Surface waters can contain a diverse range of organic pollutants, including pesticides, pharmaceuticals and industrial compounds. Effluents from wastewater treatment plants (WWTPs) are known to be point sources of micropollutants for surface waters and are currently under scrutiny for retrofitting with advanced treatment options including ozonation. While bioassays have been used for water quality monitoring, there is still limited knowledge regarding the specific contributions of individual micropollutants to overall observed effects. This is particularly true for ozonation due to the possible formation of transformation and oxidation by-products. To further investigate the use of effect-based methods, a combination of state-of-the-art chemical analysis, in-vivo and in-vitro assays are established at the University of Duisburg- Essen and its affiliated institutes IUTA and IWW. As an example, the effectiveness of a full-scale ozone treatment in combination with a fluidized moving-bed reactor as biological post-treatment for the reduction of many micropollutants without the release of relevant toxic transformation products has been assessed by such a chemical and toxicity-based approach.