• Makiko Nakano, Kazuyuki Omae, Kazuhiko Uchida, Takehiro Michikawa, Noriyuki Yoshioka, Miyuki Hirata, and Akiyo Tanaka.
• From the Department of Preventive Medicine and Public Health, School of Medicine, Keio University, Tokyo. Electronic address: nakano.makiko@z8.keio.jp.
• Chest. 2014 Nov 1;146(5):1166-75.

BackgroundDose-dependent adverse lung effects due to indium exposure have been reported in a cross-sectional study. This is a 5-year longitudinal cohort study of indium-exposed and unexposed workers, assessing indium exposure levels and its clinical lung effects.MethodsFrom 2008 to 2011, a 5-year follow-up study was conducted on 40 unexposed and 240 workers formerly or currently exposed to indium at 11 factories. Indium exposure was assessed by serum indium (In-S) (μg/L). Lung effects were assessed by subjective symptoms, serum biomarkers, spirometry, and chest high-resolution CT scan. Effect biomarkers used were Krebs von den Lungen and surfactant protein D.ResultsMean values of In-S, Krebs von den Lungen, and surfactant protein D among the workers exposed to indium at baseline declined during the 5-year follow-up by 29.8%, 27.2%, and 27.5%, respectively. Of the exposed subjects with In-S levels > 20 μg/L, 26.3% experienced emphysematous progression on high-resolution CT scan. Ninety percent (18 of 20) of workers with emphysematous progression during follow-up were current smokers at baseline, and a trend of increasing incidence of emphysematous progression at higher In-S levels was observed among the smokers (P = .005). Emphysematous changes among subjects with In-S levels > 20 μg/L were likely to progress, after adjusting for age, mean duration since initial indium exposure, and smoking history (OR = 10.49, 95% CI = 1.54-71.36).ConclusionsLong-term adverse effects on emphysematous changes were observed. The results suggest workers exposed to indium with In-S levels > 20 μg/L should be immediately removed from exposure.

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