Environmental Risk Assessment for non-target aquatic organisms consists usually of model-predicted exposure concentrations and effect data from laboratory studies. FOCUS exposure patterns are often complex, showing variable and multiple peaks. It is not clear how to relate them to much simpler exposure patterns during ecotoxicological tests. Population models are a promising tool to assess qualitatively and quantitatively the effect of time-variable concentrations on representative aquatic organisms.
As a first step a simulation model has been developed to describe the growth of relevant algae communities in dependence of variable environmental conditions (nutrients, light, and temperature) and the effects of chemical substances on these algal populations. Different algae species were chosen in terms of abundance and dominance in mesocosms, usability as representative species and data availability.
Validation of the model is described for Desmodesmus subspicatus and the applicability to other species was tested. The effect of a pesticide on the growth rate was modelled using concentration-response data of a standard growth inhibition study. Also laboratory experiments with a continuous algae culture under flow-through conditions were conducted to assess the effects of time variable exposure.