Several episodes of ''smelter disease'', previously assumed to be caused by sulphur dioxide (SO2) poisoning, have been reported in workers replacing pipes in sulphuric acid manufacturing plants. One such incident, affecting 20 men, was recorded in Akita, Japan, in July, 1993, but the protection these workers used suggested that some cause other than SO2 needed to be looked for. 10 workers were affected despite wearing respirators with SO2 cartridges, the symptoms including dyspnoea, diarrhoea, colicky pain, muscle pain and eczema with erythema. Subsequently 10 other workers using face masks with supplied air were affected, though without respiratory symptoms. Sludge in the piping contained mercuric sulphate, and mercury fumes resulted when pipes were cut with gas burners. Blood and urine measurements confirmed heavy exposure to the metal, and simulation experiments in rats showed that skin absorption was likely too. The masks with supplied air ought to have excluded both SO2 and mercury fumes. The only way to avoid smelter disease reliably is to wear an encapsulated suit that prevents inhalation and skin absorption of industrial toxins.
