National Academies Press: OpenBook

Using Oil Spill Dispersants on the Sea (1989)

Chapter: 4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills

« Previous: 3 Toxicological Testing of Dispersants and Dispersed Oil
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 165
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 166
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 167
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 168
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 169
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 170
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 171
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 172
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 173
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 174
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 175
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 176
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 177
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 178
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 179
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 180
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 181
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 182
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 183
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 184
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 185
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 186
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 187
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 188
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 189
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 190
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 191
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 192
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 193
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 194
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 195
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 196
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 197
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 198
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 199
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 200
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 201
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 202
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 203
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 204
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 205
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 206
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 207
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 208
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 209
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 210
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 211
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 212
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 213
Suggested Citation:"4 Intermediate-Scale Experiments and Field Studies of Dispersants Applied to Oil Spills." National Research Council. 1989. Using Oil Spill Dispersants on the Sea. Washington, DC: The National Academies Press. doi: 10.17226/736.
×
Page 214

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

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

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.

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~.

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

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

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.

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

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.

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-

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.

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

176 USING OIL SPILL DISPERSANTS ON THE SEA of the Royal Roads tests were consistent with an earlier test on Kuwait crude (Cormack and Nichols, 1977), but other tests using the WSL application system produced less objective results because of inadequate observations from aircraft (Smith Ed Holliday, 1979~. A 1981 field trial held off St. John's, Newfoundland was among the first to employ both remote sensing and a real-time computer simulation mode} (Gill and Ross, 1982; Intera Environmental Con- sultants, 1982~. Aerial photographs clearly indicated rapid forma- tion of an oil-in-water emulsion immediately following application of Coronet 9527. The waterborne cloud was visible from the air for 3 hr. Field tests of the effectiveness of Corex~t 9527, Corex~t 9550, and BPMA700 were conducted near Halifax, Nova Scotia in 1983 (Canadian Offshore Aerial Applications Task Force [COAATF], 1986; Gill et al., 1985; Intera Environmental Technologies, 1984; Swiss and GiD, 1984~. An acoustic monitoring system for verifying water column of} concentrations was tested, along with of! spill tracking models to predict the movement of slicks during the trial. Water samples analyzed by fluorescence and radiotracer techniques showed that 2 to 40 percent of the of} was dispersed, but because there were differing sea states for the various tests, the dispersant products were not ranked for electiveness. To better understand of] spills in an arctic environment, 16 small- scale tests with Tarsint crude oil were conducted in Mackenzie Bay, Canada in 1984 (Dickinson et al., 1985~. The dispersant BPMA700 was determined qualitatively to be the most effective; Corex~t 9527 was also effective, but took longer to disperse the oil; Cored 9550 caused oil resurfacing and was not recommended for arctic conditions. This study demonstrated that chemical dispersal of Tarsint crude oil in Beaufort Sea waters is feasible and it suggested improvements in the spray application system. More extensive arctic tests were held in the Beaufort Sea near Tuktoyaktuk, Northwest Territories in August 1986. Four slicks, each containing 2.5 bb! of aged (by aeration) Alberta sweet mixed blend, were laid down by tugboat as follows (Oi} Spill Intelligence Report, 1986c; Swiss et al., 1987a; Jones, private communication): treated with a single application of BP Enersperse 700; treated with multiple applications of BP Enersperse 700; · treated with Exxon CRX-8; and . untreated served as control. In the untreated slick, thick and thin portions of the spill were

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 177 . visually easy to distinguish (Jones, private communication). After spraying there was an obvious plume of dispersed of} in the water, and little of the thick of] was left. Wherever dispersant was sprayed a sheen was visible that in some cases covered 10 times the area of the original spill. An observer noted that the thick of} consisted of pea-sized droplets that from time to time rapidly expanded into a larger sheen (Swiss et al., 1987b). Preliminary conclusions from this study are that Alberta sweet mixed blend crude can be dispersed at 6°C, and that multiple spray- ing operations using helicopters are feasible. However, a single ap- plication at a dispersant-oi} ratio of i:10 appears to be as effective as the "multihit" technique, provided observations are made over sev- eral hours. Although the two dispersants appeared initially to have different effects, the amount of of} dispersed after several hours was the same for both (Swiss et al., 1987a). In addition to the field studies discussed above, a series of exper- imental spills were conducted on northern Baffin Island, Northwest Territories. These studies, which were primarily conducted for bi- ological observations, comprised the Baffin Island Oil SpiD Project, which is described later in this chapter. In an early test, Cormack and Nichols (1977) measured the following concentrations of chemically dispersed Ekofisk crude of! at a depth of 1 m: 16 to 48 ppm within the first 2 mini 5 to 18 ppm after 5-10 mini and ~ to 2 ppm after 1 hr 40 min. Lichtenthaler and Daling (1983) reported on seven 13-bb! re- search spins conducted with topped (initial boiling point 150°C) Statflord crude of} in May and July 1982. One release at each test time was a control (untreated), and the remainder were sprayed by boat with 200 liters (53 gal) each of three different dispersants diluted to 10 percent concentration by seawater. Forty water samples were collected under each dispersed slick at I, 2.5, 5, and 9 m. The max~- mum subsurface of} concentration was 10 ppm at ~ m with dispersant B. The authors suggested that the concentrations and effectiveness were reduced because the of] was released over 7 to 12 min. resulting in several thicker of] patches spread over wider areas of the slicks. The southern California studies (McAuliffe et al., 1981) released the oil in 3 min. and the slick was quite uniform initially, with

178 USING OIL SPILL DISPERSANTS ON THE SEA the thicker of} located in the downwind portion. In addition, no air surveillance was available in the North Sea tests, and since a spray boat was used, preferred spraying of the thick of} patches was impossible. Lichtenthaler and Dating (1983) indicated that these difficulties resulted in the low dispersant effectiveness observed: dispersant A, 6 to 19 percent; dispersant B. 17 to 22 percent; dispersant C, 2 percent; and controls, 0.7 to 2.6 percent. The dispersant ranking was consistent with laboratory tests con- ducted by Mackay and Szeto (1981~. In the summer of 1983, DeIvigne (1985) studied nine 13-bb! spills of Statfjord crude oil and a light fuel of} in the North Sea. Five of the slicks were controls, one was crude oil premixed with dispersant Finaso} OSR-5 (used for ah tests), and the remainder were aerially sprayed after being on the water for 1 hr. A single surface measure- ment indicated that the slicks were hit by dispersant that should have resulted in dispersant-oil ratios of 1:10 to 1:30 in the thick part of the slick. Measurements from a towed fluorometer at depths of 3 and 7 m, as well as 800 water samples analyzed by infrared spec- trophotometry, surprisingly indicated that dispersion was not greatly increased by dispersant spraying. Lower than expected concentra- tions of dispersed oil were measured at 3 and 7 m from the Statfjord oil-dispersant mixture (after 30 min to ~ hr 45 min. 3 m values for three samples shown were 0.14 to 3 ppm; 7 m concentrations were 0.1 to 0.3 ppm). These concentrations were somewhat higher than the aerially sprayed slicks. Deivigne attributed the ineffectiveness to poor mixing of the sprayed dispersant with the of} layer. He suggested that the disper- sant droplets penetrated through the slick or washed away from the oil layer before penetration. However, the Tow concentrations found from the dispersant-oi! premix suggest that the dispersant used was not very effective with this oil, or that the sampling did not find the highest of] slick concentrations. The values contrast markedly with those of Lichtenthaler and Daling (1985) reported below. Thirty minutes after release of the oil-dispersant premix these investigators found concentrations to exceed 100 ppm through 3 m, 12 ppm at 5 m, and 3 ppm at 10 m. LichtenthaTer and Dating (1985) conducted additional studies in the North Sea in June 1984 using a simulated fuel of] produced from

