United States
               Environmental Protection
               Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
               Research and Development
EPA/600/S-92/065
October 1992
EPA      Project Summary
               Chemical  Oil  Spill Dispersants:
               Update  State-of-the-Art on
               Mechanism of Action and
               Laboratory  Testing  for
               Performance
               John R. Clayton, Jr., James R. Payne, Siu-Fai Tsang, Victoria Frank, Paul
               Marsden, and John Harrington
                 Chemical dispersants are formula-
               tions designed to facilitate dispersion
               of an oil slick into small droplets that
               disperse to  non-problematic concen-
               trations in an underlying water column.
               This project had two primary objectives:
               (1) update information on mechanisms
               of action of dispersants  and factors
               affecting  their performance and (2)
               evaluate selected testing procedures in
               the laboratory for estimating perfor-
               mance of different dispersant agents.
               The first objective resulted in a report
               updating information on chemical dis-
               persants, their mode of action, variables
               affecting dispersant performance in the
               field as well as the laboratory, and a
               discussion of a number of laboratory
               and rapid-screen field  tests for esti-
               mating  performance, information de-
               rived in the course of  preparing this
               report was used to select three labora-
               tory testing procedures for evaluation
               of performance characteristics: the
               Revised Standard EPA test, the Swirling
               Flask test, and the IFP-Dilution test, in
               the laboratory, these three procedures
               were evaluated for their precision  of
               results in estimating dispersant perfor-
               mance, costs associated with conduct-
               ing a given procedure, and the ease of
               conducting that procedure (e.g., num-
               ber of tests performed in 8 hr, skill
               level required of an operator, and
               overall complexity of the procedure).
               The precision of results for dispersion
               performance for all  procedures was
               approximately the same (standard de-
viation of 7% to 9% in dispersion per-
formance values). Costs to perform a
procedure and ease of conducting that
procedure favored the Swirling Flask
test.
  This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research  project
that is fully documented in the two re-
ports listed at the end of this summary
(see Project Report ordering informa-
tion at back).

Introduction
  All tasks performed for this work assign-
ment were elements of the Oil Spills Re-
search Program that was initiated in re-
sponse to the Oil Pollution Act (OPA) of
1990. The work supports the EPA workgroup
concerned with revision of sub-part J (dis-
persant effectiveness and toxicity) of the
National Contingency Plan (NCP) as re-
quired by the OPA.  Primary deliverables
from SAIC to EPA's Releases  Control
Branch/Risk Reduction Engineering Labo-
ratory (RCB/RREL) include (1) a State-of-
the-Art (SOTA) report on mechanisms of
action and factors influencing dispersant
performance and (2) a laboratory evalua-
tion of candidate National Contingency Plan
protocols for testing dispersant perfor-
mance of candidate agents. The RGB may
use  information  derived from the SOTA
report as well as the laboratory studies as
part of the work assignment to  assist in
evaluation of  candidate tests for  estimat-
ing performance of dispersant agents as
                                                               Printed on Recycled Paper

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well as planning follow-on  studies  with
chemical dispersants.

State-of-the-Art Report on
Chemical Dispersants
  The SOTA report for chemical disper-
sants includes discussions of the follow-
ing topics: (1) the mechanism of action of
chemical dispersants for oil spills, (2) fac-
tors affecting the performance  of disper-
sants,  (3)  some common laboratory
methods used to measure dispersant per-
formance, (4) aspects of the  analytical
measurement of dispersant performance
in the laboratory, (5) a brief summary of
dispersant applications and their perfor-
mance in field trials and spills-of-opportu-
nity, and (6) recommendations for future
laboratory studies. The discussion of the
laboratory methods includes detailed in-
formation for a number of the more com-
monly used tests, as well as similarities
and differences among testing procedures.
Differences  among tests  are particularly
important because they may be respon-
sible for not only significant differences in
results between laboratory testing methods
but also poor correlations between labo-
ratory results and data from field tests.
Four general types of laboratory testing
methods are considered:  (a) tank tests,
(b) shake/flask tests, (c) interfacial surface
tension tests, and (d) flume  tests.  Infor-
mation is  presented for general  ap-
proaches used in laboratory studies, limi-
tations  inherent  to the laboratory  mea-
surements, and the relevance of laboratory
results to field studies or situations. Brief
descriptions also are presented for a
number of rapid field tests for estimating
dispersant  performance.  Limitations in-
herent to measurements obtained with the
latter tests are discussed.

