Metals and radionuclides are environmentally relevant contaminants, yet their potential impacts on marine organisms have not been adequately evaluated. This is especially true for exposures of longer duration and/or lower contaminant concentration (i.e. chronic) which are often more representative of real world scenarios. In this context, a suite of biomarkers at different levels of biological organisation were investigated in an ecologically relevant bivalve species, Mytilus galloprovin- cialis after exposure to nickel (a metal), zinc pyrithione (an organometal) and tritiated water (a radionuclide). These contaminants were chosen based on their differing properties, and hence, mechanisms of action. All three contaminants produced genotoxicity (DNA strand breaks, as measured by the comet assay, and induction of micronuclei [MN]). For nickel (> 1800 µg L −1 ) and tritiated water (15 MBq L−1 ), biomarkers at lower levels of biological organisation (i.e. DNA strand breaks, MN, changes in the expression of key stress response genes) were more sensitive than those at higher levels (i.e. clearance rate, attachment, tolerance of anoxia). In particular, exposure to tritiated water for 14 days resulted in DNA damage and molecular alterations without affecting higher level responses. As environmental contaminants could interact with other physical or chemical stressors in a complex environment, further exploration of biological responses revealed modulation by hyperthermia with concomitant changes in the transcriptional ex- pression of key defence genes (hsp70, hsp90, mt20, p53 and rad51). In contrast to nickel and tritiated water, exposure to both 0.2 and 2.0 µM zinc pyrithione caused significant deviation from concurrent controls for every biomarker examined, suggesting that further investigation of the environmental impacts of this contaminant is particularly necessary. Variation in biological responses induced by different contaminants suggests that potential links between levels of organisa- tion should be evaluated on a contaminant-specific basis. The integrated, multiple biomarker approach used in the current study provides a robust methodology for such studies, which could be translated to other ecologically relevant species for proper evaluation of risks to both environmental and human health.

This thesis focuses on toxicity and occurrence of hydroxylated polybrominated diphenyl ethers (OH-PBDEs) in Baltic Sea biota. The aims were to assess OH-PBDEs potency for disruption of oxidative phosphorylation (OXPHOS) and determine their and related compounds exposure in Baltic blue mussel, herring and long-tailed duck. A method for analysis of OH-PBDEs in herring and long-tailed duck plasma was also evaluated. Relevant OH-PBDEs were tested in vitro for OXPHOS disruption, using a classic rat mitochondrial respiration assay and a cell mitochondrial membrane potential assay. All compounds were found to disrupt OXPHOS either by protonophoric uncoupling and/or via inhibition of the electron transport chain. 6-OH-BDE47 and 6-OH-BDE85, were identified as particularly potent OXPHOS disruptors. Strong synergism was observed when OH-PBDEs were tested as a mixture corresponding to what is present in Baltic blue mussels. Baltic blue mussel is main feed for several species of mussel feeding sea ducks which have decreased dramatically in numbers. To assess long-tailed ducks exposure to brominated substances, liver tissue from long-tailed ducks wintering in the Baltic Sea and blue mussels were analysed. The result confirms that long-tailed duck are exposed to OH-PBDEs via their diet. However, low concentrations were found in the duck livers, which suggest low retention of these compounds despite daily intake. How the nutritional value of blue mussels as feed for sea ducks are affected by OH-PBDE exposure still needs further studies. Other species of sea ducks foraging on Baltic blue mussels during summer months can also be more exposed due to seasonal variation in primary production. Herring sampled in the Baltic Proper and Bothnian Sea, were found to contain OH-PBDEs and high levels of their methylated counterpart, MeO-PBDEs. As demethylation of MeO-PBDEs is known to occur in fish, MeO-PBDEs may pose as additional source for more toxic OH-PBDEs in herring and their roe. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript.</p>