Well, there's also Radon, lead (knock on wood), VOCs, formaldehyde... the first two are the most nasty... the last two not so much, but they are common because some "wood" and particle-board furniture and fabric/insulation materials outgas/offgas them. I can't remember all the effects of these pollutants, but of course they may affect animals differently from humans.

Trying to think of what else. Are birds OK with essential oils?