User Guide to Thresholds and Classification - Environmental ...

330User Guide for Thresholds and ClassificationsGuideline 301D). In general, the DOC Die-Away test (OECD Test Guideline 301A) and the Modified OECDScreening test (OECD Test Guideline 301E) are not suitable for testing the biodegradability of poorly solublesubstances (for example, OECD Test Guideline 301).Volatile substances should only be tested in closed systems as the Closed Bottle test (OECD Test Guideline301D), the MITI I test (OECD Test Guideline 301C) and the Manometric Respirometry test (OECD TestGuideline 301F). Results from other tests should be evaluated carefully and only considered if it can bedemonstrated, for example, by mass balance estimates, that the removal of the test substance is not a resultof volatilisation.Variation in simulation test dataA number of simulation test data may be available for certain high priority chemicals. Often such dataprovide a range of half-lives in environmental media such as soil, sediment and/or surface water. Theobserved differences in half-lives from simulation tests performed on the same substance may reflectdifferences in test conditions, all of which may be environmentally relevant. A suitable half-life in the higherend of the observed range of half-lives from such investigations should be selected for classification byemploying a weight-of-evidence approach and taking the realism and relevance of the employed tests intoaccount in relation to environmental conditions. In general, simulation test data of surface water arepreferred relative to aquatic sediment or soil simulation test data in relation to the evaluation of rapiddegradability in the aquatic environment.Decision schemeThe following decision scheme may be used as a general guidance to facilitate decisions in relation to rapiddegradability in the aquatic environment and classification of chemicals hazardous to the aquaticenvironment. A substance is considered to be not rapidly degradable unless at least one of the following isfulfilled.The substance is demonstrated to be readily biodegradable in a 28-day test for ready biodegradability.The pass level of the test (70% DOC removal or 60% theoretical oxygen demand) must be achievedwithin 10 days from the onset of biodegradation, if it is possible to evaluate this according to theavailable test data. If this is not possible, then the pass level should be evaluated within a 14-days timewindow if possible, or after the end of the test.The substance is demonstrated to be ultimately degraded in a surface water simulation test with a halflifeof < 16 days (corresponding to a degradation of > 70% within 28 days) Simulations tests shouldreflect realistic environmental conditions such as low concentration of the chemical, realistic temperatureand employment of ambient microbial biomass not pre-exposed to the chemical.The substance is demonstrated to be primarily degraded (biotically or abiotically) in the aquaticenvironment with a half-life < 16 days (corresponding to a degradation of > 70% within 28 days) and itcan be demonstrated that the degradation products do not fulfil the criteria for classification ashazardous to the aquatic environment. When these data are not available, rapid degradation may bedemonstrated if one of the following criteria is justified.January 2012 EPA0109