Dispersants: Chemistry, Environmental Fate

1
Dispersants Chemistry, Environmental Fate
Effects, and Their Use as a Spill Response Option

• Ellen Faurot-Daniels
• California Department of Fish and Wildlife
  Office of Spill Prevention and Response

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Objectives for Presentation

• Review current oil spill response technologies,
  and discuss why and when we consider dispersants
  or other ARTs as potential response options
• Provide background information on dispersants,
  how they work, and their fate and effects in the
  environment.
• Discuss historical barriers to dispersant
  application, the planning approach used in
  California, and research and planning activities
  since the Deepwater Horizon oil spill 2010.
• Review recommendations on when (and when not) to
  use dispersants in various response situations.

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Response Options at the Time of an Oil Spill

• It is important to have as many tools in the tool
  box for use in an emergency situation

• Some of the contents of the "spill response
  toolbox include, in clockwise order from the
  upper left
• Dispersants
• Boom
• Skimmers
• Burning
• Dispersants would usually be used in conjunction
  with these other cleanup techniques.

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Oil Chemistry

• Types of Oils
• Persistence of Different Oils

5
Oil Chemistry Review

• Oil is not one simple thing it is a complex
  and highly variable mixture of compounds.
• Crude oil is a mixture of mainly hydrocarbons,
  with varying small amounts o trace metals.
• Hydrocarbons (including asphaltenes and waxes)
  are the most abundant compound in crude oils.

6
Types of Hydrocarbons that are in All Oils

• LIGHT-WEIGHT COMPONENTS
• 1 to 10 carbon atoms (low molecular weight)
• evaporate and dissolve into the water-column
  rapidly (within hours) and leave no residue
• many of these compounds (such as BTEX benzene,
  toluene, ethyl benzene, xylene) are thought to be
  readily absorbed through skin, and inhaled by
  animals and humans
• BTEX hydrocarbons are carcinogens and/or
  teratogens
• potentially flammable

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Types of Hydrocarbons that are in All Oils

• MEDIUM-WEIGHT COMPONENTS
• 11 to 22 carbon atoms (medium molecular weight)
• evaporate and/or dissolve into the water column
  more slowly (over several days), with some
  residue remaining.
• not as bioavailable as lower-weight components,
  so less likely to affect animals.

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Types of Hydrocarbons that are in All Oils

• HEAVY-WEIGHT COMPONENTS
• 23 or more carbon atoms (high molecular weight)
• undergo little to no evaporation or dissolution
• Can cause chronic (long-term) effects via
  smothering or coating, and as residue in the
  water column and sediments (such as tar balls)

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Oil Persistence

• PERSISTENCE
• Refers to an oil or refined products tendency to
  remain in the environment for a long time after
  discharge.
• Persistent oils cannot be completely removed from
  the environment. In general, an oil with a
  weathering half-life of months to years is
  considered persistent.
• The more medium to heavy weight compounds
  present, the more persistent it becomes.

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Oil Groups Category Persistence
Specific Gravity Typical Examples
Group I Non-persistent N/A
Gasoline products,
condensates. Group II
Persistent lt0.85 Diesel-like products
and light crude oils Group III
Persistent 0.85 lt 0.95 Medium-grade crudes
intermediate products Group
IV Persistent 0.95 lt 1.00 Heavy crudes and
residual products Group V Persistent gt
1.00 Low API gravity products heavier
than fresh water Persistence as defined
by US 33 CFR, Section 155.1029 and CCR.
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Characteristics and Behavior of Spilled Oil in
the Marine Environment
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Weathering of OilsWhen oil is spilled on the
sea, its physical and chemical properties are
changed. This process is known as weathering.

• Physical Processes Chemical Processes
• - Evaporation - Photochemical degradation
• - Dissolution - Microbial degradation
• - Emulsification
• - Spreading
• - Natural dispersion
• - Sedimentation

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Spreading and Advection
Spreading The movement of oil horizontally on
water surface due to gravity, inertia, friction,
viscosity and surface tension. Advection The
movement of oil due to influences of winds and/or
currents. Spreading dominates during the initial
stages of a spill.
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Evaporation

• Evaporation
• The preferential transfer of light and
  medium-weight components of oil from the liquid
  phase to the vapor phase.
• Will vary depending on oil composition
• 20 - 40 loss by volume for crude oils is
  considered normal
• 75 - 100 loss by volume for many light refined
  products.
• Evaporation is the primary weathering process in
  the natural removal of oil from the water
  surface.

