United States
              Environmental Protection
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
               Research and Development
EPA/600/SR-93/113    September! 993
EPA       Project Summary

               Chemical Surface  Washing
               Agents  for  Oil Spills:  Update
               State-of-the-Art on
               Mechanisms  of Action  and
               Evaluation of Two  Laboratory
               Effectiveness Tests
               John R. Clayton, Jr., Siu-Fai Tsang, Victoria Frank, Paul Marsden, Nellie Chau,
               and John Harrington
                Chemical surface washing agents are
              formulations designed to help release
              stranded oil from shoreline substrates.
              The  U.S. Environmental Protection
              Agency (EPA), in response to the Oil
              Pollution Act of 1990, Initiated study of
              these cleaning agents. The project sum-
              marized here had two primary objec-
              tives and generated two reports. The
              first, a state-of-the-art (SOTA) report,
              updated  information on the cleaning
              agents, their mode of action, and vari-
              ables affecting their cleaning perfor-
              mance in the field and in the labora-
              tory. A number of laboratory tests for
              estimating cleaning performance were
              also  discussed. EPA's second report
              presented a detailed evaluation of two
              laboratory testing procedures for esti-
              mating the effectiveness  of the clean-
              ing agents. These were the Inclined
              Trough Test and a new Swirling Cou-
              pon  Test. Two substrates (stainless
              steel and porcelain tile) were evaluated
              for each procedure. The two procedures
              were evaluated for the precision of their
              results in estimating cleaning 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 over-
              all complexity of the procedure). The
              precision of results for cleaning perfor-
              mance were 4% to 7% (standard devia-
tion about the mean) for the Inclined
Trough Test and 10% to 12% for the
Swirling Coupon Test. Costs to per-
form a procedure also favored the In-
clined Trough Test. The number of tests
performed in 8 hr, the skill level of an
operator, and the overall complexity of
a procedure were similar for both tests.
  This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
that is documented in two reports (see
ordering information at back).

  Despite all response efforts, spilled oil
often reaches shorelines and other envi-
ronmentally sensitive areas. When the oil
arrives at the shoreline, it is usually sev-
eral days old and "weathered," so it is
thick, may be emulsified, and is frequently
difficult to  remove from shoreline sub-
  Under the proper circumstances, sur-
face washing agents can be used to miti-
gate detrimental effects of stranded oil on
natural shorelines. Such agents would be
used to remove oil because of biological
sensitivity of indigenous fauna and flora to
oil, amenity considerations of the shore-
line, or concern  about the oil refloating
and subsequently being stranded on adja-
cent shorelines. Chemical cleaning agents
do, however, have certain limitations: in-
                                                            Printed on Recycled Paper.

dlgenous fauna and flora can have a toxic
response or oil can be moved into perme-
able shorelines.
  In past years, chemical dispersants have
been applied as washing agents to clean
shorelines. By breaking oil-water surface
bonds and creating numerous small drop-
lets of oil, the dispersant helps move the
oil off of the surface and into the water
column. On the open sea, this is frequently
beneficial  since  it prevents  shoreline
washups. On the beach, however, disper-
sion Is not always desirable: dispersed oil
can worsen the contamination because oil
remains in the water  and cannot be re-
moved through flotation/skimming opera-
tions, thereby increasing the amount of oil
in the permeable shoreline sediment.
  Surface washing agents, also called
shoreline cleaning agents, are similar to
dispersants in that they also promote the
release  of oil adhered to shoreline sur-
faces; but they will not prevent the coales-
cence or reaggregation of the oil droplets.
They will allow the oil to resurface so that
it may be mechanically removed by boom-
Ing and skimming operations. Therefore,
the oil that is washed away from the sub-
strate can  be removed and further con-
tamination does not occur.

