Oil Spills On Sea Water Biology Essay


Consumption of oil and petroleum products has been exponentially increasing worldwide and the threat of oil pollution is increasing accordingly. The movement of petroleum from the oil fields to consumer involves as many as 10 to 15 transfers between many different modes of transportation including tankers, pipelines, railcars, and tank trucks. Oil is stored at transfer points and at terminals and refineries along the route. Accidents can happen during any of these transportation steps or its storage causing oil spills that have many adverse effects on the environment. Accidental incidents during transportation of oil by sea route causes oil spill on water affecting aquatic life. Sea birds are one of the most publicized species of such spill incidents, but there are many other less obvious effects such as the loss of phytoplankton and other microscopic forms of life. Oil can enter organisms by several exposure routes such as ingestion, absorption and the food chain. Animals or birds can come into direct contact with oil on the surface of water or on shorelines. Ingestion occurs when an organism directly consumes oil, usually by accident as in the case of birds when oil is ingested as they preen or groom their feathers. Absorption of volatile components of oil is a common method of exposure, especially for plants and sessile organisms, although it also occurs in birds and mammals. Fresh crude oil has a relative abundance of volatile compounds such as benzene and toluene that are readily absorbed through the skin or plant membrane and are toxic to the organism. In the present paper, oil spills on sea water and its effect over the aquatic life has been discussed as the living species particularly under seawater as well as on the shorelines are most affected of every oil spill incident on sea water.

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Most of the oils spilled into the sea worldwide are fuels (48%) followed by crude oils (29%). Grounding is the major cause of oil spills from vessels (26%) followed by collision (22%), explosion or fire (9%), ramming (9%) sinking (7%) with human error (5%) and mechanical failure (2%) causing the least number of spills [1]. There is a continuous effort from the concerned organizations to reduce the risk of oil spills by the introduction of strict new legislation, operating codes as well as new operating and maintenance procedures to minimize accidents that may lead to spills. A comparison of oil spill incidents in world and Indian waters shown in figure 1, reveals that the spill trends in India has been increased many fold during the last few decades thereby creating various environmental problems. When oil is spilled on water, a number of transformation processes occur that are referred as the �behaviour� of oil and the specific behaviour processes determine its effect on the environment. For example, if oil evaporates rapidly, cleanup is less intense, but the hydrocarbons in the oil enter the atmosphere and cause air pollution. An oil slick could be carried by surface currents or winds to a bird colony or to a shore where seals or sea lions are breeding and severely affect the wildlife and their habitat. The behaviour processes are almost entirely determined by the type of oil and the environmental conditions at the time of the spill.

Figure 1: Comparison of oil spill incidents in the world and Indian waters [2].

In a recent case of oil spill in India on August 7, 2010, there was a collision in the Mumbai harbour (Karanja Reefs, Arabian Sea), between a container vessel MSC Chitra, which was proceeding from the Jawaharlal Nehru Port to the sea and another vessel M V Khalijia III, which was proceeding towards the Mumbai Port. Khalijia III collided with the port side of MSC Chitra damaging one of its hatches leading to ingress of water and consequent listing of MSC Chitra. The bow of Khalijia III was damaged [3,4,5]. A survey of the main channel was carried out in the early morning of 9th August, 2010 and reported that MSC Chitra had in all 1219 containers, 707 in the hold and 512 on the deck. The lashings of the containers cannot hold long on account of high pressure due to the listing of the vessel. The vessel was listing about 35 degrees [6,7]. The vessel had 2662 tonnes of heavy oil in its various tanks, 245 tonnes of diesel oil and about 70 tonnes of lubricating oil at the time of the accident. After the incident, it has been reported that fuel oil appears to be leaking from one of the wing tanks. Hundreds of oil containers were floating in sea and oil spread over a large surface area on water. Three tugs were immediately used to spray dispersant under the directions of the Coast Guard.

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1.1 Spreading of Oil on Water

After an oil spill on water, the oil tends to spread into a slick over the water surface. This is especially true of the lighter products such as gasoline, diesel fuel and light crude oils which form very thin slicks. Heavier crudes and Bunker C spread to slicks several millimetres thick. Heavy oils may also form tar balls and tar mats and thus may not go through progressive stages of thinning. Oil spreads horizontally over the water surface even in the complete absence of wind and water currents. This spreading is caused by the force of gravity and the interfacial tension between oil and water. As time passes, the effect of gravity on the oil diminishes, but the force of the interfacial tension continues to spread the oil. The transition between these forces takes place in the first few hours after the spill occurs. As a rule, an oil slick on water spreads relatively quickly immediately after a spill in such a way that the outer edges of a typical slick are usually thinner than the inside of the slick but after a day or so of spreading, this effect diminishes.

