Oil Spill Pollution

DEFINITION

Oil spills include any spill of crude oil or oil distilled products (e.g., gasoline, diesel fuels, jet fuels, kerosene, Stoddard solvent, hydraulic oils, lubricating oils) that can pollute the surface of the land, air, and water environments. Oil spill pollution may comprise a variety of amounts starting with one or more gallons of oil and up to millions or even hundreds of millions of gallons spilled. The term is usually associated with the oil spills in the ocean and coastal waters.

Oil Spill Pollution refers to the negative polluting effects that oil spills have on the environments and living organisms, including humans, due to the environmental discharge of various organic compounds that make up crude oil and oil distillate products, the majority of which include various individual hydrocarbons. Hydrocarbons are made exclusively from carbon and hydrogen atoms which bind together in various ways, resulting in paraffins (or normal alkanes), isoparaffins (isoalkanes), aromatics (such as benzene or various PAHs), cycloalkanes and unsaturated alkanes (alkenes and alkynes). Other individual compounds that are present in crude oil and oil discharges include (apart from carbon and hydrogen) sulfur, nitrogen and/or oxygen atoms.

The Oil Pollution Act

The Oil Spill Pollution Act - The Oil Pollution Act is an environmental regulation adopted in 1990 in the U.S. to prevent oil spill pollution. In 1990, the Oil Pollution Act was passed by U.S. Congress and amended the existing Clean Water Act, aiming to require oil storage facilities to prepare "Facility Response Plans". Various revisions to the Act have been made in 1994 by the EPA. The revised plan obliged facility owners and operators to prepare and submit plans addressing a "worst-case scenario" of oil discharge. This regulation was meant to prevent and prepare emergency responses to oil spills. The Oil Spill Pollution Act:

established new requirements and amended the U.S. Federal Water Pollution Control Act in order to provide enhanced capabilities for oil spill response and natural resource damage assessment;
required the Coast Guard to strengthen its regulations on oil tank vessels;
included the specification that companies must have a cleanup plan in order to prevent spills that may occur and a detailed containment;
imposed liability for injuries, removal costs, and damages from incidents involving the discharge of oil into navigable waters or adjoining shorelines.

How Does Oil Spill Pollution Affect Us?

These organic compounds may affect the wildlife (including fish and birds) and humans in various ways:

Directly

by direct contact with the skin - some of the oil components could be irritants to the skin and may also penetrate into our bodies via skin absorption
through inhalation - many individual components of oil are volatile and thus may easily evaporate and while breathing can enter our bodies. Some less volatile compounds (such as PAHs) may adsorb on dust and other small particulate matter suspended in the breathing air and may get into our bodies through inhalation of small particulate matter from the air
through ingestion of contaminated water and/or particles
through emitted odors - How many of us have smelled gasoline or diesel/fuel oil and noticed the strong unpleasant smell? Usually, crude oil and its various distillates have strong unpleasant odor

Indirectly

by consuming contaminated food (some of the oil hydrocarbons such as PAHs bioaccumulate in fish and other organisms and may concentrate many times more than in water or other media)
by disrupting professional and/or recreational activities due to the oil pollution in certain areas
by decreased property values from the affected areas - it is logical to imagine the drops in house values in a polluted area;
aesthetically - by visual alteration of marine, beach and many other environments (where the oil spill occurred)
overall economic impact - in the community affected by the oil spill

How Does an Oil Spill Behave in the Environment?

Depending on where and how an oil spill occurs, it will have distinct environmental effects. For example:

a marine oil spill is usually degraded fast since water is an excellent medium for dispersion, emulsifying and microbial degradation processes. If released in the water, oil and oil products tend to accumulate at the surface of the water and float on the water. Small oil droplets may also form which may increase the surface contact with water and also the natural biodegradation of the spilled oil
an oil spill on the land may penetrate underground and move downward reaching eventually the groundwater. However, such vertical movement may be slowed done if not prevented by the presence of paved surfaces, natural clay layers or other natural or anthropogenic barriers. Oil may also move laterally along less permeable layers (including surface pavements) or with groundwater and surface waters
an oil spill in the underground (such as from pipelines or underground storage tank leaking) will likely affect the groundwater since the vertical traveling distance is reduced. Such spill may also result in oil residuals that could be entrapped underground constituting a secondary source of groundwater pollution

Much of the oil we use for machinery, vehicles and industry is deep below the surface of the Earth oftentimes in the middle of the ocean. When oils rigs or machinery malfunction or break, thousands of tons of oil can seep into the environment. Oil spill effects on environments and habitats can be catastrophic: they can kill plants and animals, disturb salinity/pH levels, pollute air/water and more.