State-of-the-Art Report On
Surface Washing Agents
  The SOTA report discusses the mecha-
nism of action of  chemical surface wash-
Ing agents, factors affecting performance
of cleaning agents,  laboratory methods
for testing performance of such agents,
an  evaluation of  these laboratory meth-
ods, and recommendations for future re-
search. The discussion of laboratory meth-
ods for performance testing presents in-
formation on the  general approach used
for laboratory tests, available information
for Identified tests, similarities  and differ-
ences among tests, the laboratory appa-
ratus required, brief summaries of the test-
Ing procedures,  differences among  the
methods,  and considerations of how the
design of a particular method might affect
results. The full report also considers com-
mon cleaning strategies  for oil stranded
on shorelines and a brief summary of ap-
plications of chemical cleaning agents and
their performance in field trials and spills-

General Mechanism of Action
of Chemical Cleaning Agents
  Chemical  agents for cleaning oiled
shorelines can be included  in three  cat-
egories: (1) nonsurfactant-based solvents,
(2) chemical dispersants, and  (3) surfac-
tant formulations especially designed to
release stranded  oil from shoreline sub-
strates  (i.e.,. surface  washing  agents).
These agents are  intended  to  release
stranded oil from shoreline surfaces (e.g.,
rock faces, cobble, gravel, sand, mud flats,
beached logs, etc.). Depending on  the
specific circumstances, chemical agents
would generally be used to release oil into
(offshore) surface waters where the oil
can be recovered by mechanical proce-
dures such as booming and skimming. In
biologically sensitive environments,  the
chemical cleaning agents should neither
facilitate dispersion of the treated oil into
the offshore water column  nor  enhance
penetration of the oil further into perme-
able shoreline substrates. Cleaning sol-
vents and surface washing agents are de-
signed to minimize  dispersion of oil into
the water column. In contrast, chemical
dispersants will not  only promote disper-
sion of oil  into water (i.e., their intended
purpose) but can also  produce elevated
concentrations of oil in permeable sedi-
ment substrates under appropriate condi-
tions. Hence, use of chemical dispersants
to clean shorelines may not be appropri-
ate, or may be limited to beaches with low
permeability or to offshore waters where
the dispersed oil can be rapidly diluted.
  The purpose of cleaning agents that do
not contain surfactants is to soften or lower
the viscosity  of the treated oil. This can
help release oil when flushed with water.
When  released, the oil  should rise to the
water's surface, as long as its overall den-
sity remains less than  that  of the water.
The oil can then be recovered by me-
chanical means.
  Surfactant-based cleaning formulations
(chemical dispersants and surface wash-
ing agents) contain solvents,  additives, and
surface-active agents (surfactants). The
solvents primarily help surfactants dissolve
in the cleaning formulations and enhance
penetration and mixing of the surfactants
into oil. Additives increase the biodegrad-
ability of the oil and improve the dissolu-
tion of the surfactants  in the  oil. Surfac-
tants, the major ingredient, contain  both
oil-compatible  and water-compatible
groups. Because of this amphiphatic na-
ture (i.e., opposing solubility tendencies),
surfactant molecules will tend  to gather at
oil/water interfaces and reduce the oil/wa-
ter interfacial tension. Although surfactants
are present in both surface washing agents
and dispersants, those  present in surface
washing agents are generally more hy-
  The  cleaning  action of  both surface
washing agents  and dispersants is basi-
cally a detergent action that reduces the
adhesion of oil to a substrate. Oil initially
adheres to a substrate surface as a film
characterized by a relatively large contact
angle between the oil and substrate. After
applying a surface washing agent or dis-
persant to the oil film, surfactant molecules
reside at the oil/water interface. The pres-
ence of the surfactants decreases the oil/
water interfacial tension; this, in turn, pro-
motes roll-up of the  oil film from the sub-
strate surface into a droplet shape (i.e.,
increasing oil/water interfacial surface area)
and reduces the  contact angle  between
the oil and substrate surface. The reduced
adhesion  helps release the oil when  the
substrate  is flushed with water. If surfac-
tant molecules remain at the oil/water in-
terface (e.g., the  more hydrophobic sur-
factants in dispersants), the oil will tend to
remain dispersed in a water column and
not re-adhere to shoreline substrates. In
contrast, the more hydrophilic surfactants
in surface washing agents have a greater
tendency to dissolve into the water phase,
which favors subsequent coalescence or
reaggregation of the oil droplets into sur-
face slicks after  release of the oil from
substrate  surfaces. As long the oil can be
mechanically recovered from a  surface
slick,  it is best  not to disperse the  drop-