Winds and currents also spread the oil out and speed up the process and elongate the oil slick in the direction of wind and currents. Oil sheens often precede heavier or thicker oil concentrations. If the winds are high (more than 20 km/h), the sheen may separate from thicker slicks and move downwind. Generally there are vertical circulation cells in the top 20 m of the sea [1]. A slick often breaks into �windrows� on the sea under the influence of either waves or zones of convergence or divergence. Oil moving along these zones is alternately concentrated and spread out by the circulation currents to form ribbons or windrows of oil rather than continuous slicks.

1.2 Movement of Oil

In addition to their natural tendency to spread, oil slicks on water are moved along the water surface primarily by surface currents and winds. If the oil slick is close to land and the wind speed is less than 10 km/h, the slick generally moves at a rate that is 100% of the surface current and approximately 3% of the wind speed. If the wind is more than about 20 km/h, however, and the slick is on the open sea, wind predominates in determining the slick�s movement. Both the wind and surface current must be considered for most situations. Effect of different wind and current directions on the movement of an oil slick has been discussed in the literature [1].

1.3 Weathering of Oil

Oil spilled on water undergoes a series of changes in physical and chemical properties termed �weathering.� The processes included in weathering are evaporation, emulsification, natural dispersion, dissolution, photo-oxidation, sedimentation, adhesion to materials, interaction with mineral fines, biodegradation, and the formation of tar balls. Weathering processes begin immediately after oil is spilled into the environment. Weathering rates are not consistent throughout the duration of an oil spill and are usually highest immediately after the spill. Most weathering processes are highly temperature-dependent and often slow to insignificant rates as temperatures approach zero degrees.


Treating the oil with specially prepared chemicals is also an option for dealing with oil spills. But care should be taken to ensure that the treated oil may be toxic to aquatic and other wildlife. Types of chemicals agents used in oil spills are:

* Dispersant: Dispersant is a common term used to label chemical spill-treating agents that promote the formation of small droplets of oil that disperse throughout the top layer of the water column.

* Sorbents: Sorption is a technique applied for treatment of oil spillage.

* Surface-washing agents: Surface-washing agents contain surfactants, but unlike dispersants, they are used to remove oil from shorelines or similar surfaces.

* Emulsion breakers: Emulsion breakers are formulations intended to break water-in-oil emulsions.

* Emulsion inhibitors: Emulsion inhibitors are similar to emulsion breakers, but are intended to prevent water-in-oil emulsions from forming.

* Solidifiers: Solidifiers or gelling agents are products that turn liquid oil into solid oil.

* Biodegradation agents: Biodegradation agents include bio enhancement agents, which contain fertilizers, and bio augmentation agents which contain microbes that degrade oil.

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2.1 Dispersants

Dispersants contain surfactants, chemicals like those in soaps and detergents, that have molecules with both a water-soluble and oil-soluble component, promote the formation of small droplets of oil that �disperse� throughout the top layer of the water column. Depending on the nature of these components, surfactants cause oil to behave in different ways in water. Surfactants or surfactant mixtures used in dispersants have approximately the same solubility in oil and water, which stabilizes oil droplets in water so that the oil will disperse into the water column. The effectiveness of a dispersant is determined by measuring the amount of oil that it puts into the water column and comparing it to the amount of oil that remains on the water surface.

The essential elements in applying dispersant are to supply enough dispersant to a given area in droplets of the correct size and to ensure that the dispersant comes into direct contact with the oil. Droplets larger than 1,000 ? m will break through the oil slick and cause the oil to collect in small ribbons, referred to as herding. This can be detected by the rapid clearance of the oil in the dispersant drop zone without the formation of the usual white to coffee-coloured plume in the water column. This is very detrimental and wastes the dispersant. Herding can also occur on thinner slicks when the droplets of dispersant are smaller [1]. The distribution of smaller droplets of dispersant is not desirable especially when spraying from the air as small droplets will blow away with the wind and probably not land on the intended oil slick.

