NOAA's Response and Restoration Blog

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

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NOAA Is Supporting Oil Spill Response in Kentucky After Tugs Collide on Mississippi River

On the evening of September 2, 2015, two tug boats collided on the Mississippi River near Columbus, Kentucky, spilling slurry oil into the river.

Early reports, which later may be corrected, indicate an estimated 120,500 gallons of oil were released from a hole in the cargo tank of a barge being towed by the tug Dewey R during the collision. The spill and ensuing response closed the river between mile markers 938 and 922, south of Paducah, Kentucky, but the waterway was reopened to vessel traffic as of September 8.

At the request of the U.S. Coast Guard, NOAA’s Office of Response and Restoration is supporting the response and sending oil spill and data management experts to the scene of the spill. NOAA scientific support coordinators are providing a variety of information for the response, including river flow forecasts, chemistry of the spilled oil, a submerged oil assessment (because this heavier oil may sink), and other information to help determine where the spill will go and what can be done to protect our waterways and keep commerce moving.

The natural resource agencies also are beginning to assess potential impacts to natural resources, a first step to determining whether restoration is needed as a result of the spill.

Updates from NOAA about this oil spill may be available on IncidentNews.

What Is Slurry Oil?

Slurry oil is a residual oil resulting from the refining process and when spilled, most of it will sink or become suspended in the water column. A U.S. Coast Guard overflight the morning of September 3 revealed a floating sheen of oil four to five miles downstream of the discharge, which is not unexpected with this type of heavy oil.

Learn more about different types of oil and their behaviors when spilled and read about a 2005 slurry oil spill in the Gulf of Mexico.

How Is an Oil Spill in a River Different Than One in the Ocean?

From dams and density to muddy waters and vegetation, rivers offer a very different environment than the ocean during an oil spill.

Read more about the kinds of unique challenges we have to consider during an oil spill in a river.

More Information About Oil Spills

Find basic information related to oil spills, cleanup, impacts, and restoration, as well as NOAA’s role during and after oil spills.

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It Took More Than the Exxon Valdez Oil Spill to Pass the Historic Oil Pollution Act of 1990

Aerial view of Exxon Valdez tanker with boom and oil on water.

While the tanker Exxon Valdez spilled nearly 11 million gallons of oil into Alaskan waters, a trifecta of other sizable oil spills followed on its heels. These spills helped pave the way for passage of the Oil Pollution Act of 1990, which would vastly improve oil spill prevention, response, and restoration. (NOAA)

If you, like many, believe oil shouldn’t just be spilled without consequence into the ocean, then you, like us, should be grateful for a very important U.S. law known as the Oil Pollution Act of 1990.

Congress passed this legislation and President George H.W. Bush signed it into law 25 years ago on August 18, 1990, which was the summer after the tanker Exxon Valdez hit ground in Prince William Sound, Alaska. On March 24, 1989, this tanker unleashed almost 11 million gallons of oil into relatively pristine Alaskan waters.

The powerful images from this huge oil spill—streams of dark oil spreading over the water, birds and sea otters coated in oil, workers in shiny plastic suits trying to clean the rocky coastline—both shocked and galvanized the nation. They ultimately motivated the 101st Congress to investigate the causes of recent oil spills, develop guidelines to prevent and clean up pollution, and pass this valuable legislation.

Yet that monumental spill didn’t fully drive home just how inadequate the patchwork of existing federal, state, and local laws were at addressing oil spill prevention, cleanup, liability, and restoration. Nearly a year and a half passed between the Exxon Valdez oil spill and the enactment of the Oil Pollution Act. What happened in the mean time?

The summer of 1989 experienced a trifecta of oil spills that drained any resources left from the ongoing spill response in Alaska. In rapid succession and over the course of less than 24 hours, three other oil tankers poured their cargo into U.S. coastal waters. Between June 23 and 24, the T/V World Prodigy spilled 290,000 gallons of oil in Newport, Rhode Island; the T/V Presidente Rivera emptied 307,000 gallons of oil into the Delaware River; and the T/V Rachel B hit Tank Barge 2514, releasing 239,000 gallons of oil into Texas’s Houston Ship Channel.

