Ngozi Maryrose Nnaji, Rosemary Uche Arinze
Heavy metals pollution has been a great concern generally due to their toxicity and persistence in environment. This study evaluated the level of pollution and health risks of heavy metals in surface irrigation water used for vegetable cultivation and sediment from Nimo vegetable farm. Three samples each from three different sampling points for water and sediment were collected in dry and rainy seasons and analyzed for Pb, Cd, Mn, Fe, Zn, Cu and Ni concentrations using Atomic Absorption Spectrophotometer. The result showed that heavy metal concentrations in the irrigation water ranged from 0.004 to 0.147mg/l, 0.119 to 0.773mg/l, 0.014 to 1.644mg/l, 0.006 to 0.056mg/l, 0.009 to 0.576mg/l, 0.040 to 0.181mg/l, 0.082 to 0.147mg/l, for Cd, Pb, Fe, Cu, Zn, Mn, and Ni respectively for the different seasons. In sediment, Cu had the lowest mean concentrations of 0.02 ± 0.01mg/l while iron had the highest mean concentrations of 6.86 ± 3.06 mg/l. The obtained results were compared with Food and Agriculture Organization and the Department of Petroleum Resources standards for surface irrigation water and sediment respectively. The heavy metal distribution in water was Fe>Pb>Mn>Cd>Ni>Cu=Zn in dry and Zn>Fe>Pb>Ni>Mn>Cu>Cd rainy seasons respectively. Overall, the heavy metals level in the water and sediment were low when compared to the standards. Computed contamination factors and pollution load index showed that the sediment were not polluted while in water, only Cu, Zn, Mn and Fe (in rainy season) showed low contamination, while Ni, Pb and Cd had moderate to very high contamination in both seasons. Hazard Index values for the heavy metals in adults and children via the water and sediment of this study is less than one (HI<1). Hence the water and sediment from this site poses no health risk to the public. Correlation analysis for metals in water and sediment showed significant and positive relationships amongst the metals which indicated that the most of the metals originate from the same source while few originate from mixed sources mainly from agricultural activities, atmospheric deposition and runoff into the irrigation water.
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