Personal indium exposure concentration in respirable dusts and serum indium level

Two-year follow-up of exposure, engineering controls, respiratory protection and respiratory health among workers at an indium-tin oxide (ITO) production and reclamation facility

OBJECTIVES

To determine whether engineering controls and respiratory protection had measurable short-term impact on indium exposure and respiratory health among current indium-tin oxide production and reclamation facility workers.

METHODS

We documented engineering controls implemented following our 2012 evaluation and recorded respirator use in 2012 and 2014. We measured respirable indium (Inresp) and plasma indium (InP) in 2012 and 2014, and calculated change in Inresp (∆Inresp) and InP (∆InP) by the 13 departments. We assessed symptoms, lung function, serum biomarkers of interstitial lung disease (Krebs von den Lungen (KL)-6 and surfactant protein (SP)-D) and chest high-resolution CT at both time points and evaluated workers who participated in both 2012 and 2014 for changes in health outcomes (new, worsened or improved).

RESULTS

Engineering controls included installation of local exhaust ventilation in both grinding departments (Rotary and Planar) and isolation of the Reclaim department. Respiratory protection increased in most (77%) departments. ∆InP and ∆Inresp often changed in parallel by department. Among 62 workers participating in both 2012 and 2014, 18 (29%) had new or worsening chest symptoms and 2 (3%) had functional decline in lung function or radiographic progression, but average KL-6 and SP-D concentrations decreased, and no cases of clinical indium lung disease were recognised.

CONCLUSIONS

Increased engineering controls and respiratory protection can lead to decreased Inresp, InP and biomarkers of interstitial lung disease among workers in 2 years. Ongoing medical monitoring of indium-exposed workers to confirm the longer-term effectiveness of preventive measures is warranted.

Assessment of Occupational Exposure to Indium Dust for Indium-Tin-Oxide Manufacturing Workers

According to recent research, indium nanoparticles (NPs) are more toxic than micro-sized particles. While cases of indium lung disease have been reported worldwide, very little research has been conducted on the occupational exposure to indium NPs. Recently, an indium-related lung disease was reported in Korea, a global powerhouse for display manufacturing. In this study, we conducted an assessment ofoccupational exposure at an indium tin oxide (ITO) powder manufacturing plant, where the first case of indium lung disease in Korea occurred. Airborne dustwas obtained from a worker's breathing zone, and area sampling in the workplace environment was conducted using real-time monitoring devices. Personal samples were analyzed for the indium concentrations in total dust, respirable dust fraction, and NPs using personal NPs respiratory deposition samplers. The total indium concentration of the personal samples was lower than the threshold limit value recommended by the American Conference of Governmental Industrial Hygienists (ACGIH TLV), which was set as occupational exposure limit (OEL). However, the respirable indium concentration exceeded the recently set ACGIH TLV for the respirable fraction of indium dust. The concentration of indium NPs ranged between 0.003 and 0.010 × 10-2 mg/m3, accounting for only 0.4% of the total and 2.7% of the respirable indium particles. This was attributed to the aggregating of NPs at the µm sub-level. Given the extremely low fraction of indium NPs in the total and respirable dust, the current OEL values, set as the total and respirable indium concentrations, do not holistically represent the occupational exposure to indium NPs or prevent health hazards. Therefore, it is necessary to set separate OEL values for indium NPs. This study covers only the process of handling ITO powder. Therefore, follow-up studies need to be conducted on other ITO sputtering target polishing and milling processes, which typically generate more airborne NPs, to further investigate the effects of indium on workers and facilitate the necessary implementation of indium-reducing technologies.

Biomonitorization of concentrations of 28 elements in serum and urine among workers exposed to indium compounds

Many studies have documented the abnormal concentrations of metals/metalloids in serum or urine of occupational workers, but no works systematically analysed the concentrations of elements in serum or urine of indium-exposed workers. This study was aimed to assess 28 elements in serum and urine from 57 individuals with occupational exposure to indium and its compounds. Control subjects were 63 workers without metal exposure. We collected information on occupation and lifestyle habits by questionnaire. Biological samples were collected to quantify elements by inductive coupled plasma-mass spectrometer. Air in the breathing zones was drawn at flow rates of 1.5-3 L/min for a sampling period of 6 to 8 h, using a Model BFC-35 pump. The average ambient indium level was 0.078 mg/m3. Serum/urine Indium levels were significantly higher in indium-exposed workers than in controls (P < 0.01). Moreover, serum/urine indium concentrations in the group with 6-14 years and ≥15 years of employment were significantly higher than those with ≤5 employment years(P < 0.05). Ten of the other 27 elements/metals measured were higher in serum/urine in indium-exposed workers compared to the controls (aluminum, beryllium, cadmium, cesium, chromium, lithium, manganese, magnesium, molybdenum and vanadium). Zinc levels in serum/urine were significantly decreased in the indium-exposed workers. Additionally, other elements/metals were higher in one specimen (serum or urine) but lower in the other (Selenium was lower in serum but higher in urine in the indium-exposed workers compared with the controls; likewise Thallium and Rubidium were higher in serum but lower in urine). Linear regression analyses, revealed significant correlations between serum and urine for indium, aluminum, arsenic, barium, cadmium, cesium, cobalt, selenium, silver, and zinc (P < 0.05). These data suggest that occupational exposure to indium and its compounds may disturb the homeostasis of trace elements in systemic circulation, indium concentrations in serum or urine appear reflective of workers' exposure to ambient indium and their years of working, respectively. The serum/urine levels of essential metals are modified by exposure to indium in occupationally exposed workers. Further studies including larger sample size and more kinds of biological sample are needed to validate our findings.