But these were far from the only oil spills plaguing U.S. waters during that time. Between the summers of 1989 and 1990, a series of ship collisions, groundings, and pipeline leaks spilled an additional 8 million gallons along the United States coastline. And that doesn’t even include another million gallons of thick fuel oil released from a shore-side facility in the U.S. Virgin Islands after it was damaged by Hurricane Hugo.

Birds killed as a result of oil from the Exxon Valdez spill.

Thanks to the Oil Pollution Act, federal and state agencies can more easily evaluate the full environmental impacts of oil spills — and then enact restoration to make up for that harm. (Exxon Valdez Oil Spill Trustee Council)

Can you imagine—or perhaps remember—sitting at home watching the news and hearing again and again about yet another oil spill? And wondering what the government was going to do about it? Fortunately, in August of 1990, Congress voted unanimously to pass the Oil Pollution Act, which promised—and has largely delivered—significantly improved measures to prevent, prepare for, and respond to oil spills in U.S. waters.

Now, 25 years later, the shipping industry has undergone a makeover in oil spill prevention, preparedness, and response. A couple examples include the phasing out of tankers with easily punctured single hulls and new regulations for driving tankers that require the use of knowledgeable pilots, maneuverable tug escorts, and an appropriate number of people on the ship’s bridge during transit.

Oil spill response research also received a boost thanks to the Oil Pollution Act, which reopened a national research facility dedicated to this topic and shuttered just before the Exxon Valdez spill.

But perhaps one of the most important elements of this law required those responsible for oil spills to foot the bill for both cleaning up the oil and for economic and natural resource damages resulting from it.

This provision also requires oil companies to pay into the Oil Spill Liability Trust Fund, a fund theoretically created by Congress in 1986 but not given the necessary authorization until the Oil Pollution Act of 1990. This fund helps the U.S. Coast Guard—and indirectly, NOAA’s Office of Response and Restoration—pay for the upfront costs of responding to marine and coastal accidents that threaten to release hazardous materials such as oil and also of assessing the potential environmental and cultural impacts (and implementing restoration to make up for them).

This week we’re saying thank you to the Oil Pollution Act by highlighting some of its successes in restoring the environment after oil spills. You can join us on social media using the hashtag #Thanks2OilPollutionAct.

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How Is an Oil Spill in a River Different Than One in the Ocean?

Boat with boom next to oil mixed with river bank vegetation.

The often complex, vegetated banks of rivers can complicate cleaning up oil spills. (NOAA)

Liquid asphalt in the Ohio River. Slurry oil in the Gulf of Mexico. Diesel in an Alaskan stream. Each of these oil spills was very different from each other, partly because they involved very different types of oils.

But even if the same type of oil were spilled in each case, the results would be just as distinct because of where they occurred—one in a large inland river, one in the open ocean, and one in a small coastal creek.

In many cases, oil tends to float. But just because an oil floats in the saltwater of the Atlantic Ocean doesn’t mean it will float in the constantly moving freshwater of the Mississippi River.

But why does that happen? And what else can we expect to be different when oil spills into a river and not the ocean?

Don’t Be Dense … Blame Density

To answer the first question: When oil floats, it is generally because the oil is less dense than the water it was spilled into. The more salt is dissolved in water, the greater the water’s density. This means that saltwater is denser than freshwater. Very light oils, such as diesel, have low densities and would float in both the salty ocean and freshwater rivers.

However, very heavy oils may sink in a river (but perhaps not on the ocean), which is what happened when an Enbridge pipeline carrying a diluted form of oil from oil sands (tar sands) leaked into Michigan’s flooded Kalamazoo River in 2010. The lighter components of the oil quickly evaporated into the air, leaving the heavier components to drift in the water column and sink to the river bottom. That created a whole slew of new challenges as responders tried new methods of first finding and then cleaning up the difficult-to-access oil.