General Mechanism  of Action
of Chemical Dispersants
  Chemical  dispersants are designed to
promote the break-up or dispersion of an
oil slick into small droplets that distribute
into a water column. The small oil droplets
should not recombine or coalesce to reform
surface slicks. Ideally, dispersed oil drop-
lets will be subject to not  only dilution to
non-problematic  concentrations in  the
water column but also enhanced microbial
degradation  as the oil-water interface in-
creases.
  A typical  commercial  chemical disper-
sant is a mixture of three types of chemi-
cals:  surface active agents (i.e., surfac-
tants), solvents, and additives.  Solvents
are primarily present to promote the dis-
solution of surfactants and additives into a
homogeneous dispersant  mixture.  Addi-
tives  may  be present for a number of
purposes such as increasing the biode-
gradability  of dispersed oil mixtures, im-
proving the dissolution of the dispersant
into an oil slick, and increasing the  long-
term stability of the dispersion. For the
actual dispersion process, however, the
most important components in the disper-
sant mixture are the surfactant molecules.
These are compounds containing Irath oil-
compatible (i.e., lippphilic or hydrophobic)
and  water-compatible (i.e., hydrophilic)
groups. Because of this amphiphatic nature
(i.e.,  opposing solubility  tendencies),  a
surfactant molecule will reside at oil-water
interfaces with the hydrophobic and hy-
drophilic groups positioned toward the oil
and water phases, respectively. As such,
the surfactant will reduce the oil-water in-
terfacial surface tension. The lowering of
oil-water interfacial surface tension will
promote dispersion of oil droplets into the
underlying water with minimal mixing en-
ergy. The oil droplets will remain dispersed
in a water column if they are small enough
to allow for natural  water currents or
Brownian motion to prevent rising to reform
surface slicks.

Factors Affecting Chemical
Dispersion of Oil and Its
Measurement
  A variety of factors have major  influ-
ences on the ability of chemical agents to
disperse oil into water in  both laboratory
tests  as well as  actual field  situations.
These factors can include physical  and
chemical properties of an oil, the compo-
sition  of a dispersant  formulation, the
method of  applying the dispersant to an
oil slick, the mixing energy available for
dispersing treated oil into a water column,
the dispersant-to-oil ratio, the oil-to-water
ratio, temperature, and salinity. Trie  sam-
pling and analysis  methods for evaluating
dispersion performance also can influence
measurement results.
  Crude and refined petroleum products
are complex mixtures of hydrocarbon
compounds that can contain compounds
in five broad categories: lower molecular
weight  (1)  aliphatics  and (2) arcimatics,
and  higher  molecular weight  (3)
asphaltenes, (4) resins,  and  (5) waxes.
Interactions between the  aliphatics,  aro-
matics, asphaltenes,  resins, and waxes
allow for  all of the  compounds to be
maintained in a liquid-oil state.  That is,
the lower molecular weight components
(i.e., the aliphatics and aromatics) act as
solvents for the less soluble, higher mo-
lecular weight  components  (i.e.,  the
asphaltenes, resins, and waxes). In  addi-
tion to inherent differences in  chemical
compositions among different parent oils,
oil that is released  onto a water surface
will undergo  a  variety  of rapid, dynamic
changes in both chemical composition and
physical  properties. Such  changes  are
known as weathering and result from se-
lective dissolution and evaporation losses
of lower molecular weight components as
well as photooxidation and microbial deg-
radation  of  selective compounds.  Com-
plex crude oil mixtures remain as relatively
stable liquid phases as long as the sol-
vency interactions occurring in the bulk oil
are maintained and thermodynamic con-
ditions remain constant. If this equilibrium
state  is changed (e.g.,  due to weathering
processes),  the solvency strength of the
oil may become insufficient to keep higher
molecular weight  components in solution
and  lead to their precipitation as  solid
particles. Accompanying changes in the
physical state and chemical  properties of
the oil can affect the way  chemical dis-
persants  interact with the oil that has un-
dergone  such changes. Despite the pre-
ceding complexities associated with dif-
ferent oils,  dispersant formulations  are
frequently designed with the  intent to deal
with  a relatively broad  range of oil types
and properties.
  The dispersant application method can
be one of the most critical elements de-
termining whether a particular dispersant
will produce  dispersion of  oil or not. In
field  situations,  dispersant is normally ap-
plied from aircraft (airplanes or helicopters)
or surface vessels (boats). The dispersant
is applied as relatively small droplets that
descend onto a slick in a manner providing
broad spatial coverage. The size of the
applied dispersant droplets is important to
successful application.  Droplets that are
too large may  penetrate through an  oil
slick without interaction. Droplets that are
too small may not reach the slick because
of air or wind transport between the appli-
cation source and the slick.
  Following  application of a chemical dis-
persant to an oil slick on water, dispersion
of the oil requires input of mixing energy
that results in injection of the oil as droplets
into  the  underlying  water  column. The
mixing energy  is generally supplied  by
ambient wave action in field situations or
mechanical  agitation of test solutions in
laboratory  systems. Dispersion  of  the
droplets into the water column is countered
by the buoyancy of the oil droplets, which
depends  on the density and size of the
droplets,  their rise velocities  as described
by Stokes'  Law,  and  natural advective
processes that result  in horizontal and
vertical transport and dilution of the oil. In
addition to mixing  energy,  other factors

