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OCR for page 165
4
Intermediate-Scale Experiments and
Field Studies of
Dispersants Applied to Oil Spills
Because the magnitude, type, and duration of effects on aquatic
organisms and ecosystems caused by of] spills depend directly on
exposure to toxic components of the oil, the effects of oil are expected
to be less if the spill is rapidly diluted by chemical dispersion. A
number of experiments at scales larger than normal laboratory size
(mesoscale) as well as field studies at sea have been conducted to
determine the physical dispersion and the subsurface concentrations
of of} components. They and their associated biological effects are
reviewed in this chapter.
PHYSICAL AND CHEMICAL STUDIES
Although laboratory tests can rank various dispersant formula-
tions as to their relative effectiveness and can be used to investigate
the effects of parameters, such as temperature, water salinity, and of!
viscosity, the real test of dispersant effectiveness is a full-sized spit! in
a test at sea. However, rigorous sea tests are expensive and difficult
to conduct, and results have often been disappointing.
An absolute measure of effectiveness in the field would require
that a very large set of water samples be taken, covering the entire
water mass within which the oil might become dispersed? as well
as an accurate measurement of the amount of of} that evaporates
from the slick under the field conditions. Very few experiments have
165
OCR for page 166
166
USING OIL SPILL DISPERSANTS ON THE SEA
attempted this approach, but it is these that provide the most direct
evidence of dispersal of oil at sea (Brown et al., 1987~.
Some studies have been set up to obtain typical water samples
from beneath a dispersant-treated or untreated slick, so as to assess
whether the concentrations of of! components exceeded potentially
toxic levels. The emphasis of others is to see if dispersants ranked
better or poorer by laboratory test would perform in the same order
on a larger scale.
As will be discussed in Chapter 5, much thought has been given
to remote monitoring systems, but there is as yet no standard method
for determining effectiveness outside the laboratory. As a result,
dispersant operations at spills of opportunity have provided only a
limited and ambiguous set of effectiveness data. The compilations
of Nichols and Parker (1985) or Fingas (1985) if taken uncritically
could be rather discouraging. In many cases, dispersal was observed
but could have been due to natural processes—adequate control
spins without chemical dispersant were unavailable. In other tests,
different observers at the same site reached different conclusions
about how much of the slick had been dispersed. The reported
effectiveness at any but the most carefully planned field trials is
extremely dependent on the types of observations or samples, the
location of the observers or sampling devices, and the dispersant
application technique.
Intermediate-Scale (Mesoscale) Studies
Some studies intermediate in size between laboratory and field
(microcosm and mesocosm) although not without limitations can
provide useful information with greater control and at less expense
than a fuB field study (Adams and Giddings, 1982~. An exam-
ple is the Controlled Ecosystem Pollution Experiment (CEPEX) in
British Columbia, Canada. Two 13-m deep CEPEX plastic* enclo-
sures moored at Saaruch Inlet were treated with 3 liters of oil (Green
et al., 1982~. In one system, Forest 9527 was added, producing a sta-
ble emulsion with average droplet size about ~ am or less (measured
by underwater photomicroscopy).
*Typical experiments are conducted using plastic (usually polyethylene) enclosures
in an open-water area. In one study (Laalce et al., 1984), the function of Ekofisk crude
oil suffering different fates was measured using tritium tracers. Only Q0037 percent of
the oil was adsorbed in the plastic walls.
OCR for page 167
INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 167
In contrast to expectations, evaporation was inhibited in the
dispersed system, which required 10 to 15 days to lose Yolatiles,
whereas the undispersed slick lost volatiles in ~ to 2 days. After 7
and 27 days, the amount of of! reaching the sediment increased by
about a factor of 10 in the enclosure where dispersant had been used.
However, the dispersed oil was more rapidly biodegraded, by a factor
of 10, with alkanes essentially oxidized in 15 days, so that in each
case only about 0.1 percent of the oil remaining in the water column
eventually was found in the sediment (Green et al., 1982~.
To test effects of dispersants in a littoral ecosystem simulating
the shadow rocky Baltic Archipelago, Linden et al. (1985, 1987)
used six pools, 8 m3 each, with a flow-through seawater system. Two
pools were exposed to 20 ppm (average initial nominal concentration)
North Sea Forties crude oil, two were exposed to 20 ppm oil with
Corexit 9550 added, and two served as controls. The differences in
biological effects between treatments were attributed to dispersed of]
remaining in the water column longer, without adhering to particles
or organisms or settling to the bottom. Because seawater flowed
continuously through the systems, the dispersed oil was more rapidly
washed out.
In-a trial using intertidal enclosures, Farke et al. (1985a,b) oiled
sand by contaminating inflowing seawater on 12 successive rising
tides with ultrasonically dispersed Arabian light crude oil, Finasol
OSR-5 dispersant, and an oil-dispersant mixture (ratio O:D of 10:1~.
With or without dispersant, average of] concentration in the water
(sampled at high tide) was about 10 ppm, and core samples showed
that less than 5 percent of the of] penetrated the deeper sediment.
Maximum concentration of of! in the top 2 cm of sediment was 560
ppm in both the oil-dispersant experiment and oil-only experiments.
After contamination was stopped, the of} concentration returned to
baseline values within 4 to 6 weeks.
Although the Parke et al. (1985a,b) study using premixed disper-
sant and of} does not fully simulate the impact of of} dispersed at sea
coming in on the tide, it is closer to that ideal than other intertidal
studies in which dispersant was applied after a beach was oiled. In
the latter studies, dispersant increased the degree of oil penetration
It is clear from this example that dispersed of} is more easily washed
out of an enclosed system than untreated oil, and there appears to
be evidence that dispersed of} adheres less to particles and sediment
than untreated of] (see Chapter 2~.
OCR for page 168
168
USING OIL SPILL DISPERSANTS ON THE SEA
Recent examples of mesoscale studies of physicochemical charac-
teristics of dispersed oils include those at the Esso Resource wave
basin in Canada (Brown et al., 1987; To et al., 1987~. These studies
show that the dispersed of} plume often is highly irregular in shape
and nonuniform in concentration. This nonuniformity can lead to
serious errors when attempting to estimate dispersant efficiency by
analyzing chemical samples from the water column. Further, these
mesoscale experiments reemphasize the need to apply dispersants
preferentially to the thicker portion of the slick in order to achieve
good overall efficiency.
American Petroleum Institute Research SpiBs
Open-ocean tests sponsored by the American Petroleum Insti-
tute in 1978 and 1979 evaluated several factors bearing on dispersant
performance and fate: oil type, sea state, and dispersant type and
dosage. The studies compared the fates of untreated and chemically
treated oil and measured total hydrocarbons in water under slicks
(McAuliffe et al., 1980, 1981~.
In four spills conducted off New Jersey, Il.7 bb! of Murban and
LaRosa crude of} were sprayed with dispersant by helicopter. Murban
crude of} changed rapidly when dispersant was immediately applied.
A distinct whitish-brown subsurface plume appeared quickly. Over
several hours, this plume grew in area and diminished in color and
visibility as the dispersed of] diluted. Rough mass-balance calcula-
tions, supported by visual and photographic observations, indicated
that Murban crude oil was almost completely dispersed (McAuliffe
et al., 1980~.
The highest total oil concentration measured under the low-
viscosity Murban (39° API gravity) crude of! was 18 ppm at ~ m at 23
min after dispersion, decreasing to less than ~ ppm at 6 m after ~ hr.
The highest dissolved hydrocarbon concentrations 40 to 50 ppb—
occurred in the samples with the highest tote] of] concentrations.
After 110 min the highest hydrocarbon ECU to Coo) concentrations
were2ppbatlm.
When dispersant was sprayed on the fresh I`a Rosa (24° AP]
gravity) crude oil, no sudden change was apparent. However, in time
this of} became a thin sheen, as contrasted with the thick, black,
asphaltic appearance of the thicker of} in the downwind, leading edge
portion of undispersed oil. About half the slick was estimated to have
been dispersed. The highest total of! concentrations measured in the
OCR for page 169
INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 169
~ ~ ~ . ~ . ~ ·~
dispersed of! plume were 2 to 3 ppm from the surface through 3 m
at 23 mitt after spraying. These concentrations also existed after an
hour, and thereafter decreased. The highest dissolved hydrocarbon
concentrations were 14 ppb at 47 min. and 9 ppb after 94 min.
The two slicks that were allowed to weather for 2 hr before
dispersant spraying showed low concentrations of oil in the water.
This was probably due to the greater area of the slick and the fact
that most of the oil was in the downwind portion of the slick. Since
the overall slick was uniformly sprayed, the thick portion where most
of the of! resided may have been undertreated. Weathering also
would have increased of} viscosities, thereby decreasing dispersant
effectiveness. These effects were clearly demonstrated during the
1979 API studies off southern California.
In the September 1979 API studies off the coast of southern
California (McAuliffe et al., 1981), nine separate 10- or 20-bb! releases
of 0.90 specific gravity (26.6° API gravity) Pru~hoe Bay (Alaskan
North SIope) crude of] took place over 2 days. These tests were
unusual in the large number of water samples taken (900), which
aDowed contours of subsurface concentrations to be obtained and a
more accurate mass-balance made. The slick areas of the 20-bb} of!
discharges were 2 to 3 ha (5 to 7 acres) at the start of aerial spraying,
10 to 30 min after release, but increased during the 30-min multipass
spraying. The average slick thickness was 0.1 to 0.2 mm initially, but
decreased as the slick area increased.
