BioBricks PubChem Annotations is an open knowledge graph providing structured access to chemical annotations originally sourced from PubChem's Annotations subset, targeting researchers in cheminformatics, toxicology, and environmental health. The graph contains over 10.7 million annotations (87.4 million triples total) describing chemical compounds through text-based annotations including regulatory data, physical properties, biological activities, and hazard information. Each annotation follows the W3C Web Annotation Data Model, linking PubChem compound identifiers to textual annotation bodies covering topics from state-level contaminant limits to chemical synthesis methods. The knowledge graph interoperates with the broader PubChem RDF ecosystem through shared compound URIs in the namespace. Annotations derive from multiple heterogeneous sources with varying licenses, documented in PubChem's source metadata.