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OCR for page 254
7
Conclusions and Recommendations
The major conclusions and recommendations provided below
stem from the findings discussed in Chapters 2 through 6. General
conclusions and recommendations are followed by those for physics
and chemistry, biological effects, ecological effects, birds and mam-
mals, and techniques, logistics, and contingency planning. Support-
ing text is cross-referenced in parentheses following each conclusion.
GENERAL CONCLUSIONS
Use of chemical dispersants can be an effective spin response and
control method, especially to minimize environmental damage, but
the application technique is critical to the success of dispersant use.
Dispersants have been shown, in laboratory tests, to be effec-
tive; that is, dispersants can remove of} from the water surface (pp.
70-79~. In a few carefully planned and monitored field tests, high
effectiveness has been documented (p. 174~. At other field tests (pp.
179-187) and at accidental spills (p. 317), reported effectiveness has
been low perhaps because application technique was inadequate,
the of! was not dispersible, the methods of measuring effectiveness
were inadequate, or untested remote-sensing methods were used. Tn-
conclusive visual results have occurred when different observers look-
ing at the same dispersant treatment have provided widely differing
estimates of effectiveness (p. 232~.
254
OCR for page 255
CONCLUSIONS AND RECOMMENDATIONS
255
RECOMMENDATION: Use of daspersants as a first re-
sponse option to oat spills should be considered along with
mechanical cleanup. Implementation of this recommendation
must consider spill size, logistical and contingency planning,
equipment and dispersant performance and! availability, ap-
propriate regulations, and personnel training.
Prompt response with dispersants is essential because the dis-
persibility of oil decreases rapidly with weathering of of} compo-
nents by evaporation (pp. 47-49, 54), which may occur in the first
few hours, and photoox~dation, which may occur over several days
(p. 49~.
RECOMMENDATIONS: Regulations and contingency plan-
ning must make provision for the associated decision-making
process and the need for rapid response.
Prior approval to fileld-test a d;tspersant immediately after a
spill, to establish dispersability when it is in doubt, should be
included in contingency plans.
The principal biological benefits or objectives of chemically dis-
persing oil effectively are to:
· prevent stranding of of} in intertidal zones (pp. 193-198~;
· reduce hazards of discharged of} to marine birds (p. 162) and
mammals lip. lam;
· enhance degradation of of} components (p. 155~; and
reduce chronic impact on some habitats, such as mangroves
(p. 206), because of the shorter persistence of oil.
Biological concerns focus on the possible expansion of the surface
area of slicks (p. 57) treated by dispersants and the effect of this
expanded slick on marine mammals and seabirds (pp. 162, 164), the
effect of dispersed of} on marine life in the water column near the
sea surface (p. 188), and the effect of of} dispersed offshore that may
reach coastal marine habitats and communities.
Laboratory bioassays at measured concentrations show that the
toxic effects per unit of dispersed of] are usually the same for chemi-
cally dispersed of] as those for physically dispersed oil (pp. 130-155~.
Acute biological effects are expected to be slight in most open-sea
applications because the dispersed of} mixes into a relatively large
volume of water, resulting in concentrations and times of exposures
that are low compared to those showing effects in laboratory studies.
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256
USING OIL SPILL DISPERSANTS ON THE SEA
Hence the overall ecological impact of oil will likely be reduced by
· ~
.lsperslon.
In shallow water with poor circulation, and in protected bays and
inlets, the acute biological effects on some organisms and habitats
from high concentrations of dispersed oil may be greater than the
effects of untreated oils (pp. 208-214~.
RECOMMENDATION: Additional ecological assessments
at sites where water is shallow and circulation is well de-
fined are needed to clarify the differences in effects between
dispersed and untreated oil.
PHYSICS AND CHEMISTRY
Oil dispersibility depends on:
. physical properties of the spilled oil, such as viscosity which
increases at lower temperatures and with time of weathering (pp.
