Furniture, Carpets, foam insulation, pressed wood: VOCs
Tobacco Smoke: Toxic and carcinogenic compunds
Old Paint: Lead
Floor and ceiling Tiles, pipe insulation: Asbestos
Rocks and soil beneath house: Radon
Household Products, pesticides, paints, cleaning fluids: VOCs and other compounds.
Fireplaces, wood stoves: Particulate Matter
Leaky or unvented gas or wood stoves and furnaces, running cars left running: CO.