The earlier chapter of this book make two important points about oil.
This means that there is a major international trade in oil.
Source: BP Statistical Review of World Energy, 1995
On average, more than 100,000,000 tonnes of crude oil are shipped every month - often in huge tankers, a few of which can hold as much as 500,000 tonnes.
With such traffic, there is always a risk of accidental oil spills, though the number of major spills (over 700 tonnes) has dropped significantly and is now less than one third of the figure for 1980.
Oil can enter the seas and oceans in many different ways. Tanker accidents make newspaper and television headlines but, in fact, oil spilt from tanker accidents is estimated by be 5% of all the oil which goes into the sea. The biggest input of petroleum hydrocarbons into the sea is from land sources.
For example, a considerable amount of oil enters the water cycle as a result of people disposing of used oil from vehicle engines onto the ground or down the drain. It then becomes a serious problem for the water company to deal with. Used oil should always be disposed of via a recycling scheme or correct disposal facilities.
Source: International Tanker Owners Pollution Federation
Source: United Nations Environment Programme Report No 50, 1993,
Impact of oil and related chemicals on the marine environment.
(Joint Gropu of Experts on the Scientific Aspects of Marine Pollution GESAMP).
The table and map give a brief summary of 20 major oil spills from tankers over the last 30 years, and their locations. Despite their large size, a number of these spills caused little or no lasting environmental damage because the oil did not reach coastlines. You may never even have heard of some of these names.
Write a short paragraph describing where these oil spills occurred. Explain any pattern you detect.
| Ship | Year | Location | Oil lost (tonnes) | |
| 1 | Atlantic Empress | 1979 | off Tobago, West Indies | 280,000 |
| 2 | ABT Summer | 1991 | 700 nautical miles off Angola | 260,000 |
| 3 | Castillo de Bellver | 1983 | off Saldanha Bay, South Africa | 257,000 |
| 4 | Amoco Cadiz | 1978 | off Brittany | 227,000 |
| 5 | Have | 1991 | Genoa, Italy | 140,000 |
| 6 | Odyseey | 1988 | 700 nautical miles off Nova Scotia | 132,000 |
| 7 | Torrey Canyon | 1967 | Scilly Isles | 119,000 |
| 8 | Urquiola | 1976 | La Coruna, Spain | 108,000 |
| 9 | Hawaiian Patriot | 1977 | 300 nautical miles off Honolulu | 99,000 |
| 10 | Independenta | 1979 | Bosphorus, Turkey | 93,000 |
| 11 | Braer | 1993 | Shetland Islands | 85,000 |
| 12 | Khark 5 | 1989 | 120 nautical miles off Atlantic coast of Morocco | 80,000 |
| 13 | Jakob Maersk | 1975 | Oporto, Portugal | 80,000 |
| 14 | Aegean Sea | 1992 | La Coruna, Spain | 72,000 |
| 15 | Katina P | 1992 | off Maputo, Mozambique | 72,000 |
| 16 | Nova | 1985 | The Gulf, 20 nautical miles off Iran | 70,000 |
| 17 | Wafra | 1971 | off Cape Agulhas, South Africa | 65,000 |
| 18 | Assimi | 1983 | 55 nautical miles off Muscat, Oman | 53,000 |
| 19 | Metula | 1974 | Magellan Straits, Chile | 53,000 |
| 20 | Exxon Valdez | 1989 | Prince William Sound, Alaska | 37,000 |
| Source: International Tanker Owners Pollution Federation | ||||
Oil is a natural substance. Under favourable conditions, if it is spilled at sea, oil can disperse and eventually degrade through natural processes.
However, crude oils and petroleum products are complex substances, and their different chemical compounds can react with sea life in a variety of ways. Some poison and kill plankton - the microscopic plants and animals on which many other sea creatures feed.
Some crude oils leave sticky residues as they weather which may either float on the surface until they reach the shore, smothering animals and seaweeds, or form solid balls of "tar".
A coating of thick oil can kill sea birds, either by poisoning them or by damaging the system which controls their body temperature.
On the other hand, the recovery potential of many marine species are such that the impacts of an oil spill are often short-lived.
Source: International Petroleum Industry Environmental Conservation Association
When spilled, some of the oil disappears from the surface of the sea (albeit into the environment) through processes such as evaporation and natural dispersion.
