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Executive Summary OVERVIEW The study of petroleum pollution in the ocean deals with two potentially opposing aspects of man' s activities: on the one hand is pollution arising from activities undertaken to meet man's needs--the extraction, transpor t, and use of petroleum for energy and chemical feedstocks--and on the other hand is the strong desire to preserve living mar ine resources both for current uses and for a legacy for future generations. In this examination of marine petroleum pollution we recognized this dual ity and attempted to examine it from a broad and, at times, somewhat distant perspective, without bias whenever Possible, so as to avoid pitfalls of misinterpretation. Petroleum is a naturally occurring substance, derived from organic materials once living but since trans- formed into a complex mixture of chemicals, consisting mainly of hydrocarbons and small amounts of other organic compounds. A small amount of petroleum has seeped into the world's oceans for at least centuries and probably millions of years, and portions of the oceans have accommodated long-term influx of some petroleum into their communities and ecosystems. The modern influx of petroleum into the marine environment is on a different scale, occurring more rapidly and over a wider area, and probably is of a different k ind . The product enter ing the oceans today, both from chronic effluent release and runoff and from sudden catastrophic spills, represents a sudden and significant input of contaminants when viewed against the much longer, but much lower, continuous presence of seepage petroleum. Also, the chemical composi- tion of this modern petroleum input often differs from that of the seepage oil, the latter being altered by the degradation processes, both physical/chemical and microbial, occurring in the marine sediments and crustal layers. In this context it must be noted that inputs of petroleum are not the only sources for many of the compounds of concern. For example, combustion of coal yields several polyouclear aromatic hydrocarbons similar to or also found in petroleum. Finally, modern petroleum input to the oceans is no longer restricted to the seep locations but now includes many waters formerly held unpolluted and pristine. Even those areas themselves free of oil exploration and -
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4 production activity are nonetheless subject to potential pollution resulting from petroleum tanker traffic. Our mandate from the Ocean Sciences Board (now the Board on Ocean Science and Policy) was to review the accomplishments since the 1975 NRC Repor t, Petroleum in the par ine Environment, to err ive at conclusions on the basis of our newer understanding of the behavior and fate of petroleum in the marine environment, and in the end to make recommendations concerning possible further research. We recognize potential environmental problems requiring further study as well as areas where much less concern is required, either as a result of new findings or because investigations are essentially completed. Inevitably, the potential impact of petroleum as part of, or together with, other contaminants in the marine environment was considered. While in some instances petroleum itself is readily seen as the identif table pollutant, as for example, in tanker spills or in known cases of chronic petroleum pollution, there are many regions where petroleum hydrocarbons are thought to form part of a more general pollution threat to the health of those environments. Waters near or receiving the effluent of urban and industrial regions serve here as primary examples. GENERAL ADVANCES: 19 73-1983 Progress in oil-pollution-related research during this past decade has been impressive. Knowledge and understanding of its problems have come about in each of the areas identified in the 1975 NRC report. Most significant of the advances in these areas are the reduction in the uncertainties regarding the rates of input and amounts of marine petroleum pollution, the increasing sophistication of the analytical methodology appl fed to chemical and biological studies, clearer identif ication of the various processes acting on petroleum in the oceans, and the clear identification of problem areas in the effects of petroleum on biota. Inputs There is now a better understanding of the data base with respect to input of petroleum into the world's oceans, especially for urban runoff, which is a major source. Progress has been made also in the design and implementation of procedures for measurement of atmospheric inputs of petroleum hydrocarbons to the marine environment, although more data are needed. In addition, over the past 8 years there has been a better definition of the various sources of input, which has led to the recognition and elimination of the problem of double bookkeeping, i.e., including a particular source in more than one category in pre- vious estimates. These advances came as a result of the discussion and deliberations of the 1973 workshop, the recommendations from which were carried forward to the present effort.
