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Executive Summary
Concern for the possible aesthetic, ecological, and economic im-
pacts of of! spills in the ocean, and the adequacy of technologies
for controlling them, led to a request from the U.S. and Canadian
governments for an assessment of the effectiveness and use of disper-
sants. The assessment was sought to establish an improved basis for
making decisions about when and how to clean up of! spills.
Dispersants, which are solvents and agents for reducing sur-
face tension, are used to remove oil slicks from the water surface.
The treated of! enters the water column as fine droplets where it
is dispersed by currents Ed subjected to natural processes, such
as biodegradation. If this process is effective, the of! may thus be
prevented from moving into sensitive environments or stranding on-
shore, thereby eliminating or reducing damage to important coastal
habitats, marine life, or coastal facilities.
This study addresses two questions about the use of dispersants:
Do they do any good? and Do they do any harm?
DO THEY DO ANY GOOD?
In a few carefully planned, monitored, and documented field
tests, as well as in laboratory tests, several dispersants have been
shown to be effective that is, they have removed a major part of
1
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2
USING OIL SPILL DISPERSANTS ON THE SEA
the oil from the water surface when properly applied to oils that were
dispersible.
However, at other field tests and at accidental spills, dispersants
have been reported to have low effectiveness. The latter results may
have been due to the use of inadequate application techniques, such
as poor targeting and distribution of aerial sprays, as well as the
possibility that the oils were not dispersible, some dispersants were
poorly formulated, or the results were inconclusive (differing reports
from several observers who used different monitoring techniques).
Resolution of these ambiguities wiD require the correct choice of dis-
persants; accurate calibration in field tests; training and competence
in application technique; and the development of more objective and
reliable monitoring methods.
Chemical dispersants have been used extensively on a few large
oil spins Stop I, Torrey Canyon, and Main Pass Block 41 Plat-
form C but no systematic documentation of effectiveness has been
published.
Much is known about why and how dispersants work. This
knowledge is largely based on empirical tests and observations made
in the laboratory and during sea trials. The general mechanism
by which surfactant chemicals disperse crude oils and some refined
products (diesel, heating oils, and bunkers) into the water column is
qualitatively understood, and quantitative studies and models are be-
ing developed to describe this process. The necessary conditions for
effective dispersal of oil in the laboratory have been established, and
dispersant compositions, which could be effective under the proper
conditions, have been developed. In addition, larger-scale laboratory
tests and field experiments at sea have more closely simulated the
action of wind, waves, and other aspects of the marine environment,
and have helped to define their influence on effectiveness.
One important aspect inadequately understood is the interaction
of various physical and chemical processes involved in oil dispersion.
Few published studies exist on the fundamental science concerning
how dispersants act on oil in water. Most of the published studies on
oil spill dispersants describe laboratory en cl sea tests of commercially
available products. These tests generally were conducted to evaluate
how well the products worked, and few studies have investigated
the interactive phenomena of surfactants (surface tension reducing
chemicals), crude oil, and water.
When dispersants are sprayed from boats or aircraft, how well
they work depends on sea conditions and application techniques as
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EXECUTIVE SUMMARY
3
wed as on the chemical nature of both the dispersants and the oil.
Application techniques have improved with experience, but are still
far from routinely optimal. A critical factor in the strategy of dis-
persant application is that the viscosity of of! increases rapidly with
weathering. Because more viscous oil is more difficult to disperse,
response within a few hours is generally essential to high effective-
ness. Some light crude oils and refined products remain dispersible
for a longer time. In addition, of} slick areas tend to expand linearly
with time, and current shear may later increase slick areas even more
rapidly; this expansion rate further emphasizes the need for early
treatment response.
DO THEY DO ANY HARM?
Concern that chemical dispersants could be toxic to marine life
has led to considerable caution in authorizing their use at spill sites.
Laboratory studies of dispersants currently in use have shown that
their acute lethal toxicities are usually lower than crude oils and their
refined products.
A wide range of sublethal effects of dispersed oil has been ob-
served in the laboratory. These occur in most cases at concentrations
comparable to or higher than those expected in the water column
during treatment (1 to 10 ppm), but seldom at concentrations less
than those found several hours after treatment of an of} slick (less
than 1 ppm). The times of exposure in the laboratory (24 to 96 hr)
are much longer than predicted exposures during slick dispersal in
the open sea (1 to 3 fur), and the effects would be expected to be
correspondingly less in the field. Direct application of dispersant to
marine life (as when birds and fur-bearing mammals or their habi-
tats accidentally are sprayed) is to be avoided, because dispersants
destroy the water-repellency and insulating capacity of fur or feath-
ers, and various components may disrupt the structural integrity of
sensitive external membranes and surfaces.
