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In Depth

Environment

Ships, spills and slicks

Last Updated August 22, 2007

Prestige
On Wednesday, Nov. 13, 2002, a furious ocean storm caught the tanker Prestige off the coast of Spain. Within a week, the Greek-owned ship had broken in half, sending its cargo of 77,000 metric tonnes of fuel oil to the briny deep, but not before enough sludge had washed ashore to seriously threaten sea birds and aquatic life.

Another tanker disaster, another assault on the environment. There are some 14,000 reported oil spills a year around the world. Many are small, easily contained and cleaned up. Others are much bigger - some very big indeed.

The Prestige disaster ranks up there with the worst of them. If its entire cargo washed ashore, environmentalists say it would be a worse disaster than the infamous spill of the Exxon Valdez in 1989, off the coast of Alaska, when 38,800 tonnes of crude oil spilled into Prince William Sound.

The Prestige carried fuel oil, which actually is more dangerous to the environment than unrefined crude. It is heavier, more toxic and more difficult to clean up than crude. Initially, Spanish government officials said most of the oil would freeze inside the sunken tanker and wouldn't leak. Later, though, the government announced that more than 80 per cent of oil — about 63,000 tonnes — had leaked out.

Worth noting:
  • The Prestige, a Greek-owned, Bahamian-flagged tanker, was bound from Latvia to Singapore.
  • By international law, tankers are the responsibility of the state that registers them, known as the "flag state." Thus, the Prestige is the responsibility of the Bahamas.
  • The Prestige was built in Japan, one of the leading shipbuilding nations in the world.
  • The Prestige was 26 years old when it sank. It was also a single-hulled tanker.
Interesting to note that since 2005, under European Union rules, tankers more than 25 years old are no longer allowed to trade with Europe. Also, the International Maritime Organization (IMO) has decided that single-hulled oil tankers must be eliminated or fitted with a double-lined hull by 2015.

Polluters responsible for clean-up

In Canada, the law makes polluters responsible for the cleanup of oil spilled in Canadian waters. They pay for cleanup and for any resulting losses from environmental damage.

Oil companies and ships operating in Canadian waters are required to set up an agreement with a certified, Canadian-based, private-sector response organization that will help them in the event of a spill.

The science of cleaning up oil

No two crude oils are exactly alike, and that plays an important part in how to clean up a slick. The different physical and chemical properties of crude and refined oils influence the physical and biological effects of an oil spill, the behaviour of a slick and the effectiveness of cleanup operations.

But the type of oil spilled isn't the only thing that affects cleanup.

Local environmental conditions like weather, tides and currents, wind speed and direction, the difference between air and sea temperature, and the presence of ice floes, affect the behaviour of spilled oil as well as the ability of crews to work on a spill.

Crews control the movement of an oil slick by containing or diverting the oil.

Floating booms are mechanical barriers that extend above and below the surface of the water to stop the flow of oil. They can be used in three ways:
  • To surround a slick completely and reduce its spread.
  • To protect harbour entrances or biologically sensitive areas.
  • To divert oil to an area where it can be recovered.
How effective a boom is depends on the wind and waves at the site.

Sorbent booms and barriers are used to absorb a moving oil slick. They only work well when a slick is thin, because once their surfaces are saturated, they can't absorb anymore.

Once oil is contained by the booms, it has to be removed from the water.

Skimmers are used to remove oil from water without changing the chemical or physical properties of the oil. How well a skimmer works depends on the type of oil spilled, the thickness of the slick and, again, the weather.

Sorbents recover oil either through absorption (the oil is drawn into porous materials) or adsorption (the oil sticks to the surface of the sorbents). They're used in the final mopping up because they get at trace amounts of oil left after skimming and can be sent into areas where skimmers can't reach.

Sorbents come in two basic types: natural organic materials like peat moss and sawdust; and synthetic sorbents like polypropylene, polyester foam, polystyrene and polyurethane. Both types are usually applied by hand, and recovered with nets, rakes, forks and pike poles.

Manual recovery of oil with buckets and shovels is common, especially when the oil has made it close to shore. Viscous oils are more easily removed by manual methods than more fluid oils.

When oil makes it to land

Cleaning up a shoreline can be very difficult and time-consuming. Usually it's a hands-on task with many people using rakes, shovels, wheelbarrows and garbage bags to do the job. Hoses are used to attempt to wash off the oil, and sorbent materials are put down to soak up oily residues.

Though these methods can be effective, some experts believe much of the biological damage observed on Alaskan beaches after the Exxon Valdez spill was caused by cleanup activities.

Sometimes chemical cleanup agents are used – but they're not allowed in fresh water or near sensitive areas. High-pressure water hoses wash oil from coarse sediments, rocks and man-made structures. Low-pressure water flushing is used to remove oil from fine sediments, shores with vegetation and marshes.

Sometimes, such as when a beach is hit by a slick, the environment is so contaminated that sand, dirt and plant material are simply removed.

Cleaning wildlife is a lot of work, expensive, and usually ineffective. Even if an oil spill is small, it can have a dramatic impact on bird and animal populations.

Not only does the oil coat the outside of the organisms affected, they often ingest it in water and on their food – effectively poisoning themselves.

Where the oil goes

After the oil is recovered, it's separated from the water, and the oil is disposed of, along with any remaining cleanup materials and other debris.

The disposal of oil and debris is regulated by local, provincial and federal governments. Relatively fresh oil may be re-refined. In other cases the recovered oil is burned.

Sometimes cleanup crews can't get to a slick because the weather is too bad. In these cases, waves recirculate the oil in the water, and natural processes eventually break the oil down.

Chemicals can also be used to disperse the oil. This helps some bird species because it removes the oil from the surface, however underwater creatures are hit instead.

Sometimes the oil is burned off the water. It must first be contained to make it thick enough, and then set alight. Studies have shown the resulting smoke plume is an acceptable trade-off under some circumstances.

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