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5 Methods Underlying the progress made in the area of inputs are the improvements in chemical methods. Several new sampling methods and dev' ces , including specialized water samplers that avoid contamination from surface film, have been developed and have led to greater confidence in subsequent data. The analysis of petroleum hydrocarbons, pyrogenic hydrocarbons derived from the atmosphere and resulting from incomplete combustion of oil, coal, wood and gas, products of metabolic alteration of petroleum by organisms, and products of chemical and biochemical transformation after oil enters the sea (e.g., metabolites and photo- chemical oxidation products), has made great strides, especially with the parallel development of glass capillary gas chromatography, high- pressure liquid chromatography, and glass capillary gas chromatography/ mass spectrometry computer systems. AS a result, there exists today an improved capability to analyze a wide range of petroleum compounds, including volat lie components, in water, sediments, and organisms , that was not possible or was achieved only with difficulty at the time of the first workshop (1973~. The intercomparability of data from different laboratories is more reliable as a result of several quality control exercises and workshops for intercalibration. Fate Describing the fate of petroleum in the marine environment is possible in a way that was not conceivable in 1973. Methods of modeling are now approaching the level of sophistication where they are of potential use in spill impact prediction. Much more is now known of the various environmental processes acting on petroleum, and much has been added to our understanding of the properties and factors relevant to the fate and effects of oil. For example, whereas the process of photochem~cal oxidation was only recognized at the time of the first report, today it is being actively researched. A major advance since the last report is the interactive biological/ chemical approach to studying petroleum in the marine environment, i.e., recognition of the need of these two disciplines to work intimately on this problem. Indeed it is rare to find studies involving one without the other. As a direct result, the role of biological alteration of petroleum is much better understood. Such processes as microbial degradation are now recognized as significant to the fate of petroleum in the marine environment, and work on establishing rates of microbial degradation for different environments is now being done. The broad outlines of metabolic pathways of petroleum degradation are being developed for bacteria, phytoplankton, and higher animals, and con- siderable work is being carried out on specialized detoxification mechanisms where these are known. It has also been shown that animals exposed to sublethal dosages take up hydrocarbons, but in most cases are able gradually to alter the various petroleum components, in some cases by conversion to compounds that are more soluble and more readily excreted, although a few of these are themselves highly toxic. Hence,
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6 accumulation by itself, under conditions of low concentrations, may not be severe. Indeed there is very 1 ittle evidence of increased accumula- tion in the higher predatory members of the food web. In terms of human health the available data do not indicate that consumption of oil- polluted seafood is a widespread problem, although we caution against complacency in the application of broad generalizations to individual local situations. Effects Studies on the biological effects of petroleum have benefited greatly from improvements in experimental study design, from the application of modeling made available by computer technology, and from the develop- ment of specialized experimental equipment. A major step forward has been the move away from lethal studies to sublethal studies, using specialized flow-through systems and the concomitant measurement of petroleum compos ition and concentration. In terms of the measurement and evaluation of the impact of petrol- eum, advances have been made along several lines of study--cellular, organismic, population, and ecosystem. Much of this advancement is due to a better understanding of the interaction of petroleum or of its components with water, sediment, and tissues and to the specialized analytical procedures developed over the last 8 years. These in turn have led to a better predictive ability to anticipate and evaluate the potential impact of oiling, whether acute (as from spills) or chronic. Extensive studies on a var iety of marine organisms have been carried out on the toxic effects of petroleum and on selected individual com- ponents. These include laboratory experiments and observations in the field made after oil spills. Significant differences In the tolerance of individual species and of different life stages in a given species have also been recorded, so that a better understanding of possible impact is available. FINDINGS AND RECOMMENDATIONS Major Findings The authors of this report conclude, based upon the evidence available, that there has been no evident irrevocable damage to marine resources on a broad oceanic scale, by either chronic inputs or Occasional major oil spills. However, specific information that would enable unequivocal assessment of the impact of oil on the environment does not yet exist, particularly, with regard to certain specific environments and conditions. We, therefore, recommend further research in a number of areas as discussed below. Despite the considerable advances made in the past 10 years, as detailed in the preceding pages, a number of significant questions remain unanswered. Frequently, the evidence on which conclusions
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7 regarding petroleum impact are based is either circumstantial or insufficient. The former may occur, as in the situation where a conclusion regarding the fate or effect of a given hydrocarbon compound has to be based on data obtained for a similar or related compound, because the relevant information is not available. In some cases, impact on one marine species must be inferred from observations made on a different but perhaps related species. The evidence is often insufficient, as when data are available for only a single life-cycle stage in an organism that normally has several such stages, each with potentially differing susceptibilities. On the other hand, assembling information on each and every organism or life-cycle stage would require an extreme effort that might not be justifiable. It therefore appears to us that more data on a number of select species would be preferable to a large amount of scattered and possibly nonintegrated data on several species. In reviewing the past 10 years, it is probably fair to say that these years have yielded a much improved understanding of the general impact of petroleum on the marine environment. Furthermore, we conclude on the evidence available that there has been no evident irrevocable damage to marine resources on a broad oceanic scale, by either chronic inputs or occasional major oil spills. Lacking, however, is the specific understanding relating to details that would enable unequivocal assessment of such impact. That understanding does not yet exist. We therefore recommend further research in a number of areas as discussed below. This recommendation stems from the many findings that very low levels of petroleum, below 0.1 mg/L, can affect such delicate biological entities as fish larvae. Continued research will result in a much improved capability to predict and assess the impact of both sudden and chronic petroleum pollution, especially in those coastal regions where oil exploration and production activities coincide with harvestable marine resources. Such further research should also lead to a better understanding of the apparent link between the polycyclic aromatic hydrocarbons, some of which may be coming from pyrolytic sources, and the more general problem of what seem to be pollution-related diseases found in commercially important fish stocks in waters receiving a mixture of contaminants. Input of Petroleum Major Finding The estimated range for the total input of petroleum from all sources is between 1.7 and 8.8 million metric tons per annum (mta), with a best estimate of 3.2 mta. We believe that this range, rather than a single-number estimate, is a more accurate summary of the state of knowledge, and reflects the uncertainties that exist in all source data. Calculations of the total input of petroleum are complex, for there are many sources, and in many cases those data that are available are minimal for the purpose. There
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8 are also wide geographical gaps in information on sources, particularly in the southern hemisphere and tropics. This range of 1.7-8.8 mta includes the single-number estimate of 6.1 mta made in the 1975 NRC report. The difference (decrease) between that earlier estimate and the current best estimate of 3.2 mta does not necessarily represent a decline in annual input of petroleum hydrocar- bons into the marine environment during this period but indicates a better estimating of individual inputs. Assessment of the available data on inputs and sources of petroleum entering the marine environment confirms the earlier conclusions of the 1975 NRC report that a considerable portion of marine petroleum pollu- tion is due to non-gas- and oil-related activities, and originates from other human activities (see Table 2.22~. These include river and terrestrial runoff from municipal, urban, and industrial sources as well as from seeps and through atmospheric transport. A significant source of petroleum pollution originates from bilge cleaning. If we are concerned over the continuing health of our oceans and if we are to develop a better understanding of the cycling and transport processes of contaminants in the marine environment, then we suggest the following steps to narrow these existing uncertainties in the inputs of oil. 1. Improved documentation of continental margins to determine the extent of submarine seepages, and to more accurately gauge their flow rates. 2. Continued monitoring of all facilities discharging petroleum hydrocarbon containing effluent. 3. Better methods for distinguishing petroleum hydrocarbons from the "oil and grease. and naturally generated hydrocarbons currently applied to municipal and industrial effluents. 4. A better accounting of petroleum inputs for the southern hemisphere, where currently there is great uncertainty as to amounts and rates of input to the oceans. Major Recommendation It is recommended that atmospheric transport of petroleum hydrocarbons, particularly by rainwater, be given priority status for research. Rain scavenging of atmospheric particles is commonly thought to be the major pathway for petroleum into the oceans from the atmosphere. Unfortunately, today there exists little or no scientific evidence or information on this potentially significant pathway. Concurrent with this is the need to determine the various processes and reactions affecting these compounds as they are transported from sources through the atmosphere into the oceans.
