1. Introduction – Oil spills are the harmful release of oil into the environment, usually in the water, sometimes killing area flora and fauna. Oil is the most common pollutant in the oceans. More than 3 million metric tons of oil contaminates the sea every year. The majority of oil pollution in the oceans comes from land. Runoff and waste from cities, industry, and rivers carries oil into the ocean. Ships cause about a third of the oil pollution in the oceans when they wash out their tanks or dump their bilge water. It is an unfortunate by-product of the storage and transportation of oil and petroleum is the occasional spill. Oil spills are very difficult to clean up.
The kind of oil spill we usually think about is the accidental or intentional release of petroleum products into the environment as result of human activity (drilling, manufacturing, storing, transporting, waste management), that floats on the surface of water bodies as a discrete mass and is carried by the wind, currents and tides. Oil spills can be partially controlled by chemical dispersion, combustion, mechanical containment and adsorption. They have destructive effects on coastal ecosystems.
Examples of an oil spill would be things like well blowouts, pipeline breaks, ship collisions or groundings, overfilling of gas tanks and bilge pumping from ships, leaking underground storage tanks, and oil-contaminated water runoff from streets and parking lots during rain storms. Marine oil spill is a serious consequence of off-shore oil drilling and its oceanic transportation. Spill control firms specialize in the prevention, containment and cleanup of industrial oil spills.
2. Characteristics of oil spill – The major spills of crude oil and its products in the sea occur during their transport by oil tankers, loading and unloading operations, blowouts, etc. When introduced in the marine environment the oil goes through a variety of transformation involving physical, chemical and biological processes. Physical and chemical processes begin to operate soon after petroleum is spilled on the sea. These include evaporation, spreading, emu1sification, dissolution, sea-air exchange and sedimentation. Chemical oxidation of some of the components of petroleum is also induced in the presence of sunlight. The degraded products of these processes include floating tar lumps, dissolved and particulate hydrocarbon materials in the water column and materials deposited on the bed.
Biological processes though slow also act simultaneously with physical and chemical processes. The important biological processes include degradation by microorganisms to carbon dioxide or organic material in intermediate oxidation stages, uptake by large organisms and subsequent metabolism, storage and discharge.
3. Types of oil spill – Crude oil and its products are highly complex mixtures. Since the fate of petroleum in the marine environment depends on the composition, a preliminary knowledge of major components and types is necessary for understanding the fate of petroleum when spilled on water. The approximate composition of an average crude oil is considered as :
Normal Type –
Gasoline (C5 – C10 ) 30%; kerosene (C10 -C12 ), 10%; light distillate oil (C12 – C 2 0), 15%; heavy distillate oil (C20 C4 0), 25% residium oil ( >C40), 20%,
By molecular type -
Paraffins (alkanes), 30%; naphthenes (cycloalkanes), 50% aromatics, 15% nitrogen, sulphur and oxygen containing compounds (NSO) 5%.
4. Behaviour of oil spill in marine environment –
(a) Spreading - Spreading of crude oil on water is probably the most important process following a spill. Apart from chemical nature of oil, the extent of spreading is affected by wind, waves and currents. Under the influence of hydrostatic and surface forces, the oil spreads quickly attaining average thickness of less than 0.03 mm within 24 h. Once a spill has thinned to the point that surface forces begin to play an important role, the oil layer is no longer continuous and uniform but becomes fragmented by wind and waves into islands where thicker layers of oil are in equilibrium with thinner films rich in surface active compounds.
(b) Evaporation - Evaporation and dissolution are the major processes degrading petroleum crude when spilled on water. The composition of oil, its surface area and physical properties, wind velocity, air and sea temperatures, turbulence and intensity of solar radiation, all affect evaporation rates of hydrocarbons. Evaporation alone will remove about 50% of hydrocarbons in an “average” crude oil on the ocean’s surface. Loss of volatile hydrocarbons increases the density and the kinematic viscosity of oil. As more volatile hydrocarbons are lost, the viscosity of the resulting oil increases and this results in breakup of slick into smaller patches. Agitation of these patches enhances incorporation of water due to increased surface area.
(c) Photo-oxidation - The natural sunlight in the presence of oxygen can transform several petroleum hydrocarbons into hydroxy compounds such as aldehydes and ketones and ultimately to low molecular weight carboxylic acids, As the products are hydrophilic, they change the solubility behaviour of the spill.
