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An inside look at the science of cleaning up and fixing the mess of marine pollution

How Would Chemical Dispersants Work on an Arctic Oil Spill?


This is a post by John Whitney, OR&R’s Scientific Support Coordinator for Alaska.

An Arctic Cod rests in an ice-covered space.

An arctic cod, a key part of the Arctic food web, rests in an ice-covered space in Alaska’s Beaufort Sea, North of Point Barrow. This species was one of the subjects of the research program on dispersant effects in the Arctic. (Shawn Harper/Hidden Ocean 2005 Expedition: NOAA Office of Ocean Exploration)

If there were a huge oil spill in the Arctic, would chemical dispersants work under the frigid conditions there?

And once dispersants break down oil into smaller droplets, how toxic are the oil and chemicals to key species in the short Arctic food web?

Would the dispersed oil and dispersant actually biodegrade in cold Arctic waters?

With Shell currently on track to drill several exploratory wells in the Chukchi and Beaufort Sea this summer, these are very timely questions—and finally, we are beginning to find some answers.

For the last three years, a special oil industry research group (called a “joint industry program”) has been trying to resolve these questions before any major oil exploration, development, and production happens off the northern Alaskan Arctic coastline. Lead scientists Dr. Jack Word of Newfields Environmental (Port Gamble, Wash.) and Dr. Robert Perkins of University of Alaska, Fairbanks, coordinated this research program to determine the viability of using dispersants on Arctic Ocean oil spills.

Oil impacts on Arctic food webs

The illustration, not associated with this study, shows potential oil spill impacts to wildlife and habitats in the Arctic Ocean. Click for larger view. Credit: NOAA/Kate Sweeney, Illustration.

Aiming for as realistic Arctic conditions as possible, they captured arctic zooplankton (krill and Calanus copepods, which are tiny marine crustaceans) as well as larval and juvenile fish (arctic cod and sculpin) from the coastal waters of the Beaufort Sea.

These organisms are key players in the Arctic food web and culturing them in order to conduct toxicity tests hopefully would reveal how negative impacts from oil and dispersants could cascade through the ecosystem. The researchers also conducted toxicity and biodegradation tests in actual waters collected from the Beaufort Sea.

Five oil companies were pooling their talents and financial resources to conduct these tests and gather information: Shell, ConocoPhillips, Statoil, ExxonMobil, and BP. As NOAA’s Scientific Support Coordinator for Alaska, I was fortunate enough to serve on a unique, yet very important, part of the group: the Technical Advisory Committee, which is composed of non-industry technical and non-technical stakeholders. We met once a month to discuss the results and advise them on ongoing scientific tests.

Drs. Word and Perkins and their colleagues recently presented the results of this research at a workshop in Anchorage, Alaska. The workshop began with Tim Nedwed of ExxonMobil making a strong case for immediate and robust access to all the major oil spill response options—mechanical methods, in situ burning, and dispersants—in order to deal with a large oil release in the Arctic or any other location.

Mechanical methods (e.g., skimmers) and in situ burning typically encounter spilled oil at low rates, historically removing only 5% to 15% of the oil on the water’s surface. This makes chemical dispersants a very attractive option when approaching a big spill using a large aircraft (such as a C-130) to deliver dispersants. After all, Dr. Nedwed pointed out, the ultimate goal of dispersants is to deliver a significant boost to the rate of oil biodegradation that happens naturally after most oil spills.

Here are some of the major findings from their research:

  1. Arctic marine species show equal or less sensitivity to petroleum after exposure than temperate (warmer water) species.
  2. The Arctic test organisms did not show significant signs of toxicity when exposed to recommended application rates of the dispersant Corexit 9500 by itself, which also tends to biodegrade on the order of several weeks to a few months.
  3. Petroleum does biodegrade with the help of indigenous microbes in the Arctic’s open waters under both summer and winter conditions.
  4. Chemical dispersants more fully degraded certain components of oil than petroleum that was physically dispersed (for example, from wind or waves breaking up an oil slick).
  5. Under various scenarios for large and small oil spills treated with Corexit 9500, the effects on populations of arctic cod, a keystone species in the Arctic, appeared to be minor to insignificant.

This workshop garnered attention from the oil industry, government regulatory and natural resource agencies, academia, Alaska North Slope residents, private consultants, and non-governmental organizations. It concluded with a brief discussion of Net Environmental Benefit Analysis, a scientific process of weighing the costs against the benefits to the environment, with emphasis on the importance of making this process both science-based and, at the same time, compatible with listening to the subsistence Alaska Native population, a significant and valuable voice in the Arctic.