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 179 Statfjord crude oil (S parts of gas oil, 250° to 350°C; ~ part heavy gas oil, 330° to 400°C; and 1 part residue, greater than 380°C). The already sprayed slicks were sampled 30 to 50 min later. The highest of! concentrations in water were 25 to 40 ppm at a depth less than 2 m. Under two untreated slicks, corresponding concentrations were less than 5 ppm, a mean of ~ samples from 2 m was 0.22 ppm. The dispersed and untreated of} concentrations are in general agreement with the 1979 AP] southern California field studies (McAuliffe et al., 1981~. The long-term effects on surface oil, ~ to 2 days after treatment with dispersant, could be important in evaluating the effectiveness of dispersants in sea tests. In both the Protecmar tests and in the Norwegian North Sea trials, Lichtenthaler and Daling ( 1985) reported that dispersants tend to act as de-emuIsifiers when weathered (water- oi] emulsified) surface of] is treated at low dosages. A small amount of dispersant apparently enhances the "natural" dispersion process by breading down the water-in-oi! emulsions and releasing for further spreading. The mass-balance calculations made in sea trials (typically 0.5 to 2 hr after treatment) only take into account the short-term effects of dispersants, which often have resulted in uncertain conclusions (see Table 4-3~. Summary of Physical and Chemical Field Test Results The tests discussed in the preceding four sections are summa- rized in Tables 4-3 and 4-4. Many pieces of quantitative informa- tion, such as of] viscosity and oil-dispersant ratio, were estimated by Nichols and Parker (1985~. Effectiveness, defined as the fraction of oil removed from the water surface, is obtained by integrating the water-column distribution as weD as allowing for evaporation from the slick. Numerical effectiveness values are given in Table 4-3 only if the authors of the cited papers gave such values. Fingas (1985) and Nichols and Parker (1985) have estimated quantitative effectiveness values from water-column concentrations; neither of these papers gives the methodology. One particular study (McAuliffe et al., 1981), in which unusu- aDy complete distributions of petroleum hydrocarbons in the water column were measured, gives the clearest indication that chemical dispersion is more effective than natural dispersion in relatively calm seas; that dispersant treatment by air is superior in most cases to

180 a, - .O A o ~ v 0 ._ 0 0 c 4, .> 4' TIC ._ a o 00 c S" a. a. 4) ~ C be ·— C Al; 4, Cat ~ 4, ~ U] V] c L. O ~ O oar o ._ AS ~ O · - .,c L. C 4, ~ a ~ E ~ -m CQ _ CO m —O ~ 00 - . — _1 ~ ~4 _ _~ e~. ~ _ _ 4~ _ . ~ ~ ° ° O ° ° _. · - _ ~ - . U. _, ~ g g ~ ~ A ~ ~ 4, ~ 4, ._ ._ ~ ~ ~ ~ ~ o~ o~ o~ U] ~ _ 4~ _ 3 3 aS C ._ ~ 4, o ~ o e~ 4, ct ~1 3 o e~L ~ ~ c° 4~ C~ :: ~ L. 4,.i o. o. o. o. °. ·0 ~ o e~ <o _ O O — ~ {D ~ ~ ~ u, o~ ~ o~ o~ oo co o~ ~ o~ a~ e~ _ . . - - 4' o - 4, - o m _~ _ _ O — — ~ - - ~ C C ~ ~ c~ ~ ~ a. O O ~ 0 ~ ~ ~ ~ ~ ~ C ~ ._ ._ . ._ __._ . X X X X c~ C~ I: :S _^ ~ ~ ~ CO CD C~ C-- - . . . . . _ _ ~ _ _ ~ _I _ - 4 ~ L' L' =~C >, ., >,~c e~ c~ ~ ~ ~ e~ ~ ~ ~ ~ ~ n:5 dV ·— CS ·~ ~ ·— 4' ~ ~ ~ 4) `~6 =~ ~, E E~ S 5, S s 3 3 ~ oo ~ ~ :% ~ ~ mmm CS 4~ ~ ~ a, O O O O = ~ = ~ ~ ~ s" ~ P-~ a~l ~1 ~1 ~1 _ ,, .. .. · - _ ~ t_ ~ ~ O Z ~ CD ~ _ ~ 4~ ~ os al O O m m m m 4) ~C ~5 ~ L. eS1 c~l a~l ~1 _I _ ~ e~ _t g :Z ~ ~ ~ 4, C C a' ~ _ _ ~ Pc V V ~ I I O aa m O ~O O ,,, O =._ - _= . . . . ~ CO ~ CO C CI. U~ U V ~ ~ a vo O~ e~ CO —U] U: LO~ e~ e~ C ~ ~ 0 C C V _ ~ ~ 0 C ~ ~ V 0 0 0 ~:zaa ~ U, U, ~ · . . . CD CD L. :^ ~ ~ :>~ :~~ ~ ~ ~ e~ ~ ~ e~ .~ ~ .~ ~ ~ ·~ ~ ·~ q, L. ~ S ~ S ~ ~ S ~ S ~ ~1 ._~' ·_ ~1 ·—~1 ·— ~ ~ ~ U, a, 3 o, ~ 3 co co a, m mm 4} ~ 4, O O O ~5 ~ ~ L. ~ ~ ~ P~ :^ m 4) m___ ..c ~ ~ ~ ~ . . . P~ ~ ~ ~

181 OG DC DO c') ~ ~ 00 E. ~ By ~ 00 Hi ~ At · . e ~ ~ Co A Y A — y o , En c As, ' - , ~ ~ E A ~ _ m ~ ~ v a - 00 cat :~.° ~ p~ O ~ Al Al All All All ~1 ~ O ~ tad _ _ ~ ~ o = O 4, 4, Pc ~ ~ Pc ~ ~ ~ ~aQ~ 8 ~~ O cat en _ en en ~ cat cat Al Al co ~ ~ ED ~ ~ ~ ~ AL _ e~ ~ _ ~ _ _ ~ c~ e~ _ e~ _ _ ,,. —~ O O O ~ ~ ~ g g t- oo e~ ~ ~ 0 0 g 0 ~ ~ ~ ~ _ ~ ~ _t ~ Z e~4 ~ _ e~ _t ~ s: "c ~ X ,e, ~e, X e ,e~ 3 ~ 3 ~ ~ ~ ~ ~ ~ ;( ~e ~C n., ~ ·~" ° .5 .5 .~ .~ .~ O O O O O O O O v v v ~ 4,, v (V, v 4,, v (,, v (,, v 4,, o o ° Z ~ ° ~ ° ~ _ ~ ~ 3 ~ Z ~ e~ ~~s ~ {0 ~ {~! ~ ~~S ~ a~ C O O O O O O ~ O a~ O a~ O a. O ~ C~ Ut oo q, ~ ~ ~ ~ ~C s~ a~ ~ L~ ~ a 4} ~ ~ ~ eC L4 ce1 ~1 ^0 ~o 3 ~ 3 3 ~ ~ ~ l O:~ ~ U~ U] U~ CQ U] ooo oo _ _ _ _ _ O O O O O O O 0.~.~.e 0.~. z z z ~ ~ ~ z ~ c~ c~ ~ 4, q, ~c ~c ~c m co 4) 4, ~ 5 L. ~4 ~4a,1 ~ ~1 0 ~ a31 ~1 ~1 O ~ c61 0`t1 a'1 0~1 0~1 aS1 _~ _ 00 CD 00 00 (D CO ~ 00 0 q~ 4~ ~ ~C ~ ~ ~ ~ ~ bO 4', 0 0 0 PO '~ '= '~ '~ ,~ .<S — — ~—~5 — — O O O O O O O O ~ O O ~ O ~ O O . - O O O ~ ~ ~ ~ ~ ~ ~, ~ ~ ~.= ~ ~." ~. - Z :Z U3GeOV] U) CQ C`0 CO << w

