THE SEA GRANT
and GOMRI
PARTNERSHIP
The mission of Sea Grant is to
enhance the practical use and
conservation of coastal, marine
and Great Lakes resources in
order to create a sustainable
economy and environment.
There are 33 university–based
Sea Grant programs throughout
the coastal U.S. These programs
are primarily supported by
the National Oceanic and
Atmospheric Administration
and the states in which the
programs are located.
In the immediate aftermath
of the Deepwater Horizon
spill, BP committed $500
million over a 10–year period
to create the Gulf of Mexico
Research Initiative, or GoMRI.
It is an independent research
program that studies the effect
of hydrocarbon releases on
the environment and public
health, as well as develops
improved spill mitigation, oil
detection, characterization
and remediation technologies.
GoMRI is led by an independent
and academic 20–member
research board.
The Sea Grant oil spill science
outreach team identifies the
best available science from
projects funded by GoMRI and
others, and only shares peer-
reviewed research results.
http://gulfseagrant.org
http://gulfresearchinitiative.org
Texas • Louisiana • Florida
Mississippi-Alabama
CHEMICAL DISPERSANTS AND THEIR
ROLE IN OIL SPILL RESPONSE
Larissa J. Graham, Christine Hale, Emily Maung-Douglass, Stephen Sempier,
LaDon Swann, and Monica Wilson
Nearly two million gallons of dispersants were used at the water’s
surface and a mile below the surface to combat oil during the
Deepwater Horizon oil spill. Many Gulf Coast residents have questions
about why dispersants were used, how they were used, and what
impacts dispersants could have on people and the environment.
On April 20, 2010, an explosion on
the Deepwater Horizon oil rig killed
11 people. The rig was located 42
miles southeast of Venice, Louisiana.
The ruptured wellhead had released
an estimated 4.9 million barrels of
Louisiana sweet crude oil before
responders capped it on July 19, 2010.
Some of this oil was collected at the site
of the wellhead. Scientists estimate that
the remainder of the oil, or about 4.1
million barrels (172 million gallons), were
released into Gulf of Mexico waters.
1,2,3,4,5
Emergency responders attempted to
clean up the oil and prevent it from
reaching the shoreline by skimming
and burning the oil at the surface. They
also applied nearly two million gallons
of dispersants to break up the oil.
This spill was the largest application of
dispersants in U.S. history.
4
The Deepwater Horizon site (NOAA photo)
FIGURE 1.
This map shows the number of days that an area was oiled during the Deepwater Horizon oil spill. Responders found oil in areas
that are shown in dark gray more days than those shown in light gray. In response to the oiling, responders applied dispersants to surface
water. The orange lines represent where dispersant was sprayed using airplanes. Responders also sprayed dispersant from boats close to the
wellhead and at subsurface depths (not shown on this map). (Environmental Response Management Application)
2
HOW DID RESPONDERS USE DISPERSANTS
DURING THE DEEPWATER HORIZON OIL
SPILL?
Responders used two types of dispersants, Corexit
9500A and Corexit 9527A, during the Deepwater
Horizon oil spill. Both are on the federal guideline
list of dispersants that can be used during a spill.
Responders first applied Corexit 9527A until they
exhausted the supply. Then they switched to Corexit
9500A and continued using it throughout the cleanup
efforts.
4,6
There are many different Corexit formulas
and product types. When we use the word “Corexit” in
this publication, we are referring to Corexit 9527A and
9500A.
During the spill, responders sprayed approximately one
million gallons of dispersants over close to 300 square
miles of oiled surface waters (Figure 1).
1,4
Responders
spraying dispersant from airplanes could not apply
them within 2.3 miles of any vessel, within 3.45 miles
of the shoreline or visible marine life, or in areas with
water depths less than 33 feet deep.
4
Responders
sprayed dispersants from boats in areas close to the
wellsite where crews were working. According to the
U.S. Coast Guard, this method reduced the amount of
dispersant in the air, increasing the safety of the working
environment. The same U.S. Coast Guard report states
that emergency responders applied 98 percent of the
dispersants more than 11 miles offshore.
4
For the first time in U.S. history, responders used
dispersants at very deep depths. They applied
approximately 771,000 gallons of Corexit 9500A nearly
one mile beneath the sea surface at the source of the
leak. They did this using a remotely operating vehicle to
inject dispersant at the site of the wellhead.
1,4
HOW DO DISPERSANTS
BREAK UP OIL?
A typical commercial dispersant contains solvents and
surfactants. Solvents help keep the chemicals mixed
and help them dissolve into the oil. Surfactants allow oil
and water to mix easily.
3
By allowing oil and water to mix, the oil slick breaks into
many smaller oil droplets. The smaller droplets mix into
the water column and then are eventually carried away
by currents, attach to particles in the water column and
settle to the bottom, or evaporate.
7
Nature’s “oil-eating”
microbes are found in our oceans and have adapted over
time to use most of the chemicals in oil as food. In the
process, they naturally remove oil from the environment.
Smaller oil droplets are more available to these “oil-
eating” microbes than large oil slicks (Figure 2).
WHEN DO RESPONDERS USE DISPERSANTS
TO CLEAN UP OIL?
Responders consider trade-offs when determining the
most effective cleanup method(s) that should be used
during an oil spill.
7,8
Applying dispersants was just one of
many strategies that emergency responders used at the
Deepwater Horizon site during the spill. Other response
activities included burning the oil at the water surface
and mechanically recovering it using skimmers or other
equipment.
Emergency responders may use dispersants when
other cleanup methods may not be as practical. For
example, the spill is very large, the water may be too
rough for other methods, or the spill may be too far
away from land to use mechanical recovery equipment.
7
Under these conditions, responders may choose to
apply dispersants to break up an oil slick. They may also
choose to use dispersants because they can be deployed
rapidly by aircraft, cutting down on the response time.
8
Dispersants and other response methods can prevent an
oil slick from reaching the shoreline. This can reduce the
FIGURE 2.
Dispersants, which are one strategy used to respond to an oil spill, contain molecules that have one end that is attracted to water
and one end that is attracted to oil. When responders apply dispersants to an oil slick, these molecules attach to the oil, allowing the oil slick
to be broken up into smaller oil droplets. These smaller droplets then mix into the water column and where they are “eaten” and further
degraded (broken down) by microbes and other organisms. (Florida Sea Grant/Anna Hinkeldey)
4
oiling of coastal wildlife and sensitive habitats, such as
coastal wetlands, mangroves, and beaches. Once these
habitats are oiled, they are very difficult to clean without
causing further damage to the area.
8
However, dispersants are not always effective. When
oil is dispersed, it is removed from the water’s surface
and harder to clean up mechanically.
8
Dispersants may
not work well on some types of oil and spraying them
on patchy oil slicks can be inefficient.
7,8
They also do not
work well under very windy conditions because they can
drift in the wind during application or waves can wash
them off the slick. When this happens, the dispersant
cannot penetrate, mix with, and break down the oil.
7
Applying dispersants beneath the water’s surface, at
the site of the wellhead, was a new technique used
during the Deepwater Horizon oil spill. One reason that
this method was approved was related to the health
of response workers and the ease of application. Deep
sea application would minimize human contact with
dispersants and could also occur at night and during foul
weather. This technique may have been more effective
at dispersing the oil because Corexit was injected
right into the wellhead. This also allowed for a quicker
response time because dispersants could be applied at
night and in foul weather.
1
HOW DID AGENCIES REGULATE AND
MONITOR DISPERSANT USE?
The
National Contingency Plan (NCP)
establishes
the framework to authorize dispersant use. This plan
outlines which dispersants emergency responders
can apply during a spill and how dispersant use will be
monitored.
9
Emergency responders use
Special Monitoring of
Applied Response Technologies (SMART)
guidelines
to monitor surface dispersant use. SMART guidelines
do not look at the effects or impacts of dispersed oil.