The most effectively dispersed 20-bb] slick was sprayed with dis-
persant concentrate from a DC-4 aircraft; the results of this test are
discussed in detail here. Figure 4-1 shows that the of! concentrations
for the first sampling run under the remaining slick and through the
dispersed of! plume (five stations were placed along the length of the
stick and two across it). The highest dispersed of} concentrations
occurred at Station 2 (center of the downwind thicker part of the
slick) with an average of 41 ppm at ~ m and 10 ppm at 3 m. A mass-
balance was estimated (by layers) by calculating the water volume
(as the slick length multiplied by two-thirds of the width) multiplied
by the average of] concentration of the seven stations. The chemical
analyses were on a weight basis. Correcting for the specific Cavity
~ . ~ ,,; is ,,
/^ ^~\ 1 . ~ . ~ ·~ ~ · ~ ~ ~ ~ ~ . ~
tu.9u~ changes the amount of oil discharged from 20 bbl to 18 bbl on
a weight basis. It was further assumed that by the time of spraying,
15 percent of the of} had evaporated. Thus the amount of of} in the
slick that was sprayed was estimated to be 15.3 bbl. The amount of
of} measured in the water column at the various depths (totaled in
OCR for page 170
170
USING OIL SPILL DISPERSANTS ON THE SEA
o
3
-
a)
C]
6
9
Stations (if)
Time After 13
Spraying (min)
Time 1322 1325
13.1 .89
o
6
_ 7.6 ! 1 1 2|
— 11.4 1 1.03 -
/ /
— 7.6 / /.58 -
~/Q~
Stations (A
Time After 32 35
Spraying (min)
Time 1 303
102
1306
54
54 20.5 /
41 ~ 41 / .86 ~ 7.4
29 I / .82,~
.47
_ pR
1309 1315 1317
1.9 2.1 .90
1.69
1.73
J
1.03
J.66
no no no
15 19
@3 ~
25 27
Amount Percentage
of Oil in of Slick
Water Dispersed
(bbl) in Water
0-2 m 6.05 39.0 (60)* Slick Size
150x500 m
g, 2-4 2.54 17.0 (25) Slick Area
7.5 Hectares
(1 8.5 Acres)
j' 4-7.5 1.42 9.3 (14) Time of Spill
1214-1217
5 7.5-10.5 0.06 0.4 (0.6) Time of Spraying
_ 1230-1 250
10.10 66.0
Totals
*Percent Distribution by Depth Interval
FIGURE ~1 Concentrations (ppm) of oil in water under a 2~bbl crude oil slick that
was sprayed i~runediately with dispersant by DC-4 aircraft, September 26, 1979; first
sample run. Percentage of slicilc dispersed in water is based on the estimated amount
of oil in the sliclc, not the amount of oil dish Bed. Source: McAuliffe et al., 1981.
Figure 4-~) was 11.2 bbI, or about 66 percent. Therefore, two-thirds
of the of} in the slick (after evaporation) was dispersed, and one-third
remained on the surface. Only 0.8 percent of naturally dispersed oil
was found under untreated (control) slicks during single sampling
runs immediately after the control slicks were released. The highest
amounts of naturally dispersed of} generally are found under fresh oil
slicks.
OCR for page 171
INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 171
Time 1331 1334 1339 1344 1350
83 4.35 8.56 7.5 .69
O : 1 1 1 1 1 ll
1 ~ 3.21 1.14 ~ 1.~ ~ 12.1 1.46 _
, ~ 2.60 ~ 1.70 9.22 ~ 6.~ I
\ — ~37 J 10.10 J ~ I /
3~ ·: j ~~ | I
6 ~ .07~4 /
9 - 02 . .05 \ \ · / /-
Stations () ~ (hi) ~ ~
Time After 41 44 49 54 60
Spraying (min) Amount Percentage
of Oil in of Slick
Time 1354 1359 Water Dispersed
3.55 .82 (bbl) in Water
-
-
a)
9 1
Stations (A
Time After 1:04
Spraying (hr:min)
1.70 1.73
_
~~m
_ .07
1.28 2.38
0-2 m 4.74 31 (35)* Slick Size
162 x 840 m
2-4 3.68
4-7.5 4.42
7.5-10.5 0.79
Totals 1 3.6
24 (27)
29 (32)
.18 —
l
1:09 *Percent Distribution by Depth Interval
89
5.2 (5.8)
Slick Area
13.6 Hectares
(34 Acres)
Time of Spill
1214-1217
Time of
Spraying
1 230-1 250
FIGURE 4-2 Concentrations (ppm) of oil in water under a 2~bbl crude oil slick that
was sprayed immediately by DC-4 mrcra£t, September 26, 1979 (day 1~; second sample
run. Source: McAuliffe et al., 1981.