Laboratory bioassays have shown that acute toxicity of dispersed
of} generally does not reside in the dispersant, but in the more toxic
fractions of the oil. Dispersed and untreated of} show the same
acute toxicity, a conclusion obscured in much of the literature by
the large number of studies that quote of! concentration as being the
total of} per unit volume of the experimental system, rather than the
actual measured dissolved and dispersed hydrocarbon concentrations
to which organisms are exposed.
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4
USING OIL SPILL DISPERSANTS ON THE SEA
The immediate ecological impact of dispersed of] varies. In open
waters, organisms on the surface wiD be less affected by dispersed
oil than by an oil slick, but organisms in the water column, par-
ticularly in the upper layers, will experience greater exposure to of!
components if the of} is dispersed. In shallow habitats with poor wa-
ter circulation, benthic organisms wiD be more immediately affected
by dispersed oil. Although some immediate biological effects of dis-
persed of} may be greater than for untreated oil, long-term effects on
most habitats, such as mangroves, are less, and the habitat recovers
faster if the of] is dispersed before it reaches that area.
RECOMMENDATIONS FOR USING DISPERSANTS
The committee recommends that dispersants be considered as a
potential first response option to of] spills, along with other response
options. Implementation of this recommendation must consider spin
size, logistical requirements, contingency planning, equipment and
dispersant performance and availability, appropriate regulations, and
personnel training.
Sensitive inshore habitats, such as salt marshes, coral reefs, sea
grasses, and mangroves, are best protected by preventing of} from
reaching them. Dispersion of of} at sea, before a slick reaches a
sensitive habitat, generally wiD reduce the overall and particularly
the chronic impact of of} on many habitats. This has been shown
by research studies that compared the biological effects of untreated
and dispersed of} released on water over the intertidal or immediate
subtidal zones at Baffin Island (arctic); Long Cove, Maine (north
temperate); and Panama (tropical). Although these studies gen-
eraDy showed that dispersed of! caused less chronic environmental
damage than of} alone, the committee recommends that additional
ecological studies be conducted, under controlled or naturally es-
tablished water circulation regimes in shadow environments, to help
define the conditions under which dispersant use will be effective and
environmentally safe.
Because the principal biological benefit of dispersant use is pre-
vention of oil stranding on sensitive shorelines, and because dis-
persability of of} decreases rapidly with weathering, prompt response
is essential. Therefore, the committee recommends that regulations
and contingency planning make rapid response possible; this includes
prior approval to field-test a dispersant immediately after a spill to
establish dispersability in cases of doubt.
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EXECUTIVE SUMMARY
SUGGESTED RESEARCH
The committee recommends:
5
· Assessment of ecological effects of dispersed oil on marine life
in shallow-water environments, and other habitats having restricted
water exchange, to better define conditions under which dispersant
use can be environmentally safe.
Research on the interaction of of] and dispersed oil with sus-
pended particulates, sediments, plankton, and benthic organisms
to establish a better quantitative basis for comparing the adhesion
properties of untreated of} and dispersant-treated oil.
Research in the mechanics of dispersed of} resurfacing and
spreading to guide improvement in dispersant application strategy
and to reduce possible impact of dispersed of} on fish larvae and
marine birds and mammals.
· Laboratory studies to determine the effect of dispersed oil,
under exposure conditions comparable to those expected in the field,
on water-repellency of fur and feathers and on the hatchability of
seabird eggs after adult birds are contaminated.
Long-term studies of the recovery of selected ecosystems from
exposure to of} and dispersed oil. Investigations at sites where the
effects of of} and dispersed of} have already been studied on a shorter-
time scale would be particularly useful.
Additional investigations on the toxic effects of both un-
treated of} and dispersed of} on surface-dwelling organisms that could
be affected by of} slicks.
· Laboratory and field research to analyze how turbulent diffu-
sion, surface circulation, and wave motion affect dispersed of} distri-
bution as a function of depth, time, and volume of spilled and treated
oil.
· A program of additional research to explore the mechanisms
by which dispersant droplets contact an of} film, mix, and penetrate
into it. The research should examine how surfactants interact with
the of} and migrate to the oil-water interface, and the microscopic
processes by which emulsions actually form.
The committee's formal conclusions and recommendations are
contained in Chapter 7.
.
Representative terms from entire chapter:
marine life