Going with the Flow

In rivers, going with the flow usually means going downstream. Except when it doesn’t. When might a river’s currents carry spilled oil upstream?

At the mouth of a river, where it meets the ocean, a large incoming tide can enter the river and overwhelm the normal downstream currents. That could potentially carry oil floating on the surface back upstream.

In open areas, such as on the ocean surface, both winds and currents have the potential to direct where spilled oil goes. And along most coasts, wind is what brings spilled oil onto shore.

In rivers, however, the downstream currents usually dominate the overall movement of oil while wind direction often determines which side of the river oil ends up on.

Locks and Other Blocks

Unlike the ocean, rivers sometimes feature structures such as dams, locks, and other barriers that block or slow down the free flow of water. During an oil spill on a river, these structures can also slow down the movement of oil.

That’s a helpful feature for responders who are trying to catch up to and clean up that oil. Frequently, dams and locks cause oil to pool up on the surface next to them. Some of the tools responders use to collect oil from these areas include skimmers, which are devices that remove thin layers of oil from the surface, and sorbent pads and booms, which are large squares and long tubes of special material that absorb oil but not water.

In fact, the banks of the river can constrain spilled oil as well. Because the oil can’t spread as far or thin as in open water, oil slicks can be thicker on rivers, and recovery efforts can be more effective.

One exception is the case of flow-over dams, known as weirs. The water passing over weirs can be very turbulent, causing oil to disperse into the water column. If it is very light oil and there’s not very much, that oil tends not to resurface and form another slick. But sheens may resurface with heavier oils that might be broken up going over a weir but later resurface as the water it is traveling in becomes calmer downstream.

Vegging Out

Oil rings on trees next to a river with boom.

Flooding on the Kalamazoo River in Michigan during the Enbridge pipeline oil spill left a ring of oil around trees and other vegetation after the river returned to its normal level. (NOAA)

Often, plants grow in rivers and line their banks, whereas many parts of the coast are open sandy or rocky beaches, which tend to be easier to clean oil off of than vegetation. (Salt marshes and mangroves being notable oceanic exceptions.) If oil gets past booms, the long floating barriers responders use to prevent the spread of oil, and leaves a coating on plants, then plant cleanup options generally include cutting, burning, treating with chemical shoreline cleaners, or flushing vegetation with low-pressure water.

Plant life actually became an issue during the oil sands spill in Michigan’s Kalamazoo River. Because this river was flooded at the time of the spill and later returned to its normal level, oil on the river surface actually became stranded in tree branches along the riverbanks.

Muddying the Waters

Another issue for oil spills in rivers is sediment. Rivers often carry a lot of sediment in their currents. (How do you think the Mississippi got its nickname “Big Muddy”?) That means when oil droplets drift into the water column of a river, the sediment has the potential to stick to the oil droplets. Eventually (depending on how strong-flowing and full of sediment a river is) some of the oil-sediment combination may settle out to the bottom of the river, usually near the river mouth as the water slows down and reaches the ocean.

One notable example is related to an oil spill that happened on the Mississippi River in New Orleans in 2008. The tanker Tintomara collided with Barge DM932, ripping it in half and releasing all of the heavy fuel oil it was carrying. Downstream of where the responders were cleaning up oil, the Army Corps of Engineers was dredging the sediments that build up at the mouth of the Mississippi and an oily sheen appeared in the collected sediment.

Responders suspected the oil from Barge DM932 had mixed with the river sediment and fell to the bottom further downstream as the river neared the Gulf of Mexico.

Learn more about oil spills in rivers at

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Orange Oil Is the New Black

Sorbent pads soaking up orange oil on the surface of a creek.

Even something as pleasant-smelling as orange peel oil can have potentially harmful effects on aquatic life. A view of the spill with some absorbent cleanup materials not far from Orange, New Jersey. (U.S. Coast Guard)

Orange is a common color in oil spill response.