John WhitneyJohn Whitney has served as the Alaskan Scientific Support Coordinator for NOAA’s Office of Response and Restoration for over 25 years. His responsibilities include primary scientific support to the U. S. Coast Guard, as well as to industry, government agencies, and stakeholders for oil spills and other hazardous materials response in Alaska’s offshore waters. John’s background is in physics and geophysics, earning a PhD in geophysics from the University of Washington in Seattle. Currently, John participates in deliberations with the Arctic Council Emergency Preparedness, Prevention, and Response working group and also chairs the dispersant working group of the Alaska Regional Response Team.

Author: Office of Response and Restoration

The National Ocean Service's Office of Response and Restoration (OR&R) provides scientific solutions for marine pollution. A part of the National Oceanic and Atmospheric Administration (NOAA), OR&R is a center of expertise in preparing for, evaluating, and responding to threats to coastal environments. These threats could be oil and chemical spills, releases from hazardous waste sites, or marine debris.

5 thoughts on “How Would Chemical Dispersants Work on an Arctic Oil Spill?

  1. 1) The BP spill at Gulf of Mexico drew a response of 47,000 personnel and 7,000 vessels, and help from many individuals and NGOs – yet failed (terribly) to handle the big spill 2 years ago, and took months to disperse the oil. Shell will have only 22 spill response vessels and a containment apparatus staged near Arctic Ocean drilling sites. How does this compare?

    2) The link that you posted tells me that the “sensitivity (oil impact on an ice habitat) to oiling is poorly studied”. This is a direct from the scientific study. Would Shell be studying this aspect further before reconsidering the Arctic Project?

    3) The same study states that “Arctic marine species show equal or less sensitivity to petroleum after exposure than temperate (warmer water) species.” It does not tell how they would react to sudden massive amounts of chemical dispersant. Would Shell be able to share your findings, if any.

    4) According to the study, the oil dispersant will “biodegrade on the order of several weeks to a few MONTHS”. Is “several weeks to a few months” acceptable, and how much of these dispersant would be ingested by our Arctic animals before it biodegrades?

    5) Article states that “Petroleum does biodegrade” – how long will this take?

    6) Article states that “Chemical dispersants more fully degraded CERTAIN components of oil” – how about the other components of oil not mentioned here.

    7) Article states that “Under various scenarios for large and small oil spills treated with Corexit 9500, the effects on populations of ARCTIC COD appeared to be minor to insignificant.” – Article did not answer explain impact on ALL other animals.

    • Hi Jennifer,
      Thanks for your questions! I have forwarded your list of questions to John Whitney and our other NOAA scientists. I’ll be sure to let you know when they get back to me.
      ~Ashley, Office of Response and Restoration

    • Thanks, Jennifer — There are a lot of questions here and we are inviting the researchers at University of Alaska, Fairbanks, who are directly involved with the dispersant studies, to respond.

      Preventing spills is always better than applying chemicals to treat a spill, and we know that dispersants and other response options always involve trade-offs. Even booms, sorbent pads, and skimmers can cause injuries to shorelines and marine life.

      We know that once oil is spilled there is no way to prevent impacts, but there are ways to reduce the impacts. Dispersants are being studied in Arctic waters to see if, overall, they would reduce impacts from a spill. And the decision to use dispersants is never taken lightly; the state and U.S. Coast Guard and other response agencies would have to make that decision during a spill. Conducting studies such as these and discussing the very same questions you raise are important parts of being prepared before spills occur.

    • Hello Jennifer,

      I am a Ph.D. student at the University of Alaska Fairbanks and conducted the biodegradation experiments mentioned in the article above. Thank you for your interest and questions! Below are my answers to your questions pertaining to biodegradation (questions 4, 5 and 6). Please let me know if you would like any additional information.

      4) According to the study, the oil dispersant will “biodegrade on the order of several weeks to a few MONTHS”. Is “several weeks to a few months” acceptable, and how much of these dispersant would be ingested by our Arctic animals before it biodegrades?

      The large range (several weeks to a few months) is due to the method in which we measured biodegradation. Corexit 9500 is made up of two types of compounds: lipophilic and hydrophilic. Lipophilic compounds dissolve in oils, lipids and nonpolar solvents. Hydrophilic compounds dissolve in water and polar solvents. Because of this, the biodegradation of Corexit 9500 cannot be quantified using traditional gas chromatography-mass spectrometry (GC-MS) analytical techniques that rely on its ability to dissolve in nonpolar solvents. Instead of using GC-MS to measure the chemical loss of the individual compounds in Corexit 9500, we measured the amount of Corexit that arctic marine microorganisms were able to completely biodegrade to carbon dioxide (which is known as mineralization). As microorganisms break down carbon compounds, they consume oxygen. In this study, treatments containing Corexit 9500 consumed oxygen at a much higher rate than treatments containing oil, suggesting that Corexit 9500 is readily biodegradable by arctic marine microorganisms.
      Unfortunately, measuring the amount of dispersant or oil that could possibly be ingested by Arctic organisms was not part of this project. The objective of this study was to determine the toxicity to arctic cod and copepods as well as determine the biodegradation of crude oil and dispersed crude oil in the arctic open water environment.

