Determination of mercury in fish fins as a non-lethal assessment method for predicting mercury levels in fish muscle tissues of two species of freshwater fish from three different aquatic environments in Ghana

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September, 2015
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Mercury concentration in various tissues (dorsal fin, caudal fin, pectoral fin, pelvic fin and anal fin) of two species of fish, tilapia (Oreochromis niloticus) and mudfish (Clarias gariepinus) from three fresh water bodies in Ghana were assessed in order to determine any relationship between them. Fifteen samples each of the two species were collected from Tono Dam at Navrongo, Hydroelectric reservoir at Kpong and White Volta at Yapei. The fish tissues were digested and analyzed by cold vapour atomic absorption spectrophotometry using an Automatic Mercury Analyzer ( Model HG-5000). For all fish tissues in all species, Hg concentrations were greatest in muscle tissue (mean muscle Hg = 0.236–0.680 µg/g wet weight), followed by fin tissues (0.03–0.09 mg/kg dry weight). The coefficient of determination (r 2 ) derived from regression analysis of species muscle Hg against fin Hg ranged between 0.349–0.823 and 0.278-0.752 for tilapia and mudfish samples from Navrongo, 0.492-0.715 and 0.14–0.37 and 0.737-0.965 for tilapia and mudfish samples respectively from Kpong and 0.413-0.893 and 0.546-0.960 for tilapia and mudfish samples from Yapei, respectively. The examination of fin tissues as predictors of muscle Hg resulted in caudal fin being the better predictor of mercury concentration in muscle of Tilapia fishes from all three location. The results for mudfish samples also indicated same. It is also noteworthy that the sensitivity of these nonlethal techniques was highly variable across species and dependent on specific life history characteristics of the fishes. The mercury level in the muscle tissues were all within the WHO limit of 5.0 µg/l and hence poses no health risk to consumers. The mercury concentration in the muscle tissues of 98% of the fishes in this research recorded results lower than the WHO limit of 0.5µg/g which implies that consumption of these fishes does not pose any threat to human health
A thesis submitted to the Department of Chemistry, Faculty of Physical Sciences, College of Science, Kwame Nkrumah University of Science & Technology, Kumasi in partial fulfillment of the requirements for the degree of Master of Philosophy (Analytical/ Environmental Chemistry) , 2015