TomD
The wood in plywood is toxic. There is a certain amount of glue in plywood which is part of the reason I don't personally burn it. Solid core plywood has a lot less glue. I might burn a piece I would not be comfortable heating with it.

What you may be referring to is the large amounts of sometime urea formaldehyde bearing glue found in particle boards and MDF The products use far larger amounts of glue to bind together dusts or chips, and often seem more cheaply made. I built some temporary shelving for a rental I lived in, out of MDF. They smelled really strongly of mushrooms and the smell stayed with them. Later I found "green" glue MDF at the local HD. Unfortunately it turned out to be a single pallet's worth only, and that is the last I have seen of that.