Here is a previous thread that discussed this issue:
My personal recommendation is to wear a dust mask while using pastels. This is more because of the potential for coughs and respiratory issues, not necessarily because of toxicity issues. An air purifier with a HEPA filter might also be a good idea, but they aren't cheap. I usually just vacuum frequently. Just try to minimize the amount of dust that gets into the air - so don't blow on your painting! Some sort of dust catching tray at the bottom of your easel is also a good idea.
As far as the toxicity goes, I think if you use the usually recommended studio practices - wash hands, do not eat while painting or let pastels into areas where you have food - then I think there is little to worry about. If you are worried about cadmiums, for example, many pastel makers do not use them, although some do. You can check Dick Blick's website to get some idea (although not 100% reliable) regarding which sticks have the warning labels.
Again, I think the biggest issue with the dust is a possibility of respiratory issues, for which a simple dust mask will usually suffice.