182 a, v 4) 4) 4, ._ ~ 4, ~ P. W ~ U] U] w o 4, o a,._ ·_ ._ W o ~ ~ o ._ ~ o ._ _ _ _ Ps ~ so c w O4 ~— ~5 :^ ·- ~=o ~ TV v - CC :^ ~ a EE ~ Me ~ ~ it, =~ c 2 .. .Oq V ~ .5 ~ ° u, its ° _' ~ ~ ~ ~ w 00 , , 0 us us us I 0 ~ V ~ ~ V of on _t _ —4 en ~ ~ I —. ~ —~ ~ ~ 0 0 0 us 0 on 0 en ~ ~ ~ oo on up 4, 43 4, 4D ~ 41, ~ ~ 0 W aW.X W 0= ~ ~ ,, ,o, _ a, ~, E c. ,,.D. ~L U, ~ 0, 0s t2 =] ~ b" ~ N 03 ~ e 2 ~ X ~ ~ ~ ~ x ', x 2 x D. ' ' - . - . - . =. ~ 0 0 0 0 e~ 0 ~ c~ e~ ~ _ ~ ~ ~ ~ ~ e~ V V ~c ~c "c ,= ,.c ,,c c e~,.~.c w w w ~ w - 3~' 3-' 3-' 3~l 3-' 3-I ~ 4', 3 t~ ~ ~ ~ ~ ~ A A A A A A '~ V c°~> oo ~ V ~°~. ~°,. - ° - ° 43 - o $~ ~d ~ ~ L. t" _ _ _ _ ~ ~q 0Q ~ ~D ~ O O ;= ·,~;;;,;;;,-0 'O O O, . ~ o S" o ~Q ._ U) 4, w 3 l cn 3 . ~ aS l 3 · ~ e o rQ L~ 4 w c, ~ 0 ~s ~C, ~ o . - ~ ~ v _ ._ w ~ ~ w V ao a' |. _' _ e ~ 0 w V b. . - ._ ~ · ~ ae ~ ,, m °°= q, 43 ~ ~ $,, ·_ .^ 4, ~ v e ~ ~ 4, ·— , -- e ~ w . - w ~ ~ ~ e ~ 8 aQ ~ v ~ _ ._ ._ ~ w ~ 0 ~ ,._ ~m m,. ~ O ~ ' ~ ~ — ~ 0 - U, 00 -

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 183 dispersant treatment by boat; that weathered of! is not dispersed as effectively as fresh oil; and that a dispersant (~) that performed poorly in laboratory tests also performed poorly in the field. These results are supported by other quantitative studies (Gill et al., 1985; Lichtenthater and Dating, 1983, 1985~. It must be emphasized that absolute measurement of dispersant effectiveness or quantitative assessment of application technique was not the primary goal of most of these studies they wanted to find out if laboratory tests comparing a series of dispersant formulations could predict the order of performance in the field, or whether toxic concentrations of petroleum components would be found beneath chemically dispersed sticks. Both questions have been partially an- swered: laboratory tests can usually predict which dispersant will be more effective; concentrations of toxic petroleum hydrocarbons un- (ler of] slicks dispersed at sea are generally Tow compared to toxicity levels for most organisms (see Chapter 3~. The biologically oriented tests, designed to test this last conclusion directly, are described in the next section. BIOLOGICALLY ORIENTED MESO COSM AND FIELD STUDIES This section discusses mesocosm and small-scale field studies of algal, microbial, and planktonic populations and describes arctic studies. Some mesoscale studies in temperate and tropical shallow subtidal areas are also described. Three significant long-term field studies provide the bulk of this section: the Baffin Island Oil Spill study of an arctic environment; the Long Cove, Maine, study of a shadow north temperate environ- ment; and the Panama study of a tropical mangrove environment. (These and related investigations are reviewed below and results are summarized in Table 4-6 at the end of this chapter.) Algal, Zooplankton, and Microbial Populations Algae, zooplankton that graze on them, and bacteria that me- diate recycling processes comprise the base of the marine food web and are of concern in the event of an oil spin. A number of field studies have examined the ejects of of} and dispersants on these or- ganisms. The effects of Ekofisk crude of! and Cored 9527 dispersant on flagellate communities were examined using in situ marine meso- cosms, 1 m in diameter by 20-m deep (Throndsen, 1982~. Changes

184 USING OIL SPILL DISPERSANTS ON THE SEA TABLE 4-4 Monitoring Methods Used at Dispereant Field Trials Water Sampling Trial Depthe Surface Sampling Location Methodology (m) Analysis Method Use Britain, Knudsen 2-15 Fluorescence Grab Water content, North Sea battles emulsification United States, Pumping to 1, 3, 6, FTIR -- -- New Jersey bottles 9 Canada, Pumping to 1, 3.5 Fluorometer, -- -- Victoria fluorometer GC and to bottles, towed fluorometer United States, Pumping to 1, 3, 6, IR, GC -- -- Long Beach bottles 9 United States Pumping to 1, 3, 6, IR -- -- Long Beach bottles 9 France, Toulon Pumping to 0.2, 0.6, IR (bottles), Sorbent -- (Proteemar bottles and 1, 2.5 turbidimeter 1&3) instrument (direct) Canada, Pumping to 1, 2, 4 Bottles not Sorbent Thickness St. John's fluorometer done, and bottles spoiled Norway, Sample bottle 1, 2.5, GC -- -- North Sea 5, 9 Britain, Pumping to 1, 3, 6, GC, Sorbent Thickness North Sea bottles 9 fluorometer Skimmer Weathering France, Pumping to 0.5, 0.7, IR (bottles), Sorbent -- Toulon bottles and 1, 2 fluorometer (Proteemar instruments and 4&5) turbidimeter (direct) Holland, Pumping to 1, 1.5, GC, IR Sorbent Weathering North Sea bottles 2, 3, 7, 10 Towed Various Fluorometere fluorometer (Q-instru- ment) Pumping to -- Droplet Dee instrument analyzer (mal~rern)

INTERMEDIATE-SCALE EXPERIMENTS AND AFIELD STUDIES 185 Dispereant Remote Sensing Sampling Sensors Use References Kromekote -- carde __ __ Pans Color Documentation photographs Photo Documentation Color photographs Color photographs and video IR Kromekote IR, UV cards Documentation Documentation Slick area Slick area surface tension Laser Documentation nuorosensor, photo __ Kromekote IR carafe _ Cormack and Nichols, 1977 McAuliffe et al., 1980 Green et al., 1982 Smith et al., 1979 McAuliffe et al., 1981 Bocard and Gatellier, 1982 Gill and Ross, 1982 IR Lichtenhaler and Dating, 1983 Documentation Cormack, 198Sb Documentation Bocard, 1985 Sorbent IR, UV Slick area Delvigne, 1983 paper GO analysis of recovered oil

186 TABLE 4-4 (Continued) USING OIL SPILL DISPERSANTS ON THE SEA Trial Location Methodology Water Sawing Depths (m) Analysis Surface Sampling Method Use Canada, Halifax Norway, North Sea Canada, Beaufort Sea Norway, lIaltenbanken Pumping to bottles and instrument Radioactive tagging (tritiated octadecane) Acoustic spectrometer Pumping to bottles and instrument Pumping to bottles In-situ fluorometer and turbidimeter Canada, In-situ 1 -- Beaufort Sea fluorometer 1, 2, 5, Fluorometer 10 (direct), GC, IR, fluorometer, counting (bottles) 0-4 Most -- Sorbent Thickness 0.5, 1, 2, GC (bottles), Sorbent Thickness 3 (5, 10) turbidimeter (direct) GC Sorbent Oil remaining KEY: FTIR--Fourier transform infrared spectroscopy; GC--gas chromatography; IR--infrared spectroscopy; SLAR--side-looking airborne radar; and UV--ultra~riolet. in species composition resulted from the addition of 500 m! (32 ppm if uniformly mixed) of oil, which appeared to promote growth of populations of amoebae. No change in flagellate diversity occurred. Adding 100-m} Corexit 9527, resulting in a concentration of 6.4 ppm, altered the community structure substantially, resulting in a shift in dominance to colorless flagellates and coccoid chIorophycae, and reduced abundance overall. In the system simulating the Baltic Archipelago (Linden et al., 1985, 1987),oilplus dispersant was added to one tank, beginning at 20 ppm oil (nominal concentration), and of} alone (nominally 20 ppm) was added to another beginning at 1 ppm. Both tanks were diluted to background levels by the fourth day, and resulting total exposure in the dispersed oil tank was approximately 80 ppm-hr. Acute effects were observed on numbers of heterotrophic bacteria, on abundance of zooplankton, and on community metabolism, but Tong-term ejects, such as decreased abundance and shifts in diversity, of untreated oil