Oil Spill Effects on Environments in Water

The oil environmental impact on water in damaging in a variety of ways. When there are oil spills in the ocean or freshwater, it does not blend with the water. Oil floats on the surface of salt and fresh water. Over a very short period of time, the oil spreads out into a very thin layer across the surface of the water. This can block sunlight from reaching oceanic environments, which can severely impact producers and, thus, the entire food chain of an ecosystem.

Effects on Marine Life and Wildlife

The effects of oil spills in the ocean are far reaching.

Marine Life Direct Impact

Marine and coastal life can be contaminated in a number of ways, through poison by ingestion, destruction of habitat and direct contact with oil. For example, when oil floats on the water surface, a marine mammal that surfaces in the center of the slick ingests the oil. Marine animals and organisms that swim through the slick area can also ingest oil through their gills.

Even if a marine animal is miles from the oil spill, but they eat another organism that was close by, they'll ingest that oil, which is poisonous. Ingesting oil can cause any number of problems besides death and sickness. If an animal or other marine organisms ingests oil, it can affect their ability to reproduce and produce viable offspring.

Oil Environmental Impact on Habitat and Wildlife

Habitat destruction is all too obvious with an oil spill. The most visible would be seen on shore, but beneath the water there is a very delicate balance in the reefs and shallow water habitats. Plankton, producers at the bottom of the food chain, are often killed by oil spills as a result of changes to the water and lack of sunlight beneath the oil slick.

This effect moves right on up the food chain. Of particular concern are the very delicate sea animals, such as clams and mussels that feed on plankton.

Direct contact with oil harms any organism that comes in contact with the oil. For example, when oil cakes the feathers of a bird, it keeps their feather from repelling water. Oil also weighs down the bird, keeping it from flying. If a bird isn't cleaned of the oil, it's a sure license to death. Many birds also ingest deadly amounts of oil trying to clean their feathers.

The same holds true for marine mammals. Marine mammal fur acts as an insulator to keep the animal warm in the coldest waters. When oil saturates the fur, it ruins the ability of the fur to retain heat. Again, marine mammals can ingest the oil when trying to clean their fur.

Atmospheric Fallout

Atmospheric fallout is the oil that pollutes the air from vehicles and planes. This oil eventually starts to fall out of the air and into oceans or onto land masses. Fallout can be heavy or light depending on the location and the amount of pollution in the air. For example, when cars run, some of the oil burned to produce energy goes into the air. This oil either travels on the air or falls out of the air. When it rains or snows, the oil is knocked out of the air and falls to create pollution in water or land, depending on the location.

Natural Seeps

Natural seeps consist of the oil that pollutes the environment naturally. The oil oozes up out of the ground and pollutes the area around it. Perhaps one of the most famous natural seeps is the La Brea Tar Pits in California, which are a seep of oil and gas forming tar. Natural seeps are unavoidable pollution as the earth pushes oil up.

Oil pollution is a serious problem, especially oil spills in the world's oceans. Oil pollution can kill animals and wildlife, sometimes wiping out entire ecosystems before a cleanup starts. The different types of pollution have varying risks of danger to animals and humans, but the pollution always has danger associated with it. There are a few types of oil pollution, which vary depending on the kind of oil.

Oil Spills

Among the most serious types of oil pollution is an oil spill. Oil spills occur for various reasons, which range from an oil ship getting damaged or similar transport issues to problems or malfunctions of equipment at oil refineries. Transportation of oil is when spills are the most likely to occur. For example, the oil spill on April 20, 2010, which spilled oil into the Gulf of Mexico occurred due to an explosion. "The Huffington Post" reported that around 205 million gallons of oil were spilled into the ocean, resulting in oil damage to beaches, the marine environments and the livelihood of fishermen.

Urban Runoff

Urban locations exhibit oil buildup on roads from vehicles. When it rains or snow melts, the oil is pushed from the roads into sewer systems and runs off into water sources. Oil gets onto the roads though a few different means. The U.S. Environmental Protection Agency (EPA) states that leaks from vehicles, spills at fuel stations and improperly discarded oil are among the main causes of runoff oil pollution. The oil floats on the water during rain or snow melt and is pushed out of a city to pollute water and natural environments in rural areas.

