Interactive Effect of Zinc Oxide Nanoparticles (ZnO NPs) and Salinity Regimes on the Bioenergetics of the Blue Mussels (Mytilus edulis, Linnaeus, 1758).

Supervisor: Inna Sokolova (University of Rostock).
The Baltic Sea is surrounded by 14 countries and the river runoff contributes 1/40 of the total Baltic Seawater and responsible for the salinity gradients in Baltic Sea. The Baltic Sea coast experiences high tourism pressure that results in a release of novel pollutants such as sunscreens into the water. As a consequence, the Baltic Sea organisms are increasingly exposed to the sunscreen components such as the zinc oxide nanoparticle (ZnO NPs). However, the potentially harmful impacts of ZnO NPs on marine organisms are not well understood and require further investigation. To understand the combined effect of salinity stress and ZnO NPs different salinity regimes (normal salinity, 15 PSU; low salinity, 5 PSU; fluctuating salinity) and environmentally relevant concentration of ZnO NPs (100μg/L) on Mytilus edulis (Linnaeus, 1758) was considered for the experimental design. After 21 days of exposure to different salinities, ZnO NPs and Zn2+ (negative control) soft tissue of M. edulis was collected to observe different physiological biomarkers such as energy reserve (Es), cellular energy allocation (CEA), proteins, lipids, carbohydrates, condition index (CI) and electron transport system (ETS). Data obtained from this study revealed that to maintain the homeostasis balance at the stressed condition, energy reserve (Es) in mussels depressed (∼27%) at fluctuating salinity compared to the controlled condition (15 PSU salinity) when treated with ZnO NPs. Analysis of the tissue levels of the three major classes of energy-rich macromolecules (carbohydrates, proteins, and lipids) showed that lipid content was decreased ∼39% at low (5 PSU) and fluctuating salinity in the soft tissue of mussels which were exposed to ZnO NPs. Therefore, a reduction in protein content (∼38%) was observed in the soft tissue of Zn2+ exposed mussels at fluctuating salinity. These findings indicate that the mechanisms of maintaining energy homeostasis might be different depending on the pollutant (Zn2+ and ZnO NPs), as the mussels used different reserves (proteins and lipids) to cover their basal energy demand when exposed to ZnO NPs or Zn2+. However, ETS activity, CEA, and, condition index remained constant which indicate that in all experimental exposures used in this study do not cause severe stress in M. edulis and likely fall into the pejus (suboptimal) range for this species. This may reflect high-stress tolerance of M. edulis which has evolved as an intertidal species and adapted to large and rapid fluctuations of the abiotic stressors in intertidal habitats.