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Health risk assessment of heavy metal contamination of some indigenous vegetables grown in oil spilled agricultural area in Ogoni Land, Rivers State, Nigeria


U. B. Onyedikachi

Abstract

This study seeks to evaluate the potential health risks associated with the consumption of selected heavy metals in soils and selected vegetables from polluted sites. The vegetable includes; Gongrenema latifolium (GL), Ocimum gratissimum(OG), Vernonia amygdalina(VA) and Talinum triangulare (TT), harvested from a crude oil polluted area in Bodocity, Ogoniland., Rivers State. The concentrations of Fe, Pb, Zn, Mg, Cd and Cr were determined using Atomic Absorption Spectroscopy (AAS). The mean concentrations of heavy metals (Fe, Pb, Zn, Mg, Cd and Cr ) for the samples ranged from 0.36±0.01 in GL (Control) to 16.82±0.01 in the polluted soil (SS); <0.0001(BDL) to 0.48 in VA obtained from polluted site; 0.19±0.00a in SS (control) to 2.67±0.01a in OG (control); 3.51±0.01b to 470.33±0.33a in TT control; BDL to 0.04±0.00b in VA polluted and  BDL to 0.03±0.00a in SS polluted (in mg/kg respectively).  Pb concentrations in VA, TT and SS in polluted site exceeded the permissible limits of 0.2mg/kg, while other heavy metal levels were within safe limits. The metals were in the order of abundance  Mg>Fe>Zn>Cr>Pb>Cd. Health Risk was assessed by computing the average Daily Intake of Heavy Metals, Target Hazard Quotient and Carcinogenic Risk for Heavy Metals. The daily intakes of Heavy metals from vegetable consumption were within the threshold values for Cr, Zn, Pb, and Cd except for contaminated soil, which exceeded the threshold value. The observed THQ of Cr, Zn, Pb and Cd were generally < 1. This observation is suggestive that consumers of vegetables from the study sites may not experience significant health risks from intake of individual metals through vegetable consumption except THQ value >1 for Fe which maybe a concern to consumers of crops planted in the Bodocity soil. The CR values of Pb, Cd and Cr in GL, VA, TT and SS were within 10-6 to10-4, indicating that consumption of vegetables grown in the oil spilled area may likely result in cancer over a period of 70 years. The CR values indicated in this study were within the predicted permissible lifetime cancer risk (10-6-10-4) for all the samples assessed, constant consumption/exposure to these Heavy metals may result in their bioaccumulation overtime which is implicated in serious health risk.


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