In aquatic systems such as rivers or ponds, input concentrations of most pollutants have been observed to fluctuate and also tend to occur in sequential input pulses. For a good risk assessment and for defining water quality criteria, effects of such exposure patterns need to be estimated appropriately. Previous studies have detected carry over toxicity in organisms exposed to sequential exposure of chemicals acting with the same mode of action, namely inhibition of acetylcholine esterase (AChE). The aim of this master thesis was first of all to test whether such carry over toxicity also occurs in sequential exposure of chemicals with different modes of action (MoA). Secondly, if such carry over does take place, then the performance of the threshold damage model in predicting the survivals of the given experiment would be tested. Additionally, the toxicodynamic parameters of DNOC were estimated in order to run the prediction. [...]