Biodegradation

Biodegradability refers to the ability of organic chemicals to biodegrade, so its decomposition by living organisms (in particular Saprobionten ) or their enzymes. Ideally, this chemical metabolism proceeds completely until mineralization, so that the organic compound is decomposed to inorganic substances such as carbon dioxide, oxygen and ammonia, the decomposition can also remain stable even when degrading transformation products.

Different understanding

Biodegradability is practically very different, depending on whether reference is made to the law or to further ideas. Industrially manufactured chemicals are considered biodegradable if they removed by biological degradation of the environment and are fed to the mineral material cycle. This raises the question of how the biological degradability is tested and is considered to what extent the reduction in the test.

The existing in the current language associated with private self - composting leads to misunderstandings, see compostability.

Biodegradation of a substance formed as intermediates transformation products also can be more problematic than the original material. From alkylphenol polyglycol ethers arise, for example in the first degradation steps Nonylphenols, the fish have harmful hormone effects. Distinguish you have here also between metabolites and transformation products. The former are caused by metabolic conversion, primarily in people while transforming products all ways of converting a substance involving. Since one abiotic processes (eg hydrolysis in water) can not be ruled out in the investigation of the biological degradability, transformation product is better for the resulting products of the term.

The sometimes used, fuzzy term " elimination " has nothing to do with a biological degradation. Elimination of substances such as in a sewage treatment plant means that these substances according to the clarification in a lower concentration can be detected as the clarification. However, these substances can also be removed by means of transformation, adsorption, sedimentation or filtration of the waste water. In the case of adsorption and sedimentation substances are, however, included in the sewage sludge, and can thus be introduced into the environment, in the case of filtration, it is a function of the filtration unit and in the case of a transformation, the transformation products be introduced into the environment.

Test method

General recognized the OECD test methods that are used in the chemical approval. Biodegradability of water-insoluble substances, such as lubricating oils can be determined by, specially designed test method CEC-L- 33-A -93. For certain surfactants continue to exist legally prescribed test procedures, which are less reliable. For classification as bioplastic also the compostability is investigated.

Ready biodegradability (OECD 301)

The tests of the OECD test series 301 (A - F ) have a rapid and complete biodegradation after under aerobic conditions. Different test methods are good or bad -soluble and volatile substances available. When a substance (usually more than 60% reduction ) is not reached the criterion for light biodegradation in the next hierarchy level (OECD 302) of the inherent biodegradability is tested.

• DOC Die-Away test (OECD 301 A): The substance is a high compared to the other tests concentration, ie 10-40 mgDOC / L ( DOC = dissolved organic carbon = dissolved organic carbon ) were tested. Over the period of 28 days, the DOC concentration is measured at defined intervals. This test can be used for adsorbing substances.
• Carbon dioxide - Development Test (OECD 301 B): The resultant by the biodegradation of the test substance carbon dioxide is analyzed regularly over 28 days and is an indicator of biodegradation. This so-called Sturm test is used for the study of poorly water soluble chemicals.
• Modified MITI Test (OECD 301 C): With a special inoculum by MITI requirements is measured over a period of 28 days of oxygen consumption at the same time, they absorb carbon dioxide. This test is appropriate for readily soluble substances.
• Closed Bottle test (OECD 301 D): The biodegradability of the test substance is determined by a period of 28 days of consumption is determined by dissolved oxygen at regular intervals. This test is used for volatile chemicals.
• Modified OECD screening test (OECD 301 E): The biodegradability of the test substance is determined by measuring the DOC for a period of 28 days. This test is used with a sufficiently water-soluble chemicals.
• Manometric respirometry (OECD 301 F): in the test bottles a defined gas space is left. In addition, a carbon dioxide adsorbing agent (for example sodium hydroxide ) is added to a particular vessel in the test bottle. During the test, oxygen is consumed in the gas space and replaced by carbon dioxide, which is taken up by the adsorbent. The resulting pressure difference is recorded by means of special pressure gauge and thus provides the biodegradation. This test is useful when the molecular formula of the substance under investigation is known, and thus a theoretical oxygen consumption can be calculated.

Inherent biodegradability (OECD 302)

The tests of the OECD test series 302 ( A - C) demonstrate a limited indeed, but in principle possible biodegradability of the tested chemical. Substances composed such tests are considered to be fundamentally or inherently biodegradable.

• The Zahn-Wellens EMPA Test (OECD 302 B) investigated the aerobic biodegradability of the substance and returns the result of the decrease of chemical oxygen demand or dissolved organic carbon on. It is the most commonly used test for the study of inherent biodegradability. It provides additional information about the adsorption of the substance tested.

Biodegradation of oil-soluble products ( CEC-L- 33-A -93)

In this method, a small amount of oil to be tested, shaken for 21 days in an inoculated mineral substrate at constant conditions. It is then extracted with Freon and infrared spectrometry analyzes. By comparing the absorption of infrared light approaches the zero days with the absorbance of the 21-day approaches to biologically degraded portion of the oil can be determined. With the CEC-L- 33-A -93 method, only the biodegradability of oil-soluble substances can be determined. It is not limited to individual substances, but can also be used to determine the degradability of finished products.

Tensidverordnungs test

Commonly found on washing and cleaning products manufacturer, after which the surfactants used here are referred to as biodegradable because they " meet all legal requirements concerning biodegradability completely ". The tests according to EU directives 82/242/EEC and 82/243/EEC (or after Tensidverordnung for German Washing and Cleansing Agents Act ) but still only see that anionic and nonionic surfactants percent with respect to their washing efficiency to 80 must be reduced; cationic surfactants are not included in the statutory test methods. The test methods examine only the primary degradation. A possibly more extensive degradation of the test substance, as described in the OECD tests is not considered here. For cationic and amphoteric surfactants for the missing similar for many other cleaning agent statutory testing requirements.

Compostability

Bioplastics are subjected to the test of compostability of plastics. This was described 54900-1 ... 3 in Germany under the 2004 replacement retracted DIN standard DIN V; the American ASTM D -6400 calls for a degradability of plastics by 60 % within 180 days, to identify products as " compostable". Recognition as a biodegradable material and compostable material occurs only when the substances are degraded within 12 weeks in an industrial composting according to European Standard EN 13432 of at least 90 %.

Dealing with persistent properties

Substances are referred to as a degradation -resistant, if they are not subject to biodegradation. If they are not decomposed by other chemical or physical degradation processes, as they are called persistent. Because of Persistenzproblematik next to the chemical and photochemical degradation and adsorption is the biodegradability of registered substances into the environment is of great importance. The biodegradability is therefore already been tested in the authorization of chemicals with the aforementioned OECD tests. According Kümmerer for sustainable chemistry as complete as possible biodegradability ( mineralization) after the application of chemicals should be considered as part of the functionality.