Figure 4-2 shows the results of a second sampling run through
the slick about an hour after spraying. During this time? the slick
had elongated as the remaining wind-driven surface slick separated
from the dispersed oil plume. The highest concentration, found at
1 m at Station 2 after 15 min (Figure 4-1), occurred from O to 6 m
at Station 4 after S4 min. The dispersed oil had diluted by mixing
downward. The mass-balance calculation at that time provided an
estimate of about 89 percent of the unevaporated oil dispersed.
A third sample run was started 3 hr after spraying, as a transect
OCR for page 172
172
USING OIL SPILL DISPERSANTS ON THE SEA
At 3 6 18 4 4
Time 1555 1558 1604 1622 1626 1630
1 .53 1 .38 .18 .23 .19 .99
o
1
-
Q
6
9
Stations
Time After
Spraying
(hr:min)
/.4r2
i`_ .64
·03 .06
.05
/ .06
0> am / .05
.25 /
/~p
.05
.06
.05
.05
I ~ / 1
.11
\ .13 .14
.11 .14
0.,
_ .03 .06 .05 .05 =
. 1 1 1 ,, ,_
1 / I
.06 / .85
1~ 2.26
in_
a
·.5'
<7_
.1 1 .49 ~
\` 1
3:05 3:08 3:14 3:32 3:36 3:40
Near Drogue
Under Downwind
Surface Slick
Slick Length 2,000 m
FIGURE 4-3 Concentrations (ppm) of oil in water under a 2~bU crude oil slick that
WE sprayed immediately by DC-4 aircraft, September 26, 1979 (day 1~; third sample
run through small downwind slick and then near drogue where dispersion occurred.
Source: McAuliffe et al., 1981.
from under the separated teardrop-shaped slick back to the drogue
that was following the dispersed oil plume in the water (Figure 4-3~.
The distance was about 2 km. Samples taken at the drogue had
concentrations of 1 to 2 ppm through 6 m and 0.5 ppm at 9 m. These
concentrations represent the further dilution of the dispersed of] with
time.
The results of these very elaborate field studies produced some
of the few quantitative mass-balances on dispersed oil that have ever
been obtained. Although a large number of samples were collected,
there can still be errors in the calculated amounts of dispersed oil.*
~ An independent check of dispersant effectiveness can be made based only on the
observed concentrations in the water. An average O.l-mm-thick ~lick, if completely
dispersed and uniformly mixed in 1 m of water, would produce a concentration of 100
ppm, 33 ppm in 3 m, and 17 ppm in 6 m. The sample stations, with the higher
concentrations shown in Figures ~1 and ~2, approach these values if the oil measured
at greater depths is added back to the shallower depths. The measured concentrations
would be even closer to the theoretical concentrations if they were corrected for volume
of oil to weight of oil, percentage of evaporation, and an estimate of the amount of slick
· .
remammg.
OCR for page 173
INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 173
Table 4-1 summarizes the effectiveness of dispersant sprayed on
seven slicks and the estimated percentage of of} naturally dispersed
under the two control slicks. Table 4-l shows the effectiveness of
aircraft versus boat spraying, a comparison of two different disper-
sants applied in the same manner, and immediate spraying versus a
2-fur delay. Aerial spraying of the fresh oil slick was more effective
than boat spraying (60 and 78 percent versus 62 percent with less
dispersant aerially applied). The reduced effectiveness of boat appli-
cation may be due principally to mixing the dispersant concentrate
with seawater (with an induction system to 2 percent concentration)
before spraying. Dispersant H (Corexit 9527) was 5 to 6 times more
effective than dispersant ~ (unidentified) (62 versus 11 percent) in
boat spraying of just the thick of} part of the fresh slick. (Labo-
ratory testing with both fresh and weathered Pru~hoe Bay crude
oil showed about this same difference.) Oil that was on the water
for 2 hr prior to spraying was not as effectively dispersed, probably
due to increased viscosity from greater Toss of volatile hydrocarbons
by evaporation. Boat spraying the entire slick uniformly was very
ineffective compared with spraying just the portion of the slick that
contained most of the oil. Too little dispersant was sprayed on the
thick areas, too much on the thin ones. This difference in effective-
ness is in accord with the basic concept that the dispersant should
be sprayed where most of the of! exists. Table 4-1 also shows that
generally the higher the rate of dispersant application, the greater
the amount of oil dispersed.
