Question: Why do we use detergents to clear oil spillages on beaches? What are the advantages and disadvantages of their usage? 

Answer:  Here is a suggested answer:

Firstly, even a small amount of oil will form a monolayer of molecules on the surface of water. This monolayer can be seen as a sheen. This is what often occurs in oil spills, making a slick on the surface of the water that is difficult to remove. In spills, the oil is heavy and this forms a coating on any animals that pass through it. The oil then often kills them because it restricts their movements and inhibits their oxygen-exchange processes. The toxins are also absorbed through the animals' skins.

A detergent is a surface-acting cleansing agent. Common detergents are made from fats, which are hydrocarbons, and sulphuric acid, and have a long chain molecular structure. The hydrocarbon tails (soluble in oil or grease) penetrate the oil, while the heads (soluble in water, but insoluble in grease) remain in the water. Because these are salts they become ionised and the oil drops become negatively charged and tend to repel one another. The detergent has a disruptive effect and can break up a slick into individual patches. By acting as an emulsifier, the detergent disperses the oil droplets so they are more thinly spread and hence reduces the effect of a large spillage.

The advantages of using detergents are they quickly clear the main source of damage to wild life i.e. the presence and high toxicity of the thick oil on the surface of the water and beaches. Detergents can also be used in cleaning oil from animals who have come into contact with the oil.

The disadvantages are that unlike soap, detergents are neither soluble nor biodegradable. Once put into water, they tend to remain there, resisting breakdown. Some detergents are considered to be 'environmentally friendly' as they do not contain phosphates or bleaches. However, there is some evidence from Italy that suggests these themselves are pollutants. Furthermore, animals which have been rescued, coated with oil, are subject to risk as care has to be taken that too much of their natural body oil is not removed, otherwise they will drown or suffer from hypothermia.

Some concern has been expressed about the residue of the detergent leading to damage to creatures that inhabit the sea bed, but as the sea has a diluting effect, this damage has not been excessive.

In summary, detergent is not an ideal solution, but is useful in oil disasters. However, we must not lose sight of the fact that it is the oil itself which is the greatest threat.

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