(d) Dispersion – Dispersion is οil-in-water emulsion resulting from the incorporation of small globules of oil into water column. Oil begins dispersing immediately on contact with water and is most significant during the first ten hours or so.
(e) Dissolution - Dissolution is another physical process in which the low molecular weight hydrocarbons as well as polar non-hydrocarbon compounds are partially lost from the oil to the water column.
(f) Degradation – Bio-degradative processes influencing fate of petroleum in aquatic environment include microbial degradation, ingestion by zooplankton, uptake by aquatic invertebrates and vertebrates as well as bio-turbation. Microorganisms capable of oxidising petroleum hydrocarbons and related compounds are widespread in nature. The rate of microbial degradation varies with the chemical complexity of the crude, the microbial populations and many of the environmental conditions.
5. Effects of petroleum crude on marine bio-system – Spilled oil poses serious threats to fresh water and marine environments, affecting surface resources and a wide range of subsurface organisms that are linked in a complex food chain that includes human food resources. Spilled oil can harm the environment in several ways, including the physical damages that directly impact wildlife and their habitats (such as coating birds or mammals with a layer of oil), and the toxicity of the oil itself, which can poison exposed organisms. The severity of an oil spill’s impact depends on a variety of factors, including the physical properties of the oil, whether petroleum-based oils or non petroleum-based oils, and the natural actions of the receiving waters on the oil.
The biological effects of oil include:
(a) Hazards to man through eating contaminated seafoods,
(b) Decrease of fisheries resources or damage to wild life such as sea birds and marine mammals,
(c) Decrease of aesthetic values due to unsighty slicks or oiled beaches,
(d) Modification of marine ecosystems by elimination of species with an initial decrease in diversity and productivity and
(e) Modification of habitats, delaying or preventing re-colonization.
When an oil spill occurs, many factors determine whether the spill will cause heavy, long lasting biological damage, comparatively little or no damage or some intermediate degree of damage. Thus for instance, if a spill occurs in a small confined area so that the oil is unable to escape, damage will be greater for a given volume and type of oil spilled than if the same volume was released in a relatively open area.
In the open sea the possible impact on biota can be on phytoplankton, zooplankton, benthos, fishery, birds, mammals, etc. whereas in coastal waters the impacts will also be on inter-tidal fauna, aquaculture, seaweeds and mangroves.
6. Combating measures -
(a) Combating at sea – Response techniques when the oil is still in the water and has not yet reached the shoreline.
(b) Combating on land – Response techniques when the oil is very close to the shoreline or has already stranded.
(c) Prevention at sea – Measures that can be taken to make extraction and transportation of oil at sea safer.
(d) Prevention on land – Measures that can be taken to avoid oils from being discharged from land-based sources into the marine environment.
7. Oil Spill Control – Oil spills can occur when there is a problem with an oil well, when a pipeline ruptures or leaks or when there is a transportation accident. Since conditions are different with each spill, different methods of spill control may be used.
(a) Some of the tools used to control oil in a spill include ‘booms’, which are floating barriers used to clean oil from the surface of water and to prevent slicks from spreading. A boom can be placed around the tanker that is spilling oil. Booms collect the oil off the water. A boom may be placed somewhere before an oil spill. They can also be placed around an entrance to the ocean, like a stream. They also can be placed around a habitat with many animals living there. These booms absorb any oil that flows around it.
The workers can also use skimmers. Skimmers are boats that can remove the oil off the water. Skimmers which use pumps or vacuums to remove oil as it float on water.
Sorbents are sponges that can collect the oil. Sorbents absorb oil when they are placed in a spill area.
(b) Sometimes chemicals called dispersants are used to break down oil and move it from the top of the water. An airplane can be used to fly over the water dropping chemicals into the ocean. The chemicals can break down the oil into the ocean. Moving the oil in this way keeps it from animals that live at the surface of the water and allows it to eventually be consumed by bacteria.
(c) A process called bioremediation may be used to accelerate the process of biodegradation of the oil after a spill. In this process, bacteria or other microbes are introduced to the environment to help oxidize the oil. Unfortunately, this process can work slowly and is not very useful for large spills.
