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Synergistic effects of DISpersant, oil and HYpoxia in a teleost fish: Investigating the impact of oil contamination in hypoxic areas and the use of dispersant as a response technique

Periodic Reporting for period 1 - DISHY (Synergistic effects of DISpersant, oil and HYpoxia in a teleost fish: Investigating the impact of oil contamination in hypoxic areas and the use of dispersant as a response technique)

Reporting period: 2015-04-30 to 2017-04-29

Coastal marine ecosystems are under anthropogenic pressures. Among these anthropogenic pressures, two major growing threats are represented by hypoxia and oil pollution. However, very little is known about the biological impacts of their interaction. Consequently, this project evaluated the potential biological effects caused by oil pollution in hypoxic situations. Furthermore, this project considered the effect of dispersant use as a response technique for oil released in hypoxic areas. The research carried out during the project assessed the interactive biological effects of dispersant, oil and hypoxia on the teleost Dicentrarchus labrax. The approach firstly evaluated the hydrocarbon contamination induced by the interaction of stressors (Work Package 1, WP1). Then, biological effects were evaluated at the sub-individual level, by assessing sensitive indicators related to oxidative stress (Work Package 2, WP2). Finally, ecologically-relevant indicators related to fish behaviour, locomotion and metabolism, were assessed at the organismal level (Work Package 3, WP3).
In summary, our results showed a persistence of hydrocarbon compounds in organisms when the fish were exposed to chemically-dispersed oil (dispersant + oil) or when hypoxic conditions follow the contamination by oil (oil +hypoxia). Surprisingly, regarding hydrocarbons bio-concentration, no cumulative effect of both interaction (dispersant+oil+hypoxia) was detected.
At the cellular level, regarding the biomarkers of antioxidant defense, some significant effects were observed in the liver. However, regarding oxidative stress, it was only observed in the gills. Such antioxidant responses and oxidative stress have been shown to be transitory, suggesting no long term impact on cellular integrity. However, many other biological parameters than just oxidative stress and antioxidant response (such as cancer development and/or DNA damage) should be observed before drawing such a conclusion about long term impact of hydrocarbon compounds on cellular integrity.
At the individual level, an important impact was observed on escape responses when fish were exposed to hypoxia or oil. Maneuverability, directionality and escape trajectories were impacted by each experimental treatment. Moreover, our results suggest a cumulative impact of oil plus hypoxia treatment on escape response parameters. Regarding the metabolic parameters, the main results showed a reduction of the aerobic metabolic scope due to oil and an even more intense reduction due to hypoxia.
To conclude, this project provides scientific results situated at the cutting edge in the field of the impact of oil pollution on marine organisms, as well as progress beyond the state of the art concerning the effect of hydrocarbons on aquatic ecosystems. Such an impact on European research and development is being achieved through publications of papers, participation to congresses and through a workshop joining together the partner organization, stakeholder and experts in oil contamination.
This project was divided in three objectives corresponding to three work packages.
The first work package (Evaluation of the Synergistic effects of oil, dispersant and hypoxia on hydrocarbons contamination) was completely achieved and, moreover, additional work was conducted to improve the scientific quality. Briefly, results of this work package showed a bioaccumulation of the PAHs lighter compounds only (e.g. naphthalene, pyrene) for contaminated fish. Interestingly, the decontamination was more effective in normoxia than in hypoxia, probably due to a lower induction of detoxication process of PAHs when fish are exposed to hypoxia.
Concerning, the second work package (Evaluation of the Synergistic effects of oil, dispersant and hypoxia on oxidative stress and antioxidant responses), some limits were observed and some changes considered. Indeed, no enzyme activity was detected in the heart and the brain so that we evaluated enzyme activity of Superoxide dismutase (SOD), Malondialdehyde (MDA), Ethoxyresorufin-O-deethylase (EROD), reduced glutathione (GSH) on the liver, the gills and the muscles of fish. Briefly, results showed a transitory response of these biomarkers, but no long-term effects. It could be of interest to observe other mechanisms and other stress (e.g. carcinogenicity and mutagenicity) induced after the decontamination period.
The third work package (Evaluation of the Synergistic effects of oil, dispersant and hypoxia on individual performance and metabolic parameters) was achieved up to 60 % and was supplemented with additional work: 2 of the 3 conditions (hypoxia and hydrocarbons contamination) were investigated, while on the other hand, twice more biological parameters were observed concerning the escape response (individual performance) of the fish and chemical analysis were conducted to complete this objective. Results showed that maneuverability, directionality and escape trajectory parameters were impacted by hydrocarbons and hypoxia. The novel integrative parameter called “distancing” showed that the higher impact was observed when fish were exposed to both hydrocarbons and hypoxia. Concerning metabolic parameters, our results showed a decrease of aerobic metabolic scope when fish are exposed to hydrocarbons and hypoxia but no summation of the effects by the treatments was observed.

Regarding the exploitation and dissemination of the results, the fellow (i) invited 2 schools to expose them the project; (ii) gave a public talk during the scientific session of the 2016 Brest's International Maritime Festival; (iii) made a web based document. This exploitation and dissemination of results is still in progress through the publication of scientific papers in journals and the dissemination in congress. Additionally, a workshop should be organized by the partner organization by the end of the year.
Results of the first and the third work package are particularly interesting since they showed respectively (i) a lower decrease of hydrocarbons compounds in organisms decontaminated in hypoxic conditions suggesting a lower resilience of hypoxic ecosystems; (ii) an impact of hydrocarbons and hypoxia on some biological parameters linked with the fitness of the individual, suggesting an impact at the population level. Such results, situated at the frontier of knowledge (since no scientific already evaluated the impact of the interaction hydrocarbons + hypoxia), will contribute to an intense progress beyond the state of the start, particularly in research fields investigating the effects of interactive parameters on marine ecosystems. The dissemination of the results will probably also contribute to highlight the novel thematic of the project and will enhance the interest for it.
Concerning the socio-economic impacts and implications, results are supposed to alert policy makers on the environmental impact of hydrocarbons contamination in hypoxic areas and also to help oil-spill responders teams in their decision-making processes. Moreover, investigation on dispersant toxicity conducted in this project could lead to innovation of environmental benefits in the framework of the partnership between the partner organization and industrials.
Taken together, outcomes of this project participate to maintain a good environmental status of the marine ecosystems.