S10-03 Alternative testing approaches in ecotoxicology with a focus on acute and chronic fish toxicity

In the European Union in 2022, more than 86,000 vertebrates were used for ecotoxicological testing for regulatory use and routine production, and 82% of these animals were fish. In recent years, progress has been made towards the development, validation, and application of alternatives to using animals in regulatory ecotoxicity testing, and the European Commission has committed to developing a roadmap to phase out the use of animals in regulatory tests for industrial chemicals, biocides, pesticides, and human and veterinary medicines, including ecotoxicity assessments. This presentation describes approaches that can already be used to reduce and replace the use of fish toxicity tests and ongoing projects. Acute and chronic fish toxicity and bioaccumulation are standard information requirements in various regulatory frameworks, although in silico tools such as QSARs and alternative OECD test methods are available. These include the cytotoxicity test using the fish cell line RTgill-W1, the fish embryo acute toxicity test, in vitro assays for hepatic clearance, and the Hyalella azteca test. It is often not possible to replace fish testing with a single alternative method, therefore, alter-native approaches can be used within weight-of-evidence analyses to provide a similar or better environmental protection level. Regarding endocrine disruption, the inclusion of standard information requirements for industrial chemicals in the EU and the role of alternative methods are under debate. Building on the threshold approach for acute fish toxicity, an Integrated Approach to Testing and Assessment (IATA) for acute fish toxicity is under development. It is meant to guide through the available knowledge on uncertainties for the use of alternative methods and potential value added for additional acute in vivo fish toxicity data. For example, given the lower sensitivity of TGs 236 and 249 to some neurotoxicants compared to acute fish toxicity based on OECD TG 203, an analysis of acute toxicity data from the EnviroTox Database indicates that fish rarely represent the most sensitive trophic level among neurotoxic chemicals. While the use of alternative approaches for acute fish toxicity assessment appears as a scientifically low hanging fruit, efforts to reduce the number of fish in chronic tests are ongoing. One project is investigating whether it is possible to use only the solvent control and to omit the water controls when solvents are used without compromising statistical power and the generation of accurate and valid results. This approach would reduce the resources required to conduct the test, including the number of fish used. Further resources must be invested in the development, validation, and application of alternative approaches to meet the Commission's goal of phasing out the use of animals in regulatory testing with a particular focus on ecotoxicity testing.