Human impact[edit]

An oil spill represents an immediate fire hazard. The Kuwaiti oil fires produced air pollution that caused respiratory distress.^{[citation needed]} The Deepwater Horizon explosion killed eleven oil rig workers.^[31] The fire resulting from the Lac-Mégantic derailment killed 47 and destroyed half of the town's centre.^{[citation needed]}

Spilled oil can also contaminate drinking water supplies. For example, in 2013 two different oil spills contaminated water supplies for 300,000 in Miri, Malaysia;^[32] 80,000 people in Coca, Ecuador.^[33] In 2000, springs were contaminated by an oil spill in Clark County, Kentucky.^[34]

Contamination can have an economic impact on tourism and marine resource extraction industries. For example, the Deepwater Horizon oil spill impacted beach tourism and fishing along the Gulf Coast, and the responsible parties were required to compensate economic victims.

Environmental effects[edit]

A surf scoter covered in oil as a result of the 2007 San Francisco Bay oil spill

A bird covered in oil from the Black Sea oil spill

In general, spilled oil can affect animals and plants in two ways: dirесt from the oil and from the response or cleanup process.^[35]^[36] There is no clear relationship between the amount of oil in the aquatic environment and the likely impact on biodiversity. A smaller spill at the wrong time/wrong season and in a sensitive environment may prove much more harmful than a larger spill at another time of the year in another or even the same environment.^[37] Oil penetrates into the structure of the plumage of birds and the fur of mammals, reducing their insulating ability, and making them more vulnerable to temperature fluctuations and much less buoyant in the water.

Animals who rely on scent to find their babies or mothers cannot due to the strong scent of the oil. This causes a baby to be rejected and abandoned, leaving the babies to starve and eventually die. Oil can impair a bird's ability to fly, preventing it from foraging or escaping from predators. As they preen, birds may ingest the oil coating their feathers, irritating the digestive tract, altering liver function, and causing kidneydamage. Together with their diminished foraging capacity, this can rapidly result in dehydration and metabolic imbalance. Some birds exposed to petroleum also experience changes in their hormonal balance, including changes in their luteinizing protein.^[38] The majority of birds affected by oil spills die from complications without human intervention.^[39]^[40] Some studies have suggested that less than one percent of oil-soaked birds survive, even after cleaning,^[41] although the survival rate can also exceed ninety percent, as in the case of the Treasure oil spill.^[42]

Heavily furred marine mammals exposed to oil spills are affected in similar ways. Oil coats the fur of sea otters and seals, reducing its insulating effect, and leading to fluctuations in body temperature and hypothermia. Oil can also blind an animal, leaving it defenseless. The ingestion of oil causes dehydration and impairs the digestive process. Animals can be poisoned, and may die from oil entering the lungs or liver.

There are three kinds of oil-consuming bacteria. Sulfate-reducing bacteria (SRB) and acid-producing bacteria are anaerobic, while general aerobic bacteria (GAB) are aerobic. These bacteria occur naturally and will act to remove oil from an ecosystem, and their biomass will tend to replace other populations in the food chain. The chemicals from the oil which dissolve in water, and hence are available to bacteria, are those in the water associated fraction of the oil.

In addition, oil spills can also harm air quality.^[43] The chemicals in crude oil are mostly hydrocarbons that contains toxic chemicals such as benzenes, toluene, poly-aromatic hydrocarbon and oxygenated polycyclic aromatic hydrocarbons.^[44] These chemicals can introduce adverse health effects when being inhaled into human body. In addition, these chemicals can be oxidized by oxidants in the atmosphere to form fine particulate matter after they evaporate into the atmosphere.^[45] These particulates can penetrate lungs and carry toxic chemicals into the human body. Burning surface oil can also be a source for pollution such as soot particles. During the cleanup and recovery process, it will also generate air pollutants such as nitric oxides and ozone from ships. Lastly, bubble bursting can also be a generation pathway for particulate matter during an oil spill.^[46] During the Deepwater Horizon oil spill, significant air quality issues were found on the Gulf Coast, which is the downwind of DWH oil spill. Air quality monitoring data showed that criteria pollutants had exceeded the health-based standard in the coastal regions.^[47]

Sources and rate of occurrence[edit]

