Comparison of bioassays with different exposure time patterns: The added value of dynamic modelling in predictive ecotoxicology

The purpose of this study was to compare Daphnia magna responses to cadmium between two toxicity experiments performed in static and flow-through conditions. As a consequence of how water was renewed, the two experiments were characterised by two different exposure time patterns for daphnids, time-varying and constant, respectively. Basing on survival, growth and reproduction, we addressed the questions of organism development and sensitivity to cadmium. Classical analysis methods are not designed to deal with the time dimension and therefore not suitable to compare effects of different exposure time patterns. We used instead a dynamic modelling framework taking all timepoints and the time course of exposure into account, making comparable the results obtained from our two experiments. This modelling framework enabled us to detect an improvement of organism development in flow-through conditions compared to static ones and infer similar sensitivity to cadmium for both exposure time patterns. ► We aimed to compare two bioassays characterised by different cadmium exposure time patterns. ► Classical analysis methods cannot distinguish time patterns, therefore are not suitable. ► Instead we used dynamic modelling taking all timepoints and the time course of exposure into account. ► Similar stress functions were inferred from time-varying and constant exposure experiments. ► Our approach may be able to predict cadmium impacts whatever the exposure time pattern.