I have checked up the use of mercury in bronze. It wasn't and it isn't, though lead has been. The poisonous effects of mercury do not match the described problems of smiths.

One poster on the science site with some experience suggested that the work operating the bellows could account for the disability. I do recall that in one case in myth (Wayland?) the damage was deliberately caused by the employer cutting the hamstrings to prevent the smith going to work for another.

Penny