User Guide to Thresholds and Classification - Environmental ...

323User Guide for Thresholds and ClassificationsTime windowThe harmonised criteria include a general requirement for all of the ready biodegradability tests onachievement of the pass level within 10 days. This is not in line with the OECD Test Guideline 301 in whichthe 10-days time window applies to the OECD ready biodegradability tests except to the MITI I test (OECDTest Guideline 301C). In the Closed Bottle test (OECD Test Guideline 301D), a 14-days window may beused instead when measurements have not been made after 10 days. Moreover, often only limitedinformation is available in references of biodegradation tests. Thus, as a pragmatic approach the percentageof degradation reached after 28 days may be used directly for assessment of ready biodegradability when noinformation on the 10-days time window is available. This should, however, only be accepted for existing testdata and data from tests where the 10-days window does not apply.(Note that the HSNO Act regulations have no requirement for a pass within a specified window.)BOD 5 /CODInformation on the five-day biochemical oxygen demand (BOD 5 ) will be used for classification purposes onlywhen no other measured degradability data are available. Thus, priority is given to data from readybiodegradability tests and from simulation studies regarding degradability in the aquatic environment. TheBOD 5 test is a traditional biodegradation test that is now replaced by the ready biodegradability tests.Therefore, this test should not be performed today for assessment of the ready biodegradability ofsubstances. Older test data may, however, be used when no other degradability data are available. Forsubstances where the chemical structure is known, the theoretical oxygen demand (ThOD) can becalculated and this value should be used instead of the chemical oxygen demand (COD).Other convincing scientific evidenceRapid degradation in the aquatic environment may be demonstrated by other data than referred to in HSNOAct criteria (a) and (b). These may be data on biotic and/or abiotic degradation. Data on primary degradationcan only be used where it is demonstrated that the degradation products shall not be classified as hazardousto the aquatic environment, that is, that they do not fulfil the classification criteria.The fulfilment of HSNO Act criterion (c), requires that the substance is degraded in the aquatic environmentto a level of > 70% within a 28-day period. If first-order kinetics are assumed, which is reasonable at the lowsubstance concentrations prevailing in most aquatic environments, the degradation rate will be relativelyconstant for the 28-day period. Thus, the degradation requirement will be fulfilled with an averagedegradation rate constant, k > -(ln 0.3 - ln 1)/28 = 0.043 day-1. This corresponds to a degradation half-life,t½ < ln 2/0.043 = 16 days.Moreover, as degradation processes are temperature dependent, this parameter should also be taken intoaccount when assessing degradation in the environment. Data from studies employing environmentallyrealistic temperatures should be used for the evaluation. When data from studies performed at differenttemperatures need to be compared, the traditional Q10 approach could be used, that is, that the degradationrate is halved when the temperature decreases by 10°C.January 2012 EPA0109