The following questions / concerns were discussed:
- Would the methods reviewed in this workshop be accepted for use in regulatory assessments under current guidance? If not, what steps would be needed to facilitate their acceptance in the future? What are the opportunities to update technical guidance?
Two general categories of methods were evaluated: fitting methods and tools, and extrapolation approaches. SSD distribution tools overviewed at the workshop included R and BurrliOz. R is a command-line based statistical programming software, which can be used to implement methods for deriving SSDs/HC5 analyses. BurrliOZ is a software specifically designed to derive SSDs/HC5. What BurrliOZ does could be also done in R. As such R is a more general software tool which, in its current form, is far less user friendly than BurrliOZ. Yet, R can be used to implement methods that can then be made available for more general use by incorporating them e.g. in a graphical user interface. BurrliOz was specifically developed to fit SSD models to data using multiple distribution types. Both provide approaches for quantifying uncertainty in HC5 estimations through rigorous statistical bases. The consensus recommendation was that both tools require more in depth evaluation and peer review before general acceptance.
Two SSD extrapolation tools were evaluated: Web-ICE and hSSD. ICE was considered to be a valuable tool for toxicity estimation to individual species, including identification of sensitive species. However, there were statistical concerns with the use of the ICE estimates within SSDs because of the potential correlation between the estimated values (e.g. how does the SSD generator deal with the correlation structure in toxicity data) that should be addressed before broad application. The hSSD tool required model ecosystem selection, potentially resulting in uncertainty in HC5 estimation and management/policy concerns. However, selecting the individual species of an ecosystem may conflict with the results of other studies that show that ecosystem sensitivity is not very dependent on ecosystem composition. The general consensus was that the hSSD tool required validation against measured SSD HC5 values and field results, and that the development of standardised model ecosystems should be considered. Both Web-ICE and hSSD were viewed as an opportunity to reduce the use of generic assessment factors.
2. Should current guidance on the use of SSDs be revised in the light of the issues and approaches discussed in this workshop, e.g. number of species?
SSDs should be the preferred alternative rather than using generic assessment factors. Their utility may increase if the 10 species/8 taxon group requirements could be relaxed with an acceptable level of uncertainty in HC5 estimation. Extrapolation tools (ICE, hSSD) and additional distribution fitting methods should be considered in the advancement of SSD regulatory applications.
3. What implications are there for the interpretation of SSDs and HC5s in risk assessment and risk management?
There is a need for balance between prescriptive guidance and user flexibility in terms of data quality, taxonomic and species number requirements, allowable extrapolation tools, and statistical approaches to HC5 estimation. Use of a priori knowledge of MOA and potentially exposed communities is recommended for determining SSD requirements. The group was uncertain on how best to apply and interpret protective values and quantitative protection goals, and what level of conservatism and subjectivity is reasonable. Peer review and uncertainty/sensitivity analyses by outside experts may facilitate an understanding of the degree of subjectivity in SSD generation. There was consensus that the interpretation of SSDs and HC5s in risk assessment and management should not follow a predefined recipe. It should be a case-by-case assessment in which all available data and knowledge are considered by experts in the field of ecological risk assessment.
4. What are the research needs?
A variety of research and development needs were considered that could improve future regulatory applications of SSDs. Incorporating dose-response or L(E)C50 confidence limits, rather than only point estimates of toxicity, could have value in representing the range of uncertainties in an SSD. A consistent theme was the need to compare SSD-based approaches to the use of generic AF values under different scenarios of data richness, and the need to explore uncertainty in relaxed (10 species/8 taxa group) requirements versus AF uncertainty and conservatism. Determination of the ecology and composition of representative ecosystems should inform requirements for taxa composition in SSDs. SSD-based estimates determined from various approaches and data richness scenarios should be compared to field data, and field monitoring should be performed to verify SSD-based predictions of community level effects. Research is also needed to determine how best to use available data (e.g. strict standardisation criteria with resulting loss of species diversity or use weighting based on data quality). The focus of SSD development has been on acute toxicity data, and chronic toxicity estimation approaches will need the same level of evaluation (e.g. minimum data sets, acute to chronic ratio estimation, lowest toxicity value approaches). Finally, there is a growing amount of information about chemicals that could be used to inform SSD development, application, and interpretation, including knowledge of ‘omics, mechanisms, chemical properties, and exposure scenarios.