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 187 Dispereant Sampling Remote Sensing Sensors Use References Filter paper IR, UV SLAR IR, UV Slick area SLAR _ IR, UV Slick area microwave and plume photography movement Slick area Swiss and Gill, experimental 1984 Lichtenthaler and Dating, 1985 Dickinson et al., 1985 Sorstrom, 1986 IR, UV Slick area, Swiss et al., photography effecti~renese 1987a, b on zooplankton and community metabolism were greater. Seawater tanks of the University of Rhode Island's Marine Eco- system Research Laboratory (MERL) were used to examine m~cro- bial responses to Kuwait crude of} alone or dispersed by Coronet 9527. Neither led to a larger bacterial population in seawater, but did lead to slightly more hydrocarbon utilizers being present, except at low temperatures (TraxTer et al., 1983; Wilson, 1980~. Biodegradation potentials were of the magnitude of nanograms per hour. The effect of of! or dispersed oil on hydrocarbon turnover rates was small. Com- pared to laboratory experiments, hydrocarbon turnover rates were lower in the MERI' experiments, and apparently were inhibited be- cause of decreased wad effects and larger water volumes. Despite this result, which was also observed in some laboratory studies (Chapter 3), both Wilson (19SO) and Traxier et al. (1983) concluded that us- ing dispersants increases exposure of the microorganisms to the bulk of! and that "in the right circumstances, chemical dispersion of of]

188 USING OIL SPILL DISPERSANTS ON THE SEA does enhance the overall oil biodegradation potential" (Traxler et al., 1983~. Mesocosms consisting of plastic bags ~ to 30 m3 in volume, sus- pended in seawater and containing a natural population of plankton, were used to investigate the effects of oil and chemically dispersed oil on phytoplankton communities in shallow water (Scholten and Kuiper, 1987~. Oil (60 to 1,000 ppb approximate concentrations) di- minished primary productivity per unit of chlorophyll, but caused el- evated biomass. This effect was attributed to reduced grazing because of mortality of copepods and planktonic bivalves. After an oil spill, a rapid succession from a diatom-dominated to a microflagellate- dominated community occurred, apparently due to exhaustion of silicate. Dispersant generally aggravated the effects. The limited volume of the plastic bag communities retained a higher concentra- tion of dissolved hydrocarbons (compare to studies in Chapter 3, "Laboratory Studies With Dispersed Oily. The mesocosm studies have shown that effects of dispersants and dispersed oil can generally be attributed to increased immediate exposures of plankton (including microbes) to hydrocarbons after oil is dispersed throughout the water (see Chapter 3, "Laboratory Studies With Dispersed Oil" and "Microbial Degradations. The observed effects are increased by longer exposure time, but some mesocosm studies showed oil concentrations decreasing only as the result of weathering and evaporation. Such experiments are more representative of isolated water bodies, for example the freshwater ponds examined by Scott Ed Glooschenko (1984~. In open-ocean waters, dispersed oil would normally be diluted before such long exposures to high concentrations could be experienced. In general, dispersed oil supported increased microbial growth, especially on plant and algal surfaces, Ad changed the composition of phytoplankton populations. Zooplankton and sometimes phyto- plankton were reduced in abundance as well. It is significant that zooplankton were contaminated with oil droplets in the oil-only treat- ment but not in the dispersed-oil treatment (Linden et al., 1987~. This condition probably reflects rapid loss washout of the dispersion or possibly adhesion of untreated oil to the zooplankton, but not the inability of zooplankters to graze the smaller dispersed oil particles. BIOS Arctic Studies A major study in the Arctic, the Baffin Island Oil Spill Project, is an excellent example of a large-scale field project with good con- /

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 189 dispersant; trots, and a longer time-scale for monitoring effects. Begun in 1980, it consisted of 4 years of multidisciplinary studies of bays off Ragged Channel, in Canada's Northwest Territories (Figure 4-4~. The area is pristine. Before the experimental spills it contained low concentra- tions of biogenic hydrocarbons, and very low amounts (less than 1 ppb) of polycyclic aromatic hydrocarbons, polycyclic aromatic nitro- gen compounds, and polycyclic saturated hydrocarbons, presumably from anthropogenic sources (Boehm et al., 1981~.* The four bays monitored during the BIOS studies were labeled: bay 7, a control; bay 9, treated with a.n underwater release of 94 bb} of of! plus · bay 10, an untreated control adjacent to bays 9 and 11; and · bay 11, which received an untreated of} slick. Bay 11 received 94 bb! of a partly weathered (by oxygen bub- bling) Virago Medio crude of} released onto the surface waters over 6 hr beginning at high tide. Onshore winds produced an even coat- ing of of} across the intertidal zone. Immediately after the release, samples revealed that more than 44 of the 94 bb} of oil were present in the oiled intertidal zone. The untreated-oil caused no immediate effects on subtidal benthic organisms, but intertidal amphipods and some larval fish were affected by physical coating (Blackall and Sergy, 1983b; Cross et al., 1983~. Fluorometer profiles found of} concentra- tions of 0.01 to 2.S ppm in the top ~ m of water. Such low subsurface concentrations are consistent with the field studies described earlier. In bay 9, which received oil plus dispersant, 94 bbl of oil were premixed with 9.4 bbl of Correct 9527. One part oil-dispersant mix- ture was diluted with 5 parts seawater and discharged subtidally via a line placed on the seafloor extending 320 m perpendicular to the shore, over 6 hr beginning at high tide. Overall, the floor of the bay was exposed to approximately 50 ppm of dispersed oil; the high- est concentrations were 167 ppm representing a maximum exposure of 300 to 500 ppm-hr (see Chapter 3~. Pre- and postspill sediment samples were collected dally, weekly, and yearly from transects along *References for the BIOS studies include BlablcaB and Sergy (1981, 1983a,b), Sergy (1985), Boehm et al. (1985), more than 30 reports issued by Environment Canada, and a special 1987 issue of the journal Arctic, Vol. 40, Supplement 1, edited by G. Sergy.

190 USING OIL SPILL DISPERSANTS ON THE SEA ~ ,~ pe Hatt (Lag~Bay103 l ~ Bay 106 5J no\ ~ :~2 Camp l (: sa~St ran deaf / ( O Expermental Oil Release Sites ~ ~ ) ~~ 2000 / ton Approx. scale in metres Bay 9. ChemCa Iy 80°00' 79C30 ) Dispersed I l l l l |oil Release Eclipse Sound ) —72°30~ ~ watt Bay 7 J ~~ ~ 1 c° :> ~ ~ Baffin~\ J Island _ FIGURE ~4 Baffin Island Oil Spill Project test sites. the 3- and 7-m depth contours. A few samples were collected from 10-m deep microplots. The dispersed oil plume moved throughout Ragged Channel (Boehm, 1983~. One control area, bay 10, adjacent to the two treated bays, was exposed by currents to dispersed oil from the treated areas. Concentrations at the seafloor were about 5 ppm, one-tenth the exposure in bay 9 (Blackall and Sergy, 1983a,b). Oil was found in bay 9 (dispersed oil) and bay 10 (adjacent control) sediments after 1 to 2 days, and in ad four bays after 2 to 3 weeks. Petroleum hydrocarbons in bay 9 sediments reached a peak of 5 ppm, 2 weeks after the

