To be safe, boil shed barbs prior to handleing them too much. They will clean nicely. The toxin acts on a complex protein based catalyst that breaks down with heat (hense, you run a stingray injury under HOT water if you are so unlucky).
I've noticed that sometimes the skin on the barb starts to die off before the barb is shed. Once the skin tissue starts to die, how much longer is the venom potent? I would think that once the skin dies, the venom won't last much longer.