Chronic pulmonary toxicity study of indium-tin oxide and indium oxide following intratracheal instillations into the lungs of hamsters

Subchronic toxicity study of indium-tin oxide nanoparticles following intratracheal administration into the lungs of rats

OBJECTIVES

We aimed to analyze the subchronic toxicity and tissue distribution of indium after the intratracheal administration of indium-tin oxide nanoparticles (ITO NPs) to the lungs of rats.

METHODS

Male Wistar rats were administered a single intratracheal dose of 10 or 20 mg In/kg body weight (BW) of ITO NPs. The control rats received only an intratracheal dose of distilled water. A subset of rats was periodically euthanized throughout the study from 1 to 20 weeks after administration. Indium concentrations in the serum, lungs, mediastinal lymph nodes, kidneys, liver, and spleen as well as pathological changes in the lungs and kidneys were determined. Additionally, the distribution of ionic indium and indium NPs in the kidneys was analyzed using laser ablation-inductively coupled plasma mass spectrometry.

RESULTS

Indium concentrations in the lungs of the 2 ITO NP groups gradually decreased over the 20-week observation period. Conversely, the indium concentrations in the mediastinal lymph nodes of the 2 ITO groups increased and were several hundred times higher than those in the kidneys, spleen, and liver. Pulmonary and renal toxicities were observed histopathologically in both the ITO groups. Both indium NPs and ionic indium were detected in the kidneys, and their distributions were similar to the strong indium signals detected at the sites of inflammatory cell infiltration and tubular epithelial cells.

CONCLUSIONS

Our results demonstrate that intratracheal administration of 10 or 20 mg In/kg BW of ITO NPs in male rats produces pulmonary and renal toxicities.

Pulmonary effects of exposure to indium and its compounds: cross-sectional survey of exposed workers and experimental findings in rodents

BACKGROUND

Many studies have shown that occupational exposure to indium and its compounds could induce lung disease. Although animal toxicological studies and human epidemiological studies suggest indium exposure may cause lung injury, inflammation, pulmonary fibrosis, emphysema, pulmonary alveolar proteinosis, and even lung cancer, related data collected from humans is currently limited and confined to single workplaces, and the early effects of exposure on the lungs are not well understood.

OBJECTIVES

This study combined population studies and animal experiments to examine the links of indium with pulmonary injury, as well as its mechanism of action. A cross-sectional epidemiological study of indium-exposed workers from China was conducted to evaluate associations between occupational indium exposure and serum biomarkers of early effect. This study also compares and analyzes the causal perspectives of changes in human serum biomarkers induced by indium compound exposure and indium exposure-related rat lung pathobiology, and discusses possible avenues for their recognition and prevention.

METHODS

This is a study of 57 exposed (at least 6 h per day for one year) workers from an indium ingot production plant, and 63 controls. Indium concentration in serum, urine, and airborne as exposure indices were measured by inductively coupled plasma-mass spectrometry. Sixteen serum biomarkers of pulmonary injury, inflammation, and oxidative stress were measured using ELISA. The associations between serum indium and 16 serum biomarkers were analyzed to explore the mechanism of action of indium on pulmonary injury in indium-exposed workers. Animal experiments were conducted to measure inflammatory factors levels in bronchoalveolar lavage fluid (BALF) and lung tissue protein expressions in rats. Four different forms of indium compound-exposed rat models were established (intratracheal instillation twice per week, 8 week exposure, 8 week recovery). Model I: 0, 1.2, 3, and 6 mg/kg bw indium tin oxide group; Model II: 0, 1.2, 3, and 6 mg/kg bw indium oxide (In₂O₃) group; Model III: 0, 0.523, 1.046, and 2.614 mg/kg bw indium sulfate (In₂(SO₄)₃) group; Model IV: 0, 0.065, 0.65, and 1.3 mg/kg bw indium trichloride (InCl₃) group. Lung pathological changes were assessed by hematoxylin & eosin, periodic acid Schiff, and Masson's staining, transmission electron microscopy, and the protein changes were determined by immunohistochemistry.