Dispersants are applied either �neat� (undiluted) or diluted in sea water. Aerial spraying, which is done from small and large fixed-wing aircraft as well as from helicopters, is the most popular application method. Spray systems on small aircraft used to spray pesticides on crops can be modified to spray dispersant. Such aircraft can perform many flights in one day and in many different conditions. Their capacities vary from about 250 to 1,000 L of dispersant. Transport aircraft with internal tanks can carry from 4,000 to 12,000 L of dispersant. Spray systems are available for boats, varying in size from 10- to 30-m wide spray booms to tanks from 1,000 to 10,000 L. As dispersant is almost always diluted with sea water to maintain a proper flow through the nozzle, extra equipment is required on the vessel to control dilution and application rates. About 10,000 to 100,000 L of dispersant can be applied a day, which would cover an area of 1,000,000 m 2 or 1 km 2. As this is substantially less than could be sprayed from a single aircraft, spray boats are rarely used for a large spill [1]. However, it is very difficult with aerial equipment to spray enough dispersant on a given area to yield a proper dispersant-to-oil ratio.

The toxicity of the dispersants used in the late 1960s and early 1970s ranged from about 5 to 50 mg/L measured as an LC 50 to the Rainbow Trout over 96 hours. But the dispersants available today vary in toxicity from 200 to 500 mg/L and contain a mixture of surfactants and a less toxic solvent. Today, oil is more toxic than the dispersants, with the LC 50 of diesel and light crude oil typically ranging from 20 to 50 mg/L, whether the oil is chemically or naturally dispersed. It has been observed that dispersed oil does not increase in toxicity as a result of the addition of dispersants [1]. The toxicity data for some products are given in table 1, 2 & 3.

2.2 Sorbents

Sorption is a popular technique applied for treatment of oil spillage. In a recent work, the potential of fly ash, a thermal power plant waste organically modified using the cationic surfactant; hexadecyl tri-methyl ammonium (HDTMA), to remove crude oil and weathered oil contaminated seawater (WOCS) has been found well suitable. The HDTMA-FA obtained after modifying fly ash can be favourably deployed as a sorbent for oil spillage. The sorption behaviour of fly ash can be greatly enhanced when organically modified with HDTMA. HDTMA-FA is also effective in removing dissolved organic carbon (DOC) present in weathered oil contaminated seawater (WOCS) making HDTMA-FA a better option compared to conventional sorbents [8].

Table 1: Toxicity of surface-washing agents [1]

Table 2: Toxicity of emulsion breaking or inhibitor agents [1]

Table 3: Toxicity of solidifiers [1]


Oil has many adverse effects on the aquatic environment. Toxic effects of oil are classified as chronic or acute, which refers to the rate of effect of toxin on an organism. Acute means toxic effects occur within a short period of exposure in relation to the life span of the organism. Acute toxicity to fish could be an effect observed within 4 days of a test. The toxic effect is induced and observable within a short time compared to the life span of the fish. Chronic means occurring during a relatively long period, usually 10% or more of the life span of the organism. Chronic toxicity refers to long-term effects that are usually related to changes in such things as metabolism, growth, reproduction or ability to survive.

The effects of exposure can be lethal or sublethal. Lethal exposure is often described in terms of the concentration of the toxicant that causes death to 50% of a test population of the species within a specified period of exposure time. This is referred to as the LC 50. For example, tests of the effects of various crude oils on the water flea show that 5 to 40 mg/L of the oil for a period of 24 hours is lethally toxic. The units of milligrams/litre (mg/L) are approximately equivalent to parts-per-million (ppm). Sublethal means detrimental to the test organism, but below the level that directly causes death within the test period. It has been found that a concentration of 2 ppm of crude oil in water causes disorientation in Daphnia magna when the organism is exposed for 48 hours. Oil can affect animals in many ways, including changing their reproductive and feeding behaviour and causing tainting and loss of habitat. Oiling of more highly developed animals such as birds may result in behavioural changes, such as failure to take care of their nests, resulting in the loss of eggs. Even a light oiling can cause some species of birds to stop laying eggs altogether [1,9]. The toxicity of water soluble fractions of petroleum oil is given in table 4.

Table 4: Aquatic toxicity of water soluble fractions of petroleum oil on various species [1].

