The "PFAS and Fluorinated Compounds in PubChem" collection (hereafter "PubChem PFAS Tree") is openly available and integrated into the Classification Browser of PubChem. It is designed to support the exploration and exchange of information on PFAS and fluorinated compounds within the community. This information is compiled and assembled using several different approaches, described further in the following sections. The online collection (shown with the first two layers of nodes in Figure ) is updated frequently and is available at .