Life jackets, rain gear, and the work vests worn by responders are often orange to make them easier to see. And don’t forget the bright orange U.S. Coast Guard helicopters that may be on scene. Floating booms are often orange for the same reason.

But generally the oil they are responding to is black or another dark color. But recently we had an orange oil spill.

No, the oil wasn’t orange colored; it was actually the oil extracted from orange peels. It is a byproduct of orange juice manufacturing and used as a flavoring and in a variety of fragrances and household cleaners.

On June 15, 2015, about 700 gallons of orange peel oil was spilled into a creek near the Passaic River, which flows into New York harbor. A large rain storm caused a wastewater pump to fail and water backed up into the facility producing the orange oil. The orange oil then was inadvertently pumped out of the facility into the creek.

Crews managed to temporarily dam the creek using sheets of plywood, keeping most of the oil from reaching the river. The spill happened in East Hanover, New Jersey, oddly not far from the city of Orange, New Jersey, (named for King William III of England, also known as William of Orange).

So why do we care about a seemingly harmless (and nice-smelling) product such as orange oil? Edible oils may be less toxic than crude oils, but spills of animal fats and vegetable oils can kill or injure wildlife. They also can end up suffocating aquatic life because microbes in the water take advantage of the temporary feast but in the process use up large amounts of the oxygen dissolved in water, leaving little oxygen for other aquatic creatures to use. This was the case when 1,400 tons of molasses were accidentally released into Honolulu Harbor in 2013, killing a number of fish.

Back to the scenario near Orange, New Jersey: a major compound in orange oil is limonene, which in very high concentrations can be toxic to fish and freshwater plankton. Fortunately, U.S. Coast Guard personnel overseeing the response reported that the responders were able to use absorbent pads to quickly sop up the released oil, which remained far below toxic levels.

Furthermore, any remaining orange oil would likely evaporate or disperse in the water over the course of several days to a couple weeks, leaving behind a sweet-smelling cleanup scene.

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How Do Oil Spills out at Sea Typically Get Cleaned Up?

This is a post by Kate Clark, Acting Chief of Staff with NOAA’s Office of Response and Restoration.

Close up of skimming device on side of a boat with oil and boom.

Skimmers come in various designs but all basically work by removing the oil layer from the surface of the water. (U.S. Coast Guard)

Whether for hanging a picture on the wall or fixing a leaky faucet, most people keep a common set of tools in their home. While some tools get more use than others, it’s good to have an array on hand to handle most repair jobs. The same is true for responding to oil spills.

Like a home repair job, each oil spill has unique aspects that call for careful consideration when deciding which tool to use. Responders keep an array of response methods in their toolkit for dealing with oil in offshore waters: skimming and booming, in situ burning, and applying dispersants.

Let’s get to know a few of those tools and the situations when they might be the most appropriate method for dealing with oil spills out at sea.

Skimming: Take a Little off the Top

Skimming is a process that removes oil from the sea surface before it reaches sensitive areas along a coastline. Sometimes, two boats will tow a collection boom, allowing oil to concentrate within the boom, where it is then picked up by a “skimmer.” From whirring disks to floating drums, skimmers come in various designs but all basically work by removing the oil layer from the surface of the water. These devices attract oil to their surfaces before transferring it to a collection tank, often on a boat. Ideal conditions for skimming are during the day when the oil slick is thick and the ocean surface is fairly calm.

The success of a skimming operation is dependent on something known as the “encounter rate.” Much like a vacuum picks up dirt from your carpet, a skimmer has to come in direct contact with the oil in order to remove it from the surface and, even then, it will still pick up some water. That’s why responders will often refer to the volume of oil removed via skimming as gallons of an oil-water mixture.

In Situ Burning: Burn After Oiling

Plumes of smoke from two fires burning oil on the ocean surface.

Burning oil “in place” (in situ) on the water’s surface requires gathering a layor of oil thick enough to sustain the burn. (NOAA)

In situ burning is the process of burning spilled oil where it is on the ocean (known as “in situ,” which is Latin for “on site”). Similar to skimming, two boats will often tow a fire-retardant collection boom to concentrate enough oil to burn. Burning is sometimes also used in treating oiled marshes.