Sea includes a wide variety of ecosystems, species and habitats such as fish, plankton, benthic invertebrates, epontic organisms, marine mammals, intertidal and shoreline organisms, marine plants as well as some other important ecosystems as described below [1,9,10,11,12,13,14]:

1. Birds: Birds are the most visible biota affected by oil spills, especially in the aquatic environment. Shoreline dwellers and feeders which include ducks, gannets and cormorants are among the most susceptible birds to oiling. Oil contaminates feathers when the birds come into contact with slicks on water or shorelines. For sea birds, this is particularly dangerous because when their feathers are oily; their insulation and buoyancy properties are decreased. Birds clean their plumage by preening and may ingest some of the oil or by eating oiled prey. Ingestion of oil may cause death or more likely sublethal effects such as gastrointestinal dysfunction, liver problems, pneumonia, and behavioural disorders. Oiling of birds may result in failure to take care of their nests, resulting in the loss of eggs. Even a light oiling can cause some species of birds to stop laying eggs altogether. It is very stressful for a wild bird to be captured and handled. Only very sick birds can generally be captured and many of the birds brought to the treatment centres are often near death and therefore less than half of the oiled birds that are cleaned and released actually survive.

2. Fish: Both pelagic (mid-water) and demersal (bottom-dwelling) fish are exposed to toxicity through aromatic hydrocarbons in the water column. Although lethal concentrations of aromatic hydrocarbons are rarely found in open seas, such concentrations can occur in confined waters, such as bays and estuaries, directly under or near spills. Whereas high concentrations of oil have caused massive fish mortality in some incidents, fish are more typically exposed to sublethal concentrations of hydrocarbons. Oil exposure can cause a range of physiological and pathological changes in fish, some of which are temporary and are not a risk to health or survival. Other sublethal effects such as the disruption of growth or decreased assimilation of food may affect long-term survival. Some of the effects noted on fish such as eye cataracts, structural changes of fins, and loss of body weight may be related to the stress of exposure and not directly to the hydrocarbons.

3. Plankton: Plankton are small plants and animals that live in the water and include phytoplankton and zooplankton. Phytoplankton are microscopic plants such as algae and diatoms that live in the top layer of the water as they depend on light for photosynthesis. Zooplankton are microscopic animals that feed primarily on phytoplankton. Plankton are important because they are at the bottom of the aquatic food chain. Thus, oil ingested or absorbed by plankton is passed higher up the food chain, until it is finally ingested by fish and mammals. Both phytoplankton and zooplankton vary in their sensitivity to whole oil or hydrocarbons in the water column. Plankton are killed by relatively low concentrations of oil, but are present in such numbers that lost individuals are replaced quickly with little detectable disturbance. Plankton also tend to depurate low concentrations of hydrocarbons within days. Sublethal effects of oil on zooplankton include narcosis, reduced feeding, and disruption of normal responses to light.

4. Benthic Invertebrates: Benthic invertebrates are generally divided into two groups, benthic infauna that resides within the bottom sediments and benthic epifauna that live mostly on the top of the sediments. Mobile forms include the slow-moving starfish, gastropods, and sea urchins and fast-moving amphipods and isopods. Tiny invertebrates that are an important food source for fish, bottom-feeding whales, and some species of birds, pass contamination up through the food chain. These species have the advantage of being able to avoid contaminated areas or to quickly recolonize them whereas it can take years for sessile organisms to recolonize an area. Benthic species can be killed when large amounts of oil accumulate on the bottom sediments as a result of sedimentation or by precipitation. Sometimes the oil itself is heavy enough to sink down to bottom. Other sublethal effects of oil on benthic invertebrates include developmental problems such as slow growth, differential growth of body parts (deformity), changes in molting times, and occasional anomalies in development of organs. Reproductive effects such as smaller brood sizes and premature release of eggs, reduced feeding, and increased respiration have also been noted in tests. Benthic invertebrates can take up hydrocarbons by feeding on contaminated material, breathing in contaminated water, and through direct absorption from sediments or water. Most invertebrates depurate hydrocarbons when the water and sediment return to a clean state or if placed in a clean environment. In severe oiling, however, depuration can take months. Sessile species may perish from prolonged exposure to contaminated sediments; however, all benthic species are affected by a short-term dose of the hydrocarbons in oil.

5. Epontic Organisms: Epontic organisms are microscopic plants and animals that live under ice. Many of these are similar to plankton and have similar responses and sensitivities to oil. Contact with oil causes death. The community may also be slow to recover because the oil can remain under the ice depending on the geographic location.

