Title: Studies on the mercury-selenium ratio of water, sediment, and fish samples from the lower Pra River
Authors and Affiliations: Vincent Nartey1, Raphael K. Klake1
1Department of Chemistry, University of Ghana, Legon, Ghana
Abstract: Mercury is a toxic metal with no known biological role in the human body. The metal enters the food chain directly as metallic precipitation in crops or after methylation in animals. It also bioconcentrates mainly as methylmercury in the trophic fish chain. Research has however shown that Selenium has a positive effect on alleviating the toxic effects of Hg. Even in freshwater environments, the bioaccumulation of Hg by biota has been seen to be retarded by elevated concentrations of Se in water of experimental ecosystems. In our study therefore we looked at the concentrations of total mercury (Hg), and total selenium (Se) in sediments, water and fish samples from four communities along the Lower Pra river in Ghana. This was done using Atomic absorption Spectroscopy. The samples were treated through wet digestion procedure with a mixture of acids, HNO3 and HClO4 in the ratio 2:1. The water samples showed selenium levels below the detection limit of 0.001mg/L while mercury levels were generally found to be higher than the levels of selenium. Inverse relationship has been observed between the selenium and mercury concentrations in water and fish. For the sediment samples, levels of mercury were found to be higher than selenium. This is probably due to the sediments serving as a sink for mercury from mining activities which are impacting Hg concentrations in the sampling area.