Spill Scenario / Option

When an oil spill occurs offshore in the polar environment the components (and degradation products) the process of natural degradation and dispersion of the spilled oil spill begins immediately in the ecosystem, albeit sometimes at slower rates than in more temperate climates. The spilled oil is incorporated into aquatic and atmospheric compartments, and may be evident in nearshore land-based compartments, as well, if the spill occurs within proximity to coastal resources. The objective of spill response actions is to isolate and contain spilled oil, and to reduce adverse consequences to the ecosystem as quickly as possible after the spill event. Consistent with international practices, initial oil spill response actions are aimed at achieving several objectives concurrently: modification of the physical and chemical nature of the spilled oil to minimize dispersion and impacts to wildlife; reduction of the concentrations of potentially toxic constituents of the spilled oil through dilution or enhancement of natural biodegradation processes; and, avoidance of impacts to populations of sensitive or less resilient aquatic and terrestrial wildlife.

In the Arctic, achieving these objectives is improved through careful spill response planning and preparedness and the use of simulation exercises involving analytical tools similar to Net Environmental Benefit Analysis (NEBA) and databases such as Arctic Consequence Analysis Tables. These tools facilitate examination of the consequences of different oil spill response strategies, and help to shape oil spill response plans that are most relevant and most effective in the environment.

Although the premise is largely the same, different terminology is sometimes used to define key concepts in the NEBA process. For the purposes of this summary, the terminology used (e.g., Potential for Exposure, Potential for Effects, and Receptor Sensitivity) is consistent with recent NEBA and Spill Impact Mitigation Analysis (SIMA) work conducted in Arctic environments.

Habitats and Resources

The Arctic is defined as the region north of the Arctic Circle (66°33' N). In general, this region is characterized by average warmest summer temperatures <10° C. The marine environment includes the Arctic Ocean, Baffin Bay, Beaufort Sea, Barents Sea, Bering Sea, Bering Strait, Chukchi Sea, Davis Strait, Denmark Strait, East Siberian Sea, Greenland Sea, Hudson Bay, Kara Sea, Laptev Sea, Nares Strait, and the Norwegian Sea.

In the Arctic, Environmental Compartments (ECs) are defined as physical features of the environment that are representative of the different primary habitats found in the Arctic. The basic compartments include the atmosphere, pelagic ocean environments, and convergence zones at the air/water, water/water, ice/water, and sediments including shorelines. Many ECs are relatively stable in position or size such as multi-year ice, river mouths, barrier islands, shorelines and submerged features and these can be mapped prior to any event. Other ECs, including annual ice and open pelagic water coverage, convergence zones of water masses, specialized ice edges such as polynyas and location of pressure ridges may vary temporally (either seasonally or inter-annually) and geospatially.

In the Arctic, Valued ecological components (VECs) are defined as species or groups of species that represent the resources at risk targeted for protection in the context of deploying different OSR actions. VECs may be isolated to one EC; however, it is more common for most Arctic species to inhabit, forage and/or spawn in several aquatic, shoreline and inland ECs and habitats. A NEBA-based analysis can be performed by combining the taxa groups present in the affected area into defined VEC groupings, except in instances where one key species or specific community is central to evaluating the level of concern. In such cases, the analysis may be customized to include species that are important to specific regions. Generally, VECs include taxa with all or some of the following characteristics:

  • Taxa that are important to the function of Arctic food webs;
  • Taxa that are representative of pelagic, benthic, and sea-ice realms;
  • Taxa that are relatively abundant;
  • Taxa that are threatened or endangered; and,
  • Taxa that may have cultural or commercial importance.

Oil spill response planning and preparedness must carefully consider changes to both environmental and ecological conditions that occur periodically in the Arctic. The condition of different nearshore and offshore ECs and the status of different VECs will vary at different times of the year in response to changing seasons, climate conditions, reproductive requirements, and food resources. In the absence of sufficient knowledge, oftentimes the conservative approach in spill response simulation exercises is to assume that EC and VEC conditions are robust regardless the time of year.

Potential for Exposure

The consequences of spilled oil and oil spill response actions on ECs and VECs reflects the potential for effects and the potential for recovery from those effects. The potential for effects is based on two factors: the exposure potential; and, the sensitivity of the taxa to exposure. Exposure potential is an important consideration for differentiating between different oil spill response options. When oil is released into the marine environment, the constituents of the spilled oil and its degradation products are incorporated into different environmental compartments, depending on the chemical and physical properties of both the spilled oil and the receiving environment.

