sevo
Fokutorendaburando
I guess 120 format is environmentally toxic but 135 isn't. Are these people idiots or liars? All this film is the same. It's just cut differently for the various formats like 8x10, 4x5, 120, 135.
120 is on a different substrate (thinner and back coated). As you yourself pointed out, there would be no point in cancelling one but not the others, if they were all the same, so we can safely assume there is a difference.
Besides, the "environmental problems" need not mean the film itself, even though things like a different base etch process or back coat might make a difference between 120 and 135/sheet. It could also be that the only production line that can coat that emulsion to that base is outdated and not up to current regulations.
Sevo