It is indeed not! But he's growing bigger, so it's unclear whether they're having any effect when he roars and generates enough fire to scorch the wall he's been thrown at, as he jumps to his feet and kicks the wall to throw himself forward.

"Continue trying to poison him when you can, use your strongest shots," Armsmaster says, and turns his halberd into a long, electrified morningstar which he hits Lung with. "Miss Militia!"