Forurens: Is the cocktail effect of environmental contaminants a threat for Arctic fish populations?

Arctic animals are exposed to a range of environmental contaminants ("contaminant cocktails") that reach the Arctic mainly through long-range transport. The contaminants are taken up by animals, and in many top predators levels are high enough to cause negative effects on health. Around the year 2000 high concentrations of persistent organic pollutants (POPs) were detected in organisms from a lake on Bjørnøya (Ellasjøen). In other lakes on Bjørnøya, e.g. Lake Laksvatn, levels of POPs are considerably lower. In the present project, the aim has been to investigate if the contaminant cocktail present in Arctic char from Ellasjøen has any effects on fish health. Laksvatn was used as a reference lake (low contaminant levels). We have used a combined field- and lab-approach to increase the knowledge concerning effects of contaminant cocktails on Arctic animals. The project has been carried out from 2013 - 2016, but also samples collected as part of a pre-project, funded by the Fram Centre, have been incorporated in the analyses. Chemical analyses of muscle- and gonad-samples show that PCB still is the dominant contaminant group in fish from the two lakes at Bjørnøya, followed by chlorinated pesticides (p,p-DDE, chlordanes, HCB). Toxic equivalent-values for dioxin-like PCBs in ovaries of the Ellasjøen char exceeded levels associated with increased egg mortality in rainbow trout. Also newer contaminants, such as new brominated flame retardants and organophosphorus flame retardants occurs in elevated concentrations in fish from Ellasjøen compared to fish from Laksvatn. A non-target screening has shown that there are few unknown contaminants present in the fish samples from Bjørnøya. In vitro studies, using hepatocytes exposed to specific substances or mixtures of pollutants, were included in the project. To ensure environmental relevance contaminant-extracts from char collected at Bjørnøya were used in exposures. Three different extracts from liver and gonads, each containing various contaminants, were prepared. The results from the in vitro exposures showed that some of the extracts were toxic to the hepatocytes at the highest concentrations, and a few induced estrogen or dioxin-like activity. The mixtures from Ellasjøen fish were more potent than the mixtures from Laksvatn fish. As part of the project also the effects of pollutants on reproductive success was investigated. Levels of steroid hormones were determined, various fecundity indicators assessed (fecundity, egg diameter, spermatokrit) and a fertilization experiment was carried out in the field. There were no associations between pollutants and levels of steroid hormones in either females or males. However, females from Ellasjøen produced fewer and smaller eggs (lower fecundity) than females from Laksvatn. Statistical analyzes showed that PCB and HCB levels in females affected the fecundity. No effects were found on egg development. However, only the earliest cell division stages were examined. A stress response test was performed in the field, and gene expression and hormone levels in the hypothalamus-pituitary-interrenal (HPI) axis were measured before and after a stress challenge (a one-hour containment stress). The results show that gene expression in the HPI axis of fish from Ellasjøen is affected, but that there are no between-lake differences in their functional response (plasma cortisol levels). The lack of any differences between populations in baseline and handling-induced plasma cortisol levels may be interpreted as an intact ability of the Ellasjøen char to cope with stressors Pollutant exposure may cause breaks in the DNA strand in exposed individuals. Also this was examined in char from Bjørnøya. Char from Ellasjøen had a higher incidence of DNA double strand breaks than char from Laksvatn, and there was a significant correlation between strand breaks and contaminant levels. The results from this project show that Arctic char from Ellasjøen is affected by the contaminant cocktail, as clear responses on the molecular and physiological levels are revealed in fish with high contaminant concentrations (e.g. alterations in gene expression, DNA strand breaks, cytotoxicity, enzyme activity). However, no clear effects on functional level have been detected (e.g. stress response). Still, reduced fecundity may lead to a decreased reproduction rate. The char in Ellasjøen has been exposed to contaminants for many years and it is possible that physiological responses are adapted to the exposure.

It is well known that the Arctic is being affected by a range of contaminants, and that levels in top predators are high enough to cause effects. While we are rapidly gaining an understanding of how individual contaminants affect communities, investigatio ns of the effects of diverse contaminant mixtures in aquatic communities are rare. Many studies on Arctic organisms has shown correlations between contaminant concentrations and different physiological responses, but the actual cause - effect relationship is usually not identified, and it is not clear which contaminant is causing the effect. The overall objective of the project proposed here is to investigate how contaminant cocktails affect the performance of Arctic charr (Salvelinus alpinus), as well as how possible interactions between different contaminants affect the observed responses. We intend to use a combined approach, using in vitro tests and fieldbased studies, to increase the knowledge concerning effects of contaminant cocktails on Arctic ani mals. The fieldstudies will be carried out in two lakes on Bjørnøya: Lake Ellasjøen and Lake Laksvatn. The two lakes are located in close proximity, but have very different contaminant loadings. Previous studies havs shown that there are high levels of se veral persistent organic pollutants in fish from Lake Ellasjøen, while levels are low in fish from Lake Laksvatn. Fieldbased studies will give information about ecologically relevant effects, but from fieldstudies alone it will be difficult to conclude wh ich components of the contaminant cocktail is excerting the observed effects. Potential effects on reproduction, immune- and stress responses will be investigated. The in vitro studies will target the mixture effects (synergistic, antagonistic or additiv e) and the results will allow us to develop markers for use in in vivo studies.