Nitrative DNA damage in lung epithelial cells exposed to indium nanoparticles and indium ions

Indium compounds have been widely used in manufacturing displays of mobile phones, computers and televisions. However, inhalation exposure to indium compounds causes interstitial pneumonia in exposed workers and lung cancer in experimental animals. 8-Nitroguanine (8-nitroG) is a mutagenic DNA lesion formed under inflammatory conditions and may participate in indium-induced carcinogenesis. In this study, we examined 8-nitroG formation in A549 cultured human lung epithelial cells treated with indium compounds, including nanoparticles of indium oxide (In₂O₃) and indium-tin oxide (ITO), and indium chloride (InCl₃). We performed fluorescent immunocytochemistry to examine 8-nitroG formation in indium-exposed A549 cells. All indium compounds significantly increased 8-nitroG formation in A549 cells at 5 ng/ml after 4 h incubation. 8-NitroG formation was largely reduced by 1400 W, methyl-β-cyclodextrin (MBCD) and monodansylcadaverine (MDC), suggesting the involvement of nitric oxide synthase and endocytosis. 8-NitroG formation in A549 cells was also largely suppressed by small interfering RNA (siRNA) for high-mobility group box-1 (HMGB1), receptor for advanced glycation and end products (AGER, RAGE) and Toll-like receptor 9 (TLR9). These results suggest that indium compounds induce inflammation-mediated DNA damage in lung epithelial cells via the HMGB1-RAGE-TLR9 pathway. This mechanism may contribute to indium-induced genotoxicity in the respiratory system.

[Study on the Establishment of a Specific Similar Exposure Group (SEG) in Personal Exposure Monitoring: A Case Report of Indium Tin Oxide Target Surface Grinding Process]

Surface grinding workers of Indium Tin Oxide target material are exposed to an indium compound with high toxicity. We divided individual exposure workers into similar exposure groups (SEG) and examined the effectiveness of the classification of SEG. Sampling was carried out twice a day for a total of 10 times, in 9 of which a work environment measurement in unit work area was performed at the same time. The classification examined two methods. One method was to set all the workers in the work place as one group (SEG1), and the other was to classify them depending on whether the workers handled the target material contained indium or not (SEG2). The group handled indium-contained material was SEG2(+) n=9, and the other was SEG2(-) n=9. Only the arithmetic mean value (AM) of four groups 2.8-27.4 µg/m³ in the SEG2(+) was lower than the measurement B value of the work environment measurement, but the AM of all the groups in SEG2(+) 2.8-276.8 µg/m³ was higher than the geometric mean value of measurement A 0.4-12.3 µg/m³. The concentration range of 100 μg/m³ or more of SEG2(+) AM was 20% of the total. This range was not recognized in the other items, and the variation of SEG2(+) was small. Even though the evaluation of SEG1 is control class 2, if revaluated on SEG2(+), 50% of the SEG2(+) were evaluated as control class 3. It is possible to efficiently manage chemical substances by establishing specific SEG properly stratified.

The toxicology of indium oxide

Indium oxide (In₂O₃) is a technologically important semiconductor essentially used, doped with tin oxide, to form indium tin oxide (ITO). It is poorly soluble in all so far tested physiologic media. After repeated inhalation, In₂O₃ particles accumulate in the lungs. Their mobilization can cause significant systemic exposure over long periods of time. An increasing number of cases of severe lung effects (characterized by pulmonary alveolar proteinosis, emphysema and/or interstitial fibrosis) in workers of the ITO industry warrants a review of the toxicological hazards also of In₂O₃. The database on acute and chronic toxicity/carcinogenicity/genotoxicity/reproductive toxicity as well skin/eye irritation and sensitization is very limited or even lacking. Short-term and subchronic inhalation studies in rats and mice revealed persistent alveolar proteinosis, inflammation and early indicators of fibrosis in the lungs down to concentrations of 1 mg/m³. Epidemiological and medical surveillance studies, serum/blood indium levels in workers as well as data on the exposure to airborne indium concentrations indicate a need for measures to reduce exposure at In₂O₃ workplaces.

Application of the ICRP respiratory tract model to estimate pulmonary retention of industrially sampled indium-containing dusts

Inhalation of indium-containing dusts is associated with the development of indium lung disease. Workers may be exposed to several different chemical forms of indium; however, their lung dosimetry is not fully understood. We characterized the physicochemical properties and measured the lung dissolution kinetics of eight indium-containing dusts. Indium dissolution rates in artificial lung fluids spanned two orders of magnitude. We used the International Commission on Radiological Protection (ICRP) human respiratory model (HRTM) to estimate pulmonary indium deposition, retention and biokinetic clearance to blood. For a two-year (median workforce tenure at facility) exposure to respirable-sized particles of the indium materials, modeled indium clearance (>99.99% removed) from the alveolar-interstitial compartment was slow for all dusts; salts would clear in 4 years, sintered indium-tin oxide (ITO) would clear in 9 years, and indium oxide would require 48 years. For this scenario, the ICRP HRTM predicted that indium translocated to blood would be present in that compartment for 3.5-18 years after cessation of exposure, depending on the chemical form. For a 40-year exposure (working lifetime), clearance from the alveolar-interstitial compartment would require 5, 10 and 60 years for indium salts, sintered ITO and indium oxide, respectively and indium would be present in blood for 5-53 years after exposure. Consideration of differences in chemical forms of indium, dissolution rates, alveolar clearance and residence time in blood should be included in exposure assessment and epidemiological studies that rely on measures of total indium in air or blood to derive risk estimates.