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NIOSH Studies Occupational Indium Exposure and Respiratory Health

Release Date: October 20, 2016

Despite the increasing use of indium tin oxide (ITO) in products ranging from touch screens and flat panel displays to solar cells and semiconductors, health concerns associated with the indium-containing compound are on the rise as well. For the period 2003 to 2010, ten cases of lung disease involving workers in ITO production, use, and indium reclamation in Japan, the United States, and China have been reported, two resulting in death. Indium exposure may result in a lung disease, which progresses from alveolar proteinosis (i.e., filling of the air sacs with a protein/lipid mixture) to fibrosis and emphysema.

Measuring the amount of indium in a worker’s blood, a form of biological monitoring, has been used in Japan to monitor exposure to ITO and assist in determining when work restrictions should be implemented. However, because few health studies have included air monitoring for indium compounds, the precise relationship between workplace exposure and the level of indium in the blood, and in addition, the risk of indium lung disease, remains unclear.

For example, do the levels of indium found in the blood reflect recent exposures to airborne indium, or do they represent cumulative exposure to airborne indium compounds that were present in the workplace over a period of years? The answer is important because if the blood indium levels represent historical rather than current airborne exposures, this limits the opportunity for effective intervention, such as implementation of engineering controls. In other words, by the time blood indium levels rise to levels of concern, the conditions causing the exposures may have changed or may no longer be present in the workplace. Similarly, without an understanding of the relationship between airborne exposure, blood indium levels, and health effects, it is difficult to establish protective exposure limits for airborne indium compounds in the workplace or protective biological limits for indium in the blood of workers.

In order to answer such questions, National Institute for Occupational Safety and Health (NIOSH) investigators and its partners conducted a study at a facility where two workers had developed indium lung disease, one of whom died. Eighty-seven ITO workers at the plant participated in the study, with three quarters working in production-related activities, and the remainder working in labs and offices. The average tenure of the group was 1.9 years.

Since no indium air monitoring had been conducted at the facility prior to the NIOSH study, investigators collected 110 personal respirable dust samples, which were analyzed for indium. Based on the sample results, and the length of time each employee worked with indium as determined from employee work histories, statistical techniques were used to develop a metric that indicated cumulative, long-term exposure to indium. In other words, the investigators “reconstructed” the employee’s past, long-term exposure based on the air sample results for various jobs coupled with the amount of time spent in the sampled jobs as determined from the work histories.

The NIOSH study reported several key findings: