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INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
Determining Which Dispersants Will Be Effective In Future Deepwater Oil Spills
Research Value:
Dispersants serve a function
similar to detergents. One of
their key components is
surfactants. These are long
molecules that have one end that
is soluble in water and one end
that is soluble in oils and fats.
Surfactants reduce the tension at
the points where oil and water
meet. With the input of mixing
energy (that in the ocean can be
provided by waves), this reduced
tension will eventually promote
the breakup of the oil into
smaller droplets that are capable
of dispersion into the water
column.
These smaller droplets give
microbes in the water greater
access to the oil to break it down.
Some microbes can use oil as an
energy source and in the process
degrade the oil into smaller, often
less harmful molecules.
Dispersants also help to remove
the oil slicks from the water
surface, thereby protecting
species of water fowl from the
suffocating effect of exposure to
petroleum.
According to the National
Oceanic and Atmospheric
Administration (NOAA), the
National Institute of Standards
and Testing (NIST), and the U.S.
Geological Survey (USGS), over
4.93 million barrels (207 million
gallons) of South Louisiana
Crude (SLC) oil were released
into the Gulf of Mexico after the
blowout of the Deepwater
Horizon well on April 20, 2010.
The amount of dispersants used
on the Deepwater Horizon spill
dwarf any other spill where
dispersants were used. The total
volume of dispersants used in the
entire Gulf spill was estimated at
1.84 million gallons.
Deepwater spills result in oil
distributed from deep in the
water column to the water
surface. One factor affecting
dispersant effectiveness is
temperature. Some dispersants
are less effective at lower
temperatures. In deepwater spills
like the Deepwater Horizon spill
in 2010, oil is released into
significantly colder water (a
typical deep water temperature
might be ~5 °C) than the water
that surface spills encounter (a
typical surface temperature in the
Gulf might be -25 °C). For the
most effective mitigation of the
effects of these deepwater spills,
which dispersants are effective at
low temperatures? Are there
some available dispersants that
would be effective at both deep
sea and surface temperatures?
This study addresses these
questions.
Research Details:
The objective of this study was to
test eight of the available
dispersants (including Corexit
9500A, which was used
extensively on the 2010
Deepwater Horizon Spill) on
SLC) oil under temperature
conditions similar to both the
deep sea (5 °C) and in the top 5
m (25 °C) in the Gulf. SLC is
similar in composition to the
Mississippi Canyon Block 252
oil from the Gulf of Mexico spill.
These same eight products were
also tested for acute toxicity to
aquatic organisms in a separate
EPA study.
This study seeks to determine
which dispersants will be effective
at the lower deep ocean
temperatures, and which ones will
be effective at the higher ocean
surface temperatures.
The National Contingency Plan
Product Schedule (NCPPS) is a
list of acceptable products like
dispersants that may be used
when an oil spill occurs. This list
is managed by EPA based on
assignment by the National
Contingency Plan. When a spill
occurs, the On-Scene
Coordinator and the Unified
Incident Command select the
U.S. Environmental Protection Agency
Office of Research and Development (ORD), National Risk Management Research Laboratory (NRMRL)
Land Remediation and Pollution Control Division (LRPCD)
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products to be used to combat the
oil spill. They rely on the
NCPPS to guide their selection.
One goal of EPA studies such as
this is to ensure effective
products are on the NCPPS.
Outcomes and Impacts:
By assessing which dispersants
are effective at low temperatures,
data from this and similar studies
will help to mitigate the
environmental effects of future
deepwateroil spills. This study
also provides information useful
in choosing effective dispersants
for surface spills. The refinement
of dispersant testing protocols
done in this study will help in
further studies that attempt to add
to the knowledge of the
effectiveness of dispersants to
protect the environment from oil
spills.
REFERENCES
Venosa, A.D., and E.L.Holder. 2012.
Determining the Dispersibility of South
Louisiana Crude Oil by Eight Oil Dispersant
Products Listed on the NCP Product
Schedule. Marine Pollution Bulletin, in press.
Hemmer, M.J., Barren, M.G., and R.M.
Greene. 2011. Comparative toxicity of eight
oil dispersant products on two Gulf of Mexico
aquatic test species. Env. Toxicol. Chem.
30(10): 2244-2252.
Kaku, V.J., Boufadel, M.C., and A.D.
Venosa. 2006. Evaluation of mixing energy in
laboratory flasks used for dispersant
effectiveness testing. ASCE J. Environmental
Eng. Div. 132:93-101.
Venosa, A.D., King, D.W., and G.A. Serial,
2002. The baffled flask test for dispersant
effectiveness: a round robin evaluation of
reproducibility and repeatability. Spill Sci. &
Technol. Bulletin. 7(5-6): 299-308.
Dispersants work in a similar way
to detergents and can help
remove surface oil slicks and
protect waterfowl.
This study used a modification of
the Baffled Flask Test (BFT),
which is being proposed to
replace the current Swirling
Flask Test (SFT) as an official
standard protocol because of
better reproducibility and mixing,
causing more dispersion.
The results indicate that
temperature was not as critical a
variable as the literature
suggested, likely because of the
low viscosity and light weight of
the SLC. Only three of the eight
dispersants tested produced
satisfactory results in the
laboratory flasks at both
temperatures.
CONTACTS
Technical Inquiries:
Albert D. Venosa
513-569-7668
EPA/ ORD/NRMRL/ LRPCD
venosa.albert(@,epa.gov
Communications:
Roger Yeardley
513-569-7548.
EPA/ORD/NRMRL/LRPCD
veardlev.roger(@,epa.gov
MORE LAND RESEARCH ON THE
WEB: www.epa.gov/nrmrl/lrpcd
National Risk Management Research Laboratory
Land Remediation and Pollution Control Division
EPA / 600/F-12/628
September 2012
www.epa.gov/nrmrl
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