Ideal conditions for in situ burning are daylight with mild or offshore winds and flat seas. The success of burning oil is dependent on corralling a layer of oil thick enough to maintain a sustained burn. Any burn operation includes careful air monitoring to ensure smoke or residue resulting from the burn do not adversely impact people or wildlife.

Chemical Dispersants: Break It Up

Releasing chemical dispersants, usually from a small plane or a response vessel, on an oil slick breaks down the oil into smaller droplets, allowing them to mix more easily into the water column. Smaller droplets of oil become more readily available to microbes that will eat them and break them down into less harmful compounds.

However, using dispersants has its drawbacks, shifting potential impacts to the marine life living in the water column and on the seafloor. Because of this, the decision to chemically disperse oil into the water column is never made lightly. This decision is often made so that much less oil stays at the surface, where it could affect birds and wildlife at the ocean surface and drift onto vulnerable coastal habitat like beaches, wetlands, and tidal flats.

Ideal conditions for chemical dispersion are daylight with mild winds and moderate seas. Chemical dispersion is never done close to the shore, in shallow waters, near coastal communities, or when there is a potential for winds to carry the chemical spray away from its intended target.

Natural dispersion can and does occur when waves at the ocean surface have enough turbulent energy to allow surface oil to mix into the water column. Applying chemical dispersants can expedite this process when there is an imminent threat associated with allowing the oil to stay on the surface.

Graphic showing methods for responding to oil spills at sea. Plane applying chemical dispersants: Chemical dispersion is achieved by applying chemicals to remove oil from the water surface by breaking  the oil into small droplets. Burning oil surrounded by boom: Also referred to as in situ burning, this   is the method of setting fire to freshly spilled oil, usually while still   floating on the water surface. Booms: Booms are long floating barriers used to   contain or prevent the spread of spilled oil. A boat skimming oil: Skimming is achieved with  boats equipped with a floating skimmer designed to remove thin layers of oil from   the surface, often with the help of booms.One Size Does Not Fit All

You may have noticed that each of these tools has one common factor limiting its effectiveness: daylight, or more precisely, visibility. Being able to see the spilled oil, often over large areas of the ocean, is critical to being able to clean it up. That means these tools become ineffective at night, during certain seasons, or in regions where prolonged darkness, fog, or clouds are the norm.

Table showing the conditions which may affect the use of different oil spill response methods at sea (skimming, burning, dispersing). Conditions are sunlight, wind, rough seas, cold, and nearshore.

Conditions which may affect the use of different oil spill response methods at sea.

Rough seas can be prohibitive for skimming and burning since these methods rely on calm conditions and collection booms to gather (and keep) oil in one place. High winds can often rule out burning and aerial dispersion as an option.

While these techniques perform best under certain, ideal conditions, responders often have to make do with the variety of conditions going on during an oil spill and can and do use these tools under less-than-ideal conditions. Their effectiveness also depends on factors such as the type or state of the spilled oil or the environment it was spilled in (e.g., sea ice).

Just like your home repairs, the job sometimes calls for a non-traditional tool or creative fix. The continued development of alternative response methods and technologies for cleaning up oil is critical for addressing oil spills in geographic areas or conditions that the traditional toolbox is not equipped to fix.

Kate Clark is the Acting Chief of Staff for NOAA’s Office of Response and Restoration. For nearly 12 years she has responded to and conducted damage assessment for numerous environmental pollution events for NOAA’s Office of Response and Restoration. She has also managed NOAA’s Arctic policy portfolio and served as a senior analyst to the National Commission on the BP Deepwater Horizon Oil Spill and Offshore Drilling.

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Who Thinks Crude Oil Is Delicious? These Ocean Microbes Do

This is a post by Dalina Thrift-Viveros, a chemist with NOAA’s Office of Response and Restoration.

Edge of oil slick at ocean surface.

