you can literally pick the shed barb up with your fingers and not worry about the toxin. it's only a problem if you pierce yourself with it. in other words, try to grab the barb by it's base, not the pointy tip. you can then do what you like with it: boil it, scrub with a toothbrush, etc.
the toxin will not stay on the barb for long once it is detached from the ray, and hot water will help break down the protein compound of the venom.