Physicochemical Parameters in Soil and Vegetable Samples from Gongulon Agricultural Site, Maiduguri, Borno State, Nigeria

Anthropogenic activities are a leading cause of metal emission, often associated with high elevated soil and plant metal concentrations. The accumulation of heavy metals and anions in soil and vegetables in the vicinity of Gungulung agricultural site were investigated. Soil samples were collected at depths of 0-5 cm, 5-10 and 10-20 cm. Soil properties including pH, electrical conductivity (EC), organic matter, organic carbon, cation exchange capacity (CEC) and heavy metals content were determined using standard procedures. Vegetable samples (spinach, Amaranthus caudatus; carrot, Daucus carota; lettuce, Lactuca sativa; cabbage, Brassica oleracea; tomato, Lycopersicon sculenetum; waterleaf, Talinum Triangulare and onion Allium cepa were used for this research. The plant samples were prepared for heavy metals and anions determination using standard procedures. Results show that the soil metal content, conductivity and organic carbon decreased with depth, suggesting anthropogenic sources of contamination while pH, organic matter and CEC decreased with depth. The results obtained from this analysis revealed that Zn and Mn show the highest concentrations, Ni shows the lowest levels. Similarly, the results also revealed that Fe, Zn and Cu show the highest concentrations, while Pb shows the lowest levels in the whole vegetables parts studied. The leaves contained much higher concentrations of heavy metals and anions than roots and stems. The concentrations of the above parameters in the vegetable samples were higher than the FAO, WHO/EU and FAO/WHO allowed limit. The high values might be attributed to the use of wastewater from river Ngada and application of sewage sludge by farmers for the irrigation of these vegetables. The results of this study suggest that the vegetables grown in the vicinity of Gugulung agricultural site are subjected to anthropogenic activities. Thus, the high values of these metals in the vegetable samples could put the consumers of these vegetables at health risk with time due to bioaccumulation.