One of the objectives of oil spill response is to reduce or eliminate the exposure potential, particularly for more sensitive or less resilient VECs. Oil spill response strategies aim to achieve this objective by either changing the chemical or physical form of the spilled oil; reducing the concentrations of any toxic constituents in the spilled oil through dilution or enhanced biodegradation; or, by moving the spilled oil away from ECs and locations inhabited by sensitive or less resilient VECs. .

In a NEBA-type analysis used to support oil spill response planning and preparedness, four primary pathways are considered for evaluation of exposure potential. Each exposure type may also result in different modes of action that may have consequences related to interference with temperature control or buoyancy, gill or lung tissue disruption during respiration, impacts on sensitive tissues, and forage behavior or foraging success if essential food resources are impacted by the spill event. .

  1. Fouling: This includes the coating of an organisms’ outer surfaces such as skin and feathers. Fouling can impact external respiratory structures, feeding structures, and swimming behavior.
  2. Respiratory: This includes contact with water dissolved or airborne volatile fractions of spilled with respiratory tissues, as well as aspiration of spilled oil, constituents of the spilled oil, or its degradation products.
  3. Direct Contact: This is related to with water dissolved or airborne volatile fraction exposure to sensitive tissues such as gills and eyes, as well as acute and chronic exposure to either fresh or weathered spilled oil, constituents of the spilled oil, or its degradation products.
  4. Uptake into Tissues: The uptake of spilled oil, constituents of the spilled oil, or its degradation products via the respiration, ingestion (either directly or via the food chain), or absorption pathways may result in the accumulation of substances to a critical body burden level sufficient to have adverse consequences to VECs.

Receptor Sensitivity

Receptor (or VEC) sensitivity to oil can be qualitatively or quantitatively estimated in Arctic risk assessment. Different pathways of exposure should be considered to ensure the exposure routes presenting the greatest risk or vulnerability for a VEC are addressed by the analysis. As described above, potential pathways of exposure include fouling (adherence of oil to the animal); respiratory (impairment of breathing or oxygen exchange in water); direct contact through acute exposure in the water-column; and direct contact through chronic exposure.

The literature reference database summarizes currently available ecotoxicity studies involving Arctic organisms exposed to different types of crude oil under specific conditions for a given amount of time. Such studies provide information on both the concentration of oil needed to elicit a negative biological effect and the relative toxicity of different OSR options.

While there are some examples of field toxicity studies, most toxicity studies performed on Arctic fish, invertebrate and algal species are laboratory studies under controlled conditions. Acute toxicity studies with Arctic species have been conducted with physically and chemically dispersed oil, in-situ burn residues with a variety of different types of oil, as well as pure PAH compounds (e.g. 2,4 methylnaphthalene). Test exposures have included continuous and “spiked” exposures. Continuous exposures are applicable to environmental scenarios where the VECs are likely to be exposed to oil and oil spill residues for a prolonged period, whereas spiked exposures simulate a declining concentration, where there is an initial pulse of oil or treated oil and then the concentration declines quickly to near background levels. Longer duration, chronic tests have been conducted with both Arctic fish and invertebrates and often evaluate sub-lethal endpoints. A summary of acute and chronic studies is presented in the literature reference databases.

The biological effects of physical contact of oil with respiratory organs (i.e. lungs and gills) and the outer body of the organism should also be considered; this is especially important for birds and marine mammals. Disruption of the insulation properties of feathers and fur resulting from oil fouling can lead to hypothermia and the loss of buoyancy.

In a NEBA evaluation, toxicity thresholds derived from species sensitivity distributions are generally used to define the potential for effects related to petroleum hydrocarbons and OSR residues such as dispersant and ISB residues.

Potential for Effects

In the Arctic, spill response planning and preparedness and the use of simulation exercises involving analytical tools similar to Net Environmental Benefit Analysis (NEBA) and databases such as Arctic Consequence Analysis Tables typically assume the potential for effects is based on consideration of the exposure potential and the sensitivity of VECs that may contact spilled oil either directly or indirectly.

