Richard Knoppow on Pyro toxicity: Source (http://www.viewcamera.com/pyro.html)
“Pyrogallic acid is toxic but one must be careful in interpreting MSDS: mostly they are written for industrial users of substances who use and store them in very large quantity.
Pyro is a sensitizer and can cause very strong skin reactions. It should be kept out of the eyes for the same reason. It is capable of causing life threatening damage if ingested in fairly large quantity. It will irritate the lungs and respiratory system if inhaled. Pyro can penetrate the skin but so can many other substances used in photography.
There have been NO studies of the chronic effects of Pyro exposure. Pyro is no more hazardous than several other developing agents. It should be treated with respect but there is no unusual hazard in using it.
Since airborne Pyro is dangerous to breathe in, it is wise to mix Pyro developers while wearing a dust mask and facial protection. You should wear nitrile gloves. Try to avoid getting the stuff into the air. It is in light flakes which become airborne easily so some care is needed.
Mixed Pyro developers are only moderately hazardous but it is a good idea not to get your hands into them. Use nitrile gloves (latex is not good enough and some people are sensitive to latex). You don't need a dust mask to use the mixed developer; it is only the airborne flakes which are hazardous. Another reason for using gloves is that Pyro produces a very persistent brown stain on anything it is on when exposed to the air including your hands and cloths.”