(d) Occasionally the slick caused by a spill is removed through a controlled burn. Workers can burn freshly spilled oil with fireproof booms to contain the oil. Burning, only works under certain wind and weather conditions. Burning is the last option to decide, as this method causes air pollution.
(e) Oil spill control on land is often conducted manually. Scooping, cleansing and scraping of the rocks and sand is performed until the oil has been removed. people can use high or low pressure hoses to spray the oil that is on the beaches. Vacuum trucks may be driven on the beaches to vacuum up the oil. They can also simply use shovels or road equipment to collect all the oil off the beaches.
8. Effects of Oil spills – Oil spills have affected many people and many industries. They affect both the economy and the environment. Some of the things affected are: (a) Marine life, (b) Local industries (often tourist industry), (c) Fishing industry.
(a) Marine life – The adverse effects of oil spills on the marine environment are well known. If spilled oil escapes the booms and skimmers reaching the shore, it contaminates the inter-tidal zone and the beaches.
Drifting oil contaminates the feathers of seabirds and the fur of seals. In the birds, it clogs and destroys the insulating and waterproofing properties of the feathers. As the bird tries to maintain its body temperature, it will exhaust its fat reserves and become weakened. It is almost impossible to replace these reserves because, in its weakened condition, whenever it flies the bird has to carry as mush as 20% extra body-weight in sodden feathers. Also, ingestion of oil during preening interferes with salt-excretion and may also have toxic side effects. Even a small amount of oiling can have lethal effects. As well, oil transferred to the surface of its eggs during incubation reduces their hatchability. The most vulnerable species are diving birds.
The various types of freshwater and marine habitats that exist in nature have different sensitivities to the harmful effects of oil contamination, as well as different abilities to recuperate. Although some organisms may be seriously injured or killed very soon after contact with the oil in a spill, other effects are more subtle and often longer lasting. In addition, oil potentially can have catastrophic effects on birds and mammals.
(b) Local industries – Oil, dead fish and birds all get washed up on the shores and the oil slick interferes in activities such as fishing, sailing, swimming etc. The local tourist industry suffers as aesthetic beauty of sea shore is lost due to oil slick. Industries that rely on clean seawater for routine operations can also suffer because operations have to be stopped while the water is cleaned.
(c) Fishing industry – The fishing industry suffers badly when an oil spill occurs. Firstly because the fish are often covered in oil, or have swallowed oil making them poisonous. Also a large number of fish die, decreasing the number of fish that could have possibly been caught.
9. Biotechnology in treating petroleum sludge and oil spills – Oil sludge, normally discharged into the sea from petroleum refineries, contains toxic compounds that are a major threat to the marine ecology. All forms of aquatic life are adversely affected, and contaminated fish, when eaten by humans, present a serious health hazard.
Biotechnology, however, has shown that particular species of bacteria and fungi, normally found in soil, can protect the marine environment by breaking down various types of hydrocarbons, the main component of petroleum. To be effective in cleaning up marine oil spills, however, micro-organisms must be able to withstand the marine environment _ for example they need to survive in high salt concentrations and to grow at low temperatures.
It may be necessary to use some of the techniques of modern biotechnology to introduce these characteristics into the appropriate oil-eating micro-organisms.
Following points to be noted in relation to oil spills:
* Oil spills can be extremely harmful to the environment and need to be cleaned up in efficient, cheap ways.
* Certain marine microorganisms can break down complex hydrocarbons for energy, and in the process can clean up spilled oil in a natural manner.
* These bacteria are structure specific, making it hard for one microorganism to clean up a mix of oil.
* A genetically modified organism that can break down multiple compounds could be used to clean spills very efficiently.
* A bacterium like Alcanivorax borkumensis could provide the base for such an organism.
* This GMO could be created by inserting the gene that codes for different hydrocarbon breakdown into Alcanivorax through a plasmid and then tested for efficiency.
[For more refer Oil Spills and Marine Biotechnology]
10. Conclusion – Accidental or deliberate, operational discharges and spills of oil from ships, especially tankers, offshore platforms and pipelines, is the most obvious and visible cause of oil pollution of the marine environment. Various natural physical, chemical and biological degradation processes are the cause of oil spills into marine environment.
The impact of oil spills can be far-reaching, from an environmental as well as a socio-economic perspective. Marine and coastal habitats, wildlife species, recreational activities, local industry, and fisheries, are among the resources and sectors that can be negatively affected by oil spills. It affects seabirds, marine mammals, fish and shellfish, and bottom-living animals. It destroys beaches, destroys aquaculture, fisheries and deteriorates health effects from cleanup operations.
11. Some of the major global marine oil spills -
(a) Argo Merchant - On December 15, 1976, the Argo Merchant ran aground on Fishing Rip (Nantucket Shoals), 29 nautical miles southeast of Nantucket Island, Massachusetts in high winds and ten foot seas. Later, the vessel broke apart and spilled its entire cargo of 7.7 million gallons of fuel oil.
(b) Amoco Cadiz - The Amoco Cadiz encountered stormy weather and ran aground off the coast of Brittany, France on March 16, 1978. Its entire cargo of 68.7 million gallons of oil spilled into the sea.
(c) Burmah Agate – On November 1, 1979, the Burmah Agate collided with the freighter Mimosa southeast of Galveston Entrance in the Gulf of Mexico, resulting explosion and a fire that affected an estimated 2.6 million gallons of oil to release into the environment, and another 7.8 million gallons to consume by the fire.
(d) Ixtoc I - The 2-mile-deep exploratory well, Ixtoc I, blew out on June 3, 1979 in the Bay of Campeche off Ciudad del Carmen, Mexico. By the time the well was brought under control in March, 1980, an estimated 140 million gallons of oil had spilled into the bay.
(e) Exxon Valdez - On March 24, 1989, the Exxon Valdez ran aground on Bligh Reef in Prince William Sound, Alaska. It spilled 10.8 million gallons of oil into the marine environment, and impacted more than 1,100 miles of non-continuous Alaskan coastline. This was the largest oil spill in the U.S. history.
(f) Barge Cibro Savannah – On March 6, 1990, the Cibro Savannah exploded and caught fire while departing the pier at the Citgo facility in Linden, New Jersey. About 127,000 gallons of oil remained unaccounted for after the incident.
(g) Megaborg - The Megaborg released 5.1 million gallons of oil as the result of a lightering accident and subsequent fire. The incident occurred 60 nautical miles south-southeast of Galveston, Texas on June 8, 1990.
(h) Jupiter - On September 16, 1990, the tank vessel Jupiter was offloading gasoline at a refinery on the Saginaw River near Bay City, Michigan, when a fire started on board and the vessel exploded.
(i) Arabian Gulf Spills – In January of the 1991 Gulf War, the Iraqi Army destroyed tankers, oil terminals, and oil wells in Kuwait, causing the release of about 900,000,000 barrels of oil. This was the largest oil spill in history.
(j) Barge Bouchard 155 – On August 10, 1993, three ships collided in Tampa Bay, Florida: the barge Bouchard 155, the freighter Balsa 37, and the barge Ocean 255. The Bouchard 155 spilled an estimated 336,000 gallons of fuel oil into Tampa Bay.
(k) Prestige - On 13th November 2002, the tanker PRESTIGE (81,564 DWT), carrying a cargo of 77,000 tonnes of heavy fuel oil, suffered hull damage in heavy seas off northern Spain. In all, it is estimated that some 63,000 tonnes were lost from the PRESTIGE.
(l) BP oil spill in the Gulf of Mexico is the world’s largest oil spill. The spill has caused extensive damage to marine and wildlife habitats, and the fishing and tourism industries.
The Deepwater Horizon, owned by Transocean and leased to BP, caught fire April 20, 2010, after an explosion and sank. The rig, with a platform bigger than a football field was one of the most modern and was drilling in 5,000 feet of water.
The massive oil spill that threatened to eclipse even the Exxon Valdez disaster spread out of control, washing ashore along the Gulf Coast. It is of grave concern.
Unique feats of engineering will be necessary to cut off the gusher more than a mile beneath the surface of the ocean and experts are warning that its success is far from certain.
In fact, oil Spill in the Gulf of Mexico just keeps getting worse and worse. The slick is getting bigger every day. The environmental havoc from this oil spill is just beginning. It threatens destruction to wetlands and sea life as well as the livelihoods of fishermen and the health of clean-up workers. Apart, dead turtles are seen washed ashore as well. In other words, a colossal damage has already been caused to wildlife and animals.