Health effects of indium compounds in animal experiments

Before 2000, very little attention had been paid to the health effects of indium, a rare metal, because there was very little information in the literature on its toxicity. A fatal case of indium-tin oxide (ITO) inhalation occurred in 2001, followed by concerns regarding occupational exposure to indium compounds and their health effects. Epidemiological studies and case reports have established a causal relationship between the inhalation of insoluble indium compounds, mainly ITO, and the development of lung damage. This review focuses on the results of animal studies of ITO and other insoluble indium compounds. Available data indicate that insoluble indium compounds such as ITO, indium arsenide (InAs), indium phosphide (InP), and copper indium gallium diselenide (CIGS) solar cell materials are toxic to the lungs of animals. In addition to lung damage, ITO nanoparticles have been found to cause kidney damage, whereas InAs, InP, and ITO cause testicular damage. Furthermore, there is compelling evidence for the carcinogenic potential of InP in long-term inhalation studies using rats and mice, which was evident in rats exposed to ITO. Based on the results of these animal experiments, the International Agency for Research on Cancer evaluated InP as probably carcinogenic to humans (Group 2A) and ITO as possibly carcinogenic to humans (Group 2 B). Based on the results of animal studies, it should be noted that occupational exposure of humans to insoluble indium compounds not only may cause lung damage, but also lung carcinogenesis and kidney or testicular damage in the future. Greater attention should be directed towards human occupational exposure to insoluble indium compounds.