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Courtesy of 
Photo courtesy of the Darwin Foundation |
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| Courtesy of
Photo courtesy of the Darwin Foundation |
Crude oil is made up of complex hydrocarbon compounds that range from light gasses to heavier tars and waxes. Oil is composed of thousands of compounds in varying quantities. No two crude oils are exactly alike because of the many different compositions.
The different physical and chemical properties of crude and refined oils are very important - they influence the physical and biological effects of an oil spill, the behaviour of a slick and the effectiveness of clean-up operations. Some oils are far more harmful to the environment and more toxic than others.
Oil spills are a problem in part because we never know when or where they will occur. Many factors affect the seriousness of a spill - the type and quantity of oil spilled; where oil is spilled (on land, near shore, in a river or lake, on the open sea); weather conditions; surrounding environment; etc. This is why prevention and preparedness are crucial.
An accidental spill is only one of several ways that oil ends up in Canadian waters. Naturally-occurring oil seeps, offshore oil and gas production, marine transportation, atmospheric fallout, waste discharges and runoff are other ways. In fact, the two major sources of oil input into the environment are municipal waste and routine tanker operations such as bilge washing.
Most accidental spills - at sea, in the Great Lakes and on land - are a combination of human error and circumstances. Weather can make navigation treacherous, heavy icing can disable a ship, equipment can fail, cold or hot weather can snap pipes, and offshore blowouts can occur at drilling sites.
Natural seeps have been discharging petroleum hydrocarbons into the marine environment for millions of years. About 200 natural underwater oil seeps have been identified around the world. In Canada, natural seepage has been observed off the coasts of Labrador as well as the north coast of Baffin Island in the Arctic.
Very. Local environmental conditions such as weather, tides and currents, wind speed and direction, the difference between air and sea temperature, and the presence of ice flows, affect the behaviour of spilled oil, as well as our ability to clean up spills quickly. Severe weather conditions can make navigation and routine manoeuvres difficult, and cause an oil spill.
Oil spills in fresh or inland waters, and especially in rivers, are more likely to contaminate shorelines. Fresh water is consumed by people, making it important to minimize contamination of drinking water sources.
When oil enters the sea, many physical, chemical and biological processes act on the oil. Many changes happen at once - the slick moves and spreads and environmental processes alter its character. Some of the processes are most important immediately after the spill; others become increasingly important as time goes on.
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Spreading Oil is lighter than water, so it floats on the surface as a slick. The slick spreads over the surface of the water due to the force of gravity. Spreading decreases steadily as time passes. |
Evaporation Evaporation causes some of the oil to transfer to the atmosphere. Lighter hydrocarbons evaporate more rapidly than heavy components. Evaporation is the most important part of weathering. |
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Dissolution Dissolution occurs when the water-soluble components of oil break down into the large volume of water surrounding the slick. Only a very small percentage of oil dissolves. |
Weathering Weathering is a progressive series of changes in oil characteristics caused by physical, chemical and biological processes. The rate of weathering is highly dependent on the type of oil spilled - the lighter it is, the faster it is likely to weather. |
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Sedimentation The force of gravity will cause some of the oil to travel through the water and settle on the bottom. |
Dispersion The spilled oil is spread into the upper layers of the water column by natural wave action. |
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Movement A slick will move in the same direction and at a similar speed as the water. It is moved by currents, tide and wind. |
Oxidation The chemical combination of hydrocarbons with oxygen is known as oxidation. Oxidation is slow compared with other weathering processes. |
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Bio-degradation Many species of marine bacteria, fungi and yeasts feed on the compounds that make up oil. Hydrocarbons consumed by these micro-organismscan be partially metabolized or completely metabolized to carbon dioxide and water. The rate of bio-degradation depends on the temperature of the oil and water mixture. |
Emulsification Emulsification is the combination of two liquids - one suspended in the other. In the case of oil, the emulsion can be either oil-in-water or water-in-oil. Milk is an oil-in-water emulsion; butter is a water-in-oil emulsion. Both types of emulsification require wave action and occur only for specific oil compositions. Water-in-oil emulsions are extremely stable and may persist for months or years after a spill. Water-in-oil emulsions containing 50 to 80 percent water are most common, and have a reddish-brown colour and grease-like consistency. They are sometimes called "chocolate mousse" because of their pudding-like appearance. |
The relationships among marine organisms, birds and mammals and their environments are complex. So are their reactions to spilled oil. Some forms of life experience subtle changes in behaviour while others cannot survive.