      5) Article states that “Petroleum does biodegrade” – how long will this take?

      Petroleum is made up of many chemical compounds that degrade at different rates. This study measured the % loss of total petroleum hydrocarbons measured by gas chromatography-mass spectrometry in incubations with fresh seawater and Alaska North Slope crude oil with no added nutrients, in order to mimic natural conditions as much as possible. After 10 days of incubation at -1°C, 36% of the petroleum was biodegraded and after 28 days, 45% was biodegraded. At the end of the experiment (63 days), 58% of Alaska North Slope crude oil was biodegraded at -1°C and continued to progress at steady rates.

      6) Article states that “Chemical dispersants more fully degraded CERTAIN components of oil” – how about the other components of oil not mentioned here.

      Microorganisms have evolved to degrade petroleum hydrocarbons as a source of energy and carbon. Even in the absence of a chemical dispersant, such as Corexit 9500, microorganisms are able to degrade the majority of petroleum hydrocarbons. However, there are petroleum compounds that are resistant to biodegradation because they are not available to degradative microorganisms, due to their solubility or chemical structure. These compounds are mainly the asphaltenes and resins (like your asphalt driveway), which are fortunately less of an environmental concern due to their low toxicity. In this study, within the first 10 days, the presence of Corexit 9500 significantly increased the removal of total oil by 11%. As the experiment continued from day 10 to day 63, the arctic marine microorganisms continued to degrade oil; however, the difference between the treatments with and without dispersant became smaller as time progressed. This suggests that the use of dispersants might help accelerate oil biodegradation in the early stages of a spill.

    • To address the remainder of your questions (1-3, 7), the blog author John Whitney, supervisor of the Scientific Support Coordinators John Tarpley, and ecologist and dispersant expert Alan Mearns have answered them here:

      1.) NOAA does not regulate the oil spill response plans of offshore oil wells, but we do review contingency plans for potential environmental impacts. The Bureau of Safety and Environmental Enforcement ( regulates offshore operations in the United States. However, we can give you a little background and a general reply.

      Your question is a good one, but not necessarily a proper comparison. You are comparing what is in a contingency plan to an actual response (the Deepwater Horizon/BP spill, which was the largest oil spill response ever, worldwide). The number of vessels and other spill response equipment (e.g., skimmers, boom, boats, barges, storage capacity, etc) required by law is based on a worst case spill scenario. Each well (oil type, depth, and pressure) is different. A spill from a well in the Gulf of Mexico is not necessarily equivalent to a well elsewhere. Vessels, pipelines, and facilities are also regulated for spill planning and response. The methods to calculate the amount of equipment is not straightforward or simple enough to explain here.

      2.) We have no knowledge of and cannot speculate on what Shell may study in the future.

      3.) We cannot speak for Shell and the release of findings. As far as how species may react to dispersants, we believe it would be no different than how they react to naturally dispersed oil. If applied correctly, the environment should not receive a “sudden massive amount of chemical dispersant.” The standard application rate is 1 part dispersant to 20 parts or more of oil.

      7.) Juvenile arctic cod were one of two species chosen for this toxicity testing activity because they are at the center of Arctic marine food webs and can be sampled and cultured. There are literally thousands of species of marine animals and plants worthy of testing, but it is not practical or economically feasible to test them all. Ecotoxicologists, under U.S. EPA guidelines for ecological risk assessment, therefore use data from smaller suites of species representing various types of organisms (crustaceans, mollusks, fish) and life stages (eggs, embryos, larvae, juveniles, and adults) and plot the resulting data to form species sensitivity distributions. The resulting data represent a wide range of sensitivities to dispersants and to toxic compounds in oil, from very tolerant (not sensitive) to very sensitive species.

      Dozens of marine and estuarine species, representing microbes and worms to crustaceans, mollusks, corals, fish, and birds, have been subjected to dispersant and dispersed oil toxicity testing. They, and their various life stages, indeed range in sensitivity to both dispersants and dispersed oil. From these several dozen species and life stages, scientists believe they can extrapolate the results to many of the other species. Furthermore, it is the most sensitive among the tested species and life stages that toxicologists use to define what is safe and what is harmful to all species.

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