Abstract
Concentration of mercury was investigated in the flesh and shell of two species of benthic mollusc, Crassostrea gasar and Tympanotonus fuscatus and in water and sediment from Makoko Creek, adjacent to the Lagos Lagoon between January to September 2019. Values obtained for physicochemical parameters in Makoko Creek (water temperature- 28.92±0.1°C; pH- 7.73±0.02; salinity- 14.23±0.05 ppt; dissolved oxygen- 5.34±0.02 mg/l; biological oxygen demand- 7.780±0.1 mg/l and chemical oxygen demand- 12.34±0.02 mg/l) were within the acceptable levels for survival, metabolism and physiology of aquatic organism. The concentration of mercury followed decreasing order as sediment >water >flesh >shell across locations for both species. For all the tested samples of C. gasar and T. fuscatus, biowater accumulation factor in flesh and shell were higher than those of bio-sediment accumulation factor. The coefficients of variance (CV %) in shells were lower than those of the flesh for both investigated mollusc species. It was shown that mercury contents of flesh or shells of C. gasar and T. fuscatu are directly affected by those of water and bottom sediment. J. Bio-Sci. 29(1): 143-151, 2021 (June)
Highlights
The contamination of aquatic ecosystem by heavy metals can persist for many years in sediments, where they hold the potential to affect aquatic biota and poses considerable environmental risks and concerns
Values obtained for physico-chemical parameters in Makoko Creek were within the acceptable levels for survival, metabolism and physiology of aquatic organism as affirmed from WHO (2004)
Higher mercury concentration was recorded in sediment than in water, possibly due to the settling ability of the metal and the inability of the water to retain mercury because of its metal density
Summary
The contamination of aquatic ecosystem by heavy metals can persist for many years in sediments, where they hold the potential to affect aquatic biota and poses considerable environmental risks and concerns. A nonessential metal naturally occurs in the environment as a result of volcanic degassing of the Earth’s crust and weathering of mercury rich geology (Yin et al 2013). While water from areas rich in mercury ores may exhibit high local mercury concentrations, industrial processes, agriculture and the combustion of fossil fuel are the most significant sources of aquatic contamination (Khoei and Bastami 2013). Mercury has no necessary function in living organism and is among the most toxic elements to man and many higher animals. As for most metals, factors known to influence mercury concentrations and accumulation in the marine organisms include metal bioavailability, season of sampling, hydrodynamics of the environment, size, sex and changes in tissue composition and reproductive cycle (Hosseini et al 2012)
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