Others with more info will probably chime-in here, but, if formaldehyde, it can be of concern...

Formaldehyde is a colorless, toxic, potentially carcinogenic, water-soluble gas, CH 2 O, having a suffocating odor, usually derived from methyl alcohol by oxidation: used chiefly in aqueous solution, as a disinfectant and preservative, and in the manufacture of various resins and plastics.

I do believe older plaques fit this definition.

Jim