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