Instead, they provide information about how to apply
dispersants and how well they are working.
10
Responders use the SMART monitoring program to
determine if dispersants are effectively breaking up oil
and, if so, how quickly.
4
The U.S. Coast Guard, National
Oceanic and Atmospheric Administration (NOAA), U.S.
Environmental Protection Agency (EPA), U.S. Centers for
Disease Control and Prevention, and the U.S. Bureau of
Safety and Environmental Enforcement were all part of
developing this program.
4
During the Deepwater Horizon
oil spill, trained observers flew over the oil slick to see if
the dispersant was working to break up the oil. Sampling
teams collected water samples to measure the amount
of dispersed oil in the water column.
Agencies used
this information to modify how they were applying the
dispersant.
4
In 2010, the U.S. EPA collected air samples off the coast
of Louisiana for four days after the aerial application
of dispersants. They tested the air for two chemicals,
2-butoxyethanol and propylene glycol. Scientists took
samples 30 minutes after dispersant application and did
Controlled burning (left) and skimming (right) are two response techniques used to remove oil from the water surface
after an oil spill. (NOAA photos)
5
not find either chemical.
11
The U.S. EPA also collected
onshore air quality samples along shoreline sites in
Louisiana, Mississippi, Alabama, and Florida. They
tested these samples for two dispersant chemicals that
were most likely to be in the air in measurable amounts
after spraying, 2-butoxyethanol and dipropylene
glycol monobutyl ether. They found low levels of both
chemicals in the air, but all were below levels that
are likely to cause negative health effects. All of the
data from these monitoring efforts are available on
U.S. EPA’s website a
t
http://www.epa.gov/bpspill/
dispersant-air-sampling.html
.
12
According to the U.S. Coast Guard’s
On-Scene
Coordinator Report
, the U.S. EPA and the U.S. Coast
Guard were satisfied with how dispersants were used
during the Deepwater Horizon oil spill. These agencies
stated that dispersants had been an important tool
for reducing the oil spill’s impact and had prevented
more damage to marshes, wetlands, beaches, and
coast’s economy. They also stated that the information
collected during the spill supported continued
application of dispersants.
4
CAN DISPERSANTS HARM MARINE
ANIMALS?
The dispersants that emergency responders use today
are less harmful to the environment than the more toxic
products used prior to 1970.
7
However, they still contain
chemicals that can have a negative impact on aquatic
life (Tables 1 & 2).
The U.S. EPA was concerned that dispersants could
hurt aquatic wildlife and so, in May 2010, they
directed BP to scale back on the use of dispersants.
To understand how dispersants could affect aquatic
wildlife, the U.S. EPA conducted independent toxicity
studies in the laboratory.
6
The U.S. EPA tested eight approved dispersants,
including Corexit 9500A, on two aquatic species: Gulf
mysid, a small shrimp, and the inland silverside, a fish
that resides in coastal waters in the Gulf of Mexico.
6
These laboratory tests looked at the acute toxicity
of dispersants. Determining the acute toxicity of a
substance can help scientists determine the lethal
concentration. However, knowing the acute toxicity
HOW MUCH IS TOO MUCH?
How a substance can affect you will depend on how harmful it is and how long and how often you are exposed
to it. Every substance is poisonous at some level. Take water, for example. Although we need water to survive,
drinking too much water can also kill us because it dilutes the concentrations of other nutrients that our body
needs to function. Researchers determine how much of a substance is “toxic” by exposing animals to different
doses of a chemical for varying amounts of time. Scientists have conducted most of the tests on small fish or
shrimp to determine how harmful chemicals found in dispersants are to animals. It is important to note that the
toxicity of a chemical will vary among different species, differing lengths of exposure time, and the other factors
that might be affecting that species at the time.
TABLE 1.
The potential health effects of the two dispersants that emergency responders used during the Deepwater Horizon oil spill are
shown above. This information was compiled from the Material Safety Data Sheets for each chemical.