If oil is spilled far from land, or if it is a light oil which is likely to evaporate quickly, almost all will be dealt with by nature, and the most appropriate response might be to take no action other than monitoring the spill and reporting to the relevant authorities (while making sure that equipment and resources can immediately be made available, if required).
A number of "clean-up" techniques can be employed. These include:
In addition, a task force can work on shores in threatened areas to rescue and clean as much wildlife as possible and to clean beaches.
These methods may be hampered by bad weather or by the fact that oil spreads quickly and also absorbs large amounts of water to form an emulsion or mousse.
If oil is washed ashore on a hard sandy beach it can be quickly and effectively cleared by manpower helped by mechanical equipment like bulldozers and trucks.
Rocky shorelines are harder to clear and it may only be possible to remove oil which has accumulated on the surface. Muddy shores and salt marshes are very difficult to clean and are often badly damaged by attempting to clear oil manually or with mechanical equipment. They are often best left to recover naturally.
Several schemes have been set up to pay compensation in the event of a serious oil spill. Two of these are international conventions developed by the International Maritime Organisation. These arrangements only apply in countries which have formally agreed to accept them. There are also two voluntary schemes set up by the tanker and oil industries, and these arrangements can apply worldwide. These arrangements have been more than adequate to compensate the victims of tanker spills, with only a very few exceptions.
Oil is highly visible, but is by no means the only pollutant which affects our seas. Nor is it the most damaging or longest lasting.
An oil spill from a tanker is serious, but needs to be seen in perspective.
Oil spillages are most frequently in the news when tankers run aground or are in collisions.
In January 1993, an oil tanker taking 85,000 tonnes of light crude oil from Norway to Canada ran aground on rocks at the southern tip of the Shetland Isles. Gales and strong seas prevented other ships coming alongside to pump the oil off and, as the tanker broke up, the oil spilled into the sea.
The seas off the Shetlands support a huge variety of marine life including shellfish, sea birds, fish, seals and otters. Many parts of the coastline have been designated as Sites of Special Scientific Interest (SSSIs).
Commercial salmon farms along the coast were also at risk, as the oil pollution threatened this multi-million pound industry. In addition, it was feared that the strong winds blowing spray onshore could contaminate grazing land for sheep adjacent to the coast and, if inhaled, the spray could be a health risk to the people of Shetland, causing respiratory problems.
The fact that there were several hours between the Braer breaking down and the vessel hitting the rocks and breaking up allowed time for emergency plans to be put into operation. (Every part of the British Isles is covered by emergency plans drawn up by central government and local authorities.)
The marine, environmental and legal departments of the Shetland Islands council were all involved, as were representatives from national government (the Departments of Transport and Environment) and members of voluntary organisations.
The techniques listed on the previous page were considered to clean up the oil and prevent of limit the damage to beaches. However, the severe weather prevented most of these techniques being employed.
As an emergency measure, a fisheries exclusion zone of several hundred square miles was enforced, in which fishing was banned. Grazing sheep were moved from coastal pastures, and fish sales were banned from the salmon farms affected.
Fortunately, the pollution problems were not as disastrous as first feared. There was no detectable mortality of sea mammals due to "Braer" oil. Plants in some fields near the coast were contaminated, some Shetlanders reported throat and skin irritations. About 1,600 sea birds were found dead during the oil spill. The total bird mortality is likely to have been higher but represents a small proportion of the Shetland bird population.
The crude oil was of a "light" grade and the slick broke up and dispersed more quickly than would have occurred had it been a heavy grade oil. The key, however, was the weather. Strong storms, even by Shetland standards, raged for weeks during and afte the accident and helped to disperse the oil naturally.
An official report into the environmental impact of the "Braer" spill concluded:
"Overall, the impact of the oil spill on the environment and ecology of South Shetland has been minimal. Adverse impacts did occur but were both localised and limited. The resilience of ecosystems and species populations has already been powerfully demonstrated, and provides confidence and reassurance for the future."
Source: The Environmental Impact of the Wreck of the Braer, published by The Scottish Office, 1994.
In the case of the "Braer" environmental damage was largely limited by natural phenomena. In other locations, and under less favourable circumstance, the damage could only be limited through human intervention, which is not always successful.