A VLCC tanker can carry 2 million barrels (320,000 m³) of crude oil. This is about eight times the amount spilled in the widely known Exxon Valdez oil spill. In this spill, the ship ran aground and dumped 260,000 barrels (41,000 m³) of oil into the ocean in March 1989. Despite efforts of scientists, managers, and volunteers over 400,000 seabirds, about 1,000 sea otters, and immense numbers of fish were killed.^[48] Considering the volume of oil carried by sea, however, tanker owners' organisations often argue that the industry's safety record is excellent, with only a tiny fraction of a percentage of oil cargoes carried ever being spilled. The International Association of Independent Tanker Owners has observed that "accidental oil spills this decade have been at record low levels—one third of the previous decade and one tenth of the 1970s—at a time when oil transported has more than doubled since the mid 1980s."

Oil tankers are just one of the many sources of oil spills. According to the United States Coast Guard, 35.7% of the volume of oil spilled in the United States from 1991 to 2004 came from tank vessels (ships/barges), 27.6% from facilities and other non-vessels, 19.9% from non-tank vessels, and 9.3% from pipelines; 7.4% from mystery spills.^[49] On the other hand, only 5% of the actual spills came from oil tankers, while 51.8% came from other kinds of vessels.^[49]

The International Tanker Owners Pollution Federation has tracked 9,351 accidental spills that have occurred since 1974.^[50] According to this study, most spills result from routine operations such as loading cargo, discharging cargo, and taking on fuel oil.^[23] 91% of the operational oil spills are small, resulting in less than 7 metric tons per spill.^[23] On the other hand, spills resulting from accidents like collisions, groundings, hull failures, and explosions are much larger, with 84% of these involving losses of over 700 metric tons.^[23]

Cleanup and recovery[edit]

A U.S. Air Force Reserve plane sprays Corexit dispersant over the Deepwater Horizon oil spill in the Gulf of Mexico.

Clean-up efforts after the Exxon Valdez oil spill.

A US Navy oil spill response team drills with a "Harbour Buster high-speed oil containment system".

Cleanup and recovery from an oil spill is difficult and depends upon many factors, including the type of oil spilled, the temperature of the water (affecting evaporation and biodegradation), and the types of shorelines and beaches involved.^[1] Physical cleanups of oil spills are also very expensive. However, microorganisms such as Fusobacteria species demonstrate an innovative potential for future oil spill cleanup because of their ability to colonize and degrade oil slicks on the sea surface.^[51]

Methods for cleaning up include:^[52]

Bioremediation: use of microorganisms^[53] or biological agents^[54] to break down or remove oil; such as Alcanivorax bacteria^[55] or Methylocella silvestris.^[56]
Bioremediation Accelerator: a binder molecule that moves hydrocarbons out of water and into gels, when combined with nutrients, encourages natural bioremediation. Oleophilic, hydrophobic chemical, containing no bacteria, which chemically and physically bonds to both soluble and insoluble hydrocarbons. The accelerator acts as a herding agent in water and on the surface, floating molecules such as phenol and BTEX to the surface of the wate, forming gel-like agglomerations. Undetectable levels of hydrocarbons can be obtained in produced water and manageable water columns. By overspraying sheen with bioremediation accelerator, sheen is eliminated within minutes. Whether applied on land or on water, the nutrient-rich emulsion creates a bloom of local, indigenous, pre-existing, hydrocarbon-consuming bacteria. Those specific bacteria break down the hydrocarbons into water and carbon dioxide, with EPA tests showing 98% of alkanes biodegraded in 28 days; and aromatics being biodegraded 200 times faster than in nature they also sometimes use the hydrofireboom to clean the oil up by taking it away from most of the oil and burning it.^[57]
Controlled burning can effectively reduce the amount of oil in water, if done properly.^[58] But it can only be done in low wind,^[59] and can cause air pollution.^[60]

