Effects of indium exposure on the lungs of workers: A cross-sectional study

Background: Indium lung disease is a new occupational disease. Indium is a rare metal used in the main form of indium-tin oxide as the electrode in flat-panel displays. The first and fatal case of interstitial pneumonia due to indium exposure have been reported in Japan in 2003, and since then 10 indium-related lung diseases were reported worldwide. In 2013, indium compounds were added to the list of substances regulated by an Ordinance on the Prevention of Hazards Due to Specified Chemical Substances (SCS) in Japan. However, indium metal (IM) is not listed as an SCS, because the lung effects of IM exposure are unknown. Aim: Our objective was to assess the association between IM exposure and its pulmonary effects. Methods: We conducted a health check including serum biomarker of interstitial pneumonia and pulmonary function tests for 109 workers exposed to IM between 2011 and 2013. The characteristics of the subjects were: mean age (41y/o), smokers (65%), mean duration of IM exposure (8.3years), and serum indium level (In-S, 0.3μg/L). We divided the subjects into 8 groups according to their types of occupation. Results: The mean values were as follows: KL-6 271U/mL; SP-D 50.6ng/mL; %VC 108%; %TLC 95%; FEV1/FVC 83%, and %DLco 93%. There was a significant dose-response relationship between In-S and KL-6. In particular, the mean In-S of the subjects who worked in the dissolution processes at ≥1000° (HDP) was significantly high compared to those in the other groups. The mean KL-6 of the HDP workers was significantly high compared to the solder and the dental technician group. Conclusions: We recommend that employers be required to give the HDP workers a medical checkup at least once a year to check In-S and KL-6.