Pulmonary Toxicity of Indium-Tin Oxide and Indium Phosphide after Intratracheal Instil- lations into the Lung of Hamsters

Indium belongs to Group III A in the periodic table and it is mainly used in the making of thin-film transistor liquid crystal displays (LCDs) for television screens, portable computer screens, pocket telephone displays and video monitors, mainly through the utilization of indiumtin oxide (ITO). ITO is a sintered alloy containing a large portion of indium oxide and a small portion of tin oxide. On the other hand, indium phosphide (InP) belongs to the III–V semiconductor compounds that are widely used in the semiconductor industry. In 2000, the total domestic indium use in Japan was comprised 83% ITO and 4% InP. Due to the increasingly frequent industrial use of ITO and InP, the potential occupational or environmental exposure to indium compounds has attracted much attention. Although some animal studies concerning the lung toxicity of indium-containing semiconductor materials, such as indium arsenide (InAs) or indium phosphide (InP), have been conducted, there are no available data concerning the pulmonary toxicity of ITO. In our previous studies , we reported severe pulmonary damage caused by InAs or InP when given to hamsters in intermittent intratracheal instillations. From those studies, we considered that indium accounted for most of the lung lesions. Since the primary constitutive element of ITO is indium, there is a fair chance that the lung toxicity of ITO will appear when exposure to ITO is via the trachea. In this study, we evaluated the pulmonary toxic effect of ITO when instilled repeatedly into the trachea of hamsters. The same dose of InP particles was also used to compare the toxicity of indium compounds. Materials and Methods