Exposure of the population of Monrovia to heavy metals through fish consumption

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Heavy metal contaminants in fish are of particular global interest because of the potential risk to humans who consume them. While attention has focused on self-caught fish, most of the fish eaten by the populace come from commercial sources. In this study, concentrations of some heavy metals were determined in muscle tissue of sixty samples covering twenty nine (29) commercial fish species from eight markets in Monrovia, Liberia. A mixture of HNO3, HClO4 and H2SO4 was used for complete oxidation of organic tissue. Total mercury was determined by cold vapour atomic absorption spectrometry technique using an automatic mercury analyzer; while the levels of Pb, Cd, Cu, Fe and Zn were determined by flame atomic absorption spectrometry using an Atomic Absorption Spectrophotometer. The muscle concentrations of Hg, Cu, Pb, Cd, Fe and Zn ranged from 0.014-0.727, 0.101-2.990, 0.027-0.256, 0.002-0.347, 2.122-6.804 and 1.783-6.013 µg g-1 wet weight respectively. Inter-metal correlations and relationships between metal concentrations and fish body size were discussed. Estimation of the dietary exposure of the consumers to these metals were determined based on data from the American Food Consumption Index and the associated risk was evaluated by comparing intakes with the Provisional Tolerable Weekly Intakes (PTWIs). Both the Hazard Quotient (HQ) and Hazard Index (HI) for Hg, Cu, Pb, Cd, Fe, and Zn in all the species were less than the USEPA guideline value of 1. This suggests that the exposure to the tested metals from the consumption of the studied fish species is not significant and is unlikely to pose any imminent health risk to the population of Monrovia.
A thesis submitted to the Department of Chemistry, Kwame Nkrumah University of Science and Technology in partial fulfillment for the award of the degree of Master of Philosophy (Analytical Chemistry) 2014