There are at least seven species of ocean bacteria that can survive by eating oil and nothing else. However, usually only a small number of oil-eating bacteria live in any given part of the ocean, and it takes a few days for their population to increase to take advantage of their abundant new food source during an oil spill. (NOAA)

Would you look at crude oil and think, “Mmm, tasty…”? Probably not.

But if you were a microbe living in the ocean you might have a different answer. There are species of marine bacteria in several families, including Marinobacter, Oceanospiralles, Pseudomonas, and Alkanivorax, that can eat compounds from petroleum as part of their diet. In fact, there are at least seven species of bacteria that can survive solely on oil [1].

These bacteria are nature’s way of removing oil that ends up in the ocean, whether the oil is there because of oil spills or natural oil seeps. Those of us in the oil spill response community call this biological process of removing oil “biodegradation.”

What Whets Their Oily Appetites?

Communities of oil-eating bacteria are naturally present throughout the world’s oceans, in places as different as the warm waters of the Persian Gulf [2] and the Arctic conditions of the Chukchi Sea north of Alaska [3].

Each community of bacteria is specially adapted for the environment where it is living, and studies have found that bacteria consume oil most quickly when they are kept in conditions similar to their natural environments [4]. So that means that if you took Arctic bacteria and brought them to an oil spill in the Gulf of Mexico, they would not eat the oil as quickly as the bacteria that are already living in the Gulf. You would get the same result in the reverse case, with the Arctic bacteria beating out the Gulf bacteria at an oil spill in Alaska.

Other factors that affect how quickly bacteria degrade oil include the amount of oxygen and nutrients in the water, the temperature of the water, the surface area of the oil, and the kind of oil that they are eating [4][5][6]. That means the bacteria that live in a given area will consume the oil from a spill in the summer more quickly than a spill in the winter, and will eat light petroleum products such as gasoline or diesel much more quickly than heavy petroleum products like fuel oil or heavy crude oil.

Oil-eating microbes fluorescing in a petri dish.

This bacteria, fluorescing under ultraviolet light in a petri dish, is Pseudomonas aeruginosa. It has been used during oil spills to break down the components of oil. (Credit: Wikimedia user Sun14916/Creative Commons Attribution-ShareAlike 3.0 Unported license)

Asphalt, the very heaviest component of crude oil, is actually so difficult for bacteria to eat that we can use it to pave our roads without worrying about the road rotting away.

What About During Oil Spills?

People are often interested in the possibility of using bacteria to help clean up oil spills, and most oil left in the ocean long enough is consumed by bacteria.

However, most oil spills last only a few days, and during that time other natural “weathering” processes, such as evaporation and wave-induced breakup of the oil, have a much bigger effect on the appearance and location of the oil than bacteria do. This is because there are usually only a small number of oil-eating bacteria in any given part of the ocean, and it takes a few days for their population to increase to take advantage of their abundant new food source.

Because of this lag time, biodegradation was not originally included in NOAA’s oil weathering software ADIOS. ADIOS is a computer model designed to help oil spill responders by predicting how much of the oil will stay in the ocean during the first five days of a spill.

However, oil spills like the 2010 Deepwater Horizon well blowout, which released oil for about three months, demonstrate that there is a need for a model that can tell us what would happen to the oil over longer periods of time. My team in the Emergency Response Division at NOAA’s Office of Response and Restoration has recognized that. As a result, version 3 of ADIOS, due to be released later in 2015, will take into account biodegradation.

My team and I used data published in scientific journals on the speed of oil biodegradation under different conditions to develop an equation that can predict how fast the components of oil will be consumed, and how the speed of this process can change based on the surface area-to-mass ratio of the oil and the climate it is in. A report describing the technical details of the model will be published in the upcoming Proceedings of the Arctic and Marine Oilspill Program Technical Seminar, which will be released after the June conference.

Including oil biodegradation in our ADIOS software will provide oil spill responders with an even better tool to help them make decisions about their options during a response. As part of the team working on this project, it has provided me with a much greater appreciation for the important role that oil-eating bacteria play in the long-term effort to keep our oceans free of oil.