RESULTS

In the production workshop, the airborne indium concentration was 78.4 μg/m³. The levels of serum indium and urine indium in indium-exposed workers were 39.3 μg/L and 11.0 ng/g creatinine. Increased lung damage markers, oxidative stress markers, and inflammation markers were found in indium-exposed workers. Serum indium levels were statistically and positively associated with the serum levels of SP-A, IL-1β, IL-6 in indium-exposed workers. Among them, SP-A showed a duration-response pattern. The results of animal experiments showed that, with an increase in dosage, indium exposure significantly increased the levels of serum indium and lung indium, as well as the BALF levels of IL‑1β, IL‑6, IL‑10, and TNF‑α and up-regulated the protein expression of SP-A, SP-D, KL-6, GM-CSF, NF-κB p65, and HO-1 in all rat models groups. TEM revealed that In₂(SO₄)₃ and InCl₃ are soluble and that no particles were found in lung tissue, in contrast to the non-soluble compounds (ITO and In₂O₃). No PAS-staining positive substance was found in the lung tissue of In₂(SO₄)₃ and InCl₃ exposure groups, whereas ITO and In₂O₃ rat models supported findings of pulmonary alveolar proteinosis and interstitial fibrosis seen in human indium lung disease. ITO and InCl₃ can accelerate interstitial fibrosis. Findings from our in vivo studies demonstrated that intra-alveolar accumulation of surfactant (immunohistochemistry) and characteristic cholesterol clefts granulomas of indium lung disease (PAS staining) were triggered by a specific form of indium (ITO and In₂O₃).

CONCLUSIONS

In indium-exposed workers, biomarker findings indicated lung damage, oxidative stress and an inflammatory response. In rat models of the four forms of indium encountered in a workplace, the biomarkers response to all compounds overall corresponded to that in humans. In addition, pulmonary alveolar proteinosis was found following exposure to indium tin oxide and indium oxide in the rat models, and interstitial fibrosis was found following exposure to indium tin oxide and indium trichloride, supporting previous report of human disease. Serum SP-A levels were positively associated with indium exposure and may be considered a potential biomarker of exposure and effect in exposed workers.

N-acetylcysteine alleviates pulmonary alveolar proteinosis induced by indium-tin oxide nanoparticles in male rats: involvement of the NF-κB signaling pathway