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9 Study Methods: Chemical Major Finding Marked progress has been made in the application and development of analytical methods to quantify petroleum components in air, water, sediments, and biota of the sea and to distinguish these components from other sources of hydrocarbons. While the purpose and main thrust of this report are an examination of petroleum in the seas, reaction products and other sources of hydro- carbons also require attention in order to provide more accurate and meaningful measurements in support of research and monitoring on inputs, fates, and effects of petroleum. These products and other sources include (1) products of metabolic alteration of petroleum by marine organisms; (2) products of chemical and photochemical alteration after oil enters the oceans; and (3) pyrogenic hydrocarbons produced during combustion of oil, coal, and other carbonaceous materials. Some of these compounds are toxic or biologically active in ways that may be deleterious to natural resource populations or to man. At the time of the 1975 report, existing analytical methods were inadequate to deal effectively with this problem, but marked progress has been made in the intervening years. Thus it is the general con- sensus that at the present time, chemical methods are available to make useful measurements on metabolites, reaction products, and nonhydrocar- bon constituents of petroleum. Study Methods: Biological Major Finding Techniques for experimental exposure of organisms to petroleum have advanced significantly. The use of controlled environment systems (mesocosms) in particular has been a significant step toward under- standing the impact of petroleum on communities. More experiments need to be conducted in the field to coordinate laboratory and field components and to validate laboratory findings. Biological interactions of different species are complex, and the presence of degradation products of petroleum in the natural environ- ment adds to the complexity, creating a gap between field-work observa- t~ons and laboratory results. Physical/Chemical Fate of Petroleum Major Findings Considerable progress has been made toward r igorously defining the var. ious processes at fecting the movement of spilled oil, and its
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10 ultimate fate. It is now estimated that evaporation can account for the loss to the atmosphere of from one- to two-thirds of the oil spilled onto the sea surface. Present knowledge suggests that almost all of the evaporated oil becomes photochemically oxidized in the atmosphere. Photochemical oxidation has also been identified as a significant process acting on of] at the sea surface. Modeling of the drift of spilled oil remains a complex and cliff icul. problem, in part because of the wide spectrum of oil types and the changing environmental conditions occurs ing dur ing a spill. The best estimate at the present time for dr if t velocity still is between 3 and 49e of the wind speed. It appears now that dissolution into the water column is considerably less important than evaporation in determining the ultimate fate of spilled oil, because of the low aqueous solubility of most components. Considerable work has been devoted in the past decade to developing a better understanding of the interaction of spilled oil with the water column, including "mousses formation, oil droplet entrainment into the water column, and sedimentation of spilled oil through eventual sorp- tion onto particulate matter in the water column. Major Finding For all these processes, the relationship between chemical composition and the formation and stability of oil-water emulsions and of the sorption characteristics between oil and organic particulate matter are only poorly known. If there is to be a better understanding of the physical and chemical behavior and fate of petroleum hydrocarbons in the marine water column, then more basic research and experimentation in this area are needed. This will yield useful information for quantitative models of greater ability for assessing the fate of petroleum inputs in various areas of the world's oceans. Biological Fate of Petroleum Major Findings Uptake of petroleum by animals, and apparently by plants, from food and/or water is universal. However, animals and, apparently , plants are able to clear their tissues by releasing the accumulated petroleum back into the water after the removal of the pollution source (s) . There appear to exist in those living systems examined various enzymatic mechanisms capable of metabolically transforming a range
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11 of petroleum hydrocarbon compounds. One notable exception appears to be the bivalves. In many cases, as in low level contamination, metabolic degradation and/or the clearing of petroleum from the tissues back to the water can balance uptake, without significant bioaccumulation of these compounds in the tissues. Microbial degradation is a major clearing mechanism for removal of petroleum pollutants from marine environments. Environmental parameters affecting the rate of biodegradation are now being defined, and some progress has been made in measuring rates of biodegradation in the oceans. Refinement and standardization of methodology are required before rate projections will be sufficiently reliable. Despite marked progress in the study of biological fates, some important aspects remain to be clarified. Thus much less is known about the fate of petroleum in marine plants, including macro-algae and phytoplankton, than in animals. As well, little is known of either the distribution, fate, or turnover of the metabolic products of petroleum hydrocarbon, after their formation within the tissues of marine organisms. It has been demonstrated that some of these derivatives may be either toxic or mutagenic. Major Recommendation It is recommended that further studies be encouraged to examine the formation and fate of metabolic derivatives of petroleum hydro- carbons taken up by marine organisms. Amounts of Hydrocarbons in the Oceans Several U.S. agencies, including the Bureau of Land Management, the National Oceanic and Atmospheric Administration, and the Environmental Protection Agency, as well as agencies of other countries, have actively supported studies on the amount of petroleum found in the water column, sediments, and organisms in the oceans. These studies yield the follow- ing major findings. Major Findings Petroleum hydrocarbon concentrations in the water column can vary by several orders of magnitude and are generally related in their amount to the proximity of petroleum sources, e.g., offshore and shore-based coastal production and refining activities, and to transportation routes and accidents.
