|Posted on Sunday, September 17, 2000 - 03:35 pm: |
Oil on troubled waters
John Crace examines how tanker spills harm the environment, and what can be done to prevent them
Tuesday September 12, 2000
Oil spills from supertankers receive a lot of publicity and a single incident can have a significant, and in some cases catastrophic, impact on both the local environment and the local economy. But oil spills are responsible for only a small proportion of oil in the sea. According to the United Nations Environment Programme (Unep), of the millions of tonnes of oil discharged into the sea, ships release only about half and much of this is deliberately flushed into the sea as tankers clean their tanks. The rest of the oil comes from routine discharges from land-based industrial plant.
Oil has been proved to affect the reproduction and physiology of fish, shellfish and plankton. However, no two oil spills produce identical effects on the environment and recovery rates may vary from a matter of weeks to more than 10 years. The key factor determining how quickly the environment can recover is the type of oil and the quantities spilt. Oil is composed of hundreds of compounds, some of which are toxic and may cause cancer, and it can be broadly divided into light crudes, which disperse easily, and heavy crudes, which form thick slicks. Light crudes may disappear more quickly from the surface, but their toxicity may last longer. There is no clear correlation between the size of a spill and the extent of the damage. Other factors that influence the environmental impact are whether dispersants are used, whether the sea is rough, the temperature of the water, the presence of bacteria that can digest the oil, whether the shore line is rocky or sandy and the mix of species in the area of the spill.
The National Centre for Scientific Research in France has estimated that a shipping incident occurs every two to three days worldwide, and between 1992 and 1999 the UK Marine Accident Investigation Branch recorded 148 tanker accidents. Between 1992 and 1999, the top five foreign flags involved in tanker accidents were the Bahamas, Norway, Gibraltar, Liberia and Malta. The two worst incidents to affect the UK in the last decade have been the Braer in 1993, when 84,500 tonnes of light crude was spilt off the Shetland Islands and the Sea Empress in 1996, when 130,000 tonnes of Forties crude was spilt off the Pembrokeshire coast.
Environmental groups believe that all new tankers should be built to a minimum design/construction standard and that all existing ships should be updated to these standards as soon as possible. They also want action taken to improve ship maintenance and crew training and believe all vessels passing through narrow, busy, dangerous or environmentally sensitive areas should be subject to compulsory pilotage.
Oil spill online
The WWF and Dynamic Distance Learning will be running an online debate for school children on how an oil spill might affect a stretch of coastline. During this internet-based project, children will be able to debate the issues with their peers and discuss their views with experts from a variety of conservation, government and maritime agencies, as well as with schools from other countries. Schools or individuals wishing to take part in the debate, which will take place between November 6 and 17, should log on to www.wwflearning.co.uk to register.