Transformation products, natural or based on human-made processes, theoretically constitute a large portion of a the exposome chemical space. Each human-made chemical could potentially have a large number of different transformation products, depending on the reaction pathways and the environmental conditions (e.g. biotic or abiotic). Some of these transformation product may be more persistent than their parent compounds and hence be even more relevant for the exposome chemical space. However, most of these structures remain unknown, even though their importance to environmental and human health has been previously demonstrated (e.g. DDT and its metabolites DDE and DDE; or disinfection byproducts). A combination of experimental and in-silico approaches are typically employed for the structural elucidation of the transformation products of chemicals. This task is carried out for one chemical and one reaction type at a time due to the complexity of such systems (e.g. photo-degradation of pharmaceuticals). To elucidate the generated transformation products, a combination of NTA/suspect analysis and in-silico prediction tools are used. The currently available in-silico tools are able to estimate the structure of a potential transformation product based on the parent structure and the reaction type. These TP structures are either used for the generation of suspect lists or as potential candidate structures during the NTA workflows. Additionally, the generated TP structures may not have their chemical standard available or may not have been measured before, increasing the complexity and the uncertainty of this task. Additionally, due to the uncertainties associated with the in-silico TP structure estimation tools and the NTA workflows, the addition of the TPs to the list of chemicals in the exposome chemical space has been an extremely slow process. In fact, most of the chemicals present in the databases such as PubChem or Norman SusDat consist of the parent structures rather than TPs, indicating the need for their expansion with TPs. 11