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that can affect dispersion performance of
an oil include the ratios of dispersant-to-
oil and oil-to-water as  well  as ambient
temperature and salinity in the water.
  Evaluation of dispersant performance in
the laboratory (as well as the field) must
incorporate  appropriate  sampling  and
analysis methods into a testing procedure.
In the numerous studies that compare dis-
persion-performance values among test-
ing procedures, agreement for results is
generally poor. At least a  portion of this
variability  is  attributable to variations in
the sampling approaches. For example,
different laboratory testing procedures will
collect test samples from reaction vessels
at various times after agitation in the re-
action vessel ends. A settling time (i.e.,
collection of  samples only after agitation
has stopped for some predefined  period
of time) may be incorporated into a testing
procedure to allow larger, less stable dis-
persed oil droplets to return to a surface
slick before smaller, more stable dispersed
oil droplets are recovered in a subsurface
water sample.
  In addition to the preceding  issues re-
lated  to sampling methodology, the ana-
lytical methods chosen to quantify amounts
of dispersed oil in samples also are  im-
portant for dispersion measurements. The
most widely used methods for quantifying
amounts of dispersed oil in laboratory test
samples involve extraction  of a water
sample with  a suitable solvent and quan-
titation by  UV-visible spectrophotometric
or (less frequently) gas chromatographic
methods. However, selection of the ana-
lytical wavelength(s) for spectrophotomet-
ric measurements can be important. Mea-
surements in different  laboratory testing
procedures have  been  made at  wave-
lengths from 340 to 620 nmeters,  with
wavelengths selected in part on the optical
(or color) characteristics of particular oils
and dispersants being tested as well as
the optical characteristics of the available
spectrophotometric system.

