ABSTRACT
The need to assess the heavy metals uptake by vegetables cultivated and irrigated with wastewater along the watercourse of a stream, have led to a controlled field experiments in Zaria Metropolis. Five heavy metals; Cadmium (Cd), Chromium (Cr), Lead (Pb), Manganese (Mn) and Zinc (Zn) were determined using the Atomic Absorption Spectrophotometer (AAS).The pollution load index (PLI), plant transfer factor (TF), daily intake of metals (DIM) and health risk index (HRI) were used to study the pollution status and the health risks the consumers may be exposed to by the consumption of the heavy metal contaminated vegetables in the metropolis. In this study, the quality of the stream (Kubanni River) contaminated with municipal wastewater and used for irrigation of carrot, spinach and cabbage was investigated at three sampling points (A, B, and C) for its heavy metal buildup. The contaminated water used for irrigation at each irrigation date, and the irrigated vegetables harvested after maturity were collected and analyzed for their metal concentrations. The results show that the stream water used for irrigation was contaminated with Cr, 0.4214mg/l, 0.291mg/l and 0.3774mg/l, and Mn, 0.245mg/l, 0.2127mg/l and 0.1618mg/l at point A, B and C respectively, which is above Food and Agriculture Organisation (FAO) threshold value. Pb and Zn were below the threshold and Cd was not detected in the wastewater samples collected during the study. The maximum Health Risk Index (HRI) was found in Daucus carota and Brassica oleracea which coincidently share the same value 0.2225. HRI of Cd, Cr, Pb, Mn, and Zn ranged between 0.17-0.19, 0.0033-0.0041, 0.1850-0.2225, 0.0236-0.0385 and 0.0168-0.0300 respectively. It was therefore concluded that irrigated crops harvested from these areas should be carefully washed and decanted after boiling before eating in order to prevent accumulation of these metals in man's body metabolism