Reporting Ship Sourced Pollution
Educational resources and information
- Kids
- Teachers
- Classroom Projects
- Protect Our Seas Educational Kit
- The Effects of Oil on Wildlife
- What Happens To Spilled Oil
- Oil Spill Information and Educational Material
- Pollution Fact Sheets
Prevention of Pollution from Ships
National Maritime Emergency Response Arrangements
AMSAs Role in Maritime Environmental Issues
Register of Local Fuel Oil Suppliers
What Happens to Spilled Oil?
(courtesy Minister of Supply and Services Canada 1994)
When oil enters the sea, many physical, chemical and biological processes act on the oil. Many changes happen at once - the slick moves and spreads and environmental processes alter its character. Some of the processes are most important immediately after the spill and other processes become increasingly important as time goes on.
Spreading
Oil is lighter than water, so it floats on the surface as a slick. The slick (or spill) spreads over the surface of the water due to the force of gravity. Spreading decreases steadily as time passes.
Dissolution
Occurs when the water-soluble components of oil break down into the large volume of water surrounding the spill. Only a very small percentage of oil dissolves.
Sedimentation
The force of gravity will cause some of the oil to travel through the water and settle on the bottom.
Movement
An oil spill will move in the same direction and at a similar speed as the water. It is moved by currents, tide and wind.
Biodegradation
Many species of marine micro-organisms or bacteria, fungi and yeasts feed on the compounds that make up oil. Hydrocarbons (oil) consumed by these micro-organisms can be partially metabolized or completely metabolized to carbon dioxide and water. The rate of biodegradation depends on the temperature of the oil and water mixture.
Evaporation
Causes some of the oil to transfer to the atmosphere. Lighter hydrocarbons evaporate more rapidly than heavy components.
Weathering
Is a progressive series of changes in oil characteristics caused by physical, chemical and biological processes. The rate of weathering is highly dependent on the type of oil spilled - the lighter it is, the faster it is likely to weather.
Dispersion
The spilled oil is spread into the upper layers of the water column by natural wave action.
Oxidation
The chemical combination of hydrocarbons with oxygen is known as oxidation. Oxidation is slow compared with other weathering processes.
Emulsification
Is the combination of two liquids - one suspended in the other. In the case of oil, the emulsion can be either oil-in-water or water in oil. Milk is an oil-in-water emulsion; butter is a water-in-oil emulsion. Both types of emulsification require wave action and occur only for specific oil compositions. Water-in-oil emulsions are extremely stable and may persist for months or years after a spill. Water-in-oil emulsions containing 50 to 80 per cent water are most common, and have a reddish-brown colour and grease like consistency. They are some times called 'chocolate mousse' because of their pudding-like appearance.