54-57~;
· the structure of the slick, such as nonuniform oil thickness
(pp. 36-41) and water-in-oil emulsion (mousse) formation (p. 49~;
· oil composition, including the relative concentrations of hy-
drocarbons and the concentrations of natural surfactants and as-
phaltenes (pp. 51-54~;
· dispersant formulation (pp. 31-35~; and
· actual dosage rate, which in turn depends on the equipment
and technique used to apply the dispersant, wind, dispersant droplet
size distribution, and rate of application.
The spreading and distribution of oil on the water surface de-
pends on complex surface circulation patterns as well as properties
of the oil, wind and sea conditions, and distribution and thickness of
the origin spin (pp. 38-47~. These circulation-related phenomena
have been observed qualitatively, but predictive theories are not yet
dependable (pp. 63-69~.
The size distribution of oil droplets dispersed in the water column
affects the stability of a dispersion. The smaller the droplets, the
more stable the dispersion (p. 58~.
Partial resurfacing of dispersed oil, after agitation ceases, occurs
under laboratory conditions. There is disagreement about its occur-
rence in practical situations because little quantitative held evidence
exists. Resurfacing of dispersed oil may be less likely than that of
OCR for page 257
CONCL USIONS AND RECOMMENDATIONS
257
untreated oil because of the smaller droplet size resulting from the
use of dispersants (pp. 59, 65~.
Chemically dispersed of} appears to adhere less to suspended
particulate matter (pp. 62, 167), biological materials (pp. 188, 199,
207), and shorelines (pp. 208-214) than does untreated oil.
Application of what is wed known about the physical properties
and molecular action of surfactants to the problem of dispersing oil
requires further experimentation and technical experience to guide
development in formulating and applying dispersants.
RECOMMENDATIONS: The following topics for experi-
mental research should be supported:
interaction of of! and dispersed oil with suspended particu-
late matter, sediments, plankton, and benthic organisms;
resurfacing, spreading, and photooxidation of diispersedl oil;
· oil-water interaction phenomena, such as the formation of
mousse, and the influences that surfactants have on this
process;
· analysis of how turbulent diffusion, surface circulation,
and wave motion affect distribution of dispersed of! as
functions of depth, time, and volume of spilled and treated
oil. These analyses will advance understanding about the
concentration of oils in the water column under various
dispersion conditions; and
scientific research concerning the mechanisms by which
droplets of dispersant contact an oilfiIm, mix and penetrate
into it, how their surfactants interact with the oft and
migrate to the oil-water interface, and the microscopic
processes by which emulsions actually form.
.
BIOLOGICAL EFFECTS
Toxicity of Dispersants
The acute lethal toxicity of most dispersants currently consid-
ered for use in the United States Ed Canada (pp. 100-123) is low
compared to the constituents and fractions of crude oils and refined
products (pp. 123-130~. This conclusion is based primarily on labo-
ratory tests. Although the most effective dispersants tend to be more
toxic, lower concentrations of these are required (p. 85~.
Water temperature has a profound influence on the toxicity of
dispersants; there are significantly higher sensitivities of organisms in
OCR for page 258
258
USING OIL SPILL DISPERSANTS ON THE SEA
warmer waters or in summer as compared to winter (pp. 116-117~.
Screening tests for a dispersant should account for the expected
seawater temperature range.
A wide range of sublethal responses, usually at high exposures,
has been observed (pp. 118-122~. The sublethal effects of disper-
sants at realistic concentrations are only partially understood. It is
unlikely, based on concentrations of dispersants that would result
from spraying in marine waters at common rates, that dispersants
would contribute significantly to lethal or sublethal toxicities (pp.
122-123~. Direct application of dispers~nts to seabirds or marine
mammals is not recommended because dispersants may diminish
their water-repelIancy and would thus be an exception to this con-
clusion (pp. 160-164~.
RECOMMENDATIONS: Biological research and toxicity
screening in the laboratory should use exposure conditions
more closely reflecting dispersant use and probable dilution in
the water column.
New products should be screened; for short-term toxicity us-
ing standard methods that would consider the physicochemical
characteristics of the dispersant solutions and lethal and sub-
lethal responses of test organisms. In addition, such standards,
if they were international, would permit reliable comparisons
of data among nations.