Oil slicks on Lake Maracaibo

Volunteers cleaning up the aftermath of the Prestige oil spill

Dispersants can be used to dissipate oil slicks.^[61] A dispersant is either a non-surface active polymer or a surface-active substance added to a suspension, usually a colloid, to improve the separation of particles and to prevent settling or clumping. They may rapidly disperse large amounts of certain oil types from the sea surface by transferring it into the water column. They will cause the oil slick to break up and form water-soluble micelles that are rapidly diluted. The oil is then effectively spread throughout a larger volume of water than the surface from where the oil was dispersed. They can also delay the formation of persistent oil-in-water emulsions. However, laboratory experiments showed that dispersants increased toxic hydrocarbon levels in fish by a factor of up to 100 and may kill fish eggs.^[62] Dispersed oil droplets infiltrate into deeper water and can lethally contaminate coral. Research indicates that some dispersants are toxic to corals.^[63] A 2012 study found that Corexit dispersant had increased the toxicity of oil by up to 52 times.^[64]
Watch and wait: in some cases, natural attenuation of oil may be most appropriate, due to the invasive nature of facilitated methods of remediation, particularly in ecologically sensitive areas such as wetlands.^[65]
Dredging: for oils dispersed with detergents and other oils denser than water.
Skimming: Requires calm waters at all times during the process.
Solidifying: Solidifiers are composed of tiny, floating, dry ice pellets,^[66]^[67]^[68] and hydrophobic polymers that both adsorb and absorb. They clean up oil spills by changing the physical state of spilled oil from liquid to a solid, semi-solid or a rubber-like material that floats on water.^[36] Solidifiers are insoluble in water, therefore the removal of the solidified oil is easy and the oil will not leach out. Solidifiers have been proven to be relatively non-toxic to aquatic and wild life and have been proven to suppress harmful vapors commonly associated with hydrocarbons such as benzene, xylene and naphtha. The reaction time for solidification of oil is controlled by the surface area or size of the polymer or dry pellets as well as the viscosity and thickness of the oil layer. Some solidifier product manufactures claim the solidified oil can be thawed and used if frozen with dry ice or disposed of in landfills, recycled as an additive in asphalt or rubber products, or burned as a low ash fuel. A solidifier called C.I.Agent (manufactured by C.I.Agent Solutions of Louisville, Kentucky) is being used by BP in granular form, as well as in Marine and Sheen Booms at Dauphin Island and Fort Morgan, Alabama, to aid in the Deepwater Horizon oil spill cleanup.
Vacuum and centrifuge: oil can be sucked up along with the water, and then a centrifuge can be used to separate the oil from the water – allowing a tanker to be filled with near pure oil. Usually, the water is returned to the sea, making the process more efficient, but allowing small amounts of oil to go back as well. This issue has hampered the use of centrifuges due to a United States regulation limiting the amount of oil in water returned to the sea.^[69]
Beach Raking: coagulated oil that is left on the beach can be picked up by machinery.

Bags of oily waste from the Exxon Valdez oil spill

Equipment used includes:^[58]

Booms: large floating barriers that round up oil and lift the oil off the water
Skimmers: skim the oil
Sorbents: large absorbents that absorb oil
Chemical and biological agents: helps to break down the oil
Vacuums: remove oil from beaches and water surface
Shovels and other road equipment: typically used to clean up oil on beaches

Prevention[edit]

Secondary containment – methods to prevent releases of oil or hydrocarbons into environment.
Oil Spill Prevention Control and Countermeasures (SPCC) program by the United States Environmental Protection Agency.
Double-hulling – build double hulls into vessels, which reduces the risk and severity of a spill in case of a collision or grounding. Existing single-hull vessels can also be rebuilt to have a double hull.
Thick-hulled railroad transport tanks.^[70]

Spill response procedures should include elements such as;

A listing of appropriate protective clothing, safety equipment, and cleanup materials required

for spill cleanup (gloves, respirators, etc.) and an explanation of their proper use;

Appropriate evacuation zones and procedures;
Availability of fire suppression equipment;
Disposal containers for spill cleanup materials; and
The first aid procedures that might be required.^[71]

Environmental Sensitivity Index (ESI) mapping[edit]

Environmental Sensitivity Index (ESI) maps are used to identify sensitive shoreline resources prior to an oil spill event in order to set priorities for protection and plan cleanup strategies.^[72]^[73] By planning spill response ahead of time, the impact on the environment can be minimized or prevented. Environmental sensitivity index maps are basically made up of information within the following three categories: shoreline type, and biological and human-use resources.^[74]

Shoreline type[edit]

Shoreline type is classified by rank depending on how easy the target site would be to clean up, how long the oil would persist, and how sensitive the shoreline is.^[75] The floating oil slicks put the shoreline at particular risk when they eventually come ashore, covering the substrate with oil. The differing substrates between shoreline types vary in their response to oiling, and influence the type of cleanup that will be required to effectively decontaminate the shoreline. In 1995, the US National Oceanic and Atmospheric Administration extended ESI maps to lakes, rivers, and estuary shoreline types.^[74] The exposure the shoreline has to wave energy and tides, substrate type, and slope of the shoreline are also taken into account—in addition to biological productivity and sensitivity. The productivity of the shoreline habitat is also taken into account when determining ESI ranking.^[76] Mangroves and marshes tend to have higher ESI rankings due to the potentially long-lasting and damaging effects of both the oil contamination and cleanup actions. Impermeable and exposed surfaces with high wave action are ranked lower due to the reflecting waves keeping oil from coming onshore, and the speed at which natural processes will remove the oil.