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12 Tar balls and other floating oil residues also vary by orders of magnitude, with highest concentrations associated with tanker shipping lanes and some mid-ocean gyres such as the Sargasso Sea. Significant decreases in these concentrations have not been observed. Petroleum hydrocarbon contamination (PHC) of marine sediments parallels that for the water column, with PHC concentrations directly related to the proximity of sewage and industr ial outfalls, dumping sites, and accidental discharges . Relatively little information is available on PHC concentrations in pelagic organisms, mainly because of analytical problems, that is, in differentiating between PHC and hydrocarbons produced by organisms in nature and micro tar balls caught in plankton net tows made in heavily traversed oceanic areas. PHCS are usually detected in samples of benthic organisms collected from polluted areas, but not from areas free of spills or other sources of input. Although the more immediate concerns are in the coastal areas that receive the major amounts of petroleum inputs, the paucity of data for the larger open ocean areas requires attention because it is a handicap to our understanding of the long-term fate of petroleum in the marine environment on a global scale. Effects Prior to the 1975 report, much of the work on effects was focused on establishing toxic and lethal thresholds and on the assessment of hydrocarbon concentrations in environmental samples. Major Finding Research since 1975 has resulted in considerable advances in the understanding of the toxicities of various petroleum components, of the effects on organisms and their life-cycle stages, and on the relative vulnerability of various mar ine ecosystems. This information has come both from experimental studies in the laboratory and from the examination of spill situations. Much has been learned, for example, regarding the impact of petroleum on intertidal and coastal ecosystems and about the effects of petroleum on various metabolic and physiological processes, especially in fish and in invertebrates such as mollusks and crustacea. Major Finding Little is known about the impact of petroleum on pelagic organisms and populations. There are also obvious gaps in our understanding
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13 of oil impact on macro-algae, on larval fish, and on polar and tropical organisms. In addition, research activity has broadened to include work on the site of action of petroleum compounds, regarding their effects as dynamic processes affecting the living organism at its var. ious levels-- enzymatic, metabolic, ultrastructural, and molecular . This has become evident from the breadth of studies brought together in this report, a range of effects extending from the ecosystem level down to the chromosomal . Effects-related research in recent years can be character ized according to two signif icant advances: a shif t toward gaining an understanding of the sublethal toxicities of petroleum, and recognition that both species and life-cycle stages vary widely in sensitivity and response. An increasing scientific awareness of a need to obtain and interlock chemical, physiological, and ecological data has provided additional momentum. AS a result, the trend is toward studies of petroleum pollution on a solid basis of chemical and biological data. However, increased depth of understanding of the effects of petroleum in the marine environment can be gained through work in certain areas, as outlined below. . Mutagenicity/Tumorigenicity. Only a small amount of information is available on the occurrence, kinds, and detection of mutagenic and tumorigenic problems in marine invertebrates and vertebrates and in marine plants. Alteration of Behavior. Perturbation of normal behavior at very low _ concentrations of petroleum (less than 0.1 mg/L) is of particular concern. Change in or cessation of feeding is an early indication of oil's toxic effects in many test animals. Yet most available data are largely anecdotal, and at least in higher organisms, ef feats on behavior are only poorly understood. Mechanisms of Toxicity. A focus of research on perturbations of physio- logical processes is recommended. While respiration, photosynthesis, AIP production, carbon assimilation, 1 ipid formation, and related processes are known to be affected by individual hydrocarbons such as naphthalene, the ultimate site, or sites, of toxic action of these compounds have yet to be determined. Polar and Tropical Environments. The polar environment poses a special problem because of almost year-round ice cover and relative inacces- sibility, compounded by large gaps in the basic data base on polar biology. While some information exists on oil and the polar environ- ment, the potential impact of a major oil spill on polar ecosystems cannot be estimated with confidence at this time. With respect to tropical regions, rather limited data are available on the effects of oil on tropical ecosystems including mangroves, coral reefs, and their associated biota. Nonetheless, these ecosystems represent a large part of the tropical coastline and are often very
