Occupational exposure to indium: what does biomonitoring tell us?

Nose-to-brain translocation and nervous system injury in response to indium tin oxide nanoparticles of long-term low-dose exposures

Indium tin oxide (ITO) is a semiconductor nanomaterial with broad application in liquid crystal displays, solar cells, and electrochemical immune sensors. It is worth noting that, with the gradual increase in worker exposure opportunities, the exposure risk in occupational production cannot be ignored. At present, the toxicity of ITO mainly focuses on respiratory toxicity. ITO inhaled through the upper respiratory tract can cause pathological changes such as interstitial pneumonia and pulmonary fibrosis. Still, extrapulmonary toxicity after nanoscale ITO nanoparticle (ITO NPs) exposure, such as long-term effects on the central nervous system, should also be of concern. Therefore, we set up exposure dose experiments (0 mg·kg-1, 3.6 mg·kg-1, and 36 mg·kg-1) based on occupational exposure limits to treat C57BL/6 mice via nasal drops for 15 weeks. Moreover, we conducted a preliminary assessment of the neurotoxicity of ITO NPs (20-30 nm) in vivo. The results indicated that ITO NPs can cause diffuse inflammatory infiltrates in brain tissue, increased glial cell responsiveness, abnormal neuronal cell lineage transition, neuronal migration disorders, and neuronal apoptosis related to the oxidative stress induced by ITO NPs exposure. Hence, our findings provide useful information for the fuller risk assessment of ITO NPs after occupational exposure.

Exposure profiles of workers from indium tin oxide target manufacturing and recycling factories in Taiwan

Indium tin oxide exposure poses a potential health risk, but the exposure assessment in occupational setting remains incomplete and continues to be a significant challenge. To this end, we investigated the association of work type, airborne indium concentration, respirable fraction of total indium, and cumulative indium exposure index (CEI) with the levels of plasma indium (P-In) and urinary indium (U-In) among 302 indium tin oxide target manufacturing and recycling workers in Taiwan. We observed that recycling-crushing produced the highest concentrations of total indium (area: 2084.8 μg/m³; personal: 3494.5 μg/m³) and respirable indium (area: 533.4 μg/m³; personal: 742.0 μg/m³). Powdering produced the highest respirable fraction of total indium (area: 58.6%; personal: 81.5%), where the workers had the highest levels of P-In (geometric mean: 2.0 μg/L) and U-In (1.0 μg/g creatinine). After adjusting for the confounder, the CEIs of powdering (β_PR = 0.78; β_PR = 0.44), bonding (β_PT = 0.61; β_PT = 0.37), and processing workers (β_PT = 0.43; β_PT = 0.28) showed significant associations with P-In and U-In, validating its utility in monitoring the exposure. Also, the respirable fraction of total indium significantly contributed to the increased levels of P-In and U-In among workers. The varying levels of relationship noted between indium exposure and the levels of P-In and U-In among workers with different work types suggested that setting the exposure limits among different work types is warranted.

Indium Uptake and Accumulation by Rice and Wheat and Health Risk Associated with Their Consumption

The increasing use of indium in high-tech industries has inevitably caused its release into the environment. However, knowledge of its environmental fate has been very limited so far. This study investigates the indium uptake and accumulation by two staple crops, rice (Oryza sativa L.) and wheat (Triticum aestivum L.), and evaluates potential risks associated with their consumption. Rice and wheat were grown on three kinds of soil, including acidic soils spiked with a high indium concentration (1.0 mmol kg^-1), which is considered the worst-case scenario, because high soil acidity promotes indium bioavailability. The results revealed that a large portion of soil indium was associated with iron hydroxides, even in acidic soils. Indium precipitates in soils resulted in relatively low availability at the plant root site. Most absorbed indium accumulated at the roots, with only a tiny portion reaching the grains. The corresponding Hazard Quotient indicated no adverse effects on human health. Due to the low translocation of indium from soil to grain, the consumption of rice and wheat grains harvested from indium-contaminated soils may pose an insignificant risk to human health. Further field studies are necessary to better elucidate the risks associated with consuming crops grown in indium-contaminated soils.