Indium-tin oxide (ITO) was previously found to have a toxic effect on lung tissues, and oxidative stress and the inflammatory response are two important mechanisms of ITO‑induced lung injury. N-acetylcysteine (NAC) has been found to exhibit antioxidant and anti‑inflammatory properties. The current study aimed to evaluate the possible protective effects of NAC against ITO nanoparticle (Nano-ITO)-induced pulmonary alveolar proteinosis (PAP) in adult male Sprague-Dawley rats, especially via modulation of nuclear factor-kappa B (NF-κB) signaling. For this purpose, 50 rats were randomly allocated into five groups (10 rats each) as follows: (1) control group; (2) saline group; (3) NAC (200 mg/kg) group; (4) PAP model group receiving a repeated intratracheal dose of Nano-ITO (6 mg/kg); and (5) PAP model+NF-κB inhibitor (NAC) group pre-treated intraperitoneally with NAC (200 mg/kg) twice per week before the administration of an intratracheal dose of Nano-ITO (6 mg/kg). Rats were then euthanized under anesthesia, and their lungs were removed for histopathological and biochemical investigations. A 6 mg/kg dose of Nano-ITO markedly altered the levels of some oxidative stress biomarkers. The histological examination of Nano-ITO-exposed rats demonstrated diffused alveolar damage that involved PAP, cholesterol crystals, alveolar fibrosis, pulmonary fibrosis, and alveolar emphysema. The immunohistochemical results of Nano-ITO-exposed rats revealed strongly positive NF-κB p65 and inhibitory kappa B kinase (IKK)-β and weakly positive inhibitor of kappa-B subunit alpha (IκB-α) staining reactivity in the nuclei of cells lining the epithelium of the bronchioles and alveoli. Moreover, Nano-ITO activated the NF-κB pathway. However, pre-treatment with NAC significantly attenuated Nano-ITO-evoked alterations in the previously mentioned parameters, highlighting their antioxidant, anti-inflammatory, and anti-apoptotic potential. The results indicated that the degree of pulmonary fibrosis and proteinosis in the NAC‑treated group was improved compared with that in the Nano-ITO-induced PAP model group. The level of malondialdehyde was also decreased overall in the NAC-treated group compared with that in the Nano-ITO-induced model group, indicating that the pulmonary fibrosis degree and oxidation levels were decreased. The present study also demonstrated that NAC increased the activity of antioxidant enzyme superoxide dismutase and total antioxidant capacity, indicating that it could alleviate oxidative stress in the lung tissue of Nano-ITO‑exposed rats. In addition, NAC reduced the production of pro‑inflammatory cytokines interleukin (IL)‑1β, IL‑6, and tumor necrosis factor (TNF)‑α, and increased the levels of anti‑inflammatory factor IL‑10. The current study demonstrated that NAC can effectively attenuate Nano-ITO‑induced lung injury by reducing oxidative damage and the inflammatory response.

Toxicokinetics and systematic responses of differently sized indium tin oxide (ITO) particles in mice via oropharyngeal aspiration exposure

Indium tin oxide (ITO) is an important semiconductor material, because of increasing commercial products consumption and potentially exposed workers worldwide. So, urgently we need to assess and manage potential health risks of ITO. Although the Occupational Exposure Limit (OEL) has been established for ITO exposure, there is still a lack of distinguishing the risks of exposure to particles of different sizes. Therefore, obtaining toxicological data of small-sized particles will help to improve its risk assessment data. Important questions raised in quantitative risk assessments for ITO particles are whether biodistribution of ITO particles is affected by particle size and to what extent systematic adverse responses is subsequently initiated. In order to determine whether this toxicological paradigm for size is relevant in ITO toxic effect, we performed comparative studies on the toxicokinetics and sub-acute toxicity test of ITO in mice. The results indicate both sized-ITO resided in the lung tissue and slowly excreted from the mice, and the smaller size of ITO being cleared more slowly. Only a little ITO was transferred to other organs, especially with higher blood flow. Two type of ITO which deposit in the lung mainly impacts respiratory system and may injure liver or kidney. After sub-acute exposure to ITO, inflammation featured by neutrophils infiltration and fibrosis with both dose and size effects have been observed. Our findings revealed toxicokinetics and dose-dependent pulmonary toxicity in mice via oropharyngeal aspiration exposure, also replenish in vivo risk assessment of ITO. Collectively, these data indicate that under the current OEL, there are potential toxic effects after exposure to the ITO particles. The observed size-dependent biodistribution patterns and toxic effect might be important for approaching the hazard potential of small-sized ITO in an occupational environment.

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.

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.

Low serum indium levels induce expression disorders of some inflammatory factors

OBJECTIVES

It has been reported that occupational exposure to indium compounds, including indium-tin oxide, can induce pulmonary inflammation resulting in serious indium lung disease. However, whether there is an early effect of indium exposure on inflammatory factor expression remains unclear.

METHODS

Twenty indium-tin oxide processing workers and 15 healthy volunteers were recruited to measure serum indium levels, respiratory symptoms, pulmonary function, and serum inflammatory factor levels.

RESULTS

Although low serum indium was detected in workers, lung abnormalities were not increased, compared with healthy population. However, serum G-CSF, IL-4, IL-5, TNF-alpha, and TNF-beta levels were significantly increased, while IL-16 and TIMP-1 were obviously down-regulated in indium-tin oxide processing workers. These inflammatory factor levels showed a significant correlation with serum indium levels.

