Application of the ICRP respiratory tract model to estimate pulmonary retention of industrially sampled indium-containing dusts

Abstract

Inhalation of indium-containing dusts is associated with the development of indium lung disease. Workers may be exposed to several different chemical forms of indium; however, their lung dosimetry is not fully understood. We characterized the physicochemical properties and measured the lung dissolution kinetics of eight indium-containing dusts. Indium dissolution rates in artificial lung fluids spanned two orders of magnitude. We used the International Commission on Radiological Protection (ICRP) human respiratory model (HRTM) to estimate pulmonary indium deposition, retention and biokinetic clearance to blood. For a two-year (median workforce tenure at facility) exposure to respirable-sized particles of the indium materials, modeled indium clearance (>99.99% removed) from the alveolar-interstitial compartment was slow for all dusts; salts would clear in 4 years, sintered indium–tin oxide (ITO) would clear in 9 years, and indium oxide would require 48 years. For this scenario, the ICRP HRTM predicted that indium translocated to blood would be present in that compartment for 3.5–18 years after cessation of exposure, depending on the chemical form. For a 40-year exposure (working lifetime), clearance from the alveolar–interstitial compartment would require 5, 10 and 60 years for indium salts, sintered ITO and indium oxide, respectively and indium would be present in blood for 5–53 years after exposure. Consideration of differences in chemical forms of indium, dissolution rates, alveolar clearance and residence time in blood should be included in exposure assessment and epidemiological studies that rely on measures of total indium in air or blood to derive risk estimates.

Keywords:

• Inhalation
• dissolution
• indium
• ITO
• biodurability
• dose metrics

Acknowledgments

The authors wish to thank NIOSH staff members M.G. Duling and R.B. Lawrence for assistance with the dissolution studies and Dr. Ji Young Park for collection of the MOUDI samples. Mention of a specific product or company does not constitute endorsement by the Centers for Disease Control and Prevention. The findings and conclusions in this report are those of the authors and do not necessarily represent the views of NIOSH.

Disclosure statement

The authors declare that they have no competing interests, financial or otherwise.

Additional information

Funding

This project was funded by NIOSH through an intramural National Occupational Research Agenda grant. The decision to submit the manuscript for publication was that of the authors and was independent of the funding source or the company from which the study materials were obtained.