Factors Affecting Release of Oil
from Surfaces
  Factors that promote release of stranded
oil from substrate surfaces  can include
physical and chemical properties of an oil,
composition of the cleaning-agent formu-
lation, characteristics of shoreline sub-
strates, method for applying a  cleaning
agent to  stranded oil, characteristics of
the flushing or washing method, ratio of
cleaning  agent-to-oil, temperature, and
salinity. Crude and refined petroleum prod-
ucts are complex mixtures of hydrocarbon
compounds that can contain compounds
in five broad categories: lower-molecular-
weight  aliphatics and  aromatics, and
higher-molecular-weight asphaltenes, res-
ins, and waxes. Interactions between these
allow all of the compounds  to be  main-
tained in a liquid-oil state. The lower-mo-
lecular-weight aliphatics and aromatics act
as solvents for the less  soluble, higher-
molecular-weight asphaltenes, resins, and
waxes. In addition to inherent differences
in chemical compositions among different
parent oils, oil that is  released onto  a
water's surface and is stranded on a shore-
line undergoes rapid, dynamic changes in
both its chemical composition and physi-
cal properties because of natural weath-
ering processes  (e.g., selective  dissolu-
tion and evaporation losses of lower-mo-
lecular-weight  components  as  well  as

photo-oxidation and microbial degradation
of selective compounds). With  loss  of
lower-molecular-weight components, the
solvency strength of  an oil may become
insufficient to keep higher-molecular-weight
components in solution and thus lead to
their precipitation as solid particles. Ac-
companying changes in the physical state
and  chemical  properties of  the oil can
affect the way cleaning  agents interact
with the oil.
  Adhesion of oil to  substrates depends
on the physical and chemical characteris-
tics of substrates: the size, surface prop-
erties, and chemical  composition of sub-
strate particles. Roughness and porosity
of individual particles  influence the degree
of penetration and persistence of oil on or
in the particles.
  How a  cleaning agent is  applied can
affect its performance: access to stranded
oil with the necessary application equip-
ment, actual method and  uniform extent
of the application, ratio of cleaning agent
to oil, method  of penetration  of the agent
into the oil (including  soak time), and sub-
sequent mobilization  or release of treated
oil from substrate surfaces by flushing with
water. In the field, the agent is generally
sprayed from  hand-held spray  packs  or
motorized/wheeled spray carts that can
access the shoreline, nearshore boats, or
aircraft. Cleaning agent-to-oil ratios of 1:2.5
to 1:5 are preferred. Following applica-
tion, soak times of 10 min to 3 hr before
washing generally appear to  be sufficient
to diffuse cleaning agents into stranded
oil. Treated oil is washed with water jets
at various pressures and temperatures,
and  additional chemicals may be used in
the wash water to assist the  cleaning ac-
tion. Increasing temperature in the wash
water assists  the  cleaning  process, al-
though the absolute temperature and vol-
ume of the water can be reduced by pre-
treating the oil with an effective cleaning

