Thursday, September 22, 2016

EMERGING RISKS: Study Correlates indium-tin oxide (ITO) in Workplace Air with Respiratory Health Effects

A growing body of research indicates that workers making and reclaiming ITO are at risk for indium lung disease. Photo from Thinkstock.

In our reliance on modern technology, previously obscure chemical compounds are making their way into the manufacturing mainstream. One of these compounds is indium-tin oxide (ITO), used to make products such as flat-panel displays, touch screens, solar panels, energy-efficient windows, and many others. Although these high-tech products may benefit the consumer, a growing body of research indicates workers making and reclaiming products containing ITO are at risk for indium lung disease. Studies describe this as a serious and potentially fatal condition that can progress from early filling of the lung’s air sacs with fluid to later lung scarring and emphysema. Indium can be detected in the blood of ITO workers, and workers with higher concentrations of indium in the blood appear to be at greater risk.

However, the precise relationship between the level of exposure to airborne indium compounds and risk of indium lung disease is unclear. For one thing, scientific evidence needed to relate workplace air concentrations of indium with concentrations in the blood of exposed workers has been lacking. In a recent study, NIOSH investigators and their partners helped to fill this gap. They recently found a correlation between the amount of indium in the workplace air and early signs of lung disease among a group of ITO workers, as reported in the peer-reviewed American Journal of Industrial Medicine.

In this study, investigators examined blood concentrations of indium, air concentrations of indium, and lung health among a group of 87 volunteer study participants currently employed in the ITO industry. They found that the amount of indium in the blood reflected the air concentration of indium and the time employed in the ITO facility. In addition, the workers exposed to respirable indium for nearly 2 or more years had more shortness of breath, lower lung function, and higher levels of markers in the blood for lung damage than did workers with fewer than 2 years of exposure. In other findings, the study showed that those health effects occurred among workers in the study group who had relatively low levels of exposure to indium in the air. Further studies of other groups of ITO workers with longer and different types of work-related exposure to indium are important to confirm this study’s findings. Even so, the findings support precautionary efforts to reduce work-related exposure to respirable indium, according to the authors.

More information is available:
Respirable Indium Exposures, Plasma Indium, and Respiratory Health Among Indium-Tin Oxide (ITO) Workers
NIOSH Pocket Guide to Chemical Hazards

Indium use has increased greatly in the past decade in parallel with the growth of flat-panel displays, touchscreens, optoelectronic devices, and photovoltaic cells. Much of this growth has been in the use of indium tin oxide (ITO). This increased use has resulted in more frequent and intense exposure of workers to indium. Starting with case reports and followed by epidemiological studies, exposure to ITO has been linked to serious and sometimes fatal lung disease in workers. Much of this research was conducted in facilities that process sintered ITO, including manufacture, grinding, and indium reclamation from waste material. Little has been known about indium exposure to workers in downstream applications. 

In 2009–2011, the National Institute for Occupational Safety and Health (NIOSH) contacted 89 potential indium-using companies; 65 (73%) responded, and 43 of the 65 responders used an indium material. Our objective was to identify current workplace applications of indium materials, tasks with potential indium exposure, and exposure controls being used. Air sampling for indium was either conducted by NIOSH or companies provided their data for a total of 63 air samples (41 personal, 22 area) across 10 companies. 

Indium exposure exceeded the NIOSH recommended exposure limit (REL) of 0.1 mg/m3 for certain methods of resurfacing ITO sputter targets, cleaning sputter chamber interiors, and in manufacturing some inorganic indium compounds. Indium air concentrations were low in sputter target bonding with indium solder, backside thinning and polishing of fabricated indium phosphide-based semiconductor devices, metal alloy production, and in making indium-based solder pastes. 

Exposure controls such as containment, local exhaust ventilation (LEV), and tool-mounted LEV can be effective at reducing exposure. In conclusion, occupational hygienists should be aware that the manufacture and use of indium materials can result in indium air concentrations that exceed the NIOSH REL. Given recent findings of adverse health effects in workers, research is needed to determine if the current REL sufficiently protects workers against indium-related diseases.