Health Risk Assessment of Selected Trace Metals in Edible Vegetables Grown in Obudu Urban Area of Cross River State Nigeria

Aim: Edible vegetables are consumed directly as food or medicine in Obudu urban area of Cross River State, yet they are sometimes grown in old wastes dumpsites where wastes containing trace metals may have been disposing of indiscriminately, with the view to tap the composted manure. The objective of this study was to assess the health risk of selected trace or heavy metals in this edible vegetables in the area.

Place and Duration of Study: Department of Chemistry Laboratory, University of Calabar, Calabar Nigeria, between January and March, and July and September 2016 for dry and rainy season respectively.

Methodology: Edible vegetable samples were collected at five different locations together with the soil samples where each vegetable was planted during the dry and rainy season of the year respectively. They were digested and their average Hg, Ni, Pb and Zn concentration was determined using the 210 VGP Buck scientific model Atomic Absorption Spectrometer (AAS). The health risk was assessed using the Target Hazard Quotients (THQ) values determined from AAS data.

Results: These showed that the mean concentration of Pb in the soil in mgkg-1 ranged from 0.011 - 0.033 and 0.010 - 0.031 for the rainy and dry season respectively, while that of Zn ranged from 0.165 - 0.635 and 0.163 - 0.627 for rainy and dry season respectively. Hg and Ni were considered string variables as they were not detected in the soil or vegetables. The average concentration of Pb and Zn accumulated by the vegetables in mgkg-1 ranged from 0.005 - 0.023 and 0.004 - 0.018 for the rainy and dry season respectively, while that of Zn ranged from 0.017 - 0.074 and 0.016 - 0.079 for the rainy and dry season respectively. The trend of the average concentration of the metals in the soil and vegetables was in the order: Zn > Pb > Hg > Ni. The THQ values of Pb and Zn were in range 0.0018-0.0101 and 0.0001-0.0004 respectively, all less than 1.

Conclusion: From the results, there is some level of heavy or trace metal concentration present in the soil and the edible vegetables in the area but the amount is still low and within the permissible limit of WHO/FAO, and there is no health risk associated with the consumption of the vegetables as far as the studied metals are concerned for now.