Biological resources[edit]

Habitats of plants and animals that may be at risk from oil spills are referred to as "elements" and are divided by functional group. Further classification divides each element into species groups with similar life histories and behaviors relative to their vulnerability to oil spills. There are eight element groups: Birds, Reptiles, Amphibians, Fish, Invertebrates, Habitats and Plants, Wetlands, and Marine Mammals and Terrestrial Mammals. Element groups are further divided into sub-groups, for example, the ‘marine mammals’ element group is divided into dolphins, manatees, pinnipeds (seals, sea lions & walruses), polar bears, sea otters and whales.^[74]^[76] Problems taken into consideration when ranking biological resources include the observance of a large number of individuals in a small area, whether special life stages occur ashore (nesting or molting), and whether there are species present that are threatened, endangered or rare.^[77]

Human-use resources[edit]

Human use resources are divided into four major classifications; archaeological importance or cultural resource site, high-use recreational areas or shoreline access points, important protected management areas, or resource origins.^[74]^[77] Some examples include airports, diving sites, popular beach sites, marinas, natural reserves or marine sanctuaries.

Estimating the volume of a spill[edit]

By observing the thickness of the film of oil and its appearance on the surface of the water, it is possible to estimate the quantity of oil spilled. If the surface area of the spill is also known, the total volume of the oil can be calculated.^[78]

	Film thickness			Quantity spread
Appearance	inches	mm	nm	gal/sq mi	L/ha
Barely visible	0.0000015	0.0000380	38	25	0.370
Silvery sheen	0.0000030	0.0000760	76	50	0.730
First trace of color	0.0000060	0.0001500	150	100	1.500
Bright bands of color	0.0000120	0.0003000	300	200	2.900
Colors begin to dull	0.0000400	0.0010000	1000	666	9.700
Colors are much darker	0.0000800	0.0020000	2000	1332	19.500

Oil spill model systems are used by industry and government to assist in planning and emergency decision making. Of critical importance for the skill of the oil spill model prediction is the adequate description of the wind and current fields. There is a worldwide oil spill modelling (WOSM) program.^[79] Tracking the scope of an oil spill may also involve verifying that hydrocarbons collected during an ongoing spill are derived from the active spill or some other source. This can involve sophisticated analytical chemistry focused on finger printing an oil source based on the complex mixture of substances present. Largely, these will be various hydrocarbons, among the most useful being polyaromatic hydrocarbons. In addition, both oxygen and nitrogen heterocyclic hydrocarbons, such as parent and alkyl homologues of carbazole, quinoline, and pyridine, are present in many crude oils. As a result, these compounds have great potential to supplement the existing suite of hydrocarbons targets to fine-tune source tracking of petroleum spills. Such analysis can also be used to follow weathering and degradation of crude spills.^[80]

Oil wastes that enter the ocean come from many sources, some being accidental spills or leaks, and some being the results of chronic and careless habits in the use of oil and oil products. Most waste oil in the ocean consists of oily stormwater drainage from cities and farms, untreated waste disposal from factories and industrial facilities, and unregulated recreational boating.

It is estimated that approximately 706 million gallons of waste oil enter the ocean every year, with over half coming from land drainage and waste disposal; for example, from the improper disposal of used motor oil. Offshore drilling and production operations and spills or leaks from ships or tankers typically contribute less than 8 percent of the total. The remainder comes from routine maintenance of ships (nearly 20 percent), hydrocarbon particles from onshore air pollution (about 13 percent), and natural seepage from the seafloor (over 8 percent).

Prevalence during Drilling versus Transportation

Offshore oil spills or leaks may occur during various stages of well drilling or workover and repair operations. These stages can occur while oil is being produced from offshore wells, handled, and temporarily stored; or when oil is being transported offshore, either by flowline, underwater pipeline, or tanker. Of the approximately 706 million gallons of waste oil in the ocean each year, offshore drilling operations contribute about 2.1 percent, and transportation accidents (both ships and tankers) account for another 5.2 percent. The amount of oil spilled or leaked during offshore production operations is relatively insignificant.