I know I’m certainly glad they think oil is delicious.

Dalina Thrift-ViverosDalina Thrift-Viveros is a Seattle-based chemist who has been providing chemistry expertise for Emergency Response Division software projects and spill responders since 2011, when she first started working with NOAA and Genwest. When she is not involved in chemistry-related activities, Dalina sings with the rock band Whiskey River and plays sax with her jazz group, The Paul Engstrom Trio.

Literature cited

[1] Yakimov, M.M., K.N. Timmis, and P.N. Golyshin. “Obligate oil-degrading marine bacteria,” Current Opinion in Biotechnology, 2007, 18(3), pp. 257-266.

[2] Hassanshahian, M., G. Emtiazi, and S.Cappello. “Isolation and characterization of crude-oil-degrading bacteria from the Persian Gulf and the Caspian Sea,” Marine Pollution Bulletin, 2012, 64, pp. 7–12.

[3] McFarlin, K.M., R.C. Prince, R. Perkins, and M.B. Leigh. “Biodegradation of Dispersed Oil in Arctic Seawater at -1°C,” PLoS ONE, 2014, 9:e84297, pp. 1-8.

[4] Atlas, R.M. “Petroleum Biodegradation and Oil Spill Bioremediation,” Marine Pollution Bulletin, 1995, 31, pp. 178-182.

[5] Atlas, R.M. and T.C. Hazen. “Oil Biodegradation and Bioremediation: A Tale of the Two Worst Spills in U.S. History,” Environmental Science & Technology, 2011, 45, pp. 6709-6715.

[6] Head, I.M., D.M. Jones, and W.F.M. Röling, “Marine microorganisms make a meal of oil,” Nature Reviews Microbiology, 2006, 4, pp. 173-182.

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Five Key Questions NOAA Scientists Ask During Oil Spills

Responders in a small boat pressure-wash rocky shore at the site of an oil spill.

Responders pressure wash the Texas shoreline after the tank ship Eagle Otome oil spill in January of 2010. (NOAA)

During an emergency situation such as an oil spill or ship grounding, scientists in NOAA’s Office of Response and Restoration are guided by five central questions as they develop scientifically based recommendations for the U.S. Coast Guard.

These recommendations help the Coast Guard respond to the incident while minimizing environmental impacts resulting from the spill and response.

Identified in the late 1980s by NOAA, these questions provide a sequential framework for identifying key information at each step that will then inform answers to subsequent questions raised during an oil spill. For example, in order to predict “where could it go?” (question two), you first need to know “what spilled?” (question one), and so on.

Questions guiding NOAA's oil spill response science, with a ship leaking oil, surrounded by boom, with flying birds and a benzene molecule.

Naturally, during a spill response, it may become necessary to revisit earlier questions or assumptions as conditions change and more—or better—information becomes available.

The Scene of the Spill

Establishing what happened is the first step. What is the scenario for this incident and where is it occurring? Gathering this information means figuring out facts such as:

  • the type of incident (e.g., pipeline rupture versus oil tanker collision).
  • the volume and types of oil involved.
  • the incident environment (e.g., stormy, calm).
  • the incident location (e.g., open ocean, near shore, water temperature).

Forecast: Cloudy with a Chance of Oil

Dr. Amy MacFadyen is a NOAA physical oceanographer who frequently works on the next step, which is predicting where the oil is going to go. In most of the spills we respond to, the oil is spilled at or near the water surface and is less dense than water. Initially, the oil will float and form a slick. Dr. MacFadyen looks at what is going on in the environment with wind and waves, which can break up the slick, causing some of the oil to mix into the water column in the form of small droplets.

An important point is that responders can potentially clean up what is on top of the water but recovering oil droplets from the water column is practically impossible. This is why it is so important to spill responders to receive accurate predictions of the movement of the surface slicks so they can quickly implement cleanup or prevention strategies.

