Then annotation content of PubChem is very rich, coming from a wide variety of sources (currently over 920 data sources contribute to PubChem). The download file contains information on several major categories. The most relevant ones for environmental applications include, for example: drug and medication information; food additives and ingredients; literature; patents; pharmacology and biochemistry; safety and hazards; toxicity; use and manufacturing. The presence of these categories in the download file makes it easy to filter results by the categories of interest. Further annotation content can be browsed using the PubChem Table of Contents (TOC) Classification Browser (the "landing page" of the classification browser at ), which provides an overview of all annotation content in PubChem -currently 598 categories (20 June 2023). The overlap of PFAS and annotation content can be explored using the PubChem saved search and Entrez functionality. Figure demonstrates how the "saved search" feature can be used to calculate how many OECD PFAS (7,448,354 CIDs, bottom row) are also agrochemicals (from the TOC heading, 3086 CIDs, of which 305 are also OECD PFAS, third row) with mass spectral data in MassBank Europe (second row: 71 CIDs that are OECD PFAS agrochemicals in MassBank Europe) or measured collision cross section (CCS) data (top row: 27 CIDs that are OECD PFAS and agrochemicals with experimental CCS values in PubChem). Each of these overlap queries can also be browsed/downloaded. Further information on how to perform these queries is available in the PubChem documentation 58 , PubChem PFAS Tree documentation and in the webinars .