Commercial detergents have largely replaced soaps because they are more effective cleaning agents...
Detergents can be tailored to particular applications such as washing hair, dishes and clothes. Unlike soaps, detergents do not form scum when used with 'hard' water.
The basic component of a synthetic detergent is a 'surface active agent' ('surfactant') which binds to grease and dirt and keeps it suspended in water. Other constituents include fillers to improve the free-flowing properties of powder detergents, foam stabilisers, optical brighteners, silicates, bleaches and fragrances. Phosphates or zeolites are added to control the alkalinity and soften the water. Foam stabilisers, optical brighteners and fragrances are not essential for detergent effectiveness. The formulation of the detergent depends on the application.
Laundry detergents usually contain surfactants to allow the water to penetrate the material, phosphates or zeolites, silicates to inhibit corrosion of washing machines, bleaches such as sodium perborate and sodium percarborate, fillers and optical brighteners. Some also contain enzymes (see Glossary) which help to make the dirt more soluble.
Dishwashing machine detergents consist almost entirely of phosphates and silicates and can be so alkaline that they may corrode some glazes, plastics, glassware and aluminium cookware. They may contain chlorine to act as a disinfectant and to remove stains (such as tannin stains caused by tea).
All synthetic detergents should be kept away from children. While most are relatively harmless to skin, some, especially dishwashing machine detergents, are extremely dangerous if swallowed or splashed into the eyes. Dishwashing machine detergents must be stored in childproof containers and the user should check that no detergent residue remains in the detergent dispenser after use. A number of children have had to be hospitalised after eating detergent residue from a machine. Some detergents smell and look appealing, so keep them away from children. Some people with sensitive skin may show an adverse reaction to the enzyme, the surfactants or other components of laundry detergents.
The Australian Standard for the biodegradability of detergents only requires 80 per cent of the product to decompose in seven to 21 days and does not consider the amount of time for the other 20 per cent to break down, nor what it degrades into. Compared to soaps, detergents are potentially more harmful to waterways because they break down more slowly or not at all. Phosphate detergents, when discharged into freshwater streams or lakes, promote the growth of algae which rot and reduce the available oxygen. In extreme cases no living things except putrefying bacteria can survive in the water. Zeolite detergents do not have this effect, so use of them is preferable. Manufacturers label washing powders containing less than five per cent phosphate 'P', while those containing less than 0.5 per cent are labelled 'NP'. Optical brighteners are not readily biodegradable.
Phosphate-free, biodegradable detergents with reduced fragrance are increasingly available (see Zeolites). Often pure soap will suffice for the laundry if its effectiveness is enhanced by using it with a water softener such as borax or washing soda.