CONCLUSIONS

Basing on our findings, we speculate that low serum indium levels may induce inflammatory responses, which may be an adaptive response or may cause lung diseases. Therefore, further experiments or follow-up is needed. However, better safeguard procedures and indium exposure reduction should be considered in ITO industry.

Evaluation of cytotoxicity, apoptosis, and genotoxicity induced by indium chloride in macrophages through mitochondrial dysfunction and reactive oxygen species generation

Due to rapid advances in the era of electronic technologies, indium has played the important material for the production of liquid crystal display screens in the semiconductor and optoelectronic industries. The present study focuses on evaluating the toxic effects and related mechanisms of indium chloride (InCl₃) on RAW264.7 macrophages. Cytotoxicity was induced by InCl₃ in a concentration- and time-dependent manner. InCl₃ had the ability to induce macrophage death through apoptosis rather than through necrosis. According to the cytokinesis-block micronucleus assay and alkaline single-cell gel electrophoresis assay, InCl₃ induced DNA damage, also called genotoxicity, in a concentration-dependent manner. Cysteine-dependent aspartate-directed protease (caspase)-3, -8, and -9 were activated by InCl₃ in a concentration-dependent manner. Mitochondria dysfunction and cytochrome c release from the mitochondria were induced by InCl₃ in a concentration-dependent manner. Downregulation of BCL2 and upregulation of BAD were induced by InCl₃ in a concentration-dependent manner. More, we proposed that InCl₃ treatment generated reactive oxygen species (ROS) in a concentration-dependent manner. In conclusion, the current study revealed that InCl₃ induced macrophage cytotoxicity, apoptosis, and genotoxicity via a mitochondria-dependent apoptotic pathway and ROS generation.

[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.

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

The rapid growth of new electronics and energy technologies requires the use of rare elements of the periodic table. For many of these elements, little is known about their environmental behavior or human health impacts. This is true for indium and gallium, two technology critical elements. Increased environmental concentrations of both indium and gallium create the potential for increased environmental exposure, though little is known about the extent of this exposure. Evidence is mounting that indium and gallium can have substantial toxicity, including in occupational settings where indium lung disease has been recognized as a potentially fatal disease caused by the inhalation of indium particles. This paper aims to review the basic chemistry, changing environmental concentrations, potential for human exposure, and known health effects of indium and gallium.

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.

Particle-induced Pulmonary Alveolar Proteinosis and Subsequent Inflammation and Fibrosis: A Toxicologic and Pathologic Review

This review analyzes the published data on cases of pulmonary alveolar proteinosis (PAP) in workers inhaling crystalline aluminum, indium, silicon, and titanium particles and possible sequelae, that is, inflammation and fibrosis, and compares these findings with those from animal experiments. In inhalation studies in rodents using crystalline indium and gallium compounds, pronounced PAP followed by inflammation and fibrosis down to very low concentration ranges have been reported. Crystalline aluminum, silicon, and titanium compounds also induced comparable pulmonary changes in animals, though at higher exposure levels. Laboratory animal species appear to react to the induction of PAP with varying degrees of sensitivity. The sensitivity of humans to environmental causes of PAP seems to be relatively low. Up to now, no cases of PAP, or other pulmonary diseases in humans, have been described for gallium compounds. However, a hazard potential can be assumed based on the results of animal studies. Specific particle properties, responsible for the induction of PAP and its sequelae, have not been identified. This review provides indications that, both in animal studies and in humans, PAP is not often recognized due to the absence of properly directed investigation or is concealed behind other forms of lung pathology.