Laboratory Tests to Evaluate
the Cleaning Performance of
Chemical Agents
  A  limited number of laboratory tests ex-
ist for evaluating the performance of chemi-
cal cleaning agents under relatively well-
controlled conditions  in a laboratory. Test-
ing procedures discussed in the  SOTA
report include the Inclined Trough Test
(Environment Canada), the Swirling Cou-
pon  Test (developed in this program), the
Glass Slide Test (CEDRE), and the Exxon*
Beach Washing Test (Table 1). Strengths
* Mention of trade names or commercial products does
 not constitute endorsement or recommendation for
and limitations associated with each test-
ing method are presented in the full SOTA
  The Inclined Trough, Swirling Coupon,
and Glass  Slide Tests use artificial sub-
strates such as stainless steel, porcelain
tile, and/or glass; the Exxon Beach Wash-
ing Test uses aquarium gravel. All of the
procedures involve  applying oil to a test
substrate and then applying a cleaning
agent that  is allowed to soak into the oil
for a 10- to  60-min period before washing.
Ideally, substrates  for  laboratory  tests
should mimic real-world materials to pro-
vide environmental  relevance  to results.
Because substrates on natural shorelines
encompass a broad variety of types and
characteristics, no single substrate would
apply to all environmental  surfaces and
situations. The gravel used in  the Exxon
Beach Washing Test comes the closest.
For routine laboratory testing, however, a
substrate should be well defined in  terms
of its morphological and chemical proper-
ties (chemical composition, surface rough-
ness, porosity, etc.), relatively uniform over
the entire  surface  (i.e., an absence of
heterogeneity), and readily available from
commercial sources. These criteria can
be satisfied for materials such as  stain-
less steel, porcelain, glass, and quartz.

Laboratory Studies
   Two laboratory tests that measure clean-
ing performance were evaluated. Primary
objectives were to obtain estimates  of the
repeatability of  measurements for clean-
ing performance with different testing meth-
ods, evaluate comparability of  results ob-
tained with the procedures for selected
cleaning agents and oils, and summarize
the qualitative ease of  conducting each
testing procedure  (i.e., how many indi-
vidual test runs can be performed in  a
given period of time, the complexity of a
testing procedure  in  relation  to the re-
quired 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 rou-
tine use.
   Common elements throughout all of the
testing procedures included the following:
oil type (Prudhoe Bay crude and Bunker
C), cleaning agent (Corexit 9580, Citrikleen
XPC, Corexit 7664, and "no agent" con-
trols), test type (Inclined Trough and Swirl-
ing Coupon), substrate type (stainless steel
and porcelain tile),  analytical wavelength
(340, 370,  and 400 meter absorbance),
and duplicate measurements for particular
  Test results relative to the primary ob-
jectives of the study are summarized in
Table 2. Separate values for cleaning per-
formance were obtained by measuring oil
that was not only released into the wash
water but  also remained on the test sub-
strate after washing. Estimates of preci-
sion (or repeatability) for values of clean-
ing performance (i.e., standard deviations
about means) were approximately 4% to
7% for the Inclined Trough Test  and 9%
to 12% for the Swirling Coupon. These
values should be viewed as preliminary
estimates, however, because they  are gen-
erated with only a limited number of oils
and  cleaning agents. Furthermore, final
estimates  for precision associated with a
given testing procedure should  incorpo-
rate  measurements from multiple labora-
tories. The number of tests  that can  be
performed in 8 hr, the cost per run, and
qualitative items such as necessary skill
level of an operator and overall complex-
ity of a testing  procedure are  approxi-
mately equivalent for the two test proce-
dures (Table 2); however, costs  required
to obtain necessary equipment to perform
the tests favor the Inclined Trough proce-
  General trends in cleaning performance
of the chemical agents for the  different
testing procedures and  substrates are il-
lustrated in Figure 1 for the two  test oils
and test methods, four testing protocols,
and  three cleaning agents. Data for the
figure are  overall means for combinations
of the particular test, substrate,  oil, and
cleaning agent.  As illustrated, cleaning
performance  is consistently higher with
Corexit 9580 and Citrikleen XPC for both
test oils and all testing procedures. Rela-
tive rankings of cleaning performance for
the three  chemical agents are generally
similar among the testing procedures for
the two test oils.  For example,  general
trends in performance values are Corexit
9580 ~  Citrikleen XPC > Corexit  7664 for
both Prudhoe Bay crude and  Bunker C. In
contrast, differences occur in absolute val-
ues  of cleaning  performance among the