Laboratory Tests for Dispersant
Performance
  A variety of  laboratory testing methods
have been  used to evaluate dispersant
performance. In general,  laboratory tests
can be placed into four categories:  (1)
tank tests with water volumes ranging from
1 to 150 L, (2) shake/flask tests that are
conducted on  a relatively smaller scale
and require  less sophisticated laboratory
equipment, (3) interfacial surface tension
tests that measure properties of the treated
oil  instead of djspersant performance di-
rectly, and  (4) flume tests using flowing
water systems  with the capacity for break-
ing/nonbreaking  waves  to  generate en-
ergy regimes that can more closely simu-
late  real-world conditions  in large water
bodies (e.g., oceans  and  coastal bays).
Each type of test uses a general approach
of (1) establishing an oil slick on water, (2)
applying dispersant to the slick, (3) apply-
ing energy to the oil-dispersant-water sys-
tem, and (4)  measuring the amount of oil
dispersed into the water.
  Significant differences are inherent to
the various methods. For example, differ-
ent methods for adding the dispersant to
oil include premixing of dispersant with oil,
slowly  pouring dispersant onto the  oil,
spraying the oil surface with a fine mist of
either  neat  dispersant or  dispersant
premixed  with seawater, or pouring the
dispersant into the water before adding
the oil. Test-specific variations  in the ratio
of the oil-to-water volumes can affect  not
only the relative performance of dispersant
surfactants  (e.g.,  hydrophilic  versus li-
pophilic)  but also the magnitude of wall-
effects in test containers. A variety of ap-
proaches have been used  to provide mix-
ing energy to test systems, such as  circu-
lating pumps and spray  hose  systems,
high velocity air streams that produce small
waves on the water's surface,  raising and
lowering  of a metal hoop in  the  water,
rotating or  shaking  separatory funnels,
shaking flasks on  a shaker  table, and
vertically flowing water in  a test cylinder.
Another variation concerns the time after
mixing ends that water samples are with-
drawn from the test solutions in the differ-
ent procedures. In summary, the wide va-
riety of test conditions can make compari-
son of results  among different methods
quite problematic.
  Detailed descriptions of the  following
procedures for evaluating performance of
chemical dispersants are presented  in the
SOTA report.
 1)   Tank tests: Mackay/Nadeau/Steelman
     (MNS) test,  Revised  Standard EPA
     test,  oscillating hoop test,  IFP-Dilu-
     tion test, and flowing cylinder test.
 2)   Shake/Flask tests: rotating flask test
     (Labofina/Warren Spring Laboratory),
     swirling flask test, and Exxon disper-
     sant effectiveness test (EXDET).
 3)   Interfacial Surface Tension tests: drop-
     weight test.
 4)   Flume tests: cascading weir test and
     Delft Hydraulics flume test.
  Table  1  summarizes  features and  es-
sential procedural components in  these
testing methods. Strengths and limitations
associated with each testing method  are
presented in the SOTA report.
  In addition to the preceding methods,
descriptions  also are presented  in  the
SOTA report for five rapid-screen field tests
for evaluating dispersant performance (the
EPA  field dispersant effectiveness test,
the API field dispersant effectiveness test,
the Mackay  simple field test, the Pelletier
screen test, and the Fina spill test kit*).
The  detailed laboratory test methods
identified in  Table 1 do not readily lend
themselves  to onsite applications  in the
field.  In  contrast,  the  rapid-screen field
tests  have been developed to provide fast,
qualitative information  regarding an  oil's
dispersibility in field situations. These rapid-
screen tests are, however, inherently lim-
ited in the scope of information that they
can provide because of their necessary
simplicity for use in field situations.

Evaluation of Laboratory Test
Procedures to  Assess
Dispersant Performance
   Primary  objectives  in evaluations of
laboratory testing procedures were to ob-
tain estimates of the repeatability of mea-
surements for dispersion performance with
different testing procedures, evaluate
comparability of results obtained with the
procedures for selected dispersant  agents
and  oils, and summarize the qualitative
ease  of conducting each testing procedure
(i.e., how many individual test runs  can be
performed in a given period of time, the
complexity of a testing procedure in relation
to the required training time and skill level
of an operator, and associated costs for
both  equipment and conduct of tests). All
of these  objectives have relevance to the
suitability of a  testing  procedure for use
as a routine laboratory testing method.
Additional advantage  could derive from
identifying one or more testing procedures
that could be performed in a  more rapid
and efficient manner than the current Re-
vised Standard EPA  protocol and  that
could provide  results  giving  dispersion-
performance rankings for different  disper-
sant  agents equivalent to those obtained
with testing  procedures used by agencies
in other countries  (e.g.,  Canada  and
countries of Western Europe).