Work Tasks as Determinants of Respirable and Inhalable Indium Exposure among Workers at an Indium-Tin Oxide Production and Reclamation Facility

Increased global demand for touch screens, photovoltaics, and optoelectronics has resulted in an increase in the production of indium-tin oxide (ITO). Occupational exposure to indium compounds is associated with the development of indium lung disease. Although many previous epidemiologic investigations highlight an excess of lung abnormalities in workplaces where ITO is produced, few assessments of occupational exposure to respirable and inhalable indium are reported to date. The objective of this study was to identify the determinants of respirable and inhalable indium at an ITO production facility to target exposure interventions. In 2012 and 2014, we conducted exposure assessments at an ITO production facility and collected full-shift personal respirable (n = 159) and inhalable (n = 57) indium samples. We also observed workers and recorded information on task duration and location, materials used, and use of personal protective equipment (PPE). Tasks (n = 121) recorded in task diaries were categorized into 40 similar task groups using the Advanced REACH Tool and process-related information. Mixed-effects models were fit separately for log-transformed respirable and inhalable indium, with random effect of subject and fixed effects of task groups. Overall, respirable and inhalable indium measurements ranged from 0.1 to 796.6 µg m-3 and 1.6 to 10 585.7 µg m-3, respectively, and were highly correlated with Spearman correlation coefficient of 0.90. The final model for respirable indium explained 36.3% of total variance and identified sanding, powder transfer tasks in reclaim, powder transfer tasks in refinery, handling indium materials, and liquid transfer tasks in ITO production as tasks associated with increased respirable indium exposure. The final model for inhalable indium explained 24.6% of total variance and included powder transfer tasks in ITO production, cleaning cylinder or tile, and handling indium material tasks. Tasks identified as strong predictors of full-shift exposure to respirable and inhalable indium can guide the use of engineering, administrative, and PPE controls designed to mitigate occupational exposure to indium. Moreover, since the tasks were aligned with REACH activities, results from this study can also be used to inform REACH activity scenarios.

A field evaluation of a single sampler for respirable and inhalable indium and dust measurements at an indium-tin oxide manufacturing facility

Indium-tin oxide production has increased greatly in the last 20 years subsequent to increased global demand for touch screens and photovoltaics. Previous studies used measurements of indium in blood as an indicator of indium exposure and observed associations with adverse respiratory outcomes. However, correlations between measurements of blood indium and airborne respirable indium are inconsistent, in part because of the long half-life of indium in blood, but also because respirable indium measurements do not incorporate inhalable indium that can contribute to the observed biological burden. Information is lacking on relationships between respirable and inhalable indium exposure, which have implications for biological indicators like blood indium. The dual IOM sampler includes the foam disc insert and can simultaneously collect respirable and inhalable aerosol. Here, the field performance of the dual IOM sampler was evaluated by comparing performance with the respirable cyclone and traditional IOM for respirable and inhalable indium and dust exposure, respectively. Side-by-side area air samples were collected throughout an indium-tin oxide manufacturing facility. Cascade impactors were used to determine particle size distribution. Several statistical methods were used to evaluate the agreement between the pairs of samplers including calculating the concordance correlation coefficient and its accuracy and precision components. One-way ANOVA was used to evaluate the effect of dust concentration on sampler differences. Respirable indium measurements showed better agreement (concordance correlation coefficient: 0.932) compared to respirable dust measurements (concordance correlation coefficient: 0.777) with significant differences observed in respirable dust measurements. The dual IOM measurements had high agreement with the traditional IOM for inhalable indium (concordance correlation coefficient: 0.997) but lower agreement for inhalable dust (concordance correlation coefficient: 0.886 and accuracy: 0.896) with a significantly large mean bias (-146.9 µg/m³). Dust concentration significantly affected sampler measurements of inhalable dust and inhalable indium. Results from this study suggest that the dual IOM is a useful single sampler for simultaneous measurements of occupational exposure to respirable and inhalable indium.

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.