In order to make predictions about oil movement, Dr. MacFadyen uses a computer model which includes ocean current and wind forecasts to generate an oil trajectory forecast map. Trajectory forecast models may be updated frequently, as conditions at the site of the spill change. Although the trajectory map shows the position of the oil, there is an element of uncertainty as the forecasts are based on other predictions, such as weather forecasts, which are not always perfect and are themselves subject to change.

To reduce uncertainty, trajectory forecasts incorporate information from trained observers flying over the slick who can confirm the actual location of the oil over the course of the spill response. MacFadyen can then incorporate that updated information as she runs the trajectory forecast model again.

A Sense of Sensitivity

In order to answer what the oil might affect, NOAA developed Environmental Sensitivity Index maps to identify what might be harmed by a spill in different habitat types. It is necessary for responders and decision makers to know what shoreline types exist in the path of the oil, as well as vulnerable species and habitats so that they can plan for the appropriate protection (such as booming) or cleanup method (such as skimming). Cleaning up oil off a sandy beach is very different than a salt marsh, mudflat, or rocky shore.

Animals, plants, and habitats at risk can include those on the water (e.g., seabirds), below the surface (e.g., fish), and on the bottom (e.g., mussels), as well as on the shoreline (e.g., marsh grasses).

Jill Petersen, manager of the Office of Response and Restoration Environmental Sensitivity Index map program, works to ensure that these maps of each U.S. coastal region are up-to-date so that this information is readily available should a spill occur.

Raise the Alarm for Harm

The next step is to look at what harm the oil could cause. When oil is released into the water, it can cause harm to marine animals and the environment. Oil contains thousands of chemical compounds. Polycyclic aromatic hydrocarbons [PDF], or PAHs as they are commonly known, are a class of oil compounds that have been associated with toxic effects in exposed organisms. Because of this, scientists frequently study PAHs in spilled oil to gauge the oil’s potential environmental impact.

However, the complexity of each oil’s chemistry and the changes that occur once it is in the environment make the assessment of risk a challenging task. In order to do so, response biologists consider the type of oil, the sensitivity of potentially exposed organisms, and how the oil is expected to behave in the environment.

Oil spills can involve releases of large volumes of oil that overwhelm whatever natural capacity there might be to absorb impacts, which leads to the photographs we see of heavy oil covering plants and animals. But recent research studies have shown that even minute amounts of petroleum can harm marine eggs and larvae—which means the decisions we make during a response are even more critical to the long-term health of the affected habitats.

NOAA marine biologist Dr. Alan Mearns is an expert on how pollution from oil harms the environment. Each year, he reviews and summarizes recent research in this field to ensure oil spill response recommendations and decisions are based on the most current science that exists.

Sending Help

A skimmer picks up oil off the surface of the Delaware River.

A skimmer picks up oil off the surface of the Delaware River after the tanker Athos spilled oil in 2004. (NOAA)

Answering the previous questions allows us to determining what can be done to help. Doug Helton, the Office of Response and Restoration’s Incident Operations Coordinator, describes possible solutions as usually falling under three categories: containing the source, cleaning up, and protecting the shore.

To contain the source means to limit the further release of pollution by plugging the leak in the pipeline or containing the spill, for example, by keeping the ship from sinking and losing its entire cargo of oil.

Cleanup on the water could be conducted by mechanical means, such as booming and skimming, or through alternative technologies, such as burning the oil in open water or using chemicals to disperse the oil.

Cleanup along the shoreline can be done manually or mechanically using methods such as pressure washing. When considering cleanup options, sometimes monitoring the situation is the best option when a response method could actually cause more harm to the environment. One example is in an oiled marsh because these habitats are especially vulnerable to oil but also to being damaged by people walking through them trying to remove oil.

In addition to providing scientific support to the U.S. Coast Guard, NOAA’s Office of Response and Restoration develops oil spill response software and mapping tools. For responders, NOAA has published a series of job aids and manuals that provide established techniques and guidelines for observing oil, assessing shoreline impact, and evaluating accepted cleanup technologies for a variety of oil spill situations.


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