Studies on the Toxicity and Distribution of Indium Compounds According to Particle Size in Sprague-Dawley Rats

Objectives: The use of indium compounds, especially those of small size, for the production of semiconductors, liquid-crystal panels, etc., has increased recently. However, the role of particle size or the chemical composition of indium compounds in their toxicity and distribution in the body has not been sufficiently investigated. Therefore, the aim of this study was to examine the effects of particle size and the chemical composition of indium compounds on their toxicity and distribution. Methods: Male Sprague-Dawley rats were exposed to two different-sized indium oxides (average particle sizes under 4,000 nm [IO_4000] and 100 nm [IO_100]) and one nano-sized indium-tin oxide (ITO; average particle size less than 50 nm) by inhalation for 6 hr daily, 5 days per week, for 4 weeks at approximately 1 mg/m(3) of indium by mass concentration. Results: We observed differences in lung weights and histopathological findings, differential cell counts, and cell damage indicators in the bronchoalveolar lavage fluid between the normal control group and IO- or ITO-exposed groups. However, only ITO affected respiratory functions in exposed rats. Overall, the toxicity of ITO was much higher than that of IOs; the toxicity of IO_4000 was higher than that of IO_100. A 4-week recovery period was not sufficient to alleviate the toxic effects of IO and ITO exposure. Inhaled indium was mainly deposited in the lungs. ITO in the lungs was removed more slowly than IOs; IO_4000 was removed faster than IO_100. IOs were not distributed to other organs (i.e., the brain, liver, and spleen), whereas ITO was. Concentrations of indium in the blood and organ tissues were higher at 4 weeks after exposure. Conclusions: The effect of particle size on the toxicity of indium compounds was not clear, whereas chemical composition clearly affected toxicity; ITO showed much higher toxicity than that of IO.