6. Seals, sea lions and walruses: Seals, sea lions and walruses are particularly vulnerable to oiling because they live on the shorelines of small islands, rocks or remote coasts. Only the young mammals are killed by severe oiling because their coats are not developed enough to provide insulation in an oiled state. Oil is often absorbed or ingested and mothers may not feed their young when they are oiled. Older seals, sea lions, and walruses can take a large amount of oiling without causing death. Oiling causes the fur to lose waterproofing and buoyancy. Brief exposure of seals, sea lions, and walruses to volatile oil causes eye irritation and longer exposure can cause more permanent eye damage. Hydrocarbons accumulate in the blubber, liver, kidney and other organs as a short-term effect, however, the long-term effects have not been observed because of the difficulty of approaching relatively healthy seals, sea lions, and walruses.

7. Whales, dolphins, and porpoises: Whales, dolphins and porpoises can be exposed to oil in the water column or on the surface when they come up to breathe but deaths of these species have not been reported as a result of oil spills. This may be due to the reason that oil does not adhere to the skins of these mammals and as they are highly mobile, they are not exposed to oil for a long period of time.

8. Polar bears: Polar bears spend much of their time in or near water, swimming between ice floes hunting seals. The potential for oiling is moderate. It was found that polar bears that are oiled ingest oil through grooming themselves, resulting in death or severe illness. Unfortunately, polar bears are attracted to oil, particularly lubricating oil, which they will actually drink. This generally causes temporary illness, but in the case of an oil spill it could result in death.

9. Otters: Otters live on or near shorelines and spend much of time on the water or feeding on crustacea on the sea floor. Otters are usually oiled in any spill near their habitats and can die after only a 30% oiling. Oil adheres to the otters� fur causing heat loss that is the most pronounced effect of oiling. Otters attempt to groom themselves after oiling and thus ingest oil, compounding their difficulty. Oiled otters are often caught and taken to rehabilitation centres for cleaning by trained specialists.

10. Intertidal Fauna: Intertidal fauna include animals that live in the shoreline zone between the high and low tides. These organisms are the most vulnerable to oil spills because they and their habitat are frequently coated during oil spills. Typical fauna include the mobile crabs, snails and shrimp, sessile barnacles and mussels, sedentary limpets, periwinkles and tube worms. Heavy oiling generally kill most of the species however, light oiling affects the immobile species most and most species take up oil. Sublethal effects include reduced growth and reproduction rate and accumulation of hydrocarbons. Both mussels and crabs will depurate or cleanse themselves of hydrocarbons when placed in clean water. Crabs also show premature or delayed molting. Mussels reduce production of attachment threads, often causing the creature to let go of its hold on its feeding surface. Other intertidal fauna show similar behaviour as a result of light oiling.

11. Intertidal algae: Intertidal algae are an important food source for much of the intertidal fauna and severely affected by an oil spill. Although readily killed by even a moderate oil spill, intertidal algae are usually the first biota to recover after a spill. Algae will re-establish on oil-coated rocks if the oil is weathered and no longer gives off volatile compounds. Like intertidal fauna, algae are also vulnerable to intrusive cleaning techniques such as washing with hot or high-pressure water and more algae are killed by these techniques than by oil. Sublethal effects include reduced reproduction and respiration rates and changes in colour.

12. Macro-algae: Macro-algae include two common groups of plants in North America, �Fucus� and �kelp�, both of which include many species and sub-species. Fucus, which often inhabit the lower intertidal and subtidal zones, are not particularly susceptible to oiling because a mucous coating prevents the oil from adhering to the plant. Heavy oil will cover Fucus, however, and cause death or sublethal effects. Kelp generally lives in deeper water and is rarely coated with oil. Both Fucus and kelp will absorb hydrocarbons in the water column. Both plants will show sublethal effects of leaf loss, colour changes, reproductive slowdown, reduced growth, and accumulation of hydrocarbons. Both plants will also slowly depurate or cleanse itself of hydrocarbons in clean water. As these plants make up the habitat for complex ecosystems including many forms of animals and other algae, the entire ecosystem can be affected if they are damaged. Recovery for both types of plants and their habitats may take years.

13. Sea grasses: Sea grasses generally inhabit the low-intertidal and sub-tidal zones and are extensive in any location around the world. Eelgrass, which is the common species in North America, is a vascular plant similar to most common water plants. Sea grasses are sensitive to hydrocarbon uptake and oiling. Eelgrass is killed by moderate hydrocarbon concentrations in the water for a few hours or low concentrations for a few days. Eelgrass will show similar sublethal effects as kelp and Fucus, and will also depurate or cleanse itself of hydrocarbons. A bed of eelgrass killed by an oil spill may take several years to recover.

