An ecotoxicodynamic reference model for sub-lethal effects of mixtures

Tjalling Jager, Jan Baas, Bas Kooijman

Dept. of Theoretical Biology, Vrije Universiteit, de Boelelaan 1085, NL-1081 HV, Amsterdam, the Netherlands

Typicial approaches for analyzing mixture toxicity data only provide a description of the data; they cannot yield insights into the underlying mechanisms. This limitation is clearly shown by the fact that these approaches cannot explain why mixture interactions change in time and differ between endpoints. To improve our understanding we need a process-based model where we can implement our knowledge about the mechanisms of toxicity, and test whether this knowledge is sufficient to explain the observed response of the organisms. Previously, Baas et al have extended the biology-based approach DEBtox to mixture effects on mortality; here we continue with sub-lethal endpoints (growth and reproduction). Because the DEBtox method process- based, it explicitly predicts the toxic effects on all endpoints in time. Model simulations reveal that deviations from the standard models (such as ‘concentration addition’) may already result from unavoidable interactions between the physiological and toxicokinetic processes in the organism.