bureau of Standards (TBS) permissible limit, suggesting that no serious health hazards are expected. Flood seem not to influence toxic elements distribution as flooded area like Ubungo darajani, Tazara mchichani and Kigogo darajani had similar levels of concentrations of studied metals compared to non flooded areas of Temeke wailers, Tegeta darajani and Bunju.

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