Combined Effects of Perfluorooctane sulfonic acid (PFOS) and Carbon dioxide (CO2) on oxidative stress responses in the gill of Atlantic cod (Gadus morhua)

Increasing levels of anthropogenic CO2 in atmosphere and aquatic environment have been regarded as significant force behind global climate changes. The aquatic environment is also a heavy recipient for pollutants embedded in among others municipal and industrial wastewater. Despite this, very little effort has currently been put in investigating the potential toxic effects of aquatic pollutants on aquatic organisms (fish) in a continuously changing aquatic environment driven by global climate change. In the present study, juvenile Atlantic cod (gadus morhua) were exposed to Perfluorooctane sulfonate (PFOS; 0, 100 and 200 μg/L) for 1hour per day in a total of 5 days, and thereafter transferred to water tanks containing; 0%, 0.3% and 0.9% CO2 for 3, 6 and 9 days. Oxidative stress responses in gills upon exposure to PFOS and elevated CO2 levels, singly or in combination were evaluated. Real-time RT PCR was in gene expression analysis of; peroxisome proliferator-activated receptor β (ppar-β), Acyl-CoA oxidase (acox) and selected antioxidant genes. Enzyme activity levels of selected antioxidant enzymes and the total content of reduced glutathione and malondialdehyde were measured spectrophotometrically. Generally, single exposure to PFOS or elevated CO2 levels had a weak effect on the transcription of peroxisomal β-oxidation related genes (ppar-β and acox). However, an increase in mRNA levels of these genes was observed upon combined exposure to both stressors (though not significantly). An apparently CO2 dependent increase in mRNA levels for gpx1 and gpx3 at day 6, and SOD activity at day 9 was observed in fish exposed to a combination of high PFOS (200 μg/L) and CO2-this indicated presence of high cytosolic ROS levels. An apparent time-dependent decrease in activity of all antioxidant enzymes was generally observed in most of the exposure groups at day 9. Overall, the alterations in gene expression and/or enzyme activities of both peroxisomal β-oxidation related genes and antioxidant defenses suggest that both PFOS and elevated CO2 might induce oxidative stress, however, combined exposure to these stressors apparently enhances this effect. The apparent interactive effect between PFOS and elevated CO2 observed in this study suggests that the toxicity of aquatic pollutants could be modified under environmental hypercapnia-and this could adversely affect aquatic organisms in numerous ways