Part 3: Spilling the facts!
Background information
What is petroleum?
Petroleum or crude oils are organic substances (organic substances are complex chemicals, all of which contain carbon atoms) made of different mixtures of hundreds of kinds of chemicals called hydrocarbons. Hydrocarbons consist of molecules of hydrogen, carbon and sometimes oxygen atoms in various proportions and arrangements.
In addition, crude oil contains inorganic substances: for example, sulphur, oxygen, nitrogen, nickel, chromium and iron.
Crude oils contain both light fractions or parts that are highly volatile (able to vapourise easily), and heavy fractions that are semi-solid like tar. Australian crude oils are light oils – they don’t contain much of the hydrocarbons used to make petrol.
What do we use petroleum for?
Crude oils are the basis of a huge range of industries on which our lifestyle has become increasingly dependent.
Plastics, paints and pesticides, medicines and pharmaceuticals, fertilisers and fuels are just a few. Nearly every non-metal product you see around you started off in oil. No wonder oil is important! The trouble is, it is non-renewable. It will run out one day.
Where do we get petroleum?
Petroleum occurs naturally in particular formations of sedimentary rocks in different parts of the world. It has to be transported from where it is produced to where it is needed. This may involve large distances over land or water – in pipes, land tankers and ocean tankers.
Accidents can happen
With developments in technology and engineering, the size of oil tankers has increased enormously. This is more efficient because large volumes of oil can be moved more easily, but when accidents occur the results can be more devastating. For example, the amount of oil spilled from the Exxon Valdez disaster in Alaska in 1989 was 11 million US gallons – enough oil to fill about 430 classrooms. To reduce the chance of oil leaking after an accident, new oil tankers now have to have double rather than single hulls. (See the diagram on the Oil spill images sheet.)
Accidents at sea are not the only way that oil ends up in the oceans. Other sources include:
Source / % of oil in the oceanCleaning of ships / 33%
Drainage into the sea from road run-off and industrial wastes / 37%
Absorption from the atmosphere / 9%
Exploration and offshore drilling / 2%
Natural seepage from cracks in the ocean floor and from erosion of sedimentary rocks / 7%
Big spills: natural disasters, mechanical failure, human error / 12%
(37million US gallons)
Unfortunately, there are some people or organisations who dump oil and wastes illegally.
What are the effects?
When oil is spilled at sea, chemical and physical changes or processes will normally cause it to break up over a period of time. These natural processes are referred to asweathering.
Sometimes the process is slowed down by rough seas, which cause tiny droplets of sea-water to be suspended in the oil, forming anemulsion– a liquid in another liquid, like a salad dressing. The emulsion is called a mousse because it looks like chocolate mousse!
The volume of the pollutant (the oil) is increased in volume three to four times because of being mixed with water. This process, referred to as emulsification, slows down the natural processes that would disperse the oil.
Some emulsions last for many months, but those with lighter oils disperse or break up more quickly. In calm conditions and higher temperatures the emulsion may separate into oil and water again
In the case of large spills or those close to the shore, it is not possible to wait for weathering of the oil to occur. The effects in the meantime could be disastrous.
Impact on marine life
The marine environment and shoreline habitatscan be affected by oil spills. How much effect the spill has depends on the kind of oil and the weather conditions at the time and following the spill. In open seas, large fish and whales can swim away from the spill, but closer to the shore the turtles, dolphins and seals are at risk, as they must come to the surface for air, and risk becoming trapped or covered by the oil spill.
Every level of the food chaincan be affected. Floating layers of oil (the slick) contaminate plankton (very small organisms drifting in the sea and providing a food source for other sea life), and can reduce the availability of light, oxygen and carbon dioxide to other marine organisms. In turn, the small fish that feed on the plankton can be contaminated as toxic (poisonous) substances taken in or absorbed by the plankton pass along the food chain.
Marine mammals and birdsmay be directly affected by the oil, either by ingesting (swallowing) it or by getting it on their fur or feathers, destroying their water repellent and insulating properties. Animals such as these are at risk of dying from the cold, or drowning.
Along rocky shores oil might smothermarine plantssuch as sea grass and kelp beds that provide food, shelter and nesting sites for many organisms. Shellfish and other organisms are affected too.
Damage control – response techniques
Once oil has spilled a decision has to be made about how to respond. What methods are available to deal with the problem?
1Natural processes
Evaporation: Light components of the oil will evaporate and the amount of evaporation depends on the proportion of volatile components in the oil. Little evaporation occurs from heavy oils. Evaporation can increase as the oil spreads because of the increase in surface area.
Oxidation: Oxygen reacts chemically with oil, breaking it down into soluble substances or into tars. Tarballs are often brought in by the waves along shorelines. Oxidation is sped up in sunlight, but it is a very slow process.
Biodegradation: Seawater contains bacteria that can partially or completely break down oil into simpler compounds that are soluble in water. In the presence of oxygen, the bacteria break down organic compounds to obtain energy and nutrients. Some kinds of oil are resistant to this. The level of nutrients in the water and the temperature of the water affect how well biodegradation works.
2Chemical methods
Dispersants are chemicals that are sprayed onto oil slicks by vessels at sea or from aeroplanes and helicopters to reduce the damage caused by floating oil. They are most effective if used within a few hours of the spill. They work by reducing the surface tension of the oil, causing it to form droplets that can disperse (spread) more easily. The droplets are then subject to natural processes such as waves and currents that help to break them down further.
Dispersants do not work well on thick oils. As dispersants are chemicals, there is also the problem of putting another pollutant in the marine environment. They have to be used under strict controls.
3Physical methods
Various mechanical or physical methods are available to keep the oil from spreading and reducing the possibility of it affecting shorelines. Booms, barriers and skimmers can be used to contain the oil in an enclosed area so that it can be removed or even diverted. Vacuum pumps can then extract the oil, or materials called sorbents can be used that soak up (absorb) the oil.
Booms (long floating barriers) tend to work well in gentle seas. They generally do not work effectively if waves are higher than a metre or currents are moving fast.
Skimmers, as the name suggests, skim the surface and are appropriate for cleaning up thin layers of oil (sheen).
On shores, shovels, bulldozers and other equipment can be used on sandy beaches. High-pressure hoses are used on rocky shores – people power too!
4Biological methods
Bioremediation:Research into adding specialist bacteria (called seeding) that degrade or break down oil has generated debate. What long-term effect would there be? What if they ‘escape’ and start attacking oil supplies eleswhere?
Another method being considered is to add fertiliser to the oil slick. The fertiliser would promote the increase in numbers of the naturally occurring micro-organisms.
Which method to use?
The kind of response technique, or combination of techniques, depends on a number of factors:
- the location of the spill
- the conditions at sea (wind, water currents)
- the type of oil
- the amount of oil.
What does it cost?
The most expensive oil spill in history was from the Exxon Valdez in 1989. Clean-up costs were about US$2.5 billion, and other costs, such as fines, penalties and claims, were estimated at US$7 billion. We don't yet know what clearing up the oil spill from the Prestige will cost.
1/5