Evaluation of metallic exposure in harbour seals (Phoca vitulina) from the North Sea using biomarkers of exposure and effects

Abstract

Harbour seals bioaccumulate contaminants such as metal trace elements (MTEs), which are present in the North Sea and consequently they are often used as bioindicators for chemical exposure. For this reason, it is increasingly necessary to use biomarkers which are early indicators of exposure to toxic substances. The MTEs are known to cause oxidative stress, which is the result of an imbalance between the amount of reactive oxygen species (ROS) produced and the implementation of antioxidants defenses. This could cause lipid peroxidation and ultimately the death of the cell. Therefore, levels of antioxidants defenses could be good biomarkers to assess MTEs exposure. While oxidative damage could be a good biomarker of effects. The aim of this study was to evaluate the relationship between the levels of MTEs contamination and biomarkers of exposure and effect. Selected biomarkers were: malondialdehyde (TBARS), total thiols, total glutathione (tGSH), Se dependent peroxydases (SeGPx), total glutathione peroxidases (GPx) and triglycerides. The first step of this study consisted to optimize assay protocols for those oxidative stress biomarkers in order to allow their assessments in the harbour seal serum. All biomarkers assays could be developed and analyzed by spectrophotometry. In a second part, biomarkers analyses were conducted in a case study aiming to link their responses to contamination of MTEs in harbour seals of the Wadden Sea. The results demonstrated that MTEs concentrations in blood cells were significant different between males and females concerning Hg and Zn, with lower concentrations in females. Although, it has not been possible to identify how MTEs influenced oxidative stress in harbour seals, the lack of correlation between Se and SeGPx may indicate that Se is not limiting for harbour seals. However, a positive correlation was noted between Ni and GPx activities, probably caused by the formation of ROS by Ni. Moreover, the Hg contamination had potentially depleted tGSH in females (negative correlation) and finally, lipid peroxidation was increasingly important when it was exposed to Ni and Pb, however, this was only observed in March and not in October. An increase of lipid peroxidation could thus be due to environmental factors. Finally, even if the measurement of biomarkers is correct, the conservation of the serum may have permitted that few correlations were found between ETMs and biomarkers.