PubChemLite is a subset of ~350,000 compounds from PubChem with environmentally relevant annotation content . In total, KOC values were predicted for 346,133 compounds (96.0% of PubChemLite) using the molecular connectivity index (MCI) model from KOCWIN . The results of the log KOC distribution are shown in Figure . Based on these predicted values log KOC, 147,930 compounds (41%) would be considered mobile and 78,107 compounds (21%) would be considered very mobile. The MCI model assigns values of 1 and 0 for chemicals when KOC predictions have been overcorrected. The large peak at log KOC 10 is an upper bound for these predictions within the MCI model output. Note that the results of this analysis will differ if the KOWbased model in KOWWIN is used. To investigate this concept in more detail on slightly smaller subsets, four compound classes: triazines, aromatic amines, PFAS and triazoles were selected based on the five suspect lists mentioned previously (UBAPMT, EAWAGPMT, UFZHSFPMT, PMTPFAS and ZEROPMBOX1) . The substructure search function of PubChem was then used to estimate the number of compounds that belong to these compound classes. An overview of these search queries can be found in Table . As can be seen in the first three rows, relatively unspecific substructures can generate very large query results. For the 1,2,3-triazole substructure over 1 million substances were found, which corresponded to a search of only 87% of the database as the search results are capped at 1 million substances. Similarly, the aromatic amines (with aniline as the searched substructure) resulted in over 1 million substances with only 2% of the database searched. The 1,3,5-triazine query resulted in 718,119 substances. The compounds classified within the OECD definition of PFAS in the PubChem PFAS tree were used to source PFAS, which contained 6,604,017 compounds at the time the queries were performed (Dec. 17 based on the predicted log KOW from XlogP3. As such the substructures used when discussing PMT/vPvM compound grouping for regulation purposes should be more specific.