For the 254 SMILES that were found to be invalid SMILES representations by OCL with normalization, all 254 contained an aromatic selenium atom "[se]" in a kekulized, non-aromatic SMILES string. In our opinion, this behaviour is correct, as there is no such thing as a single aromatic atom in a non-aromatic environment. However, this For the CDK, while the combination of RDKit normalization and CDK substructure search does not appear to work well together, the CDK substructure search works well with its own CDK as well as with OCL normalization. For the OCL results, it is interesting to note that the syntactically wrong SMILES with aromatic selenium mentioned above are corrected to non-aromatic by CDK, therefore reducing the number of invalid SMILES for the CDK+OCL combination. For the RDKit results, while the number of identified PFAS molecules was not influenced by the normalization used, the least invalid SMILES were found when using RDKit for both normalization and substructure search. Since the molVS model from RDKit returned fewer invalid entries but the same number of PFAS, this was used subsequently. Not surprisingly,