Knowledge of the chemical composition of formulations is nec-
essary for making responsible decisions about the use of of] spin
dispersants (pp. 97-100~. The chemical compositions are indicative
of toxicity and surfactant properties.
RECOMMENDATION: Information on dispersant chemi-
cal structures and formulations should! be made readily avail-
able to researchers. This information is particularly important
to studies concerning toxicological and ecological effects of dis-
persants and dlispersed oils.*
* Some committee members expressed the view that much of the information about
dispersant composition is proprietary, but a Imowledge of the general type of compound,
as would be obtained from the patent literature, would be sufficient for toxicological
assessments. Other members felt that the detailed structure of the major and minor
components is essential to achieve a biochemical understanding of toxic effects.
OCR for page 259
CONCL USIONS AND RECOMMENDATIONS
Toxicity of Dispersed Oils
259
Many earlier laboratory studies of the joint toxicity of of] and
dispersants erroneously concluded that dispersed oils were more toxic
than of} alone. These tests used nominal concentration (weight of of}
per unit volume of water in the experimental system) that incorrectly
included the untreated of! floating on the water surface as well as the
of] fraction in the water column to which the organisms were exposed.
The amount of of] in the water includes dispersed and dissolved oil, as
wed as of} that adheres to particulates. The fraction of the of} in the
water was higher when dispersants were used. A proper comparison
of the effects of chemically treated and untreated of! must be made
using only the measured of} fraction in the water, exposing test
organisms to the same actual concentration of oil in both cases (pp.
126-128~.
Based on laboratory studies, acute lethal toxicity of chemically
dispersed oils resides not in the dispersant but primarily in the oil
droplets (for some species) and the low molecular weight and dis-
solved, aromatic, and aliphatic fractions of the of! (for most species).
Acute toxicity of chemically dispersed oils is generally similar to
that of the portion of oil in the water column alone (p. 154~.
Different species and life stages show sensitivity to chemically
dispersed oils at exposures varying by 3 to 4 orders of magnitude
(pp. 130-154~.
Laboratory tests of the toxicology of dispersed of} should cover
the ranges of exposures that would be expected in the field, but
there is no commonly accepted technique for comparing laboratory
bioassay data with field exposure data. One approach is to express
exposure as an integral of concentration over time based on a "tox-
icity index" concept that concentration and time of exposure are of
equal importance in short hydrocarbon exposures.
Several studies have shown that chemically dispersed oil does
not adhere as much as untreated of! to some organisms or habitats
(e.g., mangrove trees, pp. 206-208~.
Greater adverse effects have sometimes been observed from a
few untreated of] droplets than from many chemically dispersed oil
droplets (e.g., abnormal larvae from exposed herring eggs, pp. 136-
137, 153~.
RECOMMENDATIONS: Methods for comparing laboratory
and field exposures should be developed based on sound physi-
ological, toxicological, and physicochemical principles.
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260
USING OIL SPILL DISPERSANTS ON THE SEA
Additional research should be conducte`d, or observations
made, to compare the effects of untreated oil adhesion to or-
ganisms as compared with effects from chemically `dispersed;
oil. Particular emphasis should be placed on organisms that
reside at or near the sea surface.
Biodegradation
The biodegradation of dispersant components has been demon-
strated in the laboratory and in mesocosm experiments (pp. 155-
158~.
Some laboratory studies and all mesocosm studies have shown
that the rate of biodegradation of dispersed of} is equal to or greater
than that of undispersed oil (p. 159~.
RECOMMENDATION: Further field! studies of baodegrada-
tion rates of dispersed oils and hydrocarbon components should
be undertaken, together with studies of criticalfactors control-
ling ~oiodegraclation in the field.
ECOLOGICAL EFFECTS
Exposure of communities of organisms and their habitats to oil,
dispersant, and dispersed of} depends on many factors, including (pp.
186-214~:
.
i
amount of oil dispersed;
· amount of dispersant used Ad effectiveness of dispersion;
· volume of water available for dispersal;
~ exchange of water through turbulence and vertical and hor-
zontal transport, such as local currents, tides, convergences, and
upwellings; and
· distribution and abundance of affected organisms; for ex-
ample, exposure is higher in restricted bays and estuaries than in
open-ocean situations.