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Dissolution

• Dissolution
• The transfer of oil component from a slick on the
  surface into solution in the water column.
• Light-End Components
• Tend to the be most soluble
• Evaporation and dissolution compete for the same
  oil components
• Evaporation occurs 10 - 1,000 times faster than
  dissolution.

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Natural Dispersion
Natural Dispersion The process of forming small
oil droplets that become incorporated into the
water column in the form of a dilute oil-in-water
suspension.

• Oil droplet size
• Will determine whether droplets re-combine with
  the slick or stay dispersed in the water column
• Droplets gt0.1mm will likely re-combine and come
  back to the surface
• Droplets lt 0.1 mm will stay suspended in the
  water.
• Following evaporation, natural dispersion is the
  second most important process.

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Emulsification

• Emulsification
• The mixing of seawater droplets into the oil
  spilled on the water surface.
• Since water is being added to the oil
• Emulsification will increase the total volume of
  oil (mousse) remaining in the environment, often
  by a factor of 2 or 3.

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Photo-oxidation
Photo-oxidation The process by which components
in the oil are chemically transformed through
photo-chemical reactions (in the presence of
oxygen), into new by-products.
Photo-oxidation plays a relatively minor role in
the over all weathering of spilled oil ( to
0.1/day)
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Biodegradation
Biodegradation The process where naturally
occurring bacteria and fungi consume hydrocarbons
to use as a food source. Carbon dioxide and
water are excreted as waste products.
Biodegradation is a significant process but also
a slow one.
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Oil Weathering Summary - evaporation -
spreading - advection - emulsification -
dissolution - dispersion - photo-oxidation
- sedimentation - biodegradation
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Dispersants

• Surface active agents (surfactants) with
  hydrophilic and hydrophobic components
• Used to reduce oil-water interfacial
• tension
• Effectiveness varies with weathering, salinity
  and emulsification
• Requires addition of energy

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Dispersants, continued

• Present formulations of dispersants are less
  toxic than spilled crude oil
• Present toxicity concerns are with dispersed oil
  (dispersant oil), not dispersants alone, as
  toxic PAHs from the oil slick now go into the
  water and expose other organisms
• A dispersant use decision is a determination of
  response and environmental trade-offs
• In general, the lighter the crude, the easier it
  is to disperse. However, no benefit to use of
  dispersants on spills of gasoline, diesel, or jet
  fuel, as these drive toxic parts oil oil into the
  water instead of letting them evaporate.

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How Dispersants Work -- A Pictorial

• The dispersant is applied to the water surface.
• Molecules of the dispersant attach to the oil,
  causing it to break into droplets.
• Wave action and turbulence move the
  oil-dispersant mixture from the water surface
  into the water column

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Dispersant-enhanced Bioremediation

• Breaking surface oil slicks into small droplets
  greatly increases the surface area of the oil,
  and makes the droplets more available to bacteria
  and other micro-organisms that use it as food
  source
• However, dissolved components of oil (PAHs) can
  cross cell membranes, fish gills, etc. , and may
  create new routes of exposure and toxicity
• Other contaminants in the oil (e.g., metals) must
  be broken down as well
• Ultimate break-down of hydrocarbons is into CO2
  and H2O

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Dispersant Mechanism and Chemistry
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What are Chemical Dispersants

• Chemical dispersants are mixtures that contain
  surface-active chemicals (called surfactants)
  and one or more solvents
• Surfactants have both hydrophilic and hydrophobic
  components.
• At the oil-water interface, surfactants reduce
  the surface tension.
• Oil enters the water as tiny droplets.

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How Dispersants Work

• First The dispersant is applied to the water
  surface
• Next Molecules of the dispersant attach to the
  oil, causing it to break into droplets
• Then Wave action and turbulence disperse the
  oil-dispersant mixture into the water column
• And The oil that had been concentrated at the
  surface is diluted within the water column.
• Oil is NOT removed from the water, but it is
  shifted to a part of the spill site where it is
  expected have fewer long-term environmental
  impacts.

