United States
Environmental Protection
Agency
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).
Introduction
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-
strates.
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.
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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-
of-opportunity.
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-
drophilic.
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-
lets.
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
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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
agent.
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
use.
and limitations associated with each test-
ing method are presented in the full SOTA
report.
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
groups.
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-
dure.
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
procedures.
Recommendations for Future
Research
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
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Tabla 1. Summary of Features of Laboratory Methods for Testing Performance of Oil-Cleaning Agents
Tost ID
Inclined
Trough
Swirling
Coupon
Glass
SIldB
Beach
Washing
Reference
Flngas et a/.,
1989
SAIC
(this project)
CEDRE
(unpublished)
Flocco et a/.,
1991
Substrate Oil-to-
Substrate
Contact Time
Stainless steel 10 min
Stainless 18 hr
steel/porcelain
Glass/quartz 20 min
Aquarium (not defined)
gravel
Cleaning
Agent Appl.
Method
Dropwise
Dropwise
Spray
Spray
SOR' Agent Wash Water
Soak- Add Method
Time
1:5 10 min Gravity flow
1:3 10 min Swirling
flow
1:2 10 min Spray
1:2.5 1 hr Gravity flow
Wash Water OWR * Complexity
Volume Rating *
(mL)
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
Water
4.4%
7.2%
12.0%
10.3%
Substrate
3.8%
4.8%
10.4%
8.9%
No. Tests/8 hr
24
24
24
24
Equip, cost
$305
305
1,570
1,570
Cost/Run
$32
32
32
32
Procedure
low
low
low
low
Skill Level
low
low
low
low
' 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
Agency.
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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
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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
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGES FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/113
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