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14 near heavy tanker traffic or petroleum activity. They are also bio- logically highly productive and are of great economic and cultural importance. The preliminary data that do exist indicate these tropical systems are as sensitive to oil as, if not more sensitive than, temperate coastl ines . Synergistic Toxicity. The interaction of petroleum with other non- petroleum contaminants is not well understood. Further work is needed, especially as chronic pollution of inshore waters often involves more than one contaminant. Ecosystem Effects. Population changes caused by an oil spill or by chronic pollution inevitably result in additional effects by altering food web relationship and interspecific competition in the ecosystem as a whole. Each situation is different, and the effects of any given spill or input can be quite unexpected. Underlying these concerns are the various findings that low concentrations (less than 1 mg/L) of petroleum hydrocarbons can apparently interfere with the normal behavior of marine organisms, especially the more fragile components such as the larval and juvenile forms of the marine foodchain. Continued study of a few key examples of recovery after oil spills or from well-defined chronic input sources, with adequate controls, is essential if eco- system effects and their economic significance are to be well-defined. Major Recommendations Study the effect of low concentrations of petroleum hydrocarbons on the behavior of marine organisms, particularly larval and juvenile forms. Conduct studies to examine the apparent coincidence between elevated concentrations of mutagenic/carcinogenic petroleum hydrocarbons (PAHs) and pollution-related diseases in certain fish from waters receiving a mix of contaminants. Conduct research into impacts of petroleum on polar and tropical environments. Finally, a major problem throughout this report has been the difficulty of transferring information from laboratory studies to field conditions, i.e., the difficulty in predicting impact in the field from experimental data. Little is known of the effects of petroleum on zooplankton and ichthyoplankton and of the potential impact on larval fish stocks. Nonetheless, the potential exists that under certain conditions of prolonged exposure, such impact could become significant. Also, one of the most difficult aspects of this problem has been to assess the potential impact of spills on commercially important stocks of fish and shellfish.
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15 Major Recommendation We recommend that research into the effect of petroleum on fish stocks, including larval and juvenile stocks, be extended so as to enable sensible assessment of the impact on these marine resources. The major uncertainty preventing such assessments, as with most ecosystem effects, is a limited understanding of natural fluctua- tions in populations and ecosystems. We think that major progress in determining the effects of petroleum, by itself and in concert with other contaminants, on populations and ecosystems will largely depend upon an increased understanding of short-term (years} and long-term (decades) natural fluctuations in populations and ecosystems. SUMMARY AND CONCLUSIONS Where oil has had an effect, subsequent monitoring has shown biological recovery taking place. Hydrocarbons from seeps and pyrolytic sources are part of the long-term evolution of the oceans, and results of observations made to date indicate that most living organisms can co-exist with hydrocarbons when concentrations are very low (less than 0.1 mg/L) and when the oil is weathered. It is also revealing that, of the petroleum hydrocarbons entering the marine environment, an estimated 39% derives directly from oil and gas production and transportation. However, more than 45% originates from other shipping activities and from industrial, municipal, urban, and river runoff. There is no clear indication so far that commercially important fish stocks have been severely disrupted by either chronic or catas- trophic oiling of their environment. However, present census techniques remain too crude to provide clear knowledge of standing fish stocks, while natural variabilities in the stocks probably mask such impact from petroleum as may exist. The fragmented evidence on the effects of petroleum on some larval fish and fish eggs from a few laboratory and field studies indicates that such impact is possible, although it has not been rigorously examined. This inability to transfer information obtained from laboratory studies to field conditions has been an intractable problem throughout this report. Petroleum can have a seriously adverse affect on local environ- ments, persisting, in some cases unaltered, for decades. Moreover, some petroleum compounds are carcinogens and/or mutagens and can bind to nucleic acids. Metabolic products of petroleum degradation also can be potentially hazardous. However, the data are not available to indicate that such a hazard has occurred in populations in affected environments. The greatest impact due to oiling clearly occurs in coastal areas, especially those with shallow water, and in areas where local current systems tend to contain or entrain the contaminant. Of special concern
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16 are situations of local chronic oil ing where there is low level (less than 1 mg/L) but continuous exposure, as in waters near industrialized or heavily populated coastal regions. There is a clear need to continue research on these local situations, not only because of the intrinsic toxicity of petroleum, but also because of its poorly understood but suspected synergistic impact with other contaminants. Particular concern is expressed about the potential impact of oil on tropical coastal environments--mangrove systems and coral reefs. These represent a major part of the coastline in tropical and subtropical regions and are highly significant in terms of fisheries and other resources. They have unique physical and biological characteristics that make them highly vulnerable to the effect of oiling. On for tunately, the research effor t on these ecosystems has been confined to comparatively few studies.
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