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Dispersant Formulations

• Modern formulations based on mixture of solvents
  and surfactants.
• Latest generation of dispersants designed to
  disperse oil with minimal toxicity.
• Three groups based on solvent class
• Water-Based Solvents
• Hydrocarbon-Based Solvents
• Solvent-based with lower surfactants (limited
  number in general use)

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Water-Based Solvents

• Can be diluted with water for application
• Developed for light-distillate fuels and
  low-viscosity crudes and products
• Least effective all of dispersant types

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Hydrocarbon-Based Solvents

• Hydroxy solvents These are miscible in water
  (e.g., glycol ethers) and/or with hydrocarbons
• May have over 50 surfactant composition
• Can be used neat or diluted in water stream
• Enhances mixing and penetration into more viscous
  oils
• Majority of dispersants are in this category
  (including Corexit 9500)

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Summary Mechanism and Chemistry

• Dispersants are chemicals which have hydrophilic
  and hydrophobic components.
• They lowers the surface tension at the oil-water
  interface.
• They allow oil droplets to move into the water
  column.
• Energy is required for mixing to occur.
• Once oil is dispersed, it is distributed
  throughout the water column by tides and currents.

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Fate and Transport Processes When Using
Dispersants

• Effects of weathering processes once dispersants
  are applied

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The Effects of Dispersants on Weathering of Oil
Reduced Effects Enhanced Effects

• Evaporation becomes a secondary weathering
  process
• Natural dispersion
• Emulsification rate
• Photo-oxidation
• Sedimentation/stranding

• Spreading
• Natural dissolution
• Biodegradation

35
Dispersant Toxicity

• Laboratory Test
• Information from Deepwater Horizon spill

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Short-term Toxicity Short-term exposure is
described using LC50 and EC50.

• EC50
• The concentration that causes a specific effect
  (such as reduced growth or immobility) in 50 of
  test organisms in a specified time period.

• LC50
• The concentration that causes mortality in 50
  of test organisms in a specified time period
  (usually 48 or 96 hrs)

NOEC No Observable Effects Concentration The
concentration at which no effects of any kind are
observed
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Acute Toxicity

• The greater the LC50 or EC50 value, the lower the
  toxicity (higher numbers are better)
• The range in LC50 values results from biological
  and laboratory variability
• Lab tests are either spike test (California) or
  static tests (EPA)
• Most toxicity data available have been from 96-hr
  static test, which significantly over-estimates
  exposure (NRC,1989 and 2005)

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Factors Affecting the Aquatic Toxicity of
Dispersed Oil

• Toxicity is dependent on many variables, such as
  species, life stage of the species, and water
  temperature
• Concentration and duration of exposure of
  organisms to dispersed oil will vary, and is
  critical in determining when, and to what
  organisms and habitats, the greatest risks will
  occur
• Chemical composition of the dispersant also
  affects toxicity

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California Spiked Test

• In an attempt to make a more realistic test,
  Singer et al. developed a flow-through system
  that creates a declining (spiked) exposure that
  more realistically simulates oil spill
  conditions.

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Aquatic Toxicity Data for Corexit 9500
Species Lifestage Standard Test (24 -
96 hrs) Calif. Test (24 - 96 hrs)
(static
test) (spiked
exposure)
LC50 or EC50 ppm
LC50 or EC50 ppm Crustaceans Juvenile and
adult 3.5 to 35.9
158 to 1,038 Early life stages 1
48
----2 Molluscs
Juvenile and adult 42.3

---- Early life stages
---
12.8 to 19.7 Fish Juvenile and adult
50 to gt400
--- Early life stage
25.2 to 74.7
gt1,055 Algae Adult
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--- Early life stage
0.7
--- 1 zoospores, embryos,
larvae 2 no data available
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Types of Effect and Exposure

• Acute Effects vs Chronic Effects
• Short-Term vs Long-Term Exposure

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What will be Affected?

• Untreated Spill Chemically-Dispersed Spill

• Sea Surface
• Marine birds, furred mammals,
• fishing activity)
• Water Column
• Seabed (offshore)
• Seabed (nearshore)
• Benthic species, mariculture
• Shoreline
• Marshes, shorelines

• Sea Surface
• Water Column
• Plankton, pelagic fish
• Seabed (offshore)
• Seabed (Nearshore)
• Benthic species, mariculture, corals,
  seagrasses, seawater intakes
• Shoreline

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Fate and Effects of Dispersed Oil in the Marine
Environment

• Water Column
• Bioaccumulation
• Sediments

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Concepts of Dispersed Oil Fate
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California Dispersant Plan
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California Dispersant Plan Policy Development

• RRT IX tasked each of Californias 6 area
  committees to recommend a policy for dispersant
  use in federal waters (3 200 nm from shore),
  within each Area Committees zone of operation.
• Used a Net Environmental Benefit Analysis (NEBA)
  process to evaluate risks and benefits of using
  any response approach, including no response,
  mechanical recovery, dispersants, and in-situ
  burning. (These NEBAs were very similar to the
  Ecological Risk Assessment conducted in 2006 for
  Mexico-US Pacific Coastal Border Region).
• Zone recommendations from each Area Committee
  forwarded to USCG and RRT for their approval.
• With modifications as necessary, RRT approved all
  the dispersant-use plans and they became a part
  of the RCP and NCP.