Selection and  Experimental
Design for Test Procedures
   Tests selected for evaluation in the labo-
ratory included  the currently accepted Re-
vised Standard EPA  test,  Environment
Canada's Swirling Flask test (including
three versions: premixed, 1-drop,  and 2-
drop  dispersant additions), and the IFP-
 * Mention of trade names or commercial products does
  not constitute endorsement or recommendation for
  use.

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Table 1. Summary of Features of Laboratory Methods to Test Dispersant Performance
Water
Energy Energy Volume
Test ID Source Rating1 (mL) OWRt
MNS
Revised Std.
EPA
Oscillating
hoop
IFP-dlliition\
Flowing
cylinder
Labotlna
rotating
flask
Swirling
flask
EXDET
Drop-weight
Cascading
wolf

Delft flume
High velocity 3
air stream
Pump 3
Oscillating 3
hoop
Oscillating 1-2
hoop
Vertical flow 1
ofwator
Rotating 3
vessel
Shaker table 1-2
Wrist-action 1-2
shaker
None 0
Water 2-3
passing over
weirs
Wave paddle 2-4
6000 1:600
130,000 1:1300
35,000 1:175
4000-5000 1:1000, then
decrease
1000 1:1200, than
decrease
250 1:50
120 1:1200
250 Variable
(NA)» (NA)
150,000 Variable

4,500,000 Variable
Dispersant
Application
Method
Dropwise/
premix
Dropwise
Dropwise/
premix
Dropwise
Pramtx
Dropwlso
Premix/
dropwise
Premix/
dropwise
Water-oil
interaction
Spray

Spray
DOR*
Variable
3:100 to
1:4
Variable
Variable
1:25
1:25
1:10 to
1:25
Variable
(NA)
Variable

Variable
Settling
Time
(min)
None
None
None
None
10
1
10
None
(NA)
None

None
Complexity
Rating"*
3
3
3
2
2
1
1
1
2
4

4
 'Energy Rating: 0=none; 4=highest.
 tOWR* oil-to-water ratio (v:v).
 * DOR s dispersant-to-oil ratio (v:v).
 "Complexity Rating: 1* lowest; 4 = highest.
 H (NA) * not applicable.
Dilution test (Centre de Documentation de
RecherchS et d'Experimentations sur les
Pollutions  Accidentelles  des Eaux,
Plouzane, France). Test oils used in some
or all portions of the laboratory study in-
cluded Prudhoe Bay crude, South Louisi-
ana crude, Alberta Sweet Mixed Blend
(ASMS),  Arabian  crude,  Bunker  C,  and
No. 2 fuel oil. Test dispersants used in all
portions of the study included Corexit 9527,
Coraxit CRX-8, and Enersperse 700. Com-
mon elements through tests with all of the
testing procedures included the following.
  • oil types: Prudhoe Bay  and  South
    Louisiana crudes
  • dispersant  types:  Corexit 9527,
    Corexit CRX-8, Enersperse 700, and
    "no dispersant" controls
  • test types: EPA-10 min,  EPA-2 hr,
    premixed Swirling Flask, and IFP-Di-
    lution
  • analytical wavelengths: 340, 370, and
    400 nmeter absorbance
  • duplicate measurements for particu-
    lar groups
  • water temperature  (not  a  specified
    variable of  interest for these studies,
    but one that  did exhibit slight varia-
    tions)

Results of Laboratory Tests
  Information for the primary objectives of
the laboratory study are summarized in
Table 2. Estimates of precision or repeat-
ability for  dispersion-performance values
(i.e., standard  deviations  about means)
were approximately 7% to  9%  for all of
the testing  procedures. These values
should be viewed as preliminary estimates,
however, because they are generated with
only a limited number of oils and disper-
sant agents. Furthermore, final estimates
for precision associated with a given test-
ing procedure should incorporate measure-
ments from  multiple  laboratories. The
nonquantitative criteria in Table 2 (i.e.,
number of tests that can be performed in
8  hrs; costs  associated  with equipment
acquisition, conduct of tests, and  waste
disposal; and qualitative items such as
necessary skill level of an operator and
overall complexity of a testing procedure)
favor the Swirling  Flask  procedure for
conducting multiple tests  in  a  relatively
short period of time for the least amount
of cost.
  General trends for the results of disper-
sion  performance in the laboratory tests
are illustrated in Figure 1 for the two com-
mon  test oils (Prudhoe Bay and  South
Louisiana crudes)  with the four primary
testing  procedures (Revised Standard
EPA-10 min, Revised Standard EPA-2 hr,