Oftentimes, the results of oil spill modeling conducted to support NEBA–type analytical tools are used to predict the level of potential effects for different possible exposure pathway in two ways:

  1. Where exposure concentrations are predicted by trajectory models and toxicity thresholds are available for the VECs, the predicted effects will be based on a direct comparison to identify areas that exceed effects based quantities of oil components or OSR residuals.
  2. Where exposure concentrations are predicted by trajectory models but toxicity data are not available (e.g. marine mammals) then a combination of modeling runs combined with a semi-quantitative risk estimate for species will be used to estimate the area or volume of water or air that exceeds the effects based levels.

The results of oil spill modeling inform different EC exposures to the constituents of spilled oil and consequences of different oil spill response options. The mode of action for adverse responses to these residuals will vary depending on the exposure pathway inhalation, fouling, and uptake. Information on the location and size of the EC relative to the location and trajectory of the spilled oil and oil spill response options is required to make decisions regarding response actions.

Population Exposed: An estimate of the percentage of the population in the study area that is exposed to oil or OSR residues. Such estimates are particularly important if certain VECs are absent or have a population distribution that is heavily skewed to a portion of the study area. If desired, an estimate of Population Exposed can be used in NEBA-type analyses as a multiplier to adjust the original estimate of Potential for Effects.

Recovery and Resilience

The primary objective for oil spill response is to reduce adverse impacts and foster recovery of resources in the shortest time possible. This objective reflects the desire to re-create stability within the environment after disturbance. Two aspects of EC and VEC exposure to spilled oil are important to consider in NEBA-type analysis– the time to recovery to a stable and sustainable state after an oil spill event, and the resilience of the EC and VEC to withstand the changed conditions caused by an oil spill event with minimal consequences.


The ability of ECs and VECs to recover after an oil spill event is an important consideration in oil spill response planning and preparedness and can influence decisions regarding the deployment of oil spill response options. The time to recovery of individuals, VEC populations, and communities is related to biological characteristics that contribute to survival of the VEC or ecological condition such as sensitivity of the VEC to different types of disturbance, population age structure, age to fecundity, progeny produced per year, natural mortality rates, propensity of species to congregate in high abundance, and near and far field migratory potentials.

There are two general recovery responses by which VECs recover from disruptions in the ecosystem: the migration of individuals from unaffected areas, and reproduction of affected populations. With respect to the first recovery mechanism, many Arctic VECs are widely distributed in the Arctic, adaptable to a broad range of habitat conditions, and have a large migratory range. With respect to the second recovery mechanism, the life history characteristics of the VECs control reproductive output and the ability for a population to return to pre-spill abundance or biomass condition. There are several important features that facilitate VEC recovery, including the inherent age class and mortality rates of the VEC, age to maturity (weeks to decades), fecundity, reproductive cycles and the timing of impacts relative to those cycles, age related to progeny production, and fitness of progeny for survival in a disrupted environment.

In either case, it is possible that an oil spill event or similar environmental disturbance can be sufficient to cause a regime shift whereby recovery to pre-existing conditions is unlikely. The EC and VEC evolve to a new stable and sustainable condition that may not be identical to conditions prior to the disturbance event.


Ecological resilience is an alternate way to assess recovery that focuses on the capacity of the ecosystem, or the individual EC elements of that ecosystem, to absorb temporary disturbances until the ecosystem is able to return to a state that provides essentially the same function, structure and identity as prior to the disturbance. Few research studies distinguish resilience from recovery when reporting on field work, and as such, these terms are sometimes used interchangeably. Resiliency is measured by the time it takes for the impact to be accommodated by recovery of the damaged population to pre-spill abundance or fitness levels that are equal to historical natural ranges of variation. Resilience of a community of organisms within an EC includes other species using the EC that may be co-dependent upon the VEC.

Theoretical Impact

Theoretical impact represents the combined potential for VEC exposure, effects, and recovery for the studied oil spill scenarios and OSR alternatives. By applying a framework that determines the theoretical impact for each VEC in each Arctic EC, planners and responders can examine the consequences of different oil spill response strategies and determine which strategies are most relevant and predict their effectiveness in the environment. To achieve this aim, scientific data from the literature reference portal can be used to estimate theoretical impact and implement a more quantitative NEBA analysis. Because the literature is indexed by OSR alternative and critical NEBA parameters, it can be readily paired with fate and transport modeling and mapped to relative scoring that allows for VECs and ECs to be evaluated and compared between different OSR alternatives.