In October 2015, the European Union’s Scientific Committee on Consumer Safety issued a Preliminary Opinion on Hydroxyapatite (nano). Past industrial experience with this material and participation in ISO/TC-229, Nanotechnologies, led me to submit comments on the Committee’s interpretations of physico-chemical properties, especially solubility, that in retrospect were also probing of the Committee’s collective understanding of nanomaterials. The Committee’s responses are examined against a background of other Opinions issued in the same time period. The expert’s role and responsibility, whether as an (...) individual or a group member or in representing a scientific discipline, are examined through the concept of epistemic community taken from the public policy literature. A central theme is the Committee’s framing of chemical narratives such that its administrative procedures are projected onto the nanomaterial safety literature that is itself undergoing considerable investigation and revision. Inherent to this analysis is the singular role of toxicologists in the regulatory process. A related exchange by Australian and New Zealand colleagues is examined for its parallels to the SCCS actions, and there is a cursory discussion of later SCCS Opinions regarding Hydroxyapatite (nano). (shrink)