The best strategy for protecting sensitive inshore habitats (i.e.,
littoral and shadow subtidal, polar to tropical) is to prevent undis-
persed oil from contacting them. Dispersion of of] before it reaches
these habitats may keep them from becoming oiled, or may reduce
the persistence of oil that contacts them. Thus offshore chemical
dispersal may be the best technique for reducing overall, particularly
chronic, impact of the oil in those habitats.
OCR for page 261
CONCL USI ONS A ND RE COMMENDA TI ONS
tats vary.
261
Acute effects of chemically dispersed oils on organisms and habi-
.
· Organisms near the water surface are exposed to higher con-
centrations of undispersed of! than are organisms in the water col-
umn, but organisms in the water column, particularly in the upper
layers, will experience greater short-term exposure to of} components
if the of] is dispersed (pp. 60, 168-172~. Benthic organisms, such as
mollusks, may also be exposed to higher concentrations of dispersed
oils, resulting in short-term bioaccumulation. However, long-term
harmful effects may be reduced by chemically dispersing of] rather
than not treating the spin (pp. 192, 199~.
· In a habitat with restricted water exchange, the acute effects
of dispersed oil on some organisms or marine plants may be greater
than that of of} alone. However, mangroves (pp. 206-208) and some
other intertidal habitats, such as north-temperate mudflats, are less
damaged by dispersed of} and can recover faster. Therefore, if a stick
is treated before it enters these areas, the community recovers faster.
· Intertidal areas on rocky coasts, sand and mud flats, and salt
marshes can be protected if the of} is dispersed offshore, but do not
benefit from dispersant application after the of] reaches shore. Once
of} has penetrated a salt marsh, it is best left alone (pp. 193-198~.
· Studies of the persistence of hydrocarbon fractions in a range
of habitats, with and without dispersants, show that reduction of
chronic exposure is a key to reducing biological damage (pp. 209-
213~.
· Toxic effects of untreated of] on fish have been reported in
some shallow-water environments, but the effects of dispersed of]
have not been studied (pp. 134-137, 150-154, 200-201~.
· In offshore open water, concentrations of dispersed of! wiB
be much lower than in shallower waters, or in waters with poor
circulation, and the resulting impacts will be correspondingly less
(pp. 168-172~.
No measurable effects of dispersed or untreated oil on com-
mercial fisheries and their supporting food webs have yet been found.
However, such effects, if they occur, would be difficult to detect and
measure effectively because of the mobility of most fish and many
invertebrates, the natural variability of their populations, and the
effects of overfishing on stocks.
RECOMMENDATIONS: Additional ecological studies un-
cler controlled or established water circulation in shallow en-
.
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262
USING OIL SPILL DISPERSANTS ON THE SEA
vironments should be conducted to define the conditions under
which dispersant use can be environmentally safe.
Long-term studies of the recovery of selected ecosystems ex-
posed to oil are desirable, including continued studies of those
sites where the impact of of! and dispersed of! has been com-
pared already.
BIRDS AND MAMMALS
Adverse effects of oil, dispersants, and dispersed of] have been
shown in laboratory tests on seabirds and on mammals (otter, polar
bear, and fur seal pelts) and from limited field tests and observations,
such as (pp. 160-164~:
· reduced water-repelIancy of fur and feathers (critical for ther-
mal insulation);
· reduced hatchability of eggs; and
· physiological and biochemical effects.
These laboratory results are consistent with field observations
for untreated oil, but- may not appropriately represent exposures to
dispersants and dispersed of! in the field. However, over a short
period, residual sheen from dispersed of} slicks may cover a greater
area than untreated oil, and more birds rather than fewer may be
oiled; this effect may possibly offset some biological benefits resulting
from dispersant use.
Theoretical considerations indicate that the exposure of birds
and mammals to dispersed of} in the water column may be less
damaging than exposure to untreated floating of! (p. 162~. No
definitive field studies, in which birds and mammals were exposed to
dispersed oil, have been carried out.