Dispersant used during the
Deepwater Horizon oil spill
Corexit 9500A
Corexit 9527A
Potential health effects to humans based on animal tests
Repeated or prolonged exposure may cause eye and skin irritation, dry the skin leading
to discomfort and dermatitis, or irritate the respiratory tract.
May be harmful if swallowed, effect the liver and kidney, and/or damage or irritate the
gastro-intestinal tract. Harmful if absorbed through skin or by inhalation. Repeated
or prolonged exposure may irritate the respiratory tract or existing skin condition.
Excessive exposure may cause central nervous system effects, nausea, vomiting,
anesthetic, or narcotic effects.
6
A member of U.S. Coast
Guard National Strike Force
on an overflight mission,
observing an airplane
spraying dispersant.
(NOAA photo)
does not help scientists understand the effects that the
substance can have on the reproduction, growth, or
development of an animal. Corexit 9527A was not tested
during these studies because the dispersant was no
longer being used in response efforts.
The laboratory experiments showed that none of the
dispersants, when tested alone, were more toxic to the
shrimp or silversides than oil.
Corexit 9500A and another
dispersant (JD-2000) were less toxic to silversides than
the other dispersants that were tested.
6
The U.S. EPA was also concerned about how oil mixed
with dispersant could affect aquatic life. They conducted
additional studies and found that Corexit 9500A, when
mixed with oil, had similar toxicity as the seven other
dispersants that were tested.
6
Oil alone and oil mixed
with each of the dispersants that were tested had similar
toxicity to shrimp, except when oil was mixed with one of
the dispersant tested (Nokomis 3-AA). The combination
of oil and this type of dispersant was more toxic to the
shrimp than oil alone.
6
The extent of damage that dispersants, dispersed oil, and
oil can have on aquatic life is still under debate. Some
peer-reviewed research studies have found dispersants
to be less toxic than oil alone, and other studies have
shown that dispersants or oil plus dispersant are more
toxic than oil alone.
7
The On-Scene Coordinator Report
This report documents the response efforts during the
Deepwater Horizon oil spill. It provides a timeline of the
spill and the efforts to address the potential impacts to
public health related to the spill. This report is available at
http://masgc.org/assets/uploads/publications/873/2_
coordinator_report_dwh.pdf
.
CAS #
577-11-7
111-76-2
57-55-6
64742-47-8
29911-28-2
1338-43-8
9005-65-6
9005-70-3
Di(2-ethylhexyl)
sodium sulfosuccinate
(DOSS)
2-Butoxyethanol
(Found in Corexit 9527A
only, not Corexit 9500A)
Propylene glycol
Distillates, petroleum,
hydrotreated light
Dipropylene glycol
monobutyl ether
Sorbitan, mono-(9Z)-9-
octadecenoate
Sorbitan, mono-
(9Z)-9-octadecenoate,
poly(oxy-1,2-ethanediyl)
derivatives
Sorbitan, tri-(9Z)-9-
octadecenoate, poly(oxy-
1,2-ethanediyl) derivatives
Other substances
that contain this
chemical
a,b,c
Certain cosmetics,
gelatin, chocolate
powder, beverages,
laxatives
Certain cleaners,
soaps, cosmetics,
lacquers, paints
Cosmetics,
preservatives in
food, medicines
Cleaners, paints,
varnishes
Cleaners,
degreasers, paints
Skin cream, air
freshener
Baby bath, mouth
wash, face lotion
Insect spray,
food additive
Potential health effects to humans
based on animal tests
d
Causes eye, skin, and respiratory tract irritation. May be
harmful if absorbed through the skin or inhaled. Harmful if
swallowed. May cause gastrointestinal irritation with nausea,
vomiting, and diarrhea.
Causes eye and skin irritation. May be toxic to blood, kidneys,
liver, and central nervous system. Repeated or prolonged
exposure to the substance can produce target organs
damage, including injury to red blood cells, kidney or the liver.
May cause adverse reproductive effects, birth defects, or
cancer. Severe over-exposure can result in death.
