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Published: Kem. Ind. 52 (12) (2003) 577–581
Paper reference number: KUI-36/2002
Paper type: Conference paper
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Biodegradation – Methods Overview

L. Ulm, Ž. Pavlić, V. Schiesl, D. Puntarić and Z. Šmit


Biodegradation is a process during which chemicals and other substances are broken down into simple compounds or molecules by microorganisms and they become part of the environment. The final products of biological degradation are water and carbon oxides as well as the oxides of some other elements. Determination of biodegradation methods are regulated by the Official list of the EU and by the International Standardisation Organisation (ISO), and both are officially recognized by the Republic of Croatia. The basic principle of all the biodegradability tests is, that a solution, or suspension, of the test substance in a mineral medium is inoculated and incubated under aerobic conditions, in the dark or in diffuse light. The biodegradation is monitored during a certain period of time (28 days usually) by measuring the levels of CO2, DOC or O2 (from BOD or COD). Substances are considered readily degradable if the following criteria hold true:5 If in 28-day biodegradation studies the following levels of degradation are achieved: - in tests based upon dissolved organic carbon: 70 %, - in tests based upon oxygen depletion or carbon dioxide: 60 % of the theoretical maxima. These levels of biodegradation must be achieved within 10 days of the start of degradation, which point is taken as the time when 10 % of the substance has been degraded. Biodegradability tests are used to establish the biodegradability of chemical structures and to predict the biodegradation behaviour of a test material in a natural or technical environment. Therefore, as so many factors (aerobic/anaerobic test conditions; source and concentration of the microorganisms of the inoculum; concentration of the test material; possible toxic effects of the test material under the test conditions; physical and chemical properties and bioavailability of the test material; test duration) can influence or even exclude certain methods, it is necessary to have a sufficient number of different standardized test methods to allow the choice of the best one for the specific purpose. The choice of a test depends normally on the purpose of testing or on legal requirements which have to be fulfilled. One strategy is to apply a simple low-cell density method. If a chemical degrades adequately, further testing is normally unnecessary. A low or zero value for biodegradation may be sufficient for the purpose. Otherwise the test could be repeated with an inoculum pre-exposed to the chemical, or a test with a higher cell density and a longer test period could be applied. Another strategy is to start with a high-density method to determine whether biodegradation is available at all, and to answer, if the test compound is easily biodegradable in environmental compartments by using a low-density method in the next step. The choice of a method also depends on the physical and chemical properties of the test chemical. Volatile test compounds can only be tested in closed systems such as ISO 10708.11 In some cases it may be helpful to use an adapted inoculum. Pre-adaptation could be achieved using ISO 988714 or ISO 988813 followed by test methods using the measurement of biochemical oxygen demand (ISO 9408,10 ISO 1070811 or carbon dioxide (ISO 14593).7

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biodegradation, criteria, choice of method