Analysis of bioassays with time-varying concentration

In the analysis of ecotoxicological bioassays, the concentration of the toxicants is assumed to be constant. In many situations, this is not a reasonable assumption. Evaporation of the compound, adsorption to the sediment or to the vessel, or accumulation in the organisms may cause a substantial decline in the concentration during exposure. We develop a model to analyse ecotoxicity data with time-varying external concentrations. The model is an extension of the DEBtox model (Kooijman and Bedaux, 1996) which is based on biological assumptions about toxicokinetics and toxic effects. The kinetics module translates the concentration in the environment into time-varying concentration in the tissue. The effect module translates this into effects on survival and sublethal effects. The toxicokinetics module of DEBtox is adjusted to describe several sources of variation in external concentration. The theoretical work is faced with experimental data. / Nous proposons une méthode d'analyse des bioessais, même lorsque les concentrations testées ne peuvent être maintenues au cours du temps. Cette méthode repose sur le modèle DEBtox développé par Kooijman et Bedaux (1996). La méthode est confrontée à des données expérimentales.