Concern about the effects of dispersants on birds and marine
mammals centers on a question of the extent of exposure rather than
on enhanced toxicity of the oil.
RECOMMENDATIONS: I,aboratory studies should be un-
dertaken using realistic exposure conditions (e.g., initial con-
centration of dispersed oil of 10 to 20 ppm, decreasing with
time) to assess the ability of fur and feathers to maintain
the water-repellancy criticalfor thermal insulation under dis-
persed of! exposure conditions comparable to those expected in
the field.
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CONCL USIONS AND RECOMMENDATIONS
263
Laboratory tests, under exposure conditions similar to those
expected in the field, should be conducted of the hatcha~oility of
seabird eggs that have come into contact with dispersed of! and
untreated oil.
The possible effects of ingested oilfrom exposure of loins ant!
sea mammals to dispersed and untreated oil should be observed
when possi~ole (e.g., after an accidental spil0.
TECHNIQUES, LOGISTICS, AND
CONTINGENCY PLANNING
Logistical constraints in some situations may dictate that dis-
persant use (if a dispersant can be accurately applied) will be the
preferred spill response, compared to the use of mechanical methods.
Distance to the spill, time required to mobilize equipment, the size
of the spill, and the roughness of the seas are major factors that
influence the use of dispersants (pp. 241-243~.
Oil spills of all sizes can be treated by the use of undiluted
dispersant, which is usually applied by various techniques:
.
Major spills (greater than 2,500 bbl) encompass large areas
and require rapid treatment response; the only technique that may
be capable of countering these spills is to spray from helicopters or
large aircraft (pp. 224-226~.
Moderate or small spills can be countered by spraying from
boats, but this technique is less efficient on spills greater than 1,000
bbl because of logistical limitations (pp. 222-224~.
Dispersant droplet size produced by aerial spray systems can
be controlled only within limits determined by nozzle design and the
effects of air currents produced by aircraft motion. For boat systems,
nozzle selection and flow rate determine droplet size (pp. 216-220~.
There is, as yet, no practical means of varying the application
rate of dispersants to achieve a constant dispersant-oil ratio in treat-
ing a spill (pp. 218-219~.
Operators of aircraft or boats spraying dispersant need guidance
to locate the oil and apply dispersant accurately. This guidance is
normally provided by spotter aircraft (pp. 237-238~. Remote-sensing
methods are being developed, but they are still difficult to interpret
(pp. 230-233~.
For documentation and evaluation of effectiveness, photography,
including videotape, is useful but must be interpreted cautiously
OCR for page 264
264
USING OIL SPILL DISPERSANTS ON THE SEA
because of the influence of available sunlight and sea-state conditions
on the detection of of} or dispersed of} (pp. 231-232~.
In contingency planning, as well as in its implementation, the
primary questions to be answered in deciding whether to use disper-
sants are:
215-228~?
.
208-214)?
Is the of} dispersable (pp. 50-57~?
Can dispersant be effectively applied to the of! slick (pp.
Will the use of dispersants reduce environmental damage (pp.
Contingency planning is fundamental to the effective use of dis-
persants for the following reasons:
· Equipment is specialized and availability must be assured
(pp. 241-243~.
Calibration of the spraying system is essential (pp. 228-229~.
· Training is needed on all aspects of dispersant use.
· Response must be fast because weathering decreases effec-
tiveness (pp. 54-57, 244-253~.
RECOMMENDATIONS: More reliable remote-sensing equip-
ment and easily interpreted processing systems need to be de-
veloped.
More accurate monitoring and documentation of dispersant ef-
fectiveness, on spills of various sizes and under environmental
conditions covered by contingency plans, are encouraged.
Detailed contingency planning for the use of dispersants should
include:
past experience in applying dispersants and evaluating their
effectiveness;
hazard evaluation for sensitive species, populations, com-
munities, and habitats;
familiarity with available dlispersant chemicals;
training and practice in decision making; and
training of observers to monitor daspersant application and
results.
Representative terms from entire chapter:
water column