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 191 , / -. r~ ~ Arctic A- Bay am, t ~ Baffi:\t 3 ,4/ I MA is\ Island Oil Suill Projected? ¢/W(3D :~ I! 4s;':,.~ - ,, 1 86° 84° 82° 80° 78° 76° 74O 1 1 1 1 1_ 74° _ 73o 72° 70° Lancaster Sound ~ _ rat \ --'en-'! fib\ - \ r . I 4--- Bylot ', Island <: Baffin Bay , ~ Inlet - ~ -c ~< O Kilometres 200 H H H 1 FIGURE 44 (Continued). dispersed of} release. Bay 7, the distant control, had concentrations similar to bay 10 and slightly lower than bay Il. Less there 1 percent of the dispersed oil released in bay 9 ended up in its own sediments. Macrobenthic organisms were stressed by dispersed of] in bays 9 and 10. Dissolved hydrocarbons such as hexane, benzene, toluene, and xylene as high as 9 ppm appear to have caused narcosis (Boehm and Fiest, 1982; Neff and Anderson, 1981~. Benthic sed- iment dwellers, such as clams and polychaetes, surfaced in various conditions of weakness and incapacitation. Elevated concentrations of volatile hydrocarbons in the water column were still measured the day after the spill, but by the second day they were at background levels of 30 to 50 ppb (Boehm et al., 1985, 1987~. Within 1 to 2 weeks, surfaced polychaetes and bivalves reburied themselves and the numbers of sea urchins, previously reduced, were near prespill levels (Cross and Thomson, 1982~. Systematic monitor- ing of benthic populations demonstrated that exposure to dispersed oil did not cause large-scale mortality of benthic animals. After 1 year, there were no statistically significant differences in benthic com- munity composition between bay 9 (dispersed oil) and the control

192 USING OIL SPILL DISPERSANTS ON THE SEA TABLE 4-5 Hydrocarbons in Sediment Samples ~ ~g/g dry weighta'b) Taken at "Tissue Plot" Stations at 7 m Water Depth Time Distant Control Dispersed Oil Adjusted Control Untreated Oil Period (Bay 7) (Bay9) (Bay 109) (Bay 11) Prespill 0.47 0.18 0.33 0.51 (1981; (0.26,0.85) (0.05,0.73) (0.17' 0.64) (0.19, 1.4) 1-3 Days 0.69 2.0 0.88 0.18 postepill (0.49,0.97) (1.4, 2.8) (0.52, 1.5) (0.07,0.47) 2-3 Weeks 0.93 7.8 1.6 1.0 postspill (0.58, 1.5) (4.3, 14) (0.74, 3.7) (0.54, 1.9) 1 Year later 1.2 2.2 1.7 5.3 (1982) (0.93, 1.5) (1.4,3.3) (1.3,2.1) (2.4,11.4) 2 Years later 3.2 7.6 -- 13 (1983) (1.1,9.1) (5.7,10) (9.8, 16) bDetermined by ultra~riolet/fluorescence analysis. ~Concentrations presented as geometric means with lower and upper 95 percent confidence limits shown in parentheses. CBay 10, located between bays 9 and 11, received about 10 percent of the dispersed oil received by bay 9. SOURCE: Boehm et al., 1987. bays (Blackall and Sergy, 1983b). Thus, effects from dispersed of} on benthic organisms only occurred over the short term. Table 4-5 summarizes the combined mean concentrations of petroleum hydrocarbons in sediment samples for the prespill sur- vey, 1- to 3-day postspill samples, 2- to 3-week samples, and yearly averages for 1982 and 1983 (typically 40 to 50 for each bay). The greater persistence in the untreated of} bay is evident and contrasts with the light initial levels in the sediments where oil was chemically dispersed. After ~ year, petroleum concentrations in almost all water sam- ples were low, less than 0.1 ppb. Exceptions (about 3 ppb) were found in samples from under visible of} sheens emanating from the untreated beached of} in the intertidal region of bay 11 (Boehm, 1983~. In the control (bays 7 and 10) and dispersed oil (bay 9) sediments, hydrocarbon content was only slightly higher than prespid levels, although some bay 9 samples showed relatively undegraded oil, and

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 193 more aromatics (on an absolute basis) were found in one subtidal sample than were found in the previous year. The increased oil in bays 7 and 9 sediments in 1982 and 1983 may have traveled from bay i: 11, where the untreated of} was applied. Subtidal sediments in bay Il (untreated oil), however, had in- creased to an average of 10 ppm, with values as high as 66 ppm observed (Boehm et al., 1984~. The oil had a patchy distribution, perhaps from subtidal movement of oiled sediment particles. After 1 year more than 31 bb! of the original 94 bb} of of} remained as a source for continued subtidal contamination (Blackall and Sergy, 1983b). Chemical analysis of the tissue of five species of benthic animals n bays 9 and 10 revealed that they accumulated and depurated significant concentrations of of} the first year after the spill. As an example, concentrations of up to 700 ppb, or ~g/liter (dry weight), were attained within 2 days, 2-week postspill body burdens were declining, and after 1 year they were down to 1 to 5 ~g/liter. Increased hydrocarbon content of the subtidal organisms in bay 11 appeared to reflect the increased of} content of the sediments (Cross et al., 1984; Sergy, 1985~. Although the initial impact of dispersed of} was more severe (a subsurface discharge of premixed oil-dispersant mixture certainly introduced more toxic aromatics to the water column than would a surface slick), the persistence of dispersed of} in subtidal sediments was much less (at background level after ~ year) than at the untreated of} site. Temperate ShaBow Subtidal and Intertidal Habitats Studies of temperate subtidal habitats, like the mesocosm studies of microbes and plankton above, indicate that of} concentration and length of exposure to of} constituents appear to be the controlling factors, not whether the of! is dispersed. Wells and Keizer (1975) tested the effects of of] and of} plus Oilsperse 43 on sea urchin (`Strongylocentrotus droebachiensis) popu- lations exposed to samples of water from two shore-based mesocosms (8,000 liters). After 30 days, no mortality was caused by 4-day expo- sures to water from the mesocosm treated with of} alone, at 40 ppb total extractable organics (by fluorescence). Because of the higher concentration in the dispersed of} mesocosm (250 ppm oil, up to 125 ppm dispersant), greater than 50 percent mortality resulted. Oil

194 USING OIL SPILL DISPERSANTS ON THE SEA plus dispersant was also observed to reduce mobility of the urchins, as measured by the percentage climbing the walls of the test tanks. Such of} and dispersant concentrations could be reached in inshore applications of dispersant to actual of! spins, but would be unlikely to remain so high for a month (Gordon et al., 1976~. In these tests, 50 percent of dispersed of} and 24 percent of undis- persed of} was lost by day 22 from the mesocosm. The dispersant itself was wed above the acute lethal threshold for urchins (125 ppm), and was considered to be the major cause of mortality. Mortality, larval settling, spawning, and octopus predation on littleneck clams (Protothaca staminea) were examined in small out- door tanks and in field quadrats (0.5 m2) using Trans-Mountain Western crude of} n.nCt Corex~t 9527, at 1,000 ppm of} plus 100 ppm dispersant in seawater (Hartwick et al., 1979, 1982~. Seven liters of this mixture were poured onto the field plots daily for 5 days. The stock mixture in the tank was allowed to weather naturally outdoors during this period so that each successive application was with a more weathered oil. This experimental design may simulate a usually high and repeated exposure of an intertidal environment to dispersed oil, as might occur in an estuary where a large spill was dispersed but not diluted rapidly by water circulation (Hartwick et al., 1979, 1982~. Reduced siphon activity was apparent on the first day, significant mortality occurred with the dispersed of} after 4 days, but mixing the dispersant with fresh water prior to use reduced mortality. No mortality occurred after 10 days with of] alone. Settlement of larval clams was lowest at highest concentrations of of} plus dispersant (1,000 ppm of] plus 100 ppm dispersants). Octopus predation was substantially reduced when clams were tainted with oil (Hartwick et al., 1979, 1982~. The impact of of} and of] plus Finaso} OSR-5 on the benthos in a 13-m2 intertidal mesocosm test in West Germany showed that oil- degrading bacterial populations were stimulated by the treatments, particularly by dispersed of} (Farke and Guenther, 1984; Parke et al., 1985a,b). The metabolic activity of benthic diatoms was initially stimulated. Macrofauna populations were undiminished. Feeding activity of clams (Mya), cockles (Cerastoderma), and polychaetes (Arenicola) was initially reduced with (lispersed oil, and to a greater degree by of] alone. No penetration of of} into the sediments was ob- served either with or without dispersant. No toxic effects of dispersed of} were noted. The ejects of of} on blue mussels (Mytilus edulis) were studied