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California (Marine) Dispersant Use Zones

• Pre-Approval Zones
• Federal marine waters 3-200 nm from the coast or
  island shorelines
• except
• Waters part of a National Marine Sanctuary, or
  within three miles of
• the CA/Mexico border
• (These may change pending results of ESA Section
  7 consultations
• for use of dispersants in offshore pre-approval
  zones).
• RRT Incident-Specific Approval Required Zones and
  Uses
• State marine waters (0 3 nm miles from shore)
• Waters part of a National Marine Sanctuary
• Waters within three miles of the CA/Mexico border
• Marine waters one mile from anadromous fish
  streams during times of emigration and
  immigration.
• Subsea use or use at surface for more than 4 days

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California Dispersant Plan

• Single document for the evaluation of dispersant
  use in California
• FOSC checklists and flow charts for both zone and
  use types
• Appendices for ease of referencing

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Dispersant Delivery Platforms
Information regarding all dispersant resources
available in or to California (dispersant
stockpiles, application platforms) is in the
California Dispersant Plan
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Embedded Plans and Protocols

• Special Monitoring of Applied Response
  Technologies (SMART)
• Conducted in real time, generally by Pacific
  Strike Team
• Looks for presence of dispersed oil does not
  give oil concentrations.
• Wildlife Spotting Protocols
• Seafood Safety
• Public Communications
• Short and Long-Term Monitoring for Environmental
  Concentrations Dispersed Oil Monitoring Plan
  (DOMP)
• Goal Determine where and when monitoring should
  take place.
• Data can be used for fishery closures, for NRDA
  and for validating assumptions made during the
  NEBA process for dispersant pre-approval

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Dispersants During and After Deepwater Horizon
Spill

• Both aerial spraying and subsea injection used
• Aerial spraying on surface waters
• April 22 - May 26 About 682,808 gallons
  Corexit 9527A and 9500A
• May 27 - July 19 About 293,436 gallons
  Corexit 9500A
• Sub-Total 976,244
• Subsea injection at the source
• May 9 - May 15 About 15,151 gallons of
  Corexit 9500A (2 tests)
• May 15 - July 19 About 771,000 gallons of
  Corexit 9500A
• Sub-Total 786,151
• Grand Total 1,762,395 gallons

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DWH Dispersant Use Fate and Effects

• Oil Budget (August 4, 2010 numbers)
• Directly recovered from wellhead 17
• Mechanically skimmed 3
• Evaporated or dissolved 25
• Naturally dispersed 16
• Chemically dispersed 8
• In-situ burn 5
• Residual 26

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DWH Dispersant Fate and Effects, continued

• Dispersants were applied consistent with all
  policies
• FOSC directed the response and use of
  dispersants, not the RP
• Extensive monitoring for dispersant
  effectiveness, impacts on human health, and
  impacts on water and wildlife were employed
• Additional EPA dispersant components analysis
  validated initial toxicity effects data FDA
  analysis indicated components commonly used in
  foods, cosmetics and OTC medications, and many
  are Generaly Recognized as Safe (GRAS)
• Dispersant use (surface and subsea) greatly
  reduced shoreline and wildlife impacts
• Seafood safely samples indicated uptake of oil by
  organisms did not reach levels of concern for
  human consumption
• Even with the extensive loading of dispersants
  in this response, the dispersants behaved as
  expected and there was a determination of net
  environmental benefit for their use

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Dispersant Lessons Learned by California from
Deepwater Horizon Spill

• Subsea use, and surface use of dispersants for
  more than 5 days, had not been previously
  evaluated as part of NEBA
• Subsea use and use of surface for gt5 days will
  need RRT incident-specific approval
• Rest of NEBA assumptions still seem to apply
• Biological Assessment for ESA Section 7
  submitted to NMFS and USFWS, currently under
  review
• Once ESA consultations complete, will update CDP

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Summary and Conclusions

• Dispersants have toxicity, but most toxicity
  associated with its use is that of the oil.
• In looking at dispersant-oil toxicity and
  potential environmental effects, it is important
  to clearly review mechanism of exposure, duration
  of exposure, species sensitivity and type of
  effects and weight this against same for
  undispersed oil.
• A lot is known scientifically however, there
  will never be perfect or complete information.
• Net Environmental Benefit trade-off decisions
  should be made using best available information
  at the time.

