In contrast to CMoS 15.48 which says, “Reference list entries are unneeded, though each person cited must be fully identified elsewhere in the text.” Include this information in the reference list, not as a footnote. This will probably be an incomplete reference list citation, but list as much information as is available.

Example: The ingestion of protein may increase bee susceptibility to some pesticides; beekeepers’ reliance on pollen substitutes may also make adult bees more susceptible to decline (Geraldine Wright, unpublished data).

Wright, G. n.d. Reader in Neuroethology. Institute of Neuroscience, New Castle University, Newcastle-upon-Tyne, England.