Causes mild eye, skin, respiratory, and gastrointestinal
irritation. May affect the behavior or central nervous system,
brain, metabolism, blood, respiration, cardiovascular system,
endocrine system, urinary system, and liver. Prolonged or
repeated inhalation may affect behavior, central nervous
system, and spleen. May be toxic to central nervous system.
May mutate genetic material or cause adverse reproductive
effects and birth defects.
Causes skin irritation. Repeated skin contact has resulted in
irritation and skin cancer in animals. May cause drowsiness or
dizziness. May be fatal if swallowed or enters airways.
The chemical, physical, and toxicological properties of this
chemical have not been thoroughly investigated.
Not classified as a hazardous substance or mixture.
Not classified as a hazardous substance or mixture.
Not classified as a hazardous substance or mixture.
Chemicals in
Corexit 9500A
and
Corexit 9527A
TABLE 2.
The chemicals that are found in Corexit 9500A and 9527A, the two dispersants that were used during the Deepwater Horizon
oil spill.
13
The Chemical Abstracts Service number (CAS) or unique identifier for each chemical substance, toxicity level based on tests
on animal subjects, and the potential health effects are listed for each chemical. This information was provided by the
Food and Drug
Administration (a), U.S. Department of Health and Human Services (b), Agency for Toxic Substances and Diseases Registration
(c), and Material Safety Data Sheets (d).
7
More information about these ongoing studies can be found on GoMRI’s website at
http://gulfresearchinitiative.
org
. Other publications focusing on dispersants are on the Sea Grant Oil Spill Science Outreach website at
www.
gulfseagrant.org/oilspilloutreach
.
WHAT STUDIES ARE STILL ONGOING?
Many questions remain about the impacts of dispersants
and dispersed oil on the ecosystem, environment, and
human health. The Gulf of Mexico Research Initiative
(GoMRI) and other research programs are looking
at alternative dispersant use and technology, how
dispersants react with oil under various conditions, the
environmental impacts of dispersants, and the impacts
that dispersants have on human health.
This work was made possible in part by a grant from The Gulf of Mexico
Research Initiative, and in part by the Sea Grant programs of Texas,
Louisiana, Florida and Mississippi-Alabama. The statements, findings,
conclusions and recommendations do not necessarily reflect the views of
these organizations.
MASGP-15-015
GOMSG-G-15-003
Texas • Louisiana • Florida
Mississippi-Alabama
REFERENCES
1. National Commission on the BP Deepwater Horizon
Oil Spill and Offshore Drilling. (2010). The Use of
Surface and Subsea Dispersants During the BP
Deepwater Horizon Oil Spill, Staff Working Paper No. 4.
RetrievedNovember 23, 2015, from
http://oscaction.
org/resource-center/staff-papers/
2. Griffiths, S. K. (2012). Oil Release from Macondo Well
MC252 Following the Deepwater Horizon Accident.
Environmental Science and Technology, 46, 5616-5622.
3. Coastal Response Research Center, Research Planning
Incorporated, and National Oceanic Atmospheric
Administration. (2012).
The Future of Dispersant Use
in Oil Spill Response Initiative
. Retrieved October 10,
2014, from
http://crrc.unh.edu/sites/crrc.unh.edu/
files/media/docs/Workshops/dispersant_future_11/
Dispersant_Initiative_FINALREPORT.pdf
4. US Coast Guard. (2011).
On Scene Coordinator
Report Deepwater Horizon Oil Spill: Submitted to
the National Response Team, September 2011
.
Retrieved October 10, 2014, from
https://www.uscg.
mil/foia/docs/DWH/FOSC_DWH_Report.pdf
5. Lehr, B., Bristol, S., & Possolo, A. (2010). Oil
Budget Calculator Deepwater Horizon. Technical
documentation: A report to the National Incident
Command. Retrieved August 13, 2015, from
http://www.restorethegulf.gov/sites/default/
files/documents/pdf/OilBudgetCalc_Full_HQ-
Print_111110.pdf
6. US Environmental Protection Agency. (2014). EPA’s
Toxicity Testing of Dispersants. Retrieved October
10, 2014, from
www.epa.gov/bpspill/dispersants-
testing.html
7. National Research Council of the National Academies.
(2005). Understanding Oil Spill Dispersants: Efficacy
and Effects. Washington, D.C.: The National Academies
Press.