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 195 in a mesoscale experiment simulating the Baltic Archipelago (Linden et al., 1985, 1987~. In the dispersed of} tank, of} concentration in the mussels increased more rapidly than in the mussels exposed to of! only. However, by the end of the experiment, the dispersed-oi} mussels had added about twice as much shell length as the oil-only mussels, while controls had added three times as much. Mussels exposed to of} plus dispersant exhibited reduced byssal thread pro- duction and spawning activity for the first 4 days, but recovered by day 12. With exposure to of] alone, spawning was still abnormal after 12 days (Carr and Linden, 1984~. In 3-month studies in large-scale, flow-through exposure tanks of sublethal responses of invertebrates (i.e., lobsters, scallops, clams, mussels) to nominal 50 ppm light Arabian crude, with and without Corex~t 9527, maximum measured concentrations were 1.0 to 2.2 ppm for 6 hr for of] alone, and 12.7 to 19.4 ppm for 6 hr for of! plus dispersant. No mortalities occurred, however, clams (Mya sp.) exhibited some reversible changes and reduced shed abductor muscle (Carr et al., 1985, 1986~. Other transient sublethal effects were observed in both of] and oil-dispersant treatments. For example, mud snails tried to avoid of} alone and were narcotized in oil-dispersant treatments. Hydrocarbon concentrations were initially elevated in sediments and mussel tissues in the dispersant-treated tanks, with alkylated dibenzothiophenes present in tissue after 21 days. It was not determined from these results whether chemically dispersing the oil was more or less detrimental to the animals than physical dispersion alone (Carr et al., 1986~. When dispersed oil is rapidly removed by water movement, re- covery of a habitat can in some cases be more rapid if dispersant is used. In areas with poor circulation, on the other hand, using dispersants can increase the exposure of organisms and habitats to oil, and actually increase damage. Intertidal Communities Although the primary focus of this report is the effectiveness of dispersants in open marine areas, a number of valuable intertidal studies have been conducted. They are noted here for the addi- tional understanding they shed on the overall impact of dispersed oil compared with untreated oil. Eelgrass (Zostera noltii) cover decreased when oil alone, disper- sant alone, and oil plus dispersant were applied (Baker et al., 1984~.

196 USING OIL SPILL DISPERSANTS ON THE SEA The sand and mud flat experiments showed rapid dispersion of both oil and dispersed oil, with little effect on the melofauna. However, dispersant led to greater retention of of! in the upper sediment layers, and reduced abundance of the tube worm Arenicola sp. (Rowland et al., 1981~. Biological effects of North Sea crude of} and BPllOOWD were studied by Crothers (1983~. The experiment simulates a situation in which dispersed of} washes ashore. Oil was sprayed onto 2-m2 plots during ebb tide, and dispersant was sprayed on the flood tide. Shores covered with seaweed (Focus spp.) were unaffected, and recovery was rapid. As above, limpets and small periwinkles were most affected in the short term, while barnacles showed long-term effects. Of Al treatments, oil plus dispersant was most harmful, of} alone had moderate effect, and dispersant alone was not toxic compared with controls. Dispersants SD LTX and BPllOOWD applied to Maui D-sand petroleum condensates* on rocky intertidal plots in New Zealand produced varied results among species for dispersant and weathered versus fresh condensate (Power, 1983~. In some cases, dispersant use reduced mortality of barnacles and bivalves exposed to condensate, while in other cases, mortality increased. A major study in the United Kingdom compared effects of oil and dispersants for a variety of intertidal rocky shore, salt marsh, sea- grass, sand, and mud flat habitats. Experimental plots were treated with oil, dispersants (BPllOOWD, BPllOOX, Corexit 8667, and Corexit 7664), of} plus dispersant, premixed oil plus dispersant, and no treatment (control) (Baker, 1976; Baker et al., 1984; Rowland et al., 1981~. Major effects were confined to limpets and periwinkles, which were reduced in population numbers for several months. Salt Marshes The dispersant BP1lOOWD was ineffective in cleaning an oiled salt marsh in the United Kingdom (Baker et al., 1984~. I,ong-term (1 to 2 years) reduction in Spartina anglica density and short-term loss of Salicornia spp. was noted with both of! and dispersed oil. Sal- icornia recovered after 2 years. In contrast, in Louisiana, Spartina salt marsh recovered much more rapidly (Smith et al., 1984~. Short- term effects on melofauna were observed, but by 5 to 10 weeks after *These New Zealand condensates have a 0th API gravity low specific gravity.

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 197 oiling there were no significant differences between the test plots and the controls. Although dispersant applied directly to Louisiana salt marsh plants prior to oiling caused reduced biomass by the end of the grow- ing season (Delaune et al., 1984), little evidence of of} or dispersant- caused mortality among the melofauna was found. The general con- clusion was that the Louisiana salt marsh exhibited a low sensitivity to oiling. Application of weathered Nigerian crude, fuel oil, and mousse to salt marsh, and treatment with a new Type Ill ctispersant (BP Enersperse 1037), showed that total hydrocarbon concentrations in the sediment were less for dispersant-treated oils (Little and Scales, 1987a,b). Dispersant-treated oils were more damaging in the short term, but less destabilizing to the marsh in the long term. Studies of an Atiantic Coast salt marsh exposed to weathered crude of} and Conceit 9527 provided additional information on the extent of damage and recovery of affected marsh vegetation in three vegetation zones-~Lane et al., 1987~. Sensitivities of marsh zones ranged from Marsh (high) to high marsh (Iow). Both the mid- marsh and creek-edge vegetation communities were most sensitive to the of! plus dispersant applications based on a range of morpho- logical, growth, and plant stress parameters; of! alone had the least impact, and dispersant effects were similar to dispersed oil. Intertidal Areas Artificial intertidal mudflats were treated with Forties crude of} and Finasol OSR-5 dispersant, and monitored for 10 months (Dekker and van Moorsel, 1987~. Dispers~nt plus of} had more severe short- term effects than of} alone: high mortality in cockles (Cerastoderma ecluZe), clams (Macoma balthica), and polychaetes (Arenicola ma- rina). In both treated areas, C. edule was more vulnerable to frost than in the control areas. Some of these results, which apparently contradict the results of the BIOS and Long Cove studies, are characteristic of dispersant applied directly to oiled shoreline sediments. This is distinct from the situation in which of! dispersed offshore is washed ashore by tides and currents. In the latter case, there is considerably less long-term biological impact than would be observed with untreated oil. In summary, some experiments reveal more damage to organisms when dispersants are used directly on rocky shores, and some reveal

198 USING OIL SPILL DISPERSANTS ON THE SEA less damage. However, there seems to be no strong, general ecological documentation either for or against dispersant use in these areas. Dispersant use directly on oiled intertidal and subtidal environ- ments, ranging from mud flats to marshes and seagrass beds, may facilitate the penetration of of} into the sediments and thereby in- crease ecological damage without decreasing the time necessary for recovery. Further discussions, including seagrass beds and the recent rec- ommendations of the American Society for Testing and Materials regarding application of dispersants to seagrass habitats, are covered in a later section. Temperate ShaBow Subtidal Studies: I`ong Cove and Sequim Bay A controlled field study involving of} dispersal in a large volume of shallow water is not easy to plan and conduct especially in temperate areas, such as in the United States, where it is difficult to obtain permits to discharge of} for research studies. However, in 1981, such a field study was conducted in Long Cove, Searsport, Maine, comparing the fates and effects of two 6-lob} spins of Murban crude oil, one dispersed and one untreated (Gilfi~lan et al., 1983, 1984, 1985, 1986~. The study was designed to simulate frequent small spills that occur in nearshore Maine waters. Three shallow (3.5 m) areas were boomed off for the study. In one area, 250 gal of untreated Murban crude oil were released on an ebbing tide. In a second area, 250 gal of crude mixed in an oil- dispersant ratio of 10:! with 25 gal of Corexit 9527 were released at high-water slack tide and mixed with gates towed by small boats. A third area served as a control, as did samples taken in the two test areas before the of} was released. The spill of untreated oil, released 1 hr after high tide, coated and adhered to the tidal flat as the tide receded. After two tidal cycles, oil was cleaned from the beach using conventional methods. The spill of crude of} mixed with dispersant was released over the intertidal zone at high tide in a separate section of the cove. The treated oil quickly dispersed as very fine droplets in a light-brown cloud, even under the quiescent (slack tide) conditions. Concentrations of 15 to 20 ppm of dispersed of} (exposure 20 to 30 ppm-hr) were measured 10 cm from the bottom, conforming to the range expected. Water samples taken near the surface and near the bottom showed that chemically