The toxicology of indium tin oxide

Indium tin oxide (ITO) is a technologically important semiconductor. An increasing number of cases of severe lung effects (characterized by pulmonary alveolar proteinosis and/or interstitial fibrosis) in ITO-exposed workers warrants a review of the toxicological hazards. Short- and long-term inhalation studies in rats and mice revealed persistent alveolar proteinosis, inflammation and fibrosis in the lungs down to concentrations as low as 0.01mg/m(3). In rats, the incidences of bronchiolo-alveolar adenomas and carcinomas were significantly increased at all concentrations. In mice, ITO was not carcinogenic. A few bronchiolo-alveolar adenomas occurring after repeated intratracheal instillation of ITO to hamsters have to be interpreted as treatment-related. In vitro and in vivo studies on the formation of reactive oxygen species suggest epigenetic effects as cause of the lung tumor development. Repeated intratracheal instillation of ITO to hamsters slightly affected the male sexual organs, which might be interpreted as a secondary effect of the lung damage. 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 ITO workplaces.

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.

Catalytic application of non-toxic Persia americana metabolite entrapped SnO2nanoparticles towards the synthesis of 3,4-dihydroacridin-1(2H)-ones

Synthesized green SnO₂NPs were utilized in organic synthesis. Catalytic application was explored to synthesize 3,4-dihydroacridin-1(2H)-ones.

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.

Pulmonary toxicity of indium-tin oxide production facility particles in rats

Indium-tin oxide (ITO) is used to make transparent conductive coatings for touch-screen and liquid crystal display electronics. Occupational exposures to potentially toxic particles generated during ITO production have increased in recent years as the demand for consumer electronics continues to rise. Previous studies have demonstrated cytotoxicity in vitro and animal models have shown pulmonary inflammation and injury in response to various indium-containing particles. In humans, pulmonary alveolar proteinosis (PAP) and fibrotic interstitial lung disease have been observed in ITO facility workers. However, which indium materials or specific processes in the workplace may be the most toxic to workers is unknown. Here we examined the pulmonary toxicity of three different particle samples that represent real-life worker exposures, as they were collected at various production stages throughout an ITO facility. Indium oxide (In2O3), sintered ITO (SITO) and ventilation dust (VD) particles each caused pulmonary inflammation and damage in rats over a time course (1, 7 and 90 days post-intratracheal instillation), but SITO and VD appeared to induce greater toxicity in rat lungs than In2O3 at a dose of 1 mg per rat. Downstream pathological changes such as PAP and fibrosis were observed in response to all three particles 90 days after treatment, with a trend towards greatest severity in animals exposed to VD when comparing animals that received the same dose. These findings may inform workplace exposure reduction efforts and provide a better understanding of the pathogenesis of an emerging occupational health issue.

Fractionation and release behaviors of metals (In, Mo, Sr) from industrial sludge

Little is known on the fate of rare metals in the environment and the associated risks. The fractionation and release of three metals of an industrial sludge were assessed. The average concentration ranges from 39.3 to 41.5 mg/kg for indium (In), 43.1-77.8 mg/kg for molybdenum (Mo), and 131.1-376.4 mg/kg for strontium (Sr). Sequential extraction results implied that In was mobile, while Mo and Sr were immobile. However, experimental results from effects of Eh/pH revealed that In was slightly mobile under acidic (pH 4.5) in Eh range of 210-260 mV, and immobile under alkaline conditions (9.0) in Eh range of -250 to 125 mV. The release of Mo was slightly mobile under acidic conditions. However, Mo was very mobile under alkaline conditions and it increased with decreasing Eh. The release of Sr was significant under acidic conditions; however, it was immobile under alkaline conditions. Solubility and adsorption as affected by pH, and speciation could explain their release behaviors. Discrepancy in predictions from sequential extraction and actual observation from Eh/pH experiments was discussed.

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.

