The aim of this thesis was to improve the development of models describing species sensitivity towards chemical stressors. This included unravelling decisions that might be of importance in the modelling process, obtaining a better mechanistic understanding of differences in species sensitivity, and providing recommendations for improved modelling approaches within or across different taxonomic groups in freshwater ecosystems all over the world. To accomplish this global applicability, we applied a traits-based instead of a taxonomy-based approach on the development of predictive models. A trait is a phenotypic or ecological character of an organism at individual or population level, and describes the physical characteristics, ecological niche and functional role of a species within the ecosystem. We make use of traits, because they are transferable across geographies, add mechanistic and diagnostic knowledge and can be easily translated from taxonomic analyses priory preformed. Our general conclusion is that trait-based approaches hold great potential for cross-species extrapolation, but are currently not (yet) feasible for large scale application due to restricted data availability.