INTER MEDIA TE-SCA LE EXPERIMENTS A ED FIELD ST UDIES 1 9 9 dispersed of} lost lower molecular weight hydrocarbons (below n-C~5) as the droplets mixed downward (Page et al., 1983, 1984, 1985~. Following the discharge, significant amounts of Murban crude of} were found in sediments exposed to untreated oil, mostly in the upper intertidal zone, but not in sediments exposed to the cloud of dispersed of} (GilfiHan et al., 1983, 1984~. Differences between treatments were mostly within one standard deviation (Gilfi~lan et al., 1986~. Hydrocarbons were found in clams and mussels collected from the untreated-oiT site 1 week after the spill, but were absent or near the level of detection in the same species collected from the dispersed oil site (GilfiRan et al., 1984; Page et al., 1983, 1984~. In clams and mussels from the untreated oil site, two enzyme systems were markedly elevated after the spill: glucose-6-phosphate dehydroge- nase (sugar metabolism) and aspartate amino transferase (protein metabolism). In contrast, the activities of those enzymes at the dis- persed of} site were similar to those at the control site (GilfiHan et al., 1984, 1985~. Effects on infaunal communities mirrored the chemical results. At the untreated-oi} site some species were reduced in number or elim- inated, and there were blooms of opportunistic polychaetes, changes in community structure that are consistent with observations at acci- dental oil spills. There was no evidence of adverse effects on infaunal community structure from exposure to dispersed oil, but there was clear evidence that exposure to untreated of} adversely affected com- munity structure (Gilfi~lan et al., 1983, 1984, 1985~. The more severe and long-lasting effects from the untreated of] in the Bong Cove study were attributed to greater persistence of of! in intertidal sediments. Dispersed oil, which adheres less to sediments (Harris and Wells, 1979; Little et al., 1980) and is more easily washed from the water column by tidal currents, offered less exposure than untreated oil. As in the BIOS studies, untreated oil that was stranded on the shore at Long Cove released hydrocarbons slowly, contaminating the subtidal region over a longer time than in the area where the oil had been dispersed. Both the BIOS and Long Cove studies concluded that biological effects attributable to dispersed of} were fewer and more brief. In contrast, significantly reduced diversity and increased dominance by opportunistic species occurred where the spilled of} was not dispersed. Anderson et al. (1985) studied the fate and effects of Pru~hoe

200 USING OIL SPILL DISPERSANTS ON THE SEA Bay crude, alone and with Conceit 9527, in the intertidal zone of Sequlm Bay, Washington. The sediments were placed on trays arid oiled in various ways (thorough mixing, layering) and clams were introduced into them. The sediments were placed in the field for ~ to 6 months. The premixing of sand and of} with dispersant exposed the clams to greater concentrations for a longer time than in a typical dispersed of! situation (i.e., Long Cove and BIOS). The dispersant did not affect oil retention time or penetration depth in the sediment. Dispers~nt presence was correlated with more of} uptake by Macoma. Exposures in the field for 1 to 4 months produced equivalent effects in of! and dispersed of} groups (i.e., deaths, contamination, amino acid loss). Macoma was more sensitive than Protothaca although Protothacc`'s growth was reduced by dispersed of] in the surface sedi- ments. Fate of the of! components was the same in both treatments. This study (Anderson et al., 1985) was the last of several examining the fate and ecophysiological effects of dispersed oils on intertidal mollusks. Fish Although fish are one of the primary reasons for deciding whether to employ dispersants to treat of} spins, there are only a few reliable studies that compare the effects of dispersed of} with untreated oil. Laboratory studies on fish eggs and larvae (ichthyoplankton) and on adult fish were surveyed in Chapter 3. In this section, a combined laboratory-field study of salmon homing comes as close to a field study of effects on fish as is currently available. Salmon have been studied because of their highly developed chemical sense, which might be disturbed by low concentrations of petroleum hydrocarbons (see Chapter 3~. The effects of untreated and chemically dispersed Pru~hoe Bay crude of! on the homing of salmon were measured in two experiments (Brannon et al., 1986; Nakatani et al., 1983, 1985; Nevissi et al., 1987~. In the first study, 24 adult chinook salmon (Oncorhynchus tshawytscha) were caught in a freshwater pond, anesthetized, tagged, and divided among four tanks (Nakatani et al., 1983~: . an untreated control group; · a tank with untreated Pru~hoe Bay crude of! as a 0.5 mm thick slick; · a tank containing 105 ppm of chemically dispersed crude oil (10:1 of} to dispersant); and

INTERMEDIATE-SCALE EXPERIMENTS AND FIELD STUDIES 201 . a tank containing 10.5 ppm of freshwater chemical dispersant. After a 1-fur exposure, the salmon were removed from the expo- sure tanks, held overnight in a raceway, trucked 9 km downstream, and released. Of the 215 fish released, 154 (72 percent) returned to the pond where they were caught. There was no significant difference in the percentage of return among the four groups, nor in the time it took the fish to return. Tests with coho salmon (O. kisutch) produced similar results. The methods used were the same, except that seawater was used instead of fresh water in holding Ed exposure tanks, and the tanks were outdoors, not indoors. Again, there was no statistically signifi- cant difference in the percentage of returns or time to return. Nakatani et al. (1985) concluded that, as for fresh water, there was no reason to believe short-term exposure to Pru~hoe Bay crude of} had any deleterious effect on homing success. A lower mean percentage return for coho salmon was attributed to an extensive gilInet fishery near their release point (Nakatani et al., 1985~. However, of} avoidance was observed in these studies. Before the untreated of} was added to the exposure tank, the salmon swam throughout the tank. After of} was added, the fish swam to the bottom of the tank and remained there during the I-hr exposure. Chemical senses are considered essential to homing in salmon, but these studies concluded that the olfactory systems were not impaired enough from a 1-fur exposure to interfere with homing. Histopathological analysis of the olfactory organs of the salmon showed no anomalies. Thus, while adult salmon might avoid of! (Weber et al., 1981), forced brief exposure to whole Pru~hoe Bay crude of} or chemically dispersed oil at high concentrations did not prevent or delay homing. Topical Shallow Intertidal and Subtidal Habitats Seagrasses The potential impact of dispersing an of} spill over a shallow area with a seagrass-based benthic community is of considerable concern in tropical areas. Such areas are highly diverse and productive, hence inherently valuable. Because dispersal of an of! slick introduces higher concentrations of toxic hydrocarbons into the water column in the short term, but tends to decrease the residence time of of} in the long run, it is important to compare chemically dispersed of}

202 USING OIL SPILL DISPERSANTS ON THE SEA with physically dispersed (untreated) of! on a common basis. As with laboratory studies, when effect threshold was based on total oil per unit volume (nominal concentration), chemically dispersed oil apparently had a greater impact; when effect threshold was based on actual water-accommodated hydrocarbons, there was generally little difference in the toxicity of chemically and physically dispersed oils. In this section, both laboratory and field studies with seagrasses are reviewed. Baca and Getter (1984) found similar toxicity of Pru~hoe Bay crude and chemically dispersed of! to the seagrass Thalassia tes- tudinum, using hydrocarbon concentrations measured by gas chro- matography. The dispersant (Corexit 9527) had similar acute toxic- ity to the dispersed oil, but caused more leaf discoloration at sublethal and LC50 doses. Thorhaug and Marcus (1985, 1987a,b) and Thorhaug et al. (1986) studied the effects of a range of concentrations of dispersed oils (Murban and Louisiana crudes, a.nc3 seven dispersants) on three major Caribbean and Gulf of Mexico species of subtropical and trop- ical seagrasses grown in 100-liter, aerated seawater aquaria (Table 4-6~. The mortality percentage of the three grasses, exposed for 100 hr to 75 m} of Louisiana crude of] in the aquarium (approx- imately 750 ppm nominal concentration) and 75 m] of dispersant (as instructed for that dispersant), was measured. In the aquaria containing chemically dispersed oil, the measured concentration of total water-accommodated hydrocarbons was 429 to 634 ppm; in the untreated of} aquaria the corresponding concentration was 5.6 to 10.4 ppm (Thorhaug et al., 1986~. Therefore it is not surprising that chemically dispersed oil showed a greater negative effect on species survival and growth than of} alone. In other studies, exposures were measured by gas chromatog- raphy and toxicity was measured as health, that is, browning, yel- lowing, and spotting of young blades (Thorhaug and Marcus, 1985; Thorhaug et al., 1986~. Growth rates were reduced only at extremely high exposures: when the three grasses were exposed for 100 hr to 750 ppm (nominal concentration), Thalassia was more resistant than Syringodium filiforme and Halodule wrightii. Effects were observed after 100 hr at 1,250 ppm. Response varied by species, but effects were generally greater when dispersants were present. Mortality fol- lowed the same order of sensitivities as growth. At a dosage level of 1 part (150 ppm) dispersant,. 10 parts of!

