OECD 309 aerobic mineralisation in surface water – Results from a laboratory participating in the CEFIC-LRI ECO55 ring trial

SETAC Europe 2025 -- The purpose of the aerobic mineralisation in surface water simulation biodegradation test (OECD 309 guideline) is to assess the biodegradation and mineralisation of test items in natural water at low concentrations. Under the European Chemicals Agency’s (ECHA) regulations for the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), the OECD 309 study has become the favoured test to assess persistence in the environment for industrial chemicals at 12°C (freshwater). The use of radiolabeled test item allows primary degradation and mineralisation to be assessed and mass balances to be measured. As part of the test, a reference substance is used to ensure that the natural water contains an active microbial population and that the test is therefore valid. The guideline suggests the use of either aniline or sodium benzoate and historically both have been used. It is expected that both will be substantially mineralised within a two-week incubation period. However, it is considered that aniline and sodium benzoate do not provide a sufficiently robust assessment of the viability of the natural water as they are too readily mineralised to carbon dioxide. An interlaboratory ring trial was set up to investigate the alternative reference substances caffeine and 2,4-dichlorophenoxyacetic acid (2,4-D). The results obtained by Labcorp are presented here.