Assessment of cobalt levels in wastewater, soil and vegetable samples grown along Kubanni stream channels in Zaria, Kaduna State, Nigeria
The concentration of cobalt was determined 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 show cobalt levels in wastewater were in the range of 3.77 - 15.20 mg/L for the year 2013 and 4.74 - 15.20 mg/L in 2014; 0.63 - 3.57 mg/Kg for the year 2013 and 0.99 - 4.07 mg/Kg in 2014 for the soil while the vegetables had concentrations in the range of 1.25 - 8.75 mg/Kg for the year 2013 and 2.76 - 12.45 mg/Kg in 2014. Statistical analysis revealed no significant difference in cobalt levels across the sampling locations whereas significant difference (p < 0.050) were observed in seasons for wastewater and vegetables analyzed. Pearson correlation showed substantial (r = 0.726) relationship between cobalt levels in wastewater for the year 2013 and 2014, substantial (r = 0.799) relationship for soils between these two years and substantial (r = 0.720) relationship was also obtained for vegetables cultivated in 2013 to that of 2014, respectively. Cobalt concentrations in this study were higher than maximum contaminant levels set by Standard Organizations such as WHO and FAO in wastewater while below their limits in vegetables.
Keywords: Cobalt level, Kubanni River, soil, vegetable, wastewater.