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(W/EH092) Estimating parameters for risk assessment on time variable exposure. Smit, Mathijs1, Karman, Chris1, Johnsen, Hanne2, 1 2 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. The exposure to this chemical is often assumed to be constant and continuous, while in reality exposure is more likely to be variable and/or intermittent. 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. This approach is followed in the DREAM-model (Dose Related Effects Assessment Model), which is used to assess the environmental impact of produced water discharges in the marine environment. The basis for this model is the relationship between exposure concentration, exposure time and effect, a so called 3-dimensional dose-effectcurve. For DREAM a mechanistic description to estimate effects based on dynamic body burden has been selected. This model can be used to derive the parameters that are required for the model, but is not yet suitable to do actual risk calculations. As a last step in the development process the dose-response model has been inversed, providing a method to estimate the environmental impact as a function of dynamic body burdens. In order to assess these ecotoxicological parameters of a number of PAHs and alkylated phenols, laboratory experiments were carried out with the marine copepod Acartia tonsa (see abstract Johnsen et al.) and the fish Cyprinodon variegatus. As validation of the model enclosure studies were performed (see abstract Jak et al.). The process of model development is described, together with the estimation process of model parameters using data from the extensive experimental programme, designed for the DREAM model. Key words: environmental risk assessment, time variable exposure, modelling, produced water |