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Summary and Conclusions cont.

• California has developed a dispersant-use policy,
  using scientific data, with input from all
  stakeholders within a given area planning area.
• Used a process similar to an ERA to categorize
  risk and trade-offs associated with that risk
  within the offshore planning areas.
• Developed policies and decision-making processes
  that clearly designates zones, address trustee
  and public concerns, and ensure timeliness of
  response.
• Similar process/product completed in 2006 for
  spill scenario at US/Mexico border

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Summary and Conclusions cont.

• Dispersants not recommended for
• Spills of gasoline, jet fuel, diesel or similar
  light-weight hydrocarbons
• Spills of heavy crude oils that have low initial
  dispersibility and weather quickly
• Oil sheens
• Over shallow waters (lt30-60 deep)
• Over calm waters where mixing is insufficient
  (sea state lt 3)
• Small spills
• When conventional mechanical removal or In-situ
  burn can be used to remove most of the oil
• When extremely sensitive species and habitats are
  not threatened by surface oil
• When it is unsafe for operations
• When you do not know enough about the product
  used (fate and effects once applied, toxicity)
• On shorelines or streams/rivers/lakes
• Over marine mammals or near birds
• If the spill will go offshore
• If there is no expectation of a Net
  Environmental Benefit

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Summary and Conclusions cont.

• When dispersants are worth considering
• The spilled oil is a medium-weight crude,
  considered dispersible, and has a window of
  opportunity that allows enough time for the
  dispersants to work
• You have the right application platforms,
  equipment, and trained personnel
• You have the right oceanographic and weather
  conditions
• You cannot get sufficient oil removal using more
  conventional/mechanical options
• Ocean conditions are too rough to allow safe or
  efficient mechanical recovery operations
• You know where the oil is going, and that it will
  impact sensitive resources that you cannot
  otherwise protect
• You can do the effectiveness and water quality
  monitoring that you will need
• You know enough about your dispersant product,
  and what the relative benefits and consequences
  will be of its use
• You are prepared to handle government and public
  relations
• You can demonstrate that you expect there to be a
  Net Environmental Benefit

61
Department of Fish and WildlifeOffice of Spill
Prevention and Response Response Support Unit

• Ellen Faurot-Daniels
• ellen.faurot-daniels_at_wildlife.ca.gov
• 831-649-2888 (office)
• 831-235-7320 (cell)

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What is in Corexit 9500?
Propylene glycol Common uses include commercial
foods, drugs, cosmetics, and personal care
products (e.g. toothpaste, shampoo, mouthwash).
Approved by FDA as a Generally Recognized As Safe
(GRAS) ingredient, direct and indirect food
additive. Dipropylene glycol monobutyl
ether Common uses include as a solvent for
industrial and residential cleaners/degreasers,
paints and plasticizers. Propylene glycol ethers
as a class are rapidly absorbed and exhibit low
acute toxicity by oral exposure. Dioctyl sodium
sulfosuccinate (DOSS) Common uses include wetting
and flavoring agent in food, industrial, and
cosmetic applications, and a medicinal stool
softener in over-the-counter use (e.g.,
docusate). FDA has approved this compound as a
GRAS ingredient, and as indirect and direct food
additives under prescribed conditions of use.
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What is in Corexit 9500?
Petroleum distillates, hydrotreated light
fraction Common uses include as a solvent for
paints, varnishes, polishes, and lubricants, and
general purpose cleaners and degreasers. FDA has
approved similar odorless light petroleum
hydrocarbons as indirect and direct food
additives.
Numerous chemical synonyms and trade names are
used for these materials (such as Span 80, Tween
80). Common uses are as wetting agents,
solubilizing agents, or emulsifying agents in
cosmetic and personal care products. Widely used
in food products, oral pharmaceuticals, and
parenteral products. They include GRAS
ingredients and direct and indirect food
additives commonly known as polysorbates.
Sorbitan, mono-(9Z)-9-octadecenoate Polyoxy-1,2-
ethanediyl derivatives of sorbitan, mono-(9Z)-9-oc
tadecenoatePolyoxy-1,2-ethanediyl derivatives of
sorbitan, mono-(9Z)-9-octadecenoate Polyoxy-1,2-e
thanediyl derivatives of sorbitan, tri-(9Z)-9-octa
decenoate