Biodegradation
Biodegradation is the process by which organic chemicals (ie.materials containing carbon) are broken down into simpler chemical units by the natural action of living micro-organisms. A chemical which can be broken down in this way is called "biodegradable".
In detergents, though other organic ingredients such as enzymes may also be biodegradable, the term is most often applied to the surface active agents - surfactants - contained in the product.
When detergents first came into general use in the 1950s there were problems of foaming on rivers. In this first generation of "synthetic" detergent washing powders, branched chain alkyl benzene sulphonate (ABS) was extensively used as the surfactant. The replacement of ABS by LAS,straight chain Linear Alkyl Benzene Sulphonate which was more easily biodegraded, solved the problem.
The move to using biodegradable surfactants came in the early 1960s and was, in the UK, a voluntary action by the industry. The first legal requirements were not laid down until 1973 when an EC directive was issued on surfactant biodegradability. This was implemented in the UK by the Detergent Composition Regulations 1978.
The biodegradability of the surfactants in UK products has therefore been a feature of the UK marketplace for so many years that most companies had regarded a statement about it as unnecessary. In these days of growing consumer awareness of green issues however, "biodegradable" is a word often used as an indication of a product's environmental friendliness.
It is though, only one aspect of the environmental profile of a product. For example, even though it is an important factor influencing the fate of the components of products after their disposal to the environment, other processes such as photodegradation, chemical degradation and absorption may also have an influence.
Biodegradation of detergents starts as soon as the dirty laundry water is washed down the drain. Micro-organisms (or bacteria) thrive naturally in sewers, sewage treatment plants, waterways and soil.
These bacteria break down surfactants, using them as food for energy and growth. Since there are very large numbers of bacteria at the sewage treatment plants, biodegradation takes place there very rapidly and substantially complete biodegradation is usually achieved within a few hours.
The first steps in the biodegradation process will often produce an intermediate product or metabolite and this stage is referred to as Primary Biodegradation. Subsequent action by bacteria may then result in further decomposition of the metabolites to produce simple inorganic compounds such as carbon dioxide, water and mineral salts.
This complete breakdown of the compound is known as Ultimate Biodegradation.
Primary biodegradation of a surfactant usually results in the loss of environmentally undesirable properties such as foaming ability. It is therefore very important that this stage of biodegradation takes place rapidly if undesirable effects are to be avoided.
For this reason the European Directives on surfactant biodegradability specify that the primary biodegradation of anionic and nonionic surfactants ( ie. those which have a negative charge or none) must meet a minimum standard of biodegradation.
The primary biodegje achieved in the standard duration of the laboratory test.
What really matters is what happens in the real-life situation. In practice the biodegradability of the surfactants used in UK detergents comfortably exceeds the 80% pass level and removals of 95% are observed in efficient sewage treatment plants.
A 1995 UK pilot for a European monitoring study, measured how effectively detergent surfactants were removed by sewage treatment works. The results showed a removal rate of 99.9%.
Similar studies, carried out in Spain, Germany, Italy and the Netherlands, resulted in an average surfactant removal rate of 99.2% overall.
Any residual material or metabolites released to waterways before ultimate biodegradation is complete will continue to biodegrade.
Biodegradability and the Law
Experience with foaming problems caused by the use of the poorly biodegradable ABS led to legislation controlling their biodegradability in a number of countries. The EC has therefore harmonised this legislation and the biodegradability of surfactants in detergents is the subject of a number of Council Directives.
1973 Directive (73/404) stated that all surfactants used in detergents should have an average level of biodegradability of 90%. However, no methods for testing this were laid down
1973 The second Directive (73/405) was specifically concerned with anionic surfactants used in detergents and specified laboratory methods for testing their primary biodegradability with a minimum pass level of 80% in these tests. This ensures that in real life a level of 90% is achieved.
1982 The list of acceptable tests for biodegradability was modified
(Directive 82/243). Similar test methods and criteria for non-ionic surfactants were laid out.
As yet there are no European Directives dealing specifically with cationic or amphoteric surfactants.
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