8. Coolbaugh, T., & McElroy, A. (2013). Dispersant Efficacy
and Effectiveness. Retrieved from University of New
Hampshire Coastal Response Research Center and
Center for Spills in the Environment Web site:
http://
crrc.unh.edu/sites/crrc.unh.edu/files/media/docs/
Workshops/dispersant_forum_13/Dispersant_
efficacy_effectivenes.pdf
9. US Environmental Protection Agency. (1994). National
Oil and Hazardous Substances Pollution Contingency
Plan. Retrieved October 10, 2014, from
http://www.
gpo.gov/fdsys/pkg/CFR-2011-title40-vol28/pdf/
CFR-2011-title40-vol28-part300.pdf
10. US Coast Guard, National Oceanic Atmospheric
Administration, US Environmental Protection Agency,
Centers for Disease Control and Prevention, & Minerals
Management Services. (2006) Special Monitoring of
Applied Response Technologies. Retrieved October 10,
2014, from
http://response.restoration.noaa.gov/
sites/default/files/SMART_protocol.pdf
11. US Environmental Protection Agency. (2014). Offshore
air sampling for dispersant-related compounds.
Retrieved October 13, 2014, from
http://www.epa.
gov/bpspill/dispersant-air-sampling.html
12. US Environmental Protection Agency. (2014). Mobile
Air Monitoring on the Gulf Coast: TAGA Buses.
Retrieved October 13, 2014, from
http://www.epa.
gov/bpspill/taga.html
13.
13. US Environmental Protection Agency. (2015).
Questions and answers on dispersants. Retrieved
November 20, 2015, from
http://archive.epa.gov/
bpspill/web/html/dispersants-qanda.html
GLOSSARY
Acute toxicity - Adverse (negative) effects after an organism
is exposed to one or more doses of a substance over a short
time period (often, less than 72 hours).
Corexit 9527A and 9500A – dispersants approved for use in
US waters and those that were used to minimize the presence
of surface oil slicks during the Deepwater Horizon oil spill.
Dispersants – chemicals that are used during oil spill response
efforts to break up oil slicks and can limit floating oil from
impacting sensitive ecosystems such as coastal habitats.
Microbes – very tiny organisms including bacteria, fungi,
archaea, and protists. Some microbes (bacteria and archaea)
are the oldest form of life on earth.
National Contingency Plan (NCP) – a federal document that
outlines response efforts for oil spills and other hazardous
substance spills.
Special Monitoring of Applied Response Technologies
(SMART) – a cooperative monitoring program that is used
during oil spill response efforts to determine if dispersant
application is effective.
Surfactants – compounds that work to break up oil.
Dispersants contain surfactants that break the oil slick into
smaller droplets that can more easily mix into the water
column.
Christine Hale
Texas Sea Grant
chris.hale@tamu.edu
Larissa Graham
Mississippi-Alabama Sea Grant
larissa.graham@auburn.edu
Emily Maung-Douglass
Louisiana Sea Grant
edouglass@lsu.edu
Stephen Sempier
Mississippi-Alabama Sea Grant
stephen.sempier@usm.edu
LaDon Swann
Mississippi-Alabama Sea Grant
swanndl@auburn.edu
Monica Wilson
UF/IFAS Florida Sea Grant
Extension
monicawilson447@ufl.edu
OIL SPILL SCIENCE OUTREACH TEAM
SUGGESTED CITATION
Graham, L., Hale, C., Maung-Douglass, E., Sempier, S., Swann,
L., and Wilson, M. (2016). Oil Spill Science: Chemical dispersants
and their role in oil spill response. MASGP-15-015.
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