Based on the variety of existing nanomaterials with numerous modifications, the effort of investigating environmental fate and effects will be tremendous. Hence, it will be necessary to group nanomaterials which feature similar environmental fate and effects.  Therefore, the project objective was to correlate physical-chemical data with ecotoxicological effects for selected nanomaterials and to define reference values which can serve as a basis for grouping. The report presents the development of concepts for grouping of nanomaterials with regard to their ecotoxicological effects with focus on aquatic ecotoxicity. The project was structured into five steps. First, fourteen nanomaterials were selected according to pre-defined criteria. The selected NMs were different subtypes of Ag, ZnO, TiO2, CeO2 and Cu. In a second step, their physico-chemical properties were determined in water and in all test media. Based on the results hypotheses regarding the expected ecotoxicity were formulated (third step). In a fourth step, the hypotheses were verified by testing the selected NMs in three ecotoxicological tests (acute aquatic toxicity with algae, daphnia and fish embryo according to the OECD Test Guidelines No. 201, 202 and 236). Finally, step five consisted of the compilation of a grouping concept based on nanomaterials physico-chemical parameters which were identified as relevant for the emergence of a toxic effect in aquatic organisms.