Sublethal effects in Atlantic salmon (salmo salar) exposed to metals and radiation alone or in combinations

Recently increased focus has been put on risk associated to multiple stressors, e.g exposure to metals, radiation and organic pollutants in combination. Concentrations of a stressor that alone is not able to cause a significant effect can, in combinations with other stressors, lead to significant damage through additive or synergistic effects, or in some cases also reduce the impact by acting antagonistic. The objective of the present work was to identify effects on Atlantic salmon (Salmo salar) from individual or combined exposures of copper (Cu: 10, 40 and 80 µg/L), low dose gamma radiation (?: 4, 17 and 70 mGy) and aluminium (Al: 250 µg/L) after 48 hrs of exposure. A range of endpoints were investigated; the bioavailability/reactivity of Cu and Al were determined by measuring gill accumulation of Cu and Al, effects on ion-regulatory mechanisms were determined by analysing plasma ions (sodium and chloride), general stress were determined by analysing plasma glucose, oxidative stress was determined by analysing reduced and oxidised glutathione (GSH/GSSG) and the gene expression of gamma-glutamylcysteine synthetase and glutathione peroxidase. In addition, gene expression of metallothionein was analysed as a marker for both metal exposure and oxidative stress, and ubiquitin as a marker for protein degradation. Finally, since speciation is well known to influence metal toxicity, the exposure waters were characterized with respect to physico-chemical forms of the added metals. The results show that exposure to Cu and Al alone induced measurable effects on several of the investigated endpoints. The combined metal exposure seemed to be antagonistic or less than additive for many of the endpoints, in particular when effects were assessed at the gene transcription level. Adding radiation as a co-stressor to the metals only affected the glutathione system in the lowest Cu exposure. All in all, the results indicate that complex effects may occur when fish are exposed to multiple stressors, and mode of action seems to be both stressor and (concentration) dose-dependent.