[Spot! Health] Core Material of Advanced Industries? Silent Assassin? The Two Faces of 'Indium'

Industry Workers Must Undergo Regular Checkups
'Special Health Checkup' System Introduced Since 2021

Indium image (Photo by GC Green Cross Medical Foundation)

[Asia Economy Reporter Chunhee Lee] Indium is a core material in advanced industries used in the manufacturing of electronic device liquid crystal displays and semiconductors. However, in recent years, cases of workers handling indium in workplaces complaining of interstitial lung disease or dying have been reported consecutively, drawing attention to health hazards caused by indium.

Indium is a rare metal element with a silvery-white luster and is the softest stable solid at room temperature, allowing it to be cut with a knife and causing it to stick to friction surfaces when rubbed. More than 87% of total indium demand is used in industries related to indium tin oxide (ITO) and indium zinc oxide (IZO). ITO and IZO have good conductivity and excellent visible light transmittance, making them key materials in solar cells, flat panel displays, touch screen displays, and the semiconductor industry. Workers in various display industries involved in manufacturing or recycling transparent conductive oxide materials or using related materials are highly likely to be exposed to indium directly or indirectly. The Korea Occupational Safety and Health Agency estimates that more than 9,000 Korean workers are exposed to indium directly or indirectly.

Indium generally does not have a biological role, but some indium compounds exhibit toxicity in the human body. Due to its low melting point, it undergoes several refining processes and changes into powder form, which can cause various health hazards if inhaled through the respiratory tract. The first reported case of indium occupational disease was in Japan in 1998, where a male worker in his 20s exposed to dust while polishing the surface of an ITO target for four years complained of dry cough and shortness of breath and eventually died of lung disease. Indium and tin were detected in the alveolar component analysis, and since then, cases of lung diseases such as pneumothorax, interstitial lung disease (indium lung), and pulmonary fibrosis caused by exposure to indium compounds have been reported in the United States, Japan, China, and other countries. In 2017, interstitial lung disease caused by indium was recognized as an occupational disease in Korea.

If you work in an indium handling industry, it is essential to undergo a special health examination implemented since January 2021. The special health examination is conducted to detect occupational diseases early in workers exposed to hazardous factors in the workplace and to enable appropriate treatment. The indium special health examination objectively measures serum indium concentration.

In the past, samples such as plasma, serum, whole blood, and urine have been studied for biological exposure assessment of indium. However, whole blood showed high variability, and urine had low indium concentrations, reducing its usefulness as an indicator. Therefore, serum, which has fewer interfering substances, is considered the most appropriate test indicator. To analyze indium, detection of concentrations less than one-tenth of those for existing heavy metals is required, making accurate analysis difficult with the commonly used graphite furnace atomic absorption spectrometer (AAS) for heavy metal testing. Advanced testing using inductively coupled plasma mass spectrometry (ICP-MS) is necessary.

Dr. Junhyung Lee, a specialist in diagnostic medicine at GC Green Cross Medical Foundation, advised, “Workers in workplaces related to indium must undergo the indium special health examination at least once a year. Even after stopping indium handling work, serum indium levels may remain high, or indium-related occupational diseases may be diagnosed belatedly, so it is recommended to undergo the test even after indium exposure has ceased.”