Oil spills

DEFINITION: Accidental or intentional discharges of raw or refined petroleum products on land or at sea

Oil spills pose both short- and long-term environmental threats, including injuries and deaths among fish, birds, and other wildlife; damage to shoreline recreational areas; and pollution of water supplies. Major oil spills often draw significant media attention and have been used by environmentalist organizations to raise awareness of the problems caused by the oil industry in general and pollution in particular. Oil spills occur in both terrestrial and marine settings.

Terrestrial Oil Spills

Terrestrial oil spills affect land areas, including drainage courses and bodies of surface water impounded in lakes and ponds. Subsurface waters (groundwater) are also at risk from leakage of polluted water downward through the vadose zone (zone of aeration) to the water table (zone of saturation). Some crude oil is lost during exploratory drilling, workover operations, and tank storage. Mud pits utilized during rotary drilling usually contain oil recovered from the well during testing or oil derived from an oil-based mud employed in the drilling process. Oil and brine released from wells are sometimes stored in unlined ponds, and these fluids can soak into the ground and kill beneficial microbes in the soil and plant life in the immediate area. Subsurface water can also be contaminated if the oil or brine migrates downward to the groundwater table. Runoff from these areas can enter streams and ponded bodies of water and kill fish and other aquatic animals as well as reduce the natural vegetation.

Terrestrial oil spills also occur during the loading, transportation, and offloading of petroleum from tank trucks and railroad tank cars. Petroleum pipelines, both buried and above ground, are highly vulnerable to rupture from welding defects, corrosion, earthquakes, and shifting soils. Fire is a constant danger associated with such spills. For example, during the mid-1980s, a ruptured pipeline near São Paulo, Brazil, caused the deaths of more than five hundred people and resulted in the destruction by fire of twenty-five hundred homes in the town of Vila Socco. During the 1991 Persian Gulf War, large areas of Kuwait were devastated when Iraqi soldiers damaged oil pipelines and refineries and set fire to hundreds of oil wells. That incident also illustrated the threat of groundwater contamination, as pools of oil formed near the wells and infiltrated the porous and permeable soil and rock, thereby endangering the water supply of Kuwait City and other areas. Another prominent example of a terrestrial spill came in 2015, when a rupture of a privately owned underground pipeline in California's Santa Barbara County caused a spill of more than 120,000 gallons of crude oil, the majority of which reached the ocean.

The disposal of petroleum products (diesel fuel, gasoline, kerosene, jet fuel, and used motor oil) is a significant problem worldwide, and can contribute to the risk of spills. Some of these products contain carcinogens such as benzene, toluene, and xylene, which require special handling. Many millions of gallons of used oil products are disposed of on land every year, and it was estimated in 2018 that 2600 million liters of oil waste enter the oceans per year. Of this total, 50 percent was estimated to be land-derived. These inputs include coastal city contributions from refineries, wastewater outlets, and other sources; urban runoff, including storm drains; and river runoff.

Offshore Spills

The waters of oceans and restricted seas can be polluted by oil in several ways. Oil sources include natural seeps along the ocean floor, stream runoff from the land, wastewater drainage outlets from industrial complexes, offshore drilling accidents, deliberate purging of ballast or cargo areas of ships, and accidents involving oil supertankers. The petroleum input into the marine environment from ocean-derived factors has been estimated at about 56 percent. In this estimation, 810,000 tons, or 46 percent, are illegally dumped, 21 percent from land based runoff, 18 percent industrial accidents, 8 percent air pollution, and 6 percent from oil drilling.

Supertanker accidents that result in oil spills are major events, and tend to be the highest-profile type of oil spill. Causes include shipboard explosions, collisions with other vessels, and grounding on barriers (mostly rocks or coral reefs) because of navigation error, mechanical failure, or inclement weather. Although such oil spills are often quite dramatic, and the damage they do to the environment receives extensive news media coverage, only about 5 percent of the total input of petroleum into the oceans results from supertanker spills.

When an oil spill occurs in the open ocean, the oil floats on the surface of the water because of a density contrast between the two substances; the resulting pool of oil is sometimes known as an oil slick. The lighter components of the spilled petroleum immediately begin to evaporate; also, oil-degrading bacteria in the water begin to feed on the organic deposit and multiply. Warmer water and ambient air temperatures increase the rates of bacterial growth and evaporation. The major part of petroleum dumped into the open ocean evaporates or is reduced by bacteria. With time, the oil turns into an inert, tarlike substance that becomes extremely hard; some such residues have been found with barnacles attached to them.

In areas where the spilled oil is washed ashore and subjected to intense wave action, a gooey emulsion sometimes forms. This foamy mass, which has been described as resembling chocolate mousse, coats everything along the shore, including sand-sized particles, large boulders, aquatic animals and plants, boats, and human-made shore facilities. The polluted waters can devastate resort beaches, oyster and shrimp beds, fish hatcheries, and prime fishing grounds.

