Transcript No Slide Title

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
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.
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.
Oil Chemistry
• Types of Oils
• Persistence of Different Oils
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.
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
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.
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)
Oil Persistence
PERSISTENCE:
Refers to an oil or refined product’s 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.
Oil Groups
Category
Persistence
Specific Gravity
Typical Examples
Group I
Non-persistent
N/A
Gasoline products,
condensates.
Group II
Persistent
<0.85
Diesel-like products
and light crude oils
Group III
Persistent
0.85 < 0.95
Medium-grade crudes
& intermediate
products
Group IV
Persistent
0.95 < 1.00
Heavy crudes and
residual products
Group V
Persistent
> 1.00
Low API gravity
products [heavier than
fresh water]
Persistence as defined by US 33 CFR, Section 155.1029 and CCR.
Characteristics and Behavior of
Spilled Oil in the Marine Environment
Weathering of Oils
When oil is spilled on the sea, its physical
and chemical properties are changed.
This process is known as weathering.
Physical Processes
-
-
Evaporation
Dissolution
Emulsification
Spreading
Natural dispersion
Sedimentation
Chemical Processes
-
Photochemical degradation
Microbial degradation
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.
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.
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.
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 recombine with the slick or stay dispersed
in the water column
•
Droplets >0.1mm will likely re-combine
and come back to the surface
•
Droplets < 0.1 mm will stay suspended
in the water.
Following evaporation, natural
dispersion is the second most
important process.
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.
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)
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.
Oil Weathering
Summary
- evaporation
- spreading
- advection
- emulsification
- dissolution
- dispersion
- photo-oxidation
- sedimentation
- biodegradation
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
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.
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
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
Dispersant Mechanism and
Chemistry
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.
How Dispersants Work
First:
Next:
Then:
And:
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 disperse the oil-dispersant
mixture into the water column;
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.
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)
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
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)
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.
Fate and Transport Processes
When Using Dispersants
Effects of weathering processes
once dispersants are applied
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
Dispersant Toxicity
Laboratory Test
Information from Deepwater Horizon spill
Short-term Toxicity
Short-term exposure is described
using LC50 and EC50.
LC50
The concentration that
causes mortality in 50%
of test organisms in a
specified time period
(usually 48 or 96 hrs)
EC50
The concentration that
causes a specific effect
(such as reduced growth or
immobility) in 50% of test
organisms in a specified
time period.
NOEC: No Observable Effects Concentration:
The concentration at which no effects of any kind are observed
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)
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
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.
Aquatic Toxicity Data for Corexit 9500
Species & Lifestage
Standard Test (24 - 96 hrs)
(static test)
LC50 or EC50 ppm
Calif. Test (24 - 96 hrs)
(spiked exposure)
LC50 or EC50 ppm
Crustaceans
Juvenile and adult
Early life stages 1
3.5 to 35.9
48
158 to 1,038
----2
Molluscs
Juvenile and adult
Early life stages
42.3
---
---12.8 to 19.7
Fish
Juvenile and adult
Early life stage
50 to >400
25.2 to 74.7
Algae
Adult
Early life stage
1
zoospores, embryos, larvae;
20
0.7
2
no data available
-->1,055
-----
Types of Effect and Exposure
Acute Effects vs Chronic Effects
Short-Term vs Long-Term Exposure
What will be Affected?
Untreated Spill
Sea Surface
Marine birds, furred mammals,
fishing activity)
Chemically-Dispersed Spill
Sea Surface
Water Column
Plankton, pelagic fish
Water Column
Seabed (offshore)
Seabed (offshore)
Seabed (nearshore)
Benthic species, mariculture
Shoreline
Marshes, shorelines
Seabed (Nearshore)
Benthic species, mariculture,
corals, seagrasses, seawater
intakes
Shoreline
Fate and Effects of Dispersed
Oil in the Marine Environment
Water Column
Bioaccumulation
Sediments
Concepts of Dispersed Oil Fate
California Dispersant Plan
California Dispersant Plan:
Policy Development
• RRT IX tasked each of California’s 6 area committees to
recommend a policy for dispersant use in federal waters (3 – 200
nm from shore), within each Area Committee’s 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 insitu 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 dispersantuse plans and they became a part of the RCP and NCP.
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
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
Dispersant Delivery Platforms
Information regarding all dispersant resources
available in or to California (dispersant
stockpiles, application platforms) is in the
California Dispersant Plan
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 preapproval
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
DWH Dispersant Use: Fate and Effects
• Oil Budget (August 4, 2010 numbers):
– Directly recovered from wellhead:
– Mechanically skimmed:
17%
3%
– Evaporated or dissolved:
– Naturally dispersed:
25%
16%
– Chemically dispersed:
– In-situ burn:
– Residual:
8%
5%
26%
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
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 >5 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
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.
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
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 (<30-60’ deep)
Over calm waters where mixing is insufficient (sea state < ~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”
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”
Department of Fish and Wildlife
Office of Spill Prevention and Response
Response Support Unit
Ellen Faurot-Daniels
[email protected]
831-649-2888 (office)
831-235-7320 (cell)
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.
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
Sorbitan, mono-(9Z)-9-octadecenoate
materials (such as Span 80, Tween
80). Common uses are as wetting
agents, solubilizing agents, or
Polyoxy-1,2-ethanediyl derivatives of sorbitan,
emulsifying agents in cosmetic and
mono-(9Z)-9-octadecenoatePolyoxy-1,2-ethanediyl personal care products. Widely
derivatives of sorbitan, mono-(9Z)-9-octadecenoate used in food products, oral
pharmaceuticals, and parenteral
products. They include GRAS
Polyoxy-1,2-ethanediyl derivatives of sorbitan,
ingredients and direct and indirect
tri-(9Z)-9-octadecenoate
food additives commonly known as
polysorbates.