Department of Preventive Medicine and Public Health, School of Medicine, Keio University-Background: Recent case reports and epidemiological studies suggest that inhalation of indium dust induces lung damage. Objectives: To elucidate the dose-dependent effects of indium on the lungs and to prove a causal relationship more clearly. Methods: A baseline observation was conducted on 465 workers currently exposed to indium, 127 workers formerly exposed to indium and 169 workers without indium exposure in 12 factories and 1 research laboratory from 2003 to 2006. Indium in serum (In-S) was determined as an exposure parameter, and its effects on the lungs were examined. Results: The means of In-S in the current, former and no exposure workers were 8.35, 9.63 and 0.56 ng/ml, respectively. The current and former exposure workers had significantly higher levels of KL-6, and showed significant dose-dependent increases in KL-6, SP-D, and SP-A. Current exposure workers with In-S of 3 ng/ml or above demonstrated a significant increase of KL-6 in both GM and prevalence exceeding the reference value. Approximately a quarter of the former exposure workers had interstitial changes as seen on chest HRCT. In-S of exposed workers who had been working before improvements of the working environment (Group Bef) and those who started working after improvements (Group Aft) were 12.29 and 0.81 ng/ml, respectively. Adjusted odds ratios indicated 87%, 71% and 44% reductions among Group Aft workers who exceeded the reference values of KL-6, SP-D and SP-A, respectively. Conclusion: Dose-dependent lung effects due to indium exposure were shown, and a decrease of indium exposure reduced the lung effects. An In-S value of 3 ng/ml may be a cut-off value which could be used to prevent early effects on the lungs.
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