Long-term occupational risk of rare-earth pneumoconiosis. A case report as investigated by neutron activation analysis.

A case of rare-earth (RE) pneumoconiosis is described and discussed. A man working in a lithographic laboratory as a photoengraver, and exposed to the smoke of cored carbon arc lamps over a period of 46 years developed an interstitial pneumoconiosis. Neutron activation analysis (NAA) of eight rare-earths (La, Ce, Nd, Sm, Eu, Tb, Yb and Lu) in lung and lymph node biopsies showed an abnormally high amount of these elements in comparison to the corresponding values of 11 autopsied for unexposed subjects. The estimated radiological dose due to the inhalation of natural thorium, as calculated from NAA of thorium in the biopsies, tends to exclude the effect of ionizing radiation in the pathogenesis of lung fibrosis. Effects of other potential pathogenetic agents such as coal or heavy metal dusts, other than RE, irritative agents such as nitrous and hydrofluoric vapours originated during the photoengraving process, are also discussed. The findings strongly suggest that a relationship exists between the pneumoconiosis diagnosed and the occupational exposure to rare-earth dusts calling attention to proposals for maximum permissible concentration limits of occupational exposure to RE in air.