With increasing oil exploration, production and transportation in the Arctic, predictions of the fate of spilled oil become important, including oil compound biodegradation. The use of chemical dispersants may result in increased biodegradation due to the generation of dispersions consisting of small oil droplets, but only few studies have focused on biodegradation of chemically dispersed oil in Arctic seawater. In this study we compared oil biotransformation in Arctic and temperate seawaters collected from Western Greenland (Disko Bay, surface and from 80 m depth) and a Norwegian fjord (Trondheimsfjord, surface). A naphthenic oil, premixed with a dispersant, was dispersed in the seawaters from the different sources, and the dispersions incubated in low concentrations in a carousel system at 4-5 °C for up to 64 days. Targeted oil compounds (n-alkanes, BTEX, naphthalenes and PAHs) were biotransformed in both Arctic and temperate seawaters, although the degradation was faster in the temperate seawater. In the Arctic seawater, transformation was faster in the surface than in the subsurface seawater. Calculations of biotransformation rates and half-lives of oil compound groups representing 70-80% of fresh oils also showed significantly faster depletion in the temperate than the Arctic seawater. Microbial analyses revealed differences between the bacterial communities in the seawater sources during oil biodegradation. The results emphasized, that oil compounds are biodegraded in Arctic seawater, but degradation potential and rates may vary between seawaters from different sources.

The risk of accidental oil spills in the Arctic is on the rise due to increased shipping and oil exploration activities, making it essential to calibrate parameters for risk assessment of oil spills to Arctic conditions. The toxicokinetics of crude oil components were assessed by exposing one lipid-poor (CIII) and one lipid-rich (CV) stage of the Arctic copepod Calanus hyperboreus to crude oil WSF (water-soluble fraction). Water concentrations and total body residues (BR), as well as lipid volume fractions, were measured at regular intervals during exposure and recovery. Bioconcentration factors (BCFs) and elimination rates ( k) for 26 petrogenic oil components were estimated from one-compartment models fitted to the BR data. Our parameters were compared to estimations made by the OMEGA bioaccumulation model, which uses the octanol-water partitioning coefficient ( K) in QSAR (quantitative structure-activity relationship) predictions. Our parameters for the lipid-poor CIIIs generally agreed with the OMEGA predictions, while neither the BCFs nor the ks for the lipid-rich CVs fitted within the realistic range of the OMEGA parameters. Both the uptake and elimination rates for the CVs were in general half an order of magnitude lower than the OMEGA predictions, showing an overestimation of these parameters by the OMEGA model.

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A numerical model has been developed and applied to serve the offshore industry to predict and report environmental risks associated with offshore discharges. The development has taken place over a time period of about 20 years, and is fully financed by the offshore operators. The model is fully fourdimensional (time and 3D space variations included) and covers the water column and sediment compartments.The model was first developed and applied to produced water discharges. Later, drilling discharges and coastal discharges (terminal releases) were included. At present, the "DREAM Charter" project focuses on revisions of the risk approach according to recent literature, validation of the numerical model by comparing with laboratory and field data, and also addresses the uncertainties in the predictions. Present