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Heavy metal residue in some vegetables and potential health risk assessment among consumers within Katsina North Western Nigeria

L.U Usman
R. Yerima


Ingestion of vegetables containing heavy metal is one of the main ways in which these elements enter the human body. Once entered, heavy metals are deposited in bone and fat tissues, overlapping noble minerals. Slowly released into the body, heavy metals can cause an array of diseases. This study aimed to assess the heavy metals residues in some vegetables and potential health risk among consumers within Katsina Metropolis. Six different vegetable samples comprising of cucumber (Cucumis sativus), cabbage (Brassica oleracea), lettuce (Lactuca sativa), spinach (Spinacia oleracea), red pepper (Piper nigrum) and tomato (Lycopersicum esculentus) were randomly collected from two main irrigation farmland located in Katsina Metropolis (Kofar sauri and Kofar marusa). Their level of toxic metals namely (Copper, Zinc, Cadmium, Chromium and Lead) were assessed using standard materials and methods. Results obtained were used to estimate the health risk of these heavy metals via consumption of the vegetable samples. The results from the study showed that the mean heavy metal concentration ranged between 1.10±0.00 mg/kg to 4.45±0.16 mg/kg, 1.78±0.07 mg/kg to 4.9±0.11 mg/kg, 0.02±0.00 mg/kg to 1.28±0.02 mg/kg, 1.51±0.02 mg/kg to 4.34±0.02 mg/kg and 1.05±0.01 mg/kg to 2.86±0.02 mg/kg for Cu, Zn, Cd, Cr, and Pb respectively. The concentration of Cu and Zn were found to be below permissible limit while Cd, Cr and Pb concentration exceeded the permissible limit recommended by WHO/FAO. Health risks associated with the intake of these metals were evaluated in terms of estimated daily intake (EDI), hazard quotient (HQ) and hazard index (HI). EDI value of Cu and Zn were found to be below the maximum tolerable daily intake (MTDI). The HQ of all the metals were >1, suggesting health hazards risk for the population. Moreover, HQ of Cd and Pb were greatly higher through consumption of cucumber, cabbage, lettuce and red pepper indicating significant health risks. HI was found to be higher >1 (3.32 mg/kg and 3.91 mg/kg) in adult and children respectively for consumption of spinach; however, it was much higher >1 (10.49 mg/kg and 12.4 mg/kg) in adult and children respectively for consumption of cabbage, suggesting more adverse health effects from cabbage consumption than spinach. The findings of this study shows the health risks associated with the consumption of heavy metals through the intake of some the selected vegetables within Katsina Metropolis, therefore, there is need for biomonitoring of these heavy metals in the vegetable because these are some of the main sources of food for humans in many parts of the world.

Keywords: Heavy metal, Estimated Daily Intake, Hazard Quotient, Hazard Index, Consumption