Another APT-sponsored study of dispersed versus untreated oil
was conducted at Long Cove, Searsport, Maine. The results are
presented later in this chapter.
Protecmar
The French Protecmar program's studies emphasized middIe-
scale field tests with two boats because such tests are more realistic
than laboratory tests and less expensive than fur-scale offshore tests
(Bocard et al., 1981, 1984, 1987; Desmarquest et al., 1985~. In one
test, 45.5 bib of light fuel of! was treated with undiluted Dispolene
325 sprayed from an airplane. About half the of} was dispersed within
4 hr. the thicker areas slowly disappeared after 7 hours, and only a
scattered sheen remained after 20 hr.
In a similar experiment with light fuel oil in the Mediterranean
Sea, several dispersants were sprayed from aircraft and boats (Bo-
OCR for page 174
174
USING OIL SPILL DISPERSANTS ON THE SEA
TABLE 4-1 Effectiveness of Dispereant Treatments During the 1979
Southern California Studies
Treatment
Estimated
Percentage
of Dispersant
Applieda
Percentage
of Slick
Dispersed
in Water
Sprayed immediately by plane,
day 1, dispereant H
Sprayed immediately by plane,
day 2, dispersant H
Sprayed after two hours by plane,
day 1, dispersant H
Thick oil part of slick sprayed
immediately by boat, dispernant H
Thick oil part of slick sprayed
immediately by boat, dispereant J
Entire slick sprayed immediately
by boat, dispersant H
Entire slick sprayed after
two hours by boat, dispereant H
Untreated oil
4.9
3.6
4.0
8.7
8.4
1.5
1.5
78i 16b
60 ~ 3.5b
45
62
11
8
5
0.8 ~ 0.4c
aEstimated percentage of dispereant applied to thicker part of oil slick,
Estimated to contain 90 percent of the oil.
—The mean of the first two sampling rune through the immediately aerial
sprayed slicks: day 1 first sample run, 66 percent; second sample run, 89
percent.
-The mean of one run through each of the two untreated control clicks.
SOURCE: McAuliffe et al., 1981.
card and GateHier, 1981~. For both chemical and natural dispersion,
infrared analysis of water samples detected 0.! to 0.5 ppm concen-
trations of oil. Subsurface concentrations obtained in some of the
Protecmar tests are summarized in Table 4-2. Several general con-
clusions were derived from the Protecmar tests:
.
The trend of dispersant effectiveness observed was similar
to the United Kingdom's standard test (Labofina/Warren Spring
I'aboratory), but with more viscous oils, different dispersants can
hardly be distinguished.
· The French standard test (also a version of Labofina) does
not account exactly for the variation in dispersant efficiency with oil
· ~
VlSCOSlty.
OCR for page 175
INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 175
TABLE 4-2 Subsurface Oil Concentrations After Dispereant Application in the
Proteemar Studies (Maximum Significant Values in ppm)
1 m
2 m|2.5 m
-
Trial t1 t2 t3 t1 t2 t3
Protecmar 1 2 1
Proteemar 2 1 1
Protecmar 3
Slick A 1 60 5 1 3 3
Slick B 4 3 3 5
Protecmar 4
Sprayed by 17 4 4 1 Traces Traces
Canadair CL215
All other slicks 7 4 4 3 Traces Traces
Protecmar 5 3 Traces 3 Traces
Protecmar 6
Helicopter 1 2 (1 hr Traces Traces
30 man)
Ship 4 2
NOTE: The columns t, t, and t3 are sampling times corresponding, respectively,
to 0 to 30 min. 3 to 3 or 3~) min. and 6 to 7 hr after dispereant application.
SOURCE: Bocard et al., 1987.
· The results of the IFP dilution test (Chapter 2) agree with
those obtained at sea when mixing is applied to the treated of} slick.