Oil waste from offshore drilling operations may come from disposal of oil-based drilling fluid wastes, deck runoff water, flowline and pipeline leaks, or well failures or blowouts. Disposal of offshore production waste can also pollute the ocean, as can deck runoff water, leaking storage tanks, flowline and pipeline leaks, and the wells themselves. Oil spilled from ships and tankers includes the transportation fuel used by the vessels themselves or their cargos, such as crude oil, fuel oil, or heating oil.

Over half the ocean's waste oil comes from land-based sources and from unregulated recreational boating. The heavy development in this busy California port illustrates one potential source of petroleum contamination in coastal waters. (Note dark plume in left foreground.)

Oil Spill Behavior

When oil is spilled in the ocean, it initially spreads in the water (primarily on the surface), depending on its relative density and composition. The oil slick formed may remain cohesive, or may break up in the case of rough seas. Waves, water currents, and wind force the oil slick to drift over large areas, impacting the open ocean, coastal areas, and marine and terrestrial habitats in the path of the drift.

Oil that contains volatile organic compounds partially evaporates, losing between 20 and 40 percent of its mass and becoming denser and more viscous (i.e., more resistant to flow). A small percentage of oil may dissolve in the water. The oil residue also can disperse almost invisibly in the water or form a thick mousse with the water. Part of the oil waste may sink with suspended particulate matter, and the remainder eventually congeals into sticky tar balls. Over time, oil waste weathers (deteriorates) and disintegrates by means of photolysis (decomposition by sunlight) and biodegradation (decomposition due to microorganisms). The rate of biodegradation depends on the availability of nutrients, oxygen, and microorganisms, as well as temperature.

Oil Spill Interaction with Shoreline.

If oil waste reaches the shoreline or coast, it interacts with sediments such as beach sand and gravel, rocks and boulders, vegetation, and terrestrial habitats of both wildlife and humans, causing erosion as well as contamination . Waves, water currents, and wind move the oil onto shore with the surf and tide.

Crude oil from the Sea Empress tanker spill coats a beach at Pembrokeshire, Wales in 1996. Although marine transportation accidents can result in such oil spills, they account for only about 5 percent of the waste oil that enters the ocean annually.

Beach sand and gravel saturated with oil may be unable to protect and nurture normal vegetation and populations of the substrate biomass . Rocks and boulders coated with sticky residue interfere with recreational uses of the shoreline and can be toxic to coastal wildlife.

Examples of Large Spills.

The largest accidental oil spill on record (Persian Gulf, 1991) put 240 million gallons of oil into the ocean near Kuwait and Saudi Arabia when several tankers, port facilities, and storage tanks were destroyed during war operations. The blowout of the Ixtoc I exploratory well offshore Mexico in 1979, the second largest accidental oil spill, gushed 140 million gallons of oil into the Gulf of Mexico. By comparison, the wreck of the Exxon Valdez tanker in 1989 spilled 11 million gallons of oil into Prince William Sound offshore Alaska, and ranks fifty-third on the list of oil spills involving more than 10 million gallons.

The number of large spills (over 206,500 gallons) averaged 24.1 per year from 1970 to 1979, but decreased to 6.9 per year from 1990 through 2000.

Damage to Fisheries, Wildlife, and Recreation

Oil spills present the potential for enormous harm to deep ocean and coastal fishing and fisheries. The immediate effects of toxic and smothering oil waste may be mass mortality and contamination of fish and other food species, but long-term ecological effects may be worse. Oil waste poisons the sensitive marine and coastal organic substrate, interrupting the food chain on which fish and sea creatures depend, and on which their reproductive success is based. Commercial fishing enterprises may be affected permanently.

Wildlife other than fish and sea creatures, including mammals, reptiles, amphibians, and birds that live in or near the ocean, are also poisoned by oil waste. The hazards for wildlife include toxic effects of exposure or ingestion, injuries such as smothering and deterioration of thermal insulation, and damage to their reproductive systems and behaviors. Long-term ecological effects that contaminate or destroy the marine organic substrate and thereby interrupt the food chain are also harmful to the wildlife, so species populations may change or disappear.