New interplay between interstitial and alveolar macrophages explains pulmonary alveolar proteinosis (PAP) induced by indium tin oxide particles

Occupational exposure to indium tin oxide (ITO) particles has been associated with the development of severe lung diseases, including pulmonary alveolar proteinosis (PAP). The mechanisms of this lung toxicity remain unknown. Here, we reveal the respective roles of resident alveolar (Siglec-F^high AM) and recruited interstitial (Siglec-F^low IM) macrophages contributing in concert to the development of PAP. In mice treated with ITO particles, PAP is specifically associated with IL-1α (not GM-CSF) deficiency and Siglec-F^high AM (not Siglec-F^low IM) depletion. Mechanistically, ITO particles are preferentially phagocytosed and dissolved to soluble In³⁺ by Siglec-F^low IM. In contrast, Siglec-F^high AM weakly phagocytose or dissolve ITO particles, but are sensitive to released In³⁺ through the expression of the transferrin receptor-1 (TfR1). Blocking pulmonary Siglec-F^low IM recruitment in CCR2-deficient mice reduces ITO particle dissolution, In³⁺ release, Siglec-F^high AM depletion, and PAP formation. Restoration of IL-1-related Siglec-F^high AM also prevented ITO-induced PAP. We identified a new mechanism of secondary PAP development according to which metal ions released from inhaled particles by phagocytic IM disturb IL-1α-dependent AM self-maintenance and, in turn, alveolar clearance.

Ecotoxicity assessment of ionic As(III), As(V), In(III) and Ga(III) species potentially released from novel III-V semiconductor materials

III-V materials such as indium arsenide (InAs) and gallium arsenide (GaAs) are increasingly used in electronic and photovoltaic devices. The extensive application of these materials may lead to release of III-V ionic species during semiconductor manufacturing or disposal of decommissioned devices into the environment. Although arsenic is recognized as an important contaminant due to its high toxicity, there is a lack of information about the toxic effects of indium and gallium ions. In this study, acute toxicity of As(III), As(V), In(III) and Ga(III) species was evaluated using two microbial assays testing for methanogenic activity and O₂ uptake, as well as two bioassays targeting aquatic organisms, including the marine bacterium Aliivibrio fischeri (bioluminescence inhibition) and the crustacean Daphnia magna (mortality). The most noteworthy finding was that the toxicity is mostly impacted by the element tested. Secondarily, the toxicity of these species also depended on the bioassay target. In(III) and Ga(III) were not or only mildly toxic in the experiments. D. magna was the most sensitive organism for In(III) and Ga(III) with 50% lethal concentrations of 0.5 and 3.4mM, respectively. On the other hand, As(III) and As(V) caused clear inhibitory effects, particularly in the methanogenic toxicity bioassay. The 50% inhibitory concentrations of both arsenic species towards methanogens were about 0.02mM, which is lower than the regulated maximum allowable daily effluent discharge concentration (2.09mg/L or 0.03mM) for facilities manufacturing electronic components in the US. Overall, the results indicate that the ecotoxicity of In(III) and Ga(III) is much lower than that of the As species tested. This finding is important in filling the knowledge gap regarding the ecotoxicology of In and Ga.

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.

Comparing plasma, serum and whole blood indium concentrations from workers at an indium-tin oxide (ITO) production facility

OBJECTIVE

Occupational exposure to indium compounds including indium-tin oxide (ITO) can result in potentially fatal indium lung disease. We compared plasma, serum and whole blood indium concentrations (In_P, In_S and In_B) from workers at a single ITO production facility to assess the comparability of these matrices used for biological monitoring of indium exposure.

METHOD

In_P, In_S and In_B were measured using inductively coupled mass spectrometry from consenting workers at an ITO production facility with specimen collection occurring during June-July 2014. Matched pairs from workers were assessed to determine the matrix relationships using the Pearson correlation, paired t-tests, per cent difference, linear regression and κ statistics.

RESULTS

Indium matrices were collected from 80 workers. Mean (SD) In_P, In_S and In_B were 3.48 (3.84), 3.90 (4.15) and 4.66 (5.32) mcg/L, respectively. The In_S-In_P difference was 14%; In_S was higher in all but two workers. In_P and In_S were highly correlated (r=>0.99). The In_B-In_S difference was 19%; In_B was higher in 85% of workers. The In_B-In_P difference was 34%; In_B was higher in 66% of workers. In_B was highly correlated with both In_P and In_S (r=0.97 and 0.96, respectively). κ Statistics were 0.84, 0.83 and 0.82 for In_P, In_S and In_B, respectively, for individuals with each matrix ≥1 mcg/L (p<0.01).

