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.