Effects of nitrite concentrations on soil and certain vegetables irrigated with wastewater of Kubanni stream in Zaria, Kaduna State, Nigeria

Abstract

The study examined the effect of nitrite ions in wastewater, soil and vegetables through man-made activities. Nitrite level was determined in wastewater, soil and vegetables viz., spinach (Amaranthus hybridus), lettuce (Lactuca sativa), cabbage (Brassica oleracea), carrot (Daucus carota), okra (Hibiscus esculentus), onion (Allium cepa) and tomato (Lycopersicon esculenetum) collected on seasonal basis along Kubanni stream in Zaria. The levels of nitrate in the wastewater, soils and vegetables were determined using UV/Visible and Smart Spectrophotometer. Results obtained show that nitrite concentrations ranged from 12.05 – 53.21 mg/L in the year 2013 and 1.58 – 17.09 mg/L in the year 2014 for wastewater, soil had concentrations ranged from 0.05 – 6.40 mg/kg in the year 2013 and 0.90 – 9.90 mg/kg for year 2014 while the vegetable had levels of 3.80 – 23.65 mg/kg in the year 2013 and 7.48 – 27.15 mg/kg in the year 2014. Statistical tests indicated no significant difference in nitrite levels across the locations and seasons for wastewater, soil and vegetables evaluated. Correlation results for these two years indicated low (r = 0.399, r = 0.275) relationship for wastewater and vegetables whereas negative (r = -0.290) relationship noticed for the soil. The results showed that irrigating the farmland with untreated wastewater has negative consequence on the crops grown with it and thus, cultivation of wastewater irrigated soils and vegetables should be continuously monitored to stop any possible hazard.