Ranking of dispersants for a given of} viscosity is the same as in the
field test (Desmarquest et al., 1985)
North Temperate and Arctic Tests
A number of field trials have been conducted to test effects of
dispersants in north temperate coastal and arctic habitats. In 197S,
in three experiments at Victoria, British Columbia, oil was spilled in
a semiprotected coastal area and restrained with a boom (Green et
al., 1982~. Ten percent Corex~t 9527 was applied by ship using the
Warren Spring Laboratory system. Fluorometric monitoring of water
samples showed as much as 75 percent dispersal. The highest oil
concentration was 1 ppm, which decreased to background levels (less
than 0.05 ppm) within 5 hr. in agreement with the field tests cited
above. Previous tests in CEPEX enclosures showed that microbial
oxidation of dispersed Canadian North Slope of} occurred at least 10
times faster than undispersed oil, and this may have been a factor in
the rapid disappearance of the oil (Green et al., 1982~. The results
OCR for page 204
204
USING OIL SPILL DISPERSANTS ON THE SEA
Coral Reefs
Admired throughout the world for their beauty and biological
productivity and diversity, coral reefs are generally considered a
habitat worth protecting from oil spill damage. As with seagrass
communities, there is concern that dispersal of an of] slick in shallow
water near or above a core] reef might cause greater damage than the
untreated oil, because of the higher concentrations of hydrocarbons
introduced into the water column.
Legore et al. (1983) studied the effects of untreated light Arabian
crude of} and chemically dispersed of} (20:1 Corexit 9527) on corals
that were submerged 1 m at low tide. The individual plots (2 by 2
m) were boomed with the skirts (3.5 m) extending to the bottom,
even at high tide. The initial nominal of! concentrations for the 24-hr
exposures were that of a slick 0.25-mm thick. Thus, the dispersed of!
concentration (including dissolved hydrocarbons) would have been
250 ppm if mixed uniformly. The slick remained on the surface
except for of} that may have adhered to the wads of the boom. In
5-day experiments, of} equivalent to a 0.-mm thick slick was added
initially and the same amount added on days two, four, and five.
One-day treated corals showed normal appearance and tolerated
the short exposures. Following 5-day exposure, coral recovered more
slowly from seasonal bleaching. There was also some long-term re-
duction in growth for both of} treatments. The exposures used are
high and were produced by restricting water flow by the boom skirts.
A study to simulate the effects of an of} spill moving over a coral
reef with and without the use of dispersants was done at Bermuda
(Cook and Knap, 1983; Dodge et al., 1984, 1985a,b; Knap, 1987;
Knap et al., 1983, 1985; Wyers, 1985; Wyers et al., 1986~. Corals
were exposed both in the laboratory and on the reef to Arabian light
crude dispersed with 1:20 Cored 9527 or with 1:10 BPl1OOWD.
Some corals were taken to the laboratory and then returned to their
home on the reef for recovery studies; some were actually oiled on the
reef using an enclosure. Exposures were at levels of 11 to 23 ppm for
periods of 6 to 24 hr and were similar for of] alone and dispersed oil.
There were no significant differences between the of} and dispersed
of} treatments in tissue rupture, contraction or swelling, mesenterial
filament extrusion, or pigmentation loss. Most of the observed stress
occurred during dosing. Recovery began 24 hr after oiling and was
complete in less than a week.
One of the few apparently synergistic effects was reduced pho-
tosynthesis of the zooxanthellae (symbiotic algae) within the coral
OCR for page 205
INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 205
resulting from an 8-fur exposure to 19 ppm dispersed of} and in-
hibited synthesis of lipids, particularly wax esters and triglycerides
(Cook and Knap, 1983~. Oil or dispersant alone had no such effect.
Carbon fixation was restored within 5 hr after exposure ceased, and
lipid synthesis returned to normal within 5 to 24 hr. The smaller
droplets in the chemically dispersed oil did not adhere to the corals
in contrast to the physically dispersed of} droplets, some of which
were found on coral a few weeks after exposure to 20 to 50 ppm of]
alone.
In summary, when corals were exposed to of} and dispersed
of! under field conditions, exposure to hydrocarbons was greater in
dispersant-treated plots than in untreated oiled plots. However, no
effects were observed on growth of corals exposed either to of] or
to dispersed of} for 24 hr and measured ~ year after the exposure.
Corals exposed for 5 days to the of} or dispersed of} showed reduced
growth in comparison to the controls. "Exposure to dispersed of} also
appeared to delay recovery of corals under stress by cold tempera-
tures" (ASTM, 1987, based on Birkeland et al., 1976 and Fucik et
al., 1984).
As with other organisms and habitats, the primary factor is ex-
posure to the water-soluble fraction of the oil. When toxicities are
based on such analytical measurements, there are no major differ-
ences between physically and chemically dispersed oil. Knap et al.
(1985) concluded that "in the long term, Diploria strigosa appears
relatively tolerant to brief exposures to crude of} chemically dispersed
in the water column." However, these experiments were limited to
only one coral species, and other reef organisms, such as crustaceans,
echinoderms, and other invertebrates, are known for their sensitivity
to both chemically and physically dispersed oil. Therefore protection
of the entire reef community, perhaps by dispersal of the of} offshore,
is a priority.
