|
Introduction |
|
Why be concerned? |
|
Supplier progress |
|
Potential impacts |
|
Functional groups |
|
Substance list |
|
Legislation / REACH |
|
FAQs |
|
Related Links |
|
Wash with care |
|
Environmental assessment of laundry detergents |
|
Biological degradation
|
|
The properties regarding biological degradability of a substance is of paramount importance determining the fate in the biological treatment plants used for treatment of industrial and municipal wastewater in most places in the world. If substances degrade readily in wastewater treatment plants, they will rarely have serious environmental effects. Sometimes though, the degradation products might have environmental effects different from the original substance. Slowly degradable substances might possess a risk as they tend to accumulate in the environment. The consequences may be understood only to a limited extent. Hence, it can be taken as a general recommendation to avoid use of organic synthesised substances that are slowly bio-degradable. For surfactants the primary degradation is of importance. Primary degradation means that the substance looses its original structure and properties—e.g. its surface activity. This means that the potentially negative effects in the treatment plants an in the water environment are reduced significantly. In a wider environmental perspective the complete degradation naturally is of importance. This distinction is used in the OECD-guidelines for testing of biodegradability which forms the basis also for the EU-classification system. The OECD system is briefly described below. Ready degradable substances The OECD Test Guidelines describe how to measure the bio-degradability of organic substances under not optimal conditions. The limit for ‘ready degradability’ is defined as a result where · more than 60% of the substance is mineralised within 28 days, measured by the generation of carbon dioxide (CO2) or the consumption of oxygen or · more than 70% of the substance is mineralised within 28 day measured as reduction of dissolved organic carbon (DOC) in the test mixture. The term ‘mineralised’ refers to the degradation of the organic substances to water and carbon dioxide, which is the final degradation products of all organic substances. A positive test result means that the substance tested will degrade quickly and completely in the environment. On the other hand a negative test result does not necessarily mean that the substance will not degrade in the environment. Further testing is needed to determine whether the substance is in fact poorly degradable (persistent), is potentially degradable or completely degradable (although slowly). In the EU classification system for hazardous substances and mixtures the testing for ‘ready degradability’ is a key criterion. Further details on this issue. Anaerobic degradability Over the recent years much attention has been given to the fact that some substances – in particular a surfactant like LAS – have been proven to biodegrade very slowly under oxygen free conditions (anaerobic conditions). These substances have the potential to accumulate in places with anaerobic conditions. Such oxygen free conditions are found in the sludge digestion tanks of the waste water treatment plants and in bottom sediments of rivers, lakes and the sea. The consequences of such accumulation will depend of the other properties of the substances. In the case of LAS it has been proven that if the sludge is used in agriculture – or similar situations where oxygen is present – the degradation will continue and in the end it will be complete. (More information under Surfactants - LAS). Testing for anaerobic bio-degradability can be done according to OECD TG 311, ISO 11734 or ECETOC no. 28 June 1988.
|
|
Explanatory notes on environmental properties of chemicals:
|
|
- an explanatory note: |
|
Info on specific substances The Detergent Ingredient Database (the DID-list) provides information on aerobic and anaerobic degradation of the most commonly used substances. The HERA project ‘Human and Environment Risk Assessment on ingredients of household cleaning products’, includes a valuable section with in depth assessment of specific detergent ingredients. |