CONCLUSIONS

While all matrices were highly correlated, we encourage the use of In_P and In_S to reliably compare studies across different populations using different matrices. The higher per cent difference and increased variability of In_B may limit its utility in comparisons with In_P and In_S in different populations.

Respirable indium exposures, plasma indium, and respiratory health among indium-tin oxide (ITO) workers

BACKGROUND

Workers manufacturing indium-tin oxide (ITO) are at risk of elevated indium concentration in blood and indium lung disease, but relationships between respirable indium exposures and biomarkers of exposure and disease are unknown.

METHODS

For 87 (93%) current ITO workers, we determined correlations between respirable and plasma indium and evaluated associations between exposures and health outcomes.

RESULTS

Current respirable indium exposure ranged from 0.4 to 108 μg/m(3) and cumulative respirable indium exposure from 0.4 to 923 μg-yr/m(3) . Plasma indium better correlated with cumulative (rs  = 0.77) than current exposure (rs  = 0.54) overall and with tenure ≥1.9 years. Higher cumulative respirable indium exposures were associated with more dyspnea, lower spirometric parameters, and higher serum biomarkers of lung disease (KL-6 and SP-D), with significant effects starting at 22 μg-yr/m(3) , reached by 46% of participants.

CONCLUSIONS

Plasma indium concentration reflected cumulative respirable indium exposure, which was associated with clinical, functional, and serum biomarkers of lung disease. Am. J. Ind. Med. 59:522-531, 2016. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Effects of a powered air-purifying respirator intervention on indium exposure reduction and indium related biomarkers among ITO sputter target manufacturing workers

This study aimed to evaluate the efficacy of powered air-purifying respirators (PAPRs) worn by the workers, and to investigate the effect of this application on exposure and preclinical effects in terms of workplace measuring and biomarker monitoring in ITO sputter target manufacturing plants and workers, respectively. Fifty-four workers were recruited and investigated from 2010-2012, during which PAPRs were provided to on-site workers in September 2011. Each worker completed questionnaires and provided blood and urine samples for analysis of biomarkers of indium exposure and preclinical effects. Area and personal indium air samples were randomly collected from selected worksites and from participants. The penetration percentage of the respirator (concentration inside respirator divided by concentration outside respirator) was 6.6%. Some biomarkers, such as S-In, SOD, GPx, GST, MDA, and TMOM, reflected the decrease in exposure and showed lower levels, after implementation of PAPRs. This study is the first to investigate the efficacy of PAPRs for reducing indium exposure. The measurement results clearly showed that the implementation of PAPRs reduces levels of indium-related biomarkers. These findings have practical applications for minimizing occupational exposure to indium and for managing the health of workers exposed to indium.

Implications of the Differential Toxicological Effects of III-V Ionic and Particulate Materials for Hazard Assessment of Semiconductor Slurries

Because of tunable band gaps, high carrier mobility, and low-energy consumption rates, III-V materials are attractive for use in semiconductor wafers. However, these wafers require chemical mechanical planarization (CMP) for polishing, which leads to the generation of large quantities of hazardous waste including particulate and ionic III-V debris. Although the toxic effects of micron-sized III-V materials have been studied in vivo, no comprehensive assessment has been undertaken to elucidate the hazardous effects of submicron particulates and released III-V ionic components. Since III-V materials may contribute disproportionately to the hazard of CMP slurries, we obtained GaP, InP, GaAs, and InAs as micron- (0.2-3 μm) and nanoscale (<100 nm) particles for comparative studies of their cytotoxic potential in macrophage (THP-1) and lung epithelial (BEAS-2B) cell lines. We found that nanosized III-V arsenides, including GaAs and InAs, could induce significantly more cytotoxicity over a 24-72 h observation period. In contrast, GaP and InP particulates of all sizes as well as ionic GaCl3 and InCl3 were substantially less hazardous. The principal mechanism of III-V arsenide nanoparticle toxicity is dissolution and shedding of toxic As(III) and, to a lesser extent, As(V) ions. GaAs dissolves in the cell culture medium as well as in acidifying intracellular compartments, while InAs dissolves (more slowly) inside cells. Chelation of released As by 2,3-dimercapto-1-propanesulfonic acid interfered in GaAs toxicity. Collectively, these results demonstrate that III-V arsenides, GaAs and InAs nanoparticles, contribute in a major way to the toxicity of III-V materials that could appear in slurries. This finding is of importance for considering how to deal with the hazard potential of CMP slurries.