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premixed Swirling Flask, and IFP-Dilution)
and the  three dispersants (Corexit 9527,
Corexit CRX-8, and Enersperse 700). Dis-
persion for- all test oils in all procedures
was near zero in the absence of chemical
dispersant agents. With  addition of the
dispersants, performance values were con-
sistently highest with the  EPA test.  Simi-
larities in relative trends for dispersion per-
formance with  the  different  dispersants
were observed  in the Revised  Standard
EPA and Swirling  Flask procedures  for
Prudhoe Bay crude. Trends for dispersion
performance with the different dispersants
and South Louisiana crude were less com-
parable  In the  EPA and Swirling  Flask
procedures. Relative performance trends
among dispersants In the  IFP-Dllutlon pro-
cedure did not  appear to be comparable
to either the EPA or Swirling Flask  tests.
Statistical analyses of results showed that
the major portions of differences in disper-
sion-performance values for the three pri-
mary testing procedures  (Revised  Stan-
dard EPA, premixed Swirling Flask, and
IFP-Dilution) could be accounted for by
-differences in the oils and dispersants used
in tests (i.e.,  at least 85%  of the total
variance for results with each testing pro-
cedure). Dispersion-performance values for
measurements at the three analytical
wavelengths (340, 370, and 400 nmeters)
were negligible (i.e.,  <0.5%  of the total
variance).

Recommendations for
Laboratory Studies
   Chemical dispersion of oil into water in
laboratory studies involves complex inter-
actions between many variables including
the  chemical  and  physical properties  of
oils and dispersants, the  method of  appli-
cation (and its  effectiveness) and mixing
of a dispersant with an oil, the source and
magnitude of mixing energy available to
the system, the dispersant-to-oil ratio, the
oil-to-water ratio, temperature, and the sa-
linity of the aqueous medium. Extrapola-
tion of results from dispersion performance
studies  in a  laboratory to field situations
must take into account additional compli-
cating variables including rapid changes
that occur in properties of the oil with time
(i.e., natural weathering), field application
methods and logistics,  ambient  weather
and meteorological conditions, and  local
sea-state or oceanographic conditions
(e.g., wave heights, currents, turbulent mix-
ing regimes,  etc.). The breadth of these
variables makes It unlikely that any single
laboratory test will ever be completely suit-
able to  quantify performance of chemical
dispersant agents for all possible environ-
mental scenarios. More realistically, many
laboratory test  results should be used to
apply relative rankings to performance by
various dispersant agents, including pos-
sible assignment of "pass/fail"  status to
individual dispersants. Scientific criteria to
assign  "pass/fail" status continue to  be
subjects for future discussion and study.
   Much has been  learned about perfor-
mance  of dispersants and their mecha-
nisms  of action from studies conducted
with the  variety of laboratory testing
methods shown in  Table 1.  Test results
are, however, frequently contradictory for
reasons that are probably related to test-
specific characteristics. Adoption of  stan-
dard experimental protocols (e.g., selection
of specific reference oils and dispersants,
consideration of the weathered  state of
test oils, use of specific oil-to-water ratios,
selection or not of designated settling-times
to be used in the conduct of experiments,
and  consideration  of  the  natural
dispersibilities of oils in a given test) might
lead to closer agreement in  performance
results  among testing methods. Further
advances in  testing methodologies,  how-
ever, remain to be developed and refined,
particularly as they  relate to  the environ-
mental relevance and performance of dis-
persant agents. For example, approaches
used to generate environmentally relevant
mixing energies in laboratory studies could
be improved. Continued investigation and
analysis of dispersed oil droplet sizes might
explain differences  in energy levels and
estimates of dispersion performance in dif-
ferent  laboratory testing systems, which
could lead to improved, standardized test
designs. In general, laboratory experiments
also have not been designed to evaluate
the effects of herding of oil on dispersion
results. Current testing methodologies are
Inadequate to Investigate dispersion In thin
versus thick slicks, which  Is Important for
dispersant applications at sea  because
slicks are usually nonuniform In thickness
and distribution on the water's surface. At
the same time, it Is highly  desirable that a
laboratory testing method be simple, re-
quire equipment that  is relatively easy to
acquire and fabricate, require a  minimum
of operator training and sophistication, and
allow for the conduct of a reasonably large
number of tests yielding quantifiable results
in an acceptably short period of time.
  From the standpoint of using  chemical
dispersants for mitigating effects of oil spills
in real-world situations, development and
refinement of  application  techniques and
protocols for applying dispersants in  the
field remain as critical needs. Successful
application of chemical dispersants in field
situations continues to be  extremely prob-
lematic. Further studies in areas of appli-
cation  technologies  are  definitely war-
ranted.
  All reports for the work assignment were
submitted in fulfillment of Contract No. 68-
C8-0062 by Science Applications Interna-
tional Corporation under the sponsorship
of the U.S.  Environmental Protection
Agency.
 Table 2. Results of Test Procedures Used to Evaluate Performance of Chemical Dispersant Agents
Test Procedure
Revised Standard EPA - 10 min
Revised Standard EPA -2hr
Swirling Flask (Premixed) - (2 oils)
Swirling Flask {Premixed) - (4 oils)
IFP-Dilution
-^
Standard
Deviation for
Performance
8.8%*
7.2%
7.8%
8.1%
7.2%
No. Tests/8 hr
2
2
24-36
24-36
4-5
Equip.
Cost
($)
2,280
2,280
1,225
1,225
3,160
Cost
Run
($)
600
600
22
22
202
Complexity of
Procedure
High
High
Low
Low
Moderate
Operator
Skill Level
Moderate
Moderate
Moderate
Moderate
Moderate
 * Bold values for standard deviations are estimates because variances among groups are heterogeneous by Bartlett's test for homogeneity.