14. Salt marshes: Salt marshes are important ecosystems as they are the habitat of many birds and fish that feed on a wide variety of invertebrates including crabs, snails, and worms. Some of these organisms burrow into the sediments providing a path for oil to penetrate if a spill occurs. Salt marshes are dominated by marsh grasses, the predominant one in temperate climates being �Spartina� and in the Arctic, �Puccinellia� , which has similar characteristics. The outer fringes of marshes are dominated by shrubs such as sedges. Marshes also export a large amount of plant detritus back to the sea, which contributes to the food chains of connecting water bodies. The effects of oil on a marsh depend on the amount and type of oil. Light to moderate amounts of weathered oil or oil that does not penetrate significantly will not result in massive mortality and the marsh can recover in as little as one to two years. Heavy oiling by light oil that penetrates the sediments can cause heavy mortality and the marsh can take up to 10 years to recover. Massive oiling causes loss of the plant cover, which would also affect the animals and birds living in the marsh. As �Spartina� propagates from special root parts, any cleaning activity that destroys these will kill the plants. Marshes are very sensitive to physical disturbance and intrusive cleanup could easily cause more damage than the oil itself.

15. Coral reefs: Coral reefs occupy a large part of the seas in the tropics of the Pacific and the Caribbean. They are the most diverse and complex marine communities supporting thousands of fish, algae and invertebrate species. Moderate concentrations of dissolved or dispersed hydrocarbons can kill both the coral and its occupants. Damage depends on the depth, with coral that is near the surface (down to about 6 m) being particularly vulnerable to oil. Oil also has several sublethal effects on coral, such as slowed growth or respiration and unnatural coloration.

16. Mangroves: Mangroves are trees that grow along much of the shorelines in the tropics. They provide the habitat for a wide diversity of other species. Mangroves are supported by a complex, interlaced system of prop roots. The base of the roots is in low-oxygen soil and the trees take in air through breathing holes on the prop roots. If these are oiled and most of the breathing pores are plugged, the mangrove may die. As with most plants, mangroves are subject to a number of sublethal effects including slower growth, loss of leaves, and changes in colour. It could take years to decades for mangroves to grow back in the oiled area.


Recovery refers to the ability of organisms or ecosystems to return to their original state they were in before the spill event. Recovery time varies from days to years, as in case of the ecosystem of a rocky shoreline that can recover from an oil spill within months as organisms from un-oiled areas can move in and restore the population. Another factor that influences the effects of oiling is the potential for rehabilitation of oiled animals. Birds, otters and seals are often cleaned, treated and returned to the environment. Many species cannot be rehabilitated as they are difficult to catch and the stress of being caught and kept in captivity may be worse than the effects of oiling.


* Oil spill incident on sea water causes an unrecoverable damage to the aquatic life besides the major economical loss to the nation. The literature available on the worldwide oil-spill data shows that a significant number of spill incident has been occurred in the Indian Ocean since 1968 [3]. It has been observed that the marine wild life including sea birds are the most affected species of such incidents which needs to be minimized by every possible effort globally.

* Sophisticated spill models may prove to be a good tool when dealing with oil spills that combine the latest information on oil fate and behaviour to predict where the oil will go and what state it will be in when it gets there. The limitation in accurately predicting an oil slick�s movement due to the lack of accurate estimates of water current and wind speeds along the predicted path is likely to remain a major limitation in the near future.

* Damage assessment has been recently started in several countries which involves a formal, structured examination of an oiled environment to determine how many of each species was affected by the oil spill. The objectives are to quantify the damage to the environment as much as possible and assess the total effects of a particular spill. Data are used to develop long-term restoration or cleanup plans if necessary, to assess costs, and to provide a database of spill damage. In the present scenario, it is important to optimize net environmental benefits when considering how to deal with a spill to access.

* Studies of literature on several major oil spills in the early 1970s showed that response to these spills suffered not only from a lack of equipment and specialized techniques but also from a lack of organization and expertise to deal with such emergencies. Since then, contingency plans have evolved and today often cover wide areas and pool national and even international resources and expertise. Such plans usually focus more on roles and responsibilities and providing the basis for cooperation among the appropriate response organizations.