The American Society for Testing and Materials has published a
standard guide for the use of chemical dispersants in the vicinity of
coral reefs (ASTM, 1987~. It recommends the following:
· Whenever an of] spin occurs in the general vicinity of a coral
reef, the use of dispersants should be considered to prevent floating
of] from reaching the reef.
· Dispersant-use decisions to treat of! already over a reef should
take into account the type of of} and location on the reef.
· Coral reefs with emergent portions are high-priority habitats
for protection during of] spins.
OCR for page 206
206
USING OIL SPILL DISPERSANTS ON THE SEA
· The use of dispersants over shallow submergent reefs is gener-
ally not recommended, but the potential impacts to the reef against
impacts that might occur from allowing the of} to come ashore should
be weighed.
· Dispersant use should be considered to treat oil over reefs in
water depths greater than 10 m if the alternative is to allow the of}
to impact other sensitive habitats on shore.
· Dispersant use is not recommended to treat oil already in reef
habitats having low-water exchange rates (e.g., lagoons and atolls) if
mechanical cleanup methods are possible.
Mangroves
Mangroves grow along tropical and subtropical shorelines. As
intertidal forests, they are important protectors of shorelines from
storms and currents, they provide habitat and nursery areas for
many organisms, some of which are commercially important, such
as lobsters, prawns, shellfish, and finfish (Teas, 1979), and they con-
tribute to the overall productivity of tropical marine environments.
Their importance as nursery areas and nutrient sources cannot be
overstated.
Experiments on mangroves are relevant to how the organic frac-
tion of sediment and suspended particulate matter interacts with oil
and dispersed of] (Getter and Ballou, 1985; Getter et al., 1985~. A
mangrove study begun in 1978 in Panama, indicated that exposure
of a mature red mangrove forest to of} and dispersant resulted in
many of the effects observed in the laboratory and at other spill
sites: changes in growth, respiration, transpiration, and uptake of
petroleum hydrocarbons (API, 1987~. These effects were reduced at
the site treated with of! and dispersant compared to the site treated
with oil alone (Getter and Ballou, 1985; Getter et al., 1985~.
In the Panama study two similar mangrove sites were selected
and boomed, and mangrove trees, seagrasses, and associated biota
were surveyed. One site received 380 liters (2.4 bbl) of Prudhoe Bay
crude oil, and the other site received the same quantity of oil mixed
with 19 liters (5 gal) of Corexit 9527. This oil-dispersant mixture
was formulated to simulate of] dispersing on the water within or
immediately adjacent to the mangrove forest. Thus, the dispersed
oil concentrations in the water were presumably higher than if the
oil had been dispersed before reaching the mangroves.
OCR for page 207
INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 207
Oil premixed with dispersant did not readily adhere to sedi-
ments or algal mats; it lightly coated prop roots and was evenly
distributed on the forest floor within two tidal cycles. The dispersed
oil was mostly removed from surface sediments and algal mats within
1 week, after which only a noticeable sheen remained. Similar results
were obtained in the BIOS and Long Cove studies. The three stud-
ies should be distinguished from those that treated oiled intertidal
sediment directly with dispersant.
Although less of} was retained in the mangrove peat or organic
sediments when dispersant was used, the proportion of aromatic
compounds retained was greater. Dispersed oil was taken up much
more rapidly by mangrove seedlings, but it did less long-term harm
because tidal flushing rapidly removed the dispersed of} from the
surfaces of the sediments a.n ~ algal mats. However, some undispersed
of} accumulated on the wrack at the high-tide swash line.
Untreated of! formed a slick over the enclosed area and eventually
was pushed well into the mangrove forest by waves and rising tides,
and was retained there, contaminating substrate, prop roots, beach
wrack, intertidal algal mats, crab burrows, and depressions in the
forest floor. Sediments and prop roots at the outer edge of the forest
were cleaned of heavy of} contamination after several tidal cycles,
but interior areas remained heavily oiled after 1 week. Heavily oiled
wrack was evident throughout the site, especially at the high-tide
swash line.
Inspection of the sites 120 days later confirmed these observa-
tions. Where untreated oil contacted the mangrove site, 60 to 70
percent of the plants were dead or defoliated. Where the equal vol-
ume of chemically dispersed of} came ashore, there was no evidence
of of] Ed very little damage (5 percent defoliation). This is one
of the more dramatic examples of how chemical dispersal of of! can
diminish the impact compared to untreated of} (Getter and Ballou,
1985~.
In Malaysia, another study involving mangrove trees, using of!
and Corexit 9527, gave variable results between of] versus oil plus
dispersant (Hoi-Chew, 1986; Hoi-Chaw and Meow-Chan, 1985; Lai
and Feng, 1985~. Treatments were most toxic to seedlings. Most
trials showed either no difference or that oil alone was more toxic
than dispersed oil. Mortality was found to be related to surface
deposition and uptake. The largest accumulation of of} components
occurred in leaf tissue (Lad and Feng, 1984, 1985~.