The potential damage resulting from a large oil spill in the ocean includes the loss of substantial numbers of commercial and rough fish, waterfowl, aquatic mammals, shellfish, algae, and plankton. Oil contamination reduces the amount of oxygen in the water column, and this can cause the deaths of large numbers of fish in polluted areas. Millions of fish died as a result of the 1989 Exxon Valdez disaster in Alaskan waters, for example, and the entire Alaskan fishing industry was seriously threatened. Although that event is considered a major disaster and remains one of the most infamous oil spills in history, it is not considered among the ten largest documented oil spills worldwide by volume. One of the biggest marine oil spills in history occurred following an explosion at the Deepwater Horizon oil rig in April 2010 in the Gulf of Mexico, uncapping a sea-floor oil gusher that flowed for nearly three months before it was recapped. An estimated 4.9 million barrels were discharged into the gulf, causing widespread and serious damage to marine and coastal wildlife, beaches, estuaries, and wetlands along the Gulf Coast and severely affecting the local fishing and tourism industries.

Marine oil spills have devasting effects on wildlife. Shellfish in bays and marshes can perish in oil-polluted waters from asphyxiation or toxicity, and harmful conditions can remain for years. For example, shellfish in a salt marsh in Massachusetts were quarantined for more than five years after heating oil was spilled nearby in 1969, and traces of petroleum persisted for decades. When seabirds come into contact with spilled oil to the extent that their feathers are soaked, they lose the ability to fly and float, as well as their natural body insulation. Many such birds starve to death, die from exposure, or drown. The Exxon Valdez disaster resulted in the deaths of more than 200,000 seabirds. During the Persian Gulf War, more than 20,000 birds perished from oil-related causes. Oil spills also cause the deaths of aquatic mammals, which die from the loss of their food supply, exposure to cold, or poisoning when they ingest the toxic oil. Following the Deepwater Horizon oil spill, dolphins and sea turtles died in record numbers, and many stillborn dolphins and stranded sea turtles were found. By 2020, a decade after the disaster, environmental and marine experts continued to study the ongoing impacts of the Deepwater Horizon spill on marine and coastal wildlife.

Cleanup Procedures

Oil spills in the open ocean have been reduced due to several techniques and safety measures. Igniting the slick, if attempted shortly after a spill, can be effective; however, if the volatile components of the oil have evaporated, it is difficult to start and maintain such fires. In 1967, when the damaged supertanker Torrey Canyon began to founder and break up off the coast of England, Great Britain’s air force dropped bombs in an effort to ignite the oil that remained in the vessel.

Another technique used to reduce the damage caused by oil slicks is the application of chemicals such as detergents in an attempt to disperse the oil droplets. This procedure is not viable if the temperature of the water is too low for the chemicals to be effective. Floating booms are sometimes used to confine oil streamers or protect inlet areas. These barriers are useful if the waves are not too high. Skimmers may be used to collect floating oil during the early stages of a spill. Plant material (threshed hay, peat moss, or wood shavings) or pulverized rock (chalk or claystone) is sometimes spread over slicks to absorb the oil. Plant material can then be removed and burned or buried in sealed containers; applied rock particles absorb the oil, clump together, and sink to the ocean floor. In many parts of the oceans, oil-eating microbes (mostly bacteria) utilize petroleum as a nutrient. If these microbes are not present or exist only in small numbers in the area, engineered microbes can be introduced. Under ideal temperature and ocean chemistry conditions, the bacteria will rapidly multiply and consume the oil slick. This technique is known as bioremediation. Other factors such as wave action, timing, and scale can also affect the effectiveness of such methods, however, and the use of dispersants can kill oil-eating microbes.

In nearshore areas, beach sand and boulders can be steamed clean or washed with water or solvents. Pools of oil can be vacuumed into tank trucks and hauled away from the site. The recovered oil can sometimes be processed into useful products. Plant material can also be applied to crude oil along the shoreline. After the 1969 Santa Barbara oil spill, the beaches along the California coast were coated by approximately ten thousand barrels of gooey oil. Numerous volunteers helped spread fresh hay along the beachfront and later recovered the oil-soaked plant material. Volunteer workers have saved many birds and mammals at animal centers set up after large spills; workers wash the animals with solvents to remove oil and often hold them until their normal body resilience returns.

Even cleanup efforts can damage flora and fauna, however. Hot water used in cleaning or walking over fragile organisms can harm them, for instance. Animals that are cleaned often die shortly thereafter, and if they do survive, such animals may not reproduce. Therefore, environmentalists and authorities in various countries have worked to reevaluate typical cleanup procedures and develop more effective methods. A large marine oil spill in the Indian Ocean from a carrier vessel that ran aground off the coast of Mauritius in 2020 brought particular attention to the need for alternative cleanup policies and technologies, as it involved a newer, more complicated low-sulfur fuel about which the potential environmental impacts were lesser known.

Health Effects

Human health can also be adversely affected by oil spills. Cleanup workers, animal rescuers, and nearby residents who are exposed to the volatile organic compounds and other petroleum components may exhibit respiratory, gastric, and dermatological ailments in the near term. People living near an oil spill may also have difficulty getting adequate nutrition and water or otherwise maintaining their livelihoods as drinking water, game animals, fish, or surrounding croplands become contaminated. In the short-term, these individuals may experience memory loss, dizziness, headache, chest pain, fatigue, rashes or coughing.

The long-term effects of human exposure to oil components and cleanup chemicals remain subject to debate. For one, it can be difficult to isolate a precise cause of conditions such as cancer, lung dysfunction, or developmental disorders. Nevertheless, certain petroleum constituents such as benzene have been associated with neurological effects and cancers among industry workers. Oil exposure has also been potentially linked to other long-term symptoms including low platelet blood counts, low hemoglobin, breathing problems, liver problems, lung problems, and heart problems.

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