INTERMEDIA TE-SCA LE EXPERIMENTS A ND FIELD STUDIES 203 TABLE 4-6 Mortality Percentage of Seagrasses Caused by Louisiana Crude Oil and Dispereants Dispersanta Thalassia Halodule SYrinzodium Finasol OSR-7 0 7 7 Jansol~r-60 10 41 12 Cold Clean 500 16 21 18 Corexit 9550 22 58 63 Corexit 9527 26 76 84 OFC D-609 35 73 86 Conoco K(K) 65 97 98 aAll treatments contained oil and dispersant. SOURCE: Thorhaug and Marcus, 1987a,b. (l,SOO ppm), and 10,000 parts water, no significant mortality oc- curred (Thorhaug and Marcus, 1987a,b). The American Society for Testing and Materials (1987) has re- viewed the literature to 1985 on the effects of of] and dispersants on seagrasses, and recommends the following use guidelines: . If there is a possibility that an of! slick will strand on intertidal portions of seagrass beds, dispersant use would be most effective while an of} slick is still offshore to prevent the of! from impacting the grass bed. Dispersant-use decisions to treat of} already over a seagrass bed should ultimately take into account the depth of the seagrass bed and the potential for dilution of the dispersed oil. · The use of dispersants over shallow submerged seagrass beds is generally not recommended, but should weigh the potential impact to the seagrass beds against impacts that might occur from aDowing the of] to come ashore. · Dispersant use should be considered to treat oiT over seagreass beds in water deeper than 10 m if the alternative is to allow the of! to impact other sensitive habitats onshore. Dispersant use is not recommended in shallow lagoons or areas of restricted flushing rates. Related field and ecological studies of the effects of o~l and dis- persed oil on salt marshes were discussed earlier.

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

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.

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.

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

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

209 Go C5) To - a~ - ._ o ~5 ·E s v . - o m ._ U] ._ a' o LO' ._ L' o I' o it U] m ¢ 02 ._ al a. DO EN U. O ~ ~~5 ~ ^. ·- Ct. ~ ~ . ~ ·- Do Pe4 'I' ' Go- I,4- CD ~ ._ Go c, ~ 0 _ a) 3 ~ ~ ~ ~ o C `, - °2 . ~ ~ ~ ~ _ m C) ~ 7 ~~ ~ , ,~ , ~ 3_-' u~7 1 ~ ~ 3 O U] O O z; + O es _ do ad'= ~ ' ) ~ ~ 'I ~

210 m ~ r ~ al _` V - ~ m 1 ~ m ~ ¢ ~ 00 — — 00 ~:5 to ~ ~ ~ ~— ~ ~ — - 00 _ ~ ~ I: ~ ~ ~ ~ D ~ — · U — a, E ~ !~;(,1FiHE %; ~ 1/1 m ~ 0 0 ~ ;= °' ~ . Hi- U ~~ ~ ~ ( ~

211 . — oo oo _- . ~ ~ ~ ~ ~ ~ `, _ ,~ ~ I, o, _ =a · ' HE ~ =S 5~ 5 ~ ~ ~ ~ ~ Id c ~ ~ a= m v ~ ~ a: · a + ~ ~ ~ + i} ~ ~ ~,~ 5 ~f ~~ ;~ d ,, E ~ ~1 ~ D _ ~ o ~ .e ~ ~ ~ ~ ~ ~ X O ~ Z; 0 .. _ ~~ ' ''a ~7 · ~ " ,5 ~^ Ida ~ 3 ~ I 1O _ ~~ ~~ ~~ ~~ ~ v

212 m C) m m Cat CD oO _ O) _ en ~ _ ~ 03 G a, ~ ~ _ ~ o C - -it ~ ~ ,~ Ens _ ~ h - - =- C o _ i ~ ~ i i ~ ~ 2 ~ ~ ~ ~ o es ~ - c ~ + ~ o c ~ _ - ~ o =S i] S igo0 =~ Too i U) ~ U] ~ U] ~ U] ~ ~ ¢

213 . ~ Do · ~ Go . . C53 Go o =— C. ~ -m ~ O ~ ~ — ~ ~ Amos to J _ 3 O a o TIC ~ ·~ ~ 3 q, TIC—D ° ~ L' o Q ~ of 4D ~ SO o ~ ~ ~ ~ ~ ~ . ' a ~ c ~ ,, 3 0 C:1 D o V o ~ V l.. ·— ~ Ha ~ ~ 1 ~ _ ~ _ ~ ~ ~ 0 ~ ~ ~~ . P4 c. ~— - to 0 .. -0 ha & ~ In ~ 0 c `d 3 ._- CO Go - rS be Arc - o ~ ,Q n, ~ — o o a+ ~ o- - o 0 ~ 0 ,.Q ·— 0 a~ _ c~ a~ ~ ~o c ~ ~ 0 0 ~ —a 0 aa 0 + I .. e~ 0 ~ ~ _I _ _= _o .v _ ~ v 0 ~Y CS' ~ .o ~c .v 4o 00 0 - .c 0 . o. - v 3 ~ _ V ~ ~ C' ~ ~ o ~o X _ _ p, a, e~ C~ ~ Y Y _ o I, ~ ~ .~ V ~ ._ _ ~ oo ._ · - <5) Cr` ~ oo 43, _ ~ .— ~ oo _ °o oo CO ~ ~ ~ ~ a, _ ~ ~— _ _1 —~ ~ _ ~ ~ C. · ~ :~ - ,,, ~ ~ 3 ~ ~ ~ a' ~ ~ v ~ 3 :^ ~n . C o C .i* a' ~ ~ ~C ~, ~ _ ~ ~ --^ ~ . _ ° ~ ~ ~ 4,, ~C ~ aC o ~ o _ o5 1 o ~ o o ~V .3 ~ ,,~C ._ ~ ~ O CO 0 ~ -=a+ ~a+ ~0 ~ 0 ~ ~ 0 . a - o . — aa ~ 0 ~ ~a 3 _ + _a O ~30 ._ _ _ be o V =°-m £,," =_ 0= m ~ ~ - ,,, ~ ._ v ~ ~ ~x.0 O O ~ v v ~ CQ ._ 1 1 a · a~ . a~ - - . o 1 a + o . - . o 1 1 o · - o L. I,C o v 1 1 v ·—

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.

Next: 5 How Dispersants Are Used: Techniques, Logistics, Monitoring, and Application Strategies »
Using Oil Spill Dispersants on the Sea Get This Book
×
Buy Paperback | $100.00
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

While major oil spills are rare, oil slicks can have disastrous environmental and economic consequences. This book summarizes research on the use of chemical dispersants: their effectiveness and limitations and the results of using them in different spill situations. Based on laboratory and field research as well as on actual case histories, this book contains a clear-cut set of recommendations for action, planning, and research. Of special interest is the chapter on the biological effects of oil itself and of oil treated with chemical dispersants.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  6. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  7. ×

    View our suggested citation for this chapter.

    « Back Next »
  8. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!