In experiments to find how to save mangroves that were already
OCR for page 208
208
USING OIL SPILL DISPERSANTS ON THE SEA
oiled, Teas et al. (1987) treated mangrove trees with of} and after
~ day washed them with high-pressure seawater or with a nonionic
water-based dispersant. Oil killed many of the trees (within 30
months) whether or not they were spray-washed the next day.
To simulate the case in which the mangrove forest was impacted
by oil dispersed) offshore, some plots received of} plus glyco] ether-
based dispersant. These plots did not show significantly more deaths
than untreated control plots. The results of this study imply that
it is not possible to save trees already oiled by washing them with
dispersant, but that if the of} is dispersed offshore, the trees can be
protected.
In summary, mangroves can be protected from of} damage by
dispersing the of} offshore, but if the untreated of} comes into the
forest it can cause serious harm that may require 20 years or more
for mature tree regrowth.
SUMMARY
Boehm (1985) in summarizing the BIOS studies concluded, in
agreement with Mackay and Hossain (1982), that chemical dispersion
reduced the affinity of of! for solid particles as long as the dispersant-
oi} micelIar association persisted. Further, dispersal reduces the
probability of an of! mass coming ashore, and often reduces the long-
term impact of that which does reach the shore or intertidal zone.
This is borne out by most of the field studies reviewed above (Table
4-7~.
Dispers~nts never increased sorption of of} to sediments and
in a few experiments decreased sorption of of} to organisms. The
distinction must be made between dispersed of} coming ashore, which
generally did not penetrate sediment, and dispersant applied to an
oiled intertidal sediment, where treated of} usually penetrated more
deeply than the untreated oil.
In subtidal areas, use of dispersants may increase toxicity to
benthic fauna and plants, at least in the short term, but may reduce
long-term effects of oil. In some intertidal areas, such as mud flats,
dispersed oil coming in with the tide had little or no effect, while
untreated oil caused longer-term effects (e.g., Long Cove, Searsport,
Maine study). Once oil has penetrated salt marshes, the best ap-
proach is to leave it alone. Dispersant applications in a marsh show
little benefit, as is the case with oil stranding on a beach.
Benthic organisms respond differently to oil over the short versus
OCR for page 209
209
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214
USING OIL SPILL DISPERSANTS ON THE SEA
the long term. Dispersed of! may occur in sufficient concentrations
to cause immediate mortality for various groups, including commer-
ciaDy important shellfish. Reproduction and feeding behavior may
also be negatively affected. Bioaccumulation and tainting occur to a
greater extent in the short term in filter feeders when dispersants are
used, since concentrations in the water are elevated. Over the Tong
term, more bioaccumulation of of} occurs in deposit feeders when
dispersants are not used.
In general, it appears that intertidal and subtidal macroaIgae
(seaweeds) can be damaged by heavy oiling as measured in labo-
ratory studies but are often not damaged in field oiling situations.
Dispersant use would not increase damage and, based on one study
in the United Kingdom (Crothers, 1983), might decrease it. Exper-
imental observations and results are scarce and often contradictory;
in some field experiments, dispersed of} had no effects on Scolds,
whereas in other exposures, red algae suffered tissue damage and
inhibited growth when chronically exposed to dispersed crude oil.
Only first-generation dispersants have been shown to cause major
effects on seaweeds on shorelines.
Effects on vascular plants vary depending on species and habi-
tat type. For subtidal seagrasses and vegetation in salt marshes,
dispersant use directly on vegetation or in shadow waters with low
circulation may increase the harmful effects of of! because of in-
creased hydrocarbon concentration in subsurface waters and subse-
quent absorption by plants. Dispersants are not especially effective
in preventing damage to oil-covered plants in low-energy salt marsh
environments.
Tropical mangroves may be protected if the oil is dispersed be-
fore an untreated slick strands within the mangrove forest. This is
especially true for mature mangroves. Short-term toxicity to indi-
vidual organisms within the mangrove ecosystem may be higher, but
con~munitv recovery is enhanced bv the oil being dispersed prior to
O ~ —-— — ~ ~
entry.
On coral reefs the use of dispersants, if it is able to reduce
exposure to oil, wiB benefit the reef in the long run even though there
may be short-term deleterious effects on photosynthesis of symbiotic
algae within the coral and on other reef organisms.
Use of dispersants does not appear to affect homing of salmon.
Representative terms from entire chapter:
oil spill
