Evaluation of mercury and selenium concentrations in the edible tissue of freshwater fish from the Volta Lake in Ghana

Abstract

Edward Ebow Kwaansa-Ansah1, Noah K Asare-Donkor1, Anthony A Adimado1, Dong-ha Nam

Background: The study of mercury (Hg) and selenium (Se) bioaccumulation in fish is of great importance in order to evaluate the extent of mercury and selenium contamination in the aquatic environment and their possible health risk for humans, considering their antagonistic interactions. Methods: Total selenium, total mercury, and methyl mercury were determined in one hundred and ninety-nine (199) fish samples belonging to twenty-six (26) different species at various trophic levels in the Volta Lake in Ghana. Total mercury and methyl mercury were determined with a Direct Mercury Analyzer and Selenium with ICP-MS.The concentrations of total mercury, methyl mercury, and total selenium in fish were related to the preferred prey and their bioavailability in the freshwater environment. Results: There was an increase in concentration of total mercury, methyl mercury and total selenium at successive higher trophic levels of the food chain suggesting that they all biomagnified throughout the food chain. There were statistically significant correlations (p<0.005) between total mercury, methyl mercury and total selenium concentrations for all the fish species studied. The molar ratios of total selenium to total mercury and total selenium to methyl mercury in all the fish studied regardless of their positions in the trophic levels were found to be approximately equal to one suggesting protective effects of selenium on methyl mercury toxicity. Conclusion: This confirms the antagonistic effect of selenium on methyl mercury in fish tissue from the Volta Lake. None of the fish had selenium concentrations above the limit of 3000 ng/g (w/w) considered damaging for fish and other aquatic organisms. Again, none of the fish had methyl mercury and total mercury concentrations exceeding the WHO/FAO guideline values of 300 ng/g and 500 ng/g above which potential health effect could occur.