Recommendations for Future
  Overall, there is concern as to  whether
any of the four existing tests are appropri-
ate measures of surface washing agent
effectiveness. There  are two  problems:
none of the tests measure the amount of
oil remaining on the surface after wash-
ing, and none of the tests account for how
easily oil is removed from the water after
being washed off the  surface. Therefore,
more research is needed before a surface

Tabla 1.  Summary of Features of Laboratory Methods for Testing Performance of Oil-Cleaning Agents
Tost ID
Flngas et a/.,
(this project)
Flocco et a/.,
Substrate Oil-to-
Contact Time
Stainless steel 10 min
Stainless 18 hr
Glass/quartz 20 min
Aquarium (not defined)
Agent Appl.
SOR' Agent Wash Water
Soak- Add Method
1:5 10 min Gravity flow
1:3 10 min Swirling
1:2 10 min Spray
1:2.5 1 hr Gravity flow
Wash Water OWR * Complexity
Volume Rating *
20 1:67 2
250 1:5200 2
560 1:1000 1
100 1:36 3
* SOR - shoreline cleaning agent-to-oil ratio (v.v; assume oil density of 0.9 g/mL).
* OWR - oll-to-water ratio (V.v; assume oil density of 0.9 g/mL).
* Complexity Rating: 1 - lowest; 3 = highest.
Tabla 2.  Results of Test Procedures Used to Evaluate Performance of Shoreline Cleaning Agents

                              Standard Deviation for
                             Oil Recovery in Fraction
Complexity of   Operator
Test Procedure
Inclined Trough-stainless
Inclined Trough-tile
Swirling Coupon-stainless
Swirling Coupon-tile
No. Tests/8 hr
Equip, cost
Skill Level
 ' Bold values for standard deviations are estimates because variances among groups are heterogeneous by Bartlett's test for homogeneity.
washing agent effectiveness test can be
adopted as a regulatory tool.
  The major conclusion  of this study is
that the overall performance of the two
surface washing agent effectiveness tests
evaluated is  similar, but that the costs for
the Inclined Trough Test  are lower. How-
ever, more research is needed to deter-
mine if an improved test can  be devel-
oped which  may be used to better mea-
sure the cleanliness of a surface or evalu-
ate how well oil may be removed from
water after it Is washed from a surface.
  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

                                                             Prudhoe Bay crude
                    cleaning performance due to agent (%)
                   trough-stainless    trough-tile    coupon-stainless   coupon-tile
                                               test ID
                                                              Bunker C
                   cleaning performance due to agent (%)
                   trough-stainless    trough-tile    coupon-stainless   coupon-tile
                                               test ID
Figure 1.     Cleaning performance for four testing protocols with two oils and three cleaning agents.
             Values are means from replicate measurements.
                                                                               *U.S. GOVERNMENT PRINTING OFFICE: W - 750-071/80MZ



John R. Clayton, Jr., Slu-Fa! Tsang, Victoria Frank, PaulMarsden, Nellie Chau,
  and John Harrington are with Science Applications International Corporation,
  San Diego, CA 92121.                               ,_ ,   ,
Choudry Sarwar Is the EPA Technical Project Monitor (see below).
Completed reports produced in the project are the following:
(1) "Clayton JR  Jr. 1992. Chemical Shoreline Cleaning Agents for Oil Spills:
  Update State-of-the-Art on Mechanisms of Action and Factors Influencing
  Performance. Final Report." (Order No.  PB93-203693; Cost: $27.00,
                -F. Tsang, V. Frank, P. Marsden, N. Chau, and J. Harrington.
   1992. Chemical Shoreline Cleaning Agents: Evaluation of Two Laboratory
   Procedures for Estimating Performance. Final Report." (Order No. PB93-
   203701; Cost: $19.50, subject to change)
 The reports will be available only from:
        National Technical Information Service
        5285 Port Royal Road
        Springfield, VA 221 61
        Telephone: 703-487-4650
 The EPA Technical Project Monitor 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

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  Penalty for Private Use
   PERMIT No. G-35