 |
| Oil spill |
Oil is a critical resource for the world. Millions of barrels of oil are shipped from where the oil is taken from the Earth to where it is processed (refined) into substances varying from fuel to plastics.
Because the world’s demand for crude oil is great, oil must be shipped in large quantities by oceanic tankers, barges on inland waters, and pipelines that run over the land and under the sea. When there is a mistake or accident that causes oil to spill from any of these means of transport, damage to the water, beaches, and economy can be devastating.
Oil (also known as petroleum) is a naturally occurring thick liquid mixture of the elements hydrogen and carbon combined to form chemicals known as hydrocarbons. The oil taken from the ground (or seafloor) is called crude oil.
    |
Crude oil is then pumped or shipped to plants (refineries) where the crude oil is converted into fuels such as gasoline and home heating oil, or turned into chemicals that are used in hundreds of other products such as plastic.
In addition to accidental spills, oil can also be spilled during routine processes of cleaning ships and pipelines as well as when loading and unloading ships.
Evidence is mounting that the combined effects of these small spills in ports or local waters can cause substantial damage over time. More spectacular and damaging, however, are the sudden spills associated with the sinking or damage to an oil tanker or oil drilling platform at sea.
Oil pollution of waters
The total spillage of petroleum into the oceans through human activities is estimated to range from one million tons to two million tons of oil every year.
Although this is less than about one-thousandth of the amount of oil shipped every year (0.1%), the effects can be very damaging if the concentration of oil (for example, the amount of oil in a liter or gallon of water) in a small area becomes too large.
The most damaging oil spills arise from disabled ocean tankers or drilling platforms, from barges or ships on inland waters, or from blowouts of wells or damaged pipelines. Damage is also caused by the relatively frequent spills and discharges from refineries.
Large quantities of oil are also spilled when tankers clean out the petroleum residues from their huge storage compartment, sometimes dumping the oil and water mixture directly into the ocean.
After the spill
 |
| After the spill |
After oil is spilled into the environment, it spreads out or sinks (dissipates) in a number of ways. Spreading refers to the process by which spilled petroleum moves and disperses itself over the surface of water.
The resulting slick can then be transported away from the initial site of the spill by currents and winds. The rate and degree of spreading are affected by the thickness (viscosity) of the oil, wind speed, and waves.
If a spill is near enough to land, a mixture of oil and water called a mousse can wash up on the shore. The mousse combines with sand on the shore to form sticky patties that can harden into asphalt like lumps (material similar to that used to make roads).
At sea, the mousse eventually forms tar balls and in the vicinity of frequently traveled tanker routes world-wide, tar balls can be commonly found floating offshore and on beaches.
Ecological damages of oil spills
Even small oil spills can cause important change in ecologically sensitive environments. For example, a small discharge of oily bilge (wastewater) washings from the tanker Stylis during a routine cleaning of its petroleum-storage compartments caused the deaths of about 30,000 seabirds, because the oil was spilled in a place where the birds were abundant.
Studies made after large oceanic spills have shown that the ecological damage can be severe. After the Torrey Canyon spill in 1967, hundreds of miles of the coasts of southern England and the Brittany region of France were polluted by oily mousse.
The oil pollution caused severe ecological damage and many different life forms suffered from exposure to petroleum. The ecological damages were made much worse by some of the cleanup methods, because of the highly toxic detergents and dispersants that were used.
 |
| Ecological damages |
The effects of oil spills can be harmful both immediately and over time. For example, the Torrey Canyon spill caused the deaths of at least 30,000 birds, but it also resulted in a large population of surviving birds that experienced difficulty in laying eggs for many years after the spill.
The damage caused by detergents and dispersants (chemicals used to break up spills) during the cleanup of shorelines polluted by the Torrey Canyon spill provided an important lesson. Subsequent cleanups of oil spills involved the use of less toxic chemicals.
In 1978, the Amoco Cadiz was wrecked in the same general area as the Torrey Canyon. Considerable ecological damage was also caused by this accident. However, the damage was less intense than that caused by the Torrey Canyon because less-toxic detergents and dispersants were used during the cleanup.