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                                                           Prudhoe Bay Crude
                     Mean DIspersant Performance (%)
                       EPA - 10 mln     EPA - 2 hr        Sw. Flask-premix  IFP-dilution
                                                     Test ID
                                                         South Louisiana Crude
                    Mean DIspersant Performance (%)
                                                                                                                    C9527
                                                                                                                    EN700
                        EPA - 10 mln      EPA - 2 hr         Sw. Flask-premix   IFF'-dilution
                                                   Test ID
Figure 1.  DIspersant performance for four testing procedures with two oils and three dispersants. Values are means from replicate measurements.
                                                                                               •U.S. Government Printing Office: 1992— 648-080/60139

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 John R. Clayton, Jr., Siu-Fai Tsang, Victoria Frank, Paul Marsden, and John Harrington are with
     Science Applications International Corporation, San Diego, CA 92121. James R. Payne is
     with Sound Environmental Services, Inc., Carlsbad, CA 92008
 ChoudhrySarwaris the EPA Project Officer (see below).
 Completed reports produced in the project are the following:
 (1) "Chemical Oil Spill Dispersants: Update  State-of-the-Art on Mechanisms of Action and
     Factors Influencing Performance with Emphasis on Laboratory Studies. Final Report,"
     (OrderNo. PB92-222 207/AS; Cost: $19.00, subject to change)
 (2) " Chemical Oil Spill Dispersants: Evaluation of Three Laboratory Procedures for Estimating
     Performance. Final Report," (Order No. PB92-222 041/AS; Cost: $26.00, subject to change)
 Both reports will be available only from:
         National Technical Information Service
         5285 Port Royal Road
         Springfield, VA22161
         Telephone: 703-487-4650
 The EPA Project Officer can be contacted at:
         Risk Reduction Engineering Laboratory
         U.S. Environmental Protection Agency
         Edison, NJ 08837-3679
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268

Official Business
Penalty for Private Use
$300
     BULK RATE
POSTAGE & FEES PAID
         EPA
   PERMIT No. G-35
EPA/600/S-92/065

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