Information on the degradability of chemicals is an essential requirement for hazard assessment (e.g. for classification and labelling), environmental risk assessment (for chemical safety assessment) and persistency assessments (for PBT/vPvB assessment). At the STEP (Simulation Testing for Environmental Persistence) workshop held in 2004 a number of potential improvements to the biodegradation screening tests were identified. These included extending the test duration for poorly water soluble substances, conducting the study at lower test substance concentrations and using information on primary biodegradation. The STEP workshop concluded that "a number of enhancements for increasing the reliability of the'ready' screening tests had been identified" and "that further guidance needed to be developed in this area as a matter of urgency".
During the preparation of the technical guidance documents for REACH, modifications and enhancements to biodegradation tests were identified by the REACH Implementation Project (RIP 3.3) endpoint working group on degradation. These enhancements were aimed at increasing the environmental relevance and predictability of biodegradation and environmental persistence. One of the enhancements proposed addressed the impact of inoculum density and diversity of biodegradation potential as demonstrated by Thouand et al. (1995). This study demonstrated that the probability of biodegradation increased at higher biomass concentrations due to the greater likelihood that competent degraders would be present. Increasing the microbial biomass levels may be a useful approach that could increase environmental realism, reduce the variability within and between tests, and increase the predictive nature of the tests. Understanding the relationship between biomass density, its diversity and the outcome of the biodegradation study for a range of inoculum sources can be seen as a valuable approach to developing knowledge in this area.
Simulation Testing of Environmental Persistence (STEP): report of a two-day workshop held in Rotterdam, 4 and 5 October, 2004. Editors: CT Bowmer and MA Leopold.
Thouand et al. (1995): G Thouand, P Friant, F Bois, A Cartier, A Maul, JC Block, Bacterial inoculum density and probability of para-nitrophenol biodegradability test response, Ecotoxicol Environ Saf 1995, 30, 274-282.
- Develop methods to increase both the density and diversity of microbial biomass for use in biodegradation screening studies.
- Understand the impact of the biomass and its density on the data generated. Address the relationship between density, diversity and test volume; comparison of different approaches to pre-concentrate biomass.
- Develop an approach that can be used to assess the biodegradability of chemicals, in fresh and marine waters, without having to conduct the full suite of approaches developed in this research.
Investigate the probability of biodegradation of a range of chemicals (Reference/validation set), addressing:
- A range of inoculum sources
- Test substance concentration
- Variable microbial biomass levels
Consider potential impacts on the signal to noise ratio:
- Identify/suggest sources of noise in such studies.
- Develop approaches that reduce the background levels of organic carbon if appropriate.
- Consider alternative endpoints to assess biodegradation.
Develop a strategy/testing approach for how to address other chemicals and what conditions should be used in such tests.
Short interim reports on progress are required at 6-monthly intervals. It is expected that the findings will be developed into a peer reviewed publication, following presentation at a suitable scientific conference.