This International Standard specifies a method for the evaluation of the biodegradability ("ultimate" or "primary") of organic compounds. The conditions described in this International Standard are much more favorable for biodegradation than those specified in the methods for biodegradability described in ISO 7827, ISO 9408 and ISO 9439. The method applies to organic compounds which are a) soluble at the concentration used under the test conditions; b) non-volatile, or which have a negligible vapour pressure under the test conditions; c) not lost by foaming from the test solution; d) not significantly adsorbable on glass and activated sludge; e) not inhibitory to the test micro-organisms at the concentration chosen for the test. Inhibitory effects can be determined by using a suitable test method (e.g. see ISO 8192). If the test compound is toxic, the test concentration has to be lower or a pre-exposed inoculum can be used. NOTE 1 Additionally, or alternatively, the semicontinuous activated sludge (SCAS) units may be used to provide sludge exposed to the test compound, in order to see whether the sludge becomes adapted, to be used as inocula in other biodegradation tests.