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2P Modelling ecotoxic effects (MOP/152) Simultaneous modelling of multiple endpoints in life-cycle toxicity tests. Jager, Tjalling1, Crommentuijn, Trudie2, Van Gestel, Kees1, Kooijman, Bas1, 1 Vrije Universiteit, Amsterdam, NH, The Netherlands2 Ministry of Housing, Spatial Planning and The Environment, The Hague, ZH, The Netherlands ABSTRACT- The translation of results from standard toxicity tests to effects on populations is hampered by the use of a fixed (arbitrary) exposure time and the focus on a single endpoint only. These problems can be partly overcome by following more endpoints over the entire life cycle, but these studies are notoriously hard to analyse. The DEBtox model is a spin-off from the theory of Dynamic Energy Budgets (DEB). Toxicants can affect energetic parameters of organisms like maintenance, assimilation etc. In this study, we extend DEBtox to describe life-cycle toxicity tests. To this end, we took an existing data set for the springtail Folsomia candida, exposed to cadmium, chlorpyrifos and triphenyltin in their food. Mortality, growth and reproduction were followed over 120 days. Some adaptations to the model were necessary to accommodate this type of study: implementing the simultaneous assessment of all endpoints, and including the effects of senescence. The extended DEBtox is able to describe the data sets satisfactorily, with only few (biologically relevant) parameters, including two time-independent no-effect concentrations (for survival and growth/reproduction) with confidence intervals. Model fits indicate the most likely mode of action: Cd affects assimilation, triphenyltin affects maintenance costs, and chlorpyrifos affects reproduction directly (probably by increasing the energy costs for reproduction, although a receptor-mediated effect is also possible). Furthermore, the results suggest quite complicated interactions between chemical stress and senescence. The estimated parameters are subsequently used to predict population growth rate as a function of the exposure concentration. Key words: life-cycle toxicity, modelling, Folsomia candida, toxicity testing |
