Use of and Occupational Exposure to Indium in the United States

Abstract

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.

The toxicology of indium tin oxide

“…The data on the exposure to indium at the workplace indicate that some concentrations in the air were partly much higher than the concentrations in the inhalation studies in rats and mice causing marked lung toxicity (Chonan et al, 2007;Choi and An 2016;Cummings et al, 2013Cummings et al, , 2016Hines et al, 2013;NIOSH, 2012;Wu et al, 2014). It therefore seems necessary to take measures for reducing the exposure at the workplace and to review the current exposure limits still valid e.g.…”

“…Cleaning sputter or evaporation chambers used to deposit ITO resulted in personal indium air concentrations of 0.072-5.4 mg/m 3 . The authors concluded among others, that research is needed to evaluate the adequacy of the current recommended exposure limit (REL) of 0.1 mg/m 3 for protecting workers (Hines et al, 2013).…”

“…ITO may be formed directly during a coating process, e.g., reactive sputtering from indium-tin alloy targets in the presence of oxygen. The sintered tiles, or targets, are ground and cut to the customer's specifications for sputtering (Cummings et al, 2013;Hines et al, 2013;NTP, 2009). …”

Exposure Potential and Health Impacts of Indium and Gallium, Metals Critical to Emerging Electronics and Energy Technologies

“…Indium is used mainly in indium tin oxide (ITO) coatings for flat panel and liquid crystal displays (7). It is also used in LEDs and high-efficiency photovoltaic cells, markets that have seen rapid growth and are predicted to continue expanding (6,8). A relatively small use of indium, though one that could lead to significant exposure, is the use of a radioisotope 111 In for medical imaging and biodistribution studies (7,9).…”

Assessing risk of indium lung disease to workers in downstream industries

“…The extent of occupational exposure to ITO and other indium‐containing compounds in these downstream industries in the United States remains largely unknown. Hines et al [] found that workers at ITO thin film deposition companies were exposed to indium between sputtering runs when ITO targets were resurfaced or during cleaning of chamber interiors and shields. In fact, personal indium air concentration reached 5.4 mg/m 3 for cleaning sputter or evaporation chambers [Hines et al, ], which is orders of magnitude above the Japanese respirable exposure limit of 0.3 μg/m 3 [MHLW, ].…”