Birds
Oil kills birds in many ways. Oiled birds may die from loss of insulation, drowning or direct poisoning from oil, or the toxic effects can be passed on to their offspring. Even worse, oil on water can actually attract birds, increasing the risk.
Unfortunately, cleaning oiled birds assists only a small percentage of those involved in an oil spill. Survival rates for treated birds are relatively low, given the large investment of time, effort and resources.
Many species of birds on the Great Lakes, and along the Pacific and Atlantic coasts are very vulnerable to spills. They include oldsquaw, mergansers and other diving ducks, loons and grebes. Therefore, emphasis should be placed on preventing damage to birds by avoiding spills in critical wildlife areas, and scaring birds away when a spill has occurred.
Fish
Fish in their early life stages are sensitive to oil in the water column. Eggs may not hatch and young fish may die. Adult fish are mobile and generally avoid areas of heavy contamination. When oil is dissolved or dispersed, however, it may be taken up through their gills or eaten, and may accumulate in the liver, gall bladder and stomach. This may result in tainting of the flesh, making the fish unacceptable for consumption. Fish can break down small quantities of hydrocarbons, cleaning themselves of the contaminants completely within weeks of exposure.
Molluscs, worms and shrimp live on or in the bottom sediments near the shore. Many, including oysters, clams, crabs, scallops and lobsters, are commercially important. These creatures may suffer from direct smothering by oiling, the toxic effect of the lighter fractions of oil, or by eating oil-sediment particles. Many will naturally clean themselves when the source is removed if the oil concentration is low, but tainting is a serious risk, making these organisms unsaleable for a period of time.
While oil rarely kills fish outright, it can and does have long-term sublethal effects such as reduced reproduction and loss of stamina, and may affect both feeding and respiration. Chronic oil pollution in areas such as harbours and estuaries can have serious long-term effects on fish populations. Chronic pollution may also damage marine plants such as marsh grasses, causing feeding areas and cover for fish to disappear.
Because marine life is particularly vulnerable at certain stages in its life, e.g., in spawning season or when concentrated for feeding or migration, the timing of a spill can be critical in terms of the types of effects suffered.
Marine Mammals
The effects of oil on marine mammals vary. Marine mammals, such as northern fur seals, sea otters, newborn harp seals and steller sea lion pups, that rely on their fur for insulation are more sensitive to oil, since oiled fur is a poor insulator. They may ingest some of the oil while trying to clean their fur. By contrast, mammals such as whales, walruses, sea lions and most seals, that rely on fat for insulation are less affected by oil on the surface of their body. All exposed mammals are troubled by oil in and around their eyes and nostrils.
Marine Plants
Many marine plants, including kelp, marsh grass, mangroves and sea grasses, are also affected by oil spills. Plants that occupy the area between high and low tides are most at risk from spilled oil as they may be directly coated by oil stranded by a receding tide. Marine plants are able to recover once the oil has been removed or has degraded. These plant communities play a vital role in the habitat, and loss of plant cover can have a significant impact on other organisms in the ecosystem.
People Are Affected Too!
Oil spills affect many human activities. Harbours, marinas and tourist beaches are often closed. Fishing and hunting may be temporarily suspended, altering traditional lifestyles for Native people and resulting in lost income for commercial fisheries (especially fish farms), fishing guides and outfitters. Oil can coat boats and fishing gear and extensive cleaning may be required. If people fear that fish may be tainted, they will often stop buying fish, resulting in a loss of income for fishermen, fish plant workers and others. In freshwater environments, spills can create special problems, such as contaminated drinking water.
How Long Do The Problems Last?
Many factors affect how quickly an area will recover from an oil spill. Some environments are more sensitive than others. Recovery times vary from weeks for bedrock shorelines where there are high-energy waves, to months for exposed beaches, to several years or even decades for marshes and salt flats. Oil which becomes embedded in sediments may substantially reduce the productive capacity of fish habitats for years or decades.
Sensitive areas are always identified as priorities in oil spill response plans.