Coastal areas are usually thickly populated and attract many recreational activities and related facilities that have been developed for fishing, boating, snorkeling and scuba diving, swimming, nature parks and preserves, beaches, and other resident and tourist attractions. Oil waste that invades and pollutes these areas and negatively affects human activities can have devastating and long-term effects on the local economy and society. Property values for housing tend to decrease, regional business activity declines, and future investment is risky.

Long-term Fate of Oil on Shore

The fate of oil residues on shore depends on the spilled oil's composition and properties, the volume of oil that reaches the shore, the types of beach and coastal sediments and rocks contacted by the oil, the impact of the oil on sensitive habitats and wildlife, weather events, and seasonal and climatic conditions. Some oils evaporate, disperse, emulsify, weather, and decompose more easily than others. The weather and seasonal and climatic conditions may accelerate or delay these processes.

In 2000, several thousand penguins were affected by a fuel oil spill after the iron-ore carrier Treasure sank off South Africa. Many oil-soaked birds were cleaned and released.

Oil waste that coalesces into a tar-like substance or that saturates sediments above the surf and tide level is especially persistent. Efforts to remove the oil and clean, decontaminate, and remediate an oil-impacted shoreline may make the area more visibly attractive, but may be more harmful than helpful in terms of actual recovery.

Cleanup and Recovery

The techniques used to clean up an oil spill depend on oil characteristics and the type of environment involved; for example, open ocean, coastal, or wetland . Pollution-control measures include containment and removal of the oil (either by skimming, filtering, or in situ combustion), dispersing it into smaller droplets to limit immediate surficial and wildlife damage, biodegradation (either natural or assisted), and normal weathering processes. Individuals of large-sized wildlife species are sometimes rescued and cleaned, but micro-sized species are usually ignored.

Oil spill countermeasures to clean up and remove the oil are selected and applied on the basis of many interrelated factors, including ecological protection, socioeconomic effects, and health risk. It is important to have contingency plans in place in order to deploy pollution control personnel and equipment efficiently.

Environmental Recovery Rates.

The rate of recovery of the environment when an oil spill occurs depends on factors such as oil composition and

Workers clean up an oil refinery spill that polluted Anacortes Bay, Washington. The floating ring of absorbent pads trailing behind the boat is being used to contain some of the oil that has spilled.

properties and the characteristics of the area impacted, as well as the results of intervention and remediation. Physical removal of oil waste and the cleaning and decontaminating of the area assist large-scale recovery of the environment, but may be harmful to the substrate biomass. Bioremediation efforts—adding microorganisms, nutrients, and oxygen to the environment—can usually boost the rate of biodegradation.

Because of the type of oil spilled and the Arctic environment in which it spilled, it is estimated that the residue of the Exxon Valdez oil spill will be visible on the Alaskan coast for 30 years.

Costs and Prevention

The costs of an oil spill are both quantitative and qualitative. Quantitative costs include loss of the oil, repair of physical facilities, payment for cleaning up the spill and remediating the environment, penalties assessed by regulatory agencies, and money paid in insurance and legal claims. Qualitative costs of an oil spill include the loss of pristine habitat and communities, as well as unknown wildlife and human health effects from exposure to water and soil pollution.

Prevention of oil spills has become a major priority; and of equal importance, efforts to contain and remove oil that has spilled are considered to be prevention of secondary spills. The costs associated with oil spills and regulations governing offshore facilities and operations have encouraged the development of improved technology for spill prevention. The Oil Pollution Act of 1990 was enacted by the U.S. Congress to strengthen oil spill prevention, planning, response, and restoration efforts. Under its provisions, the Oil Spill Liability Trust Fund provides cleanup funds for oil pollution incidents.

Responsibility for the prevention of oil spills falls upon individuals as well as on governments and industries. Because the sources of oil waste in the ocean are generally careless, rather than accidental, truly effective prevention of oil spills involves everyone.

Oceans are polluted by oil on a daily basis from oil spills, routine shipping, run-offs and dumping.

Oil spills make up about 12% of the oil that enters the ocean. The rest come from shipping travel, drains and dumping.
An oil spill from a tanker is a severe problem because there is such a huge quantity of oil being spilt into one place.
Oil spills cause a very localised problem but can be catastrophic to local marine wildlife such as fish, birds and sea otters.
Oil cannot dissolve in water and forms a thick sludge in the water. This suffocates fish, gets caught in the feathers of marine birds stopping them from flying and blocks light from photosynthetic aquatic plants.

Pollution Caused by Oil Spills