&EPA
www.epa.gov/research
science    in  ACTION
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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