Impact of wastewater on nitrate concentrations in soil and vegetables grown along Kubanni River, Zaria in Kaduna State, Nigeria

Abstract

The concentration of nitrate was evaluated in wastewater, soil and vegetable (carrot, lettuce, onion, spinach, cabbage, tomato and okra) samples collected on seasonal basis from January, 2013 to September 2014 along Kubanni stream channels in Zaria. The results showed nitrate levels in wastewater were in the range of 23.05-283.54 mg/L for the year 2013 and 16.85-68.05 mg/L in the year 2014; soil had concentrations in the range of 2.20-20.50 mg/kg for 2013 and 7.27-29.57 mg/kg for the second year while the vegetable had concentrations in the range of 3.80-23.65 mg/Kg for the year 2013 and 7.48-27.15 mg/Kg in year 2014. Statistical analysis revealed no significant difference in nitrate concentrations across the locations and seasons for wastewater, soil and vegetables analyzed. Pearson correlation results revealed negative (r = -0.263) relationship between nitrate levels in wastewater for year 2013 and year 2014, likewise negative (r = -0.217) relationship was obtained for vegetables planted in the year 2013 and 2014 whereas negligible (r = 0.137) relationship was recorded in the soil for these years. Nitrate concentrations obtained in this study was higher than maximum contaminant levels set by Standard Organization such as WHO and FAO for wastewater whereas the soil and vegetable of the sampling sites were not contaminated with nitrate ions.