Mercury accumulation in European perch (Perca fluviatilis) in Lake Mjøsa. Effect on the activity of Superoxide dismutase and Glutathione peroxidase enzymes.

Mercury pollution in freshwater is widespread and a concern to human health. Administering mercury chloride to organisms under study to determine the acute toxicity of mercury has been a common approach in studying pathology and response of antioxidant enzymes. Little is documented on antioxidant response in freshwater fish living in their natural habitat in a lake that is moderately polluted with mercury. To address this question, levels of Mercury in white muscle and livers of European Perch (Perca fluviatilis) from Lake Mjøsa were studied. Age and length of fish were used to study the correlation of mercury levels against antioxidant response (enzyme activity). The fish samples used in the experiment were caught in June 2012 and May 2013. Enzyme activity analysis was determined on two antioxidant enzymes, Superoxide dismutase (SOD) and Glutathione peroxidase (GPx). The activity analysis of SOD was carried out using a non-enzyme superoxide generator. The results revealed mercury presence in studied samples in a range between 0.15 ppm and 1.69 ppm in the white muscle, and between 0.12 ppm and 1.81 ppm in the liver. Regression analysis using linear model, revealed age and length of fish correlated positively against mercury concentration in both white and liver tissues. Superoxide dismutase activity correlated negatively against [Hg]muscle, [Hg]liver and fish length, while total protein concentration was positively correlated against [Hg]muscle and [Hg]liver. No correlation was observed between SOD enzyme activity and [protein]. The negative enzyme activity observed in this study is a remarkable observation and opposite of what acute toxicity studies previously reported. The results can be concluded that chronic mercury exposure in the natural habitat may reduce enzyme activity, but the lost activity is compensated for by more protein production. In vitro addition of mercury chloride during enzyme activity analysis only reduced signal intensity instead of enzyme activity, an observation that may mean that mercury ions reacted with the superoxide ions and escape as vapour, without binding to the enzyme molecules