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(65-01) Modelling effects of time variable exposure to toxic agents. Smit, Mathijs*,1, Karman, Chris1, 1 TNO-MEP, Den Helder, Netherlands ABSTRACT- Environmental risk assessment is generally based on the comparison of the exposure concentration of a chemical with the sensitivity of the ecosystems for this chemical, which is derived from toxicological data. For the exposure concentration of a chemical often the maximum or average concentration is assumed to be constant, thus resulting in continuous exposure, while in reality exposure is more likely to be variable and/or intermittent. Assuming a constant exposure concentration would mean a great loss of valuable information. As a result of monitoring and/or dispersion modelling of chemicals, the actual spatial and time variable concentrations in the aquatic environment can be estimated. Taking into account the variation in time would increase realism in effect and risk assessment, but this implies that also the relationship between time and effects must be defined. Several approaches have been developed to account for the influence of exposure time on environmental effects. Time to event modelling is the most recent approach to include time in environmental risk assessment, and is implemented in the DEBtox-model (Dynamic Energy Budgets). The basis for this model is the relationship between exposure concentration, exposure time and effect, so-called 3-dimensional dose-response curves. Model descriptions have been set up to relate effects to internal concentrations (body burdens) and external concentrations. Two examples will be presented to illustrate the application of this model for time variable exposure and effects. In the first example the results of an extended research program will be evaluated which show how mortality and reproduction effects of PAHs and alkylated phenols from produced water releases are estimated. Conducting many exposure experiments in the lab as well as in marine zooplankton enclosures carries out calibration and validation of the model for fish and zooplankton. The second example shows how this model can be used to define an optimal dosing regime of biocides with optimal disinfection properties and a minimum of ecological side effects. Both examples show the additional value of this method additional to conventional RA techniques. Key words: ERA, DEBtox, time variable exposure, effect model |