Early changes in clinical, functional, and laboratory biomarkers in workers at risk of indium lung disease

RATIONALE

Occupational exposure to indium compounds, including indium-tin oxide, can result in potentially fatal indium lung disease. However, the early effects of exposure on the lungs are not well understood.

OBJECTIVES

To determine the relationship between short-term occupational exposures to indium compounds and the development of early lung abnormalities.

METHODS

Among indium-tin oxide production and reclamation facility workers, we measured plasma indium, respiratory symptoms, pulmonary function, chest computed tomography, and serum biomarkers of lung disease. Relationships between plasma indium concentration and health outcome variables were evaluated using restricted cubic spline and linear regression models.

MEASUREMENTS AND MAIN RESULTS

Eighty-seven (93%) of 94 indium-tin oxide facility workers (median tenure, 2 yr; median plasma indium, 1.0 μg/l) participated in the study. Spirometric abnormalities were not increased compared with the general population, and few subjects had radiographic evidence of alveolar proteinosis (n = 0), fibrosis (n = 2), or emphysema (n = 4). However, in internal comparisons, participants with plasma indium concentrations ≥ 1.0 μg/l had more dyspnea, lower mean FEV1 and FVC, and higher median serum Krebs von den Lungen-6 and surfactant protein-D levels. Spline regression demonstrated nonlinear exposure response, with significant differences occurring at plasma indium concentrations as low as 1.0 μg/l compared with the reference. Associations between health outcomes and the natural log of plasma indium concentration were evident in linear regression models. Associations were not explained by age, smoking status, facility tenure, or prior occupational exposures.

CONCLUSIONS

In indium-tin oxide facility workers with short-term, low-level exposure, plasma indium concentrations lower than previously reported were associated with lung symptoms, decreased spirometric parameters, and increased serum biomarkers of lung disease.

Use of and occupational exposure to indium in the United States

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/m(3) 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.

Visualisation of sentinel lymph node with indium-based near infrared emitting Quantum Dots in a murine metastatic breast cancer model

Due to its non-invasiveness, high temporal resolution and lower cost, fluorescence imaging is an interesting alternative to the current method (blue dye and radiocolloid) of sentinel lymph node (SLN) mapping in breast cancer. Near-infrared (NIR) emitting cadmium-based Quantum Dots (QDs) could be used for this purpose; however, their wide application is limited because of the toxicity of heavy metals composing the core. Our recent work demonstrated that indium-based QDs exhibit a weak acute local toxicity in vivo compared to their cadmium-based counterparts. In the present study we confirmed the weak toxicity of CuInS(2)/ZnS QDs in different in vitro models. Further in vivo studies in healthy mice showed that In-based QDs could be visualised in SLN in a few minutes after administration with a progressive increase in fluorescence until 8 h. The quantity of indium was assessed in selected organs and tissues by inductively coupled plasma - mass spectroscopy (ICP-MS) as a function of post-injection time. QD levels decrease rapidly at the injection point in the first hours after administration with a parallel increase in the lymph nodes and to a lesser extent in the liver and spleen. In addition, we observed that 3.5% of the injected indium dose was excreted in faeces in the first 4 days, with only trace quantities in the urine. Metastatic spread to the lymph nodes may hamper its visualisation. Therefore, we further performed non-invasive fluorescence measurement of QDs in SLN in tumour-bearing mice. Metastatic status was assessed by immunohistology and molecular techniques and revealed the utmost metastatic invasion of 36% of SLN. Fluorescence signal was the same irrespective of SLN status. Thus, near-infrared emitting cadmium-free QDs could be an excellent SLN tracer.