Sintered indium-tin oxide particles induce pro-inflammatory responses in vitro, in part through inflammasome activation

Indium-tin oxide (ITO) is used to make transparent conductive coatings for touch-screen and liquid crystal display electronics. As the demand for consumer electronics continues to increase, so does the concern for occupational exposures to particles containing these potentially toxic metal oxides. Indium-containing particles have been shown to be cytotoxic in cultured cells and pro-inflammatory in pulmonary animal models. In humans, pulmonary alveolar proteinosis and fibrotic interstitial lung disease have been observed in ITO facility workers. However, which ITO production materials may be the most toxic to workers and how they initiate pulmonary inflammation remain poorly understood. Here we examined four different particle samples collected from an ITO production facility for their ability to induce pro-inflammatory responses in vitro. Tin oxide, sintered ITO (SITO), and ventilation dust particles activated nuclear factor kappa B (NFκB) within 3 h of treatment. However, only SITO induced robust cytokine production (IL-1β, IL-6, TNFα, and IL-8) within 24 h in both RAW 264.7 mouse macrophages and BEAS-2B human bronchial epithelial cells. Our lab and others have previously demonstrated SITO-induced cytotoxicity as well. These findings suggest that SITO particles activate the NLRP3 inflammasome, which has been implicated in several immune-mediated diseases via its ability to induce IL-1β release and cause subsequent cell death. Inflammasome activation by SITO was confirmed, but it required the presence of endotoxin. Further, a phagocytosis assay revealed that pre-uptake of SITO or ventilation dust impaired proper macrophage phagocytosis of E. coli. Our results suggest that adverse inflammatory responses to SITO particles by both macrophage and epithelial cells may initiate and propagate indium lung disease. These findings will provide a better understanding of the molecular mechanisms behind an emerging occupational health issue.

Genotoxicity of indium tin oxide by Allium and Comet tests

Genotoxic effects of indium tin oxide (ITO) were investigated on root cells of Allium cepa by employing both Allium and Comet assays. A. cepa roots were treated with the aqueous dispersions of ITO at 5 different concentrations (12.5, 25, 50, 75, and 100 ppm) for 4 h. Exposure of ITO significantly increased mitotic index, and total chromosomal aberrations by the Allium test. While chromosome laggards, stickiness, disturbed anaphase-telophase and anaphase bridges were observed in anaphase-telophase cells, c-metaphase and binuclear cells were observed in other cells. A significant increase in DNA damage was also observed at all concentrations of ITO by the Comet assay. These results indicate that ITO exhibits genotoxic activity in A. cepa root meristematic cells.

Macrophage solubilization and cytotoxicity of indium-containing particles as in vitro correlates to pulmonary toxicity in vivo

Macrophage-solubilized indium-containing particles (ICPs) were previously shown in vitro to be cytotoxic. In this study, we compared macrophage solubilization and cytotoxicity of indium phosphide (InP) and indium-tin oxide (ITO) with similar particle diameters (∼ 1.5 µm) and then determined if relative differences in these in vitro parameters correlated with pulmonary toxicity in vivo. RAW 264.7 macrophages were treated with InP or ITO particles and cytotoxicity was assayed at 24 h. Ionic indium was measured in 24 h culture supernatants. Macrophage cytotoxicity and particle solubilization in vitro were much greater for InP compared with ITO. To correlate changes in vivo, B6C3F1 mice were treated with InP or ITO by oropharyngeal aspiration. On Days 14 and 28, bronchoalveolar lavage (BAL) and pleural lavage (PL) fluids were collected and assayed for total leukocytes. Cell differentials, lactate dehydrogenase activity, and protein levels were also measured in BAL. All lavage parameters were greatly increased in mice treated with InP compared with ITO. These data suggest that macrophage solubilization and cytotoxicity of some ICPs in vitro are capable of predicting pulmonary toxicity in vivo. In addition, these differences in toxicity were observed despite the two particulate compounds containing similar amounts of indium suggesting that solubilization, not total indium content, better reflects the toxic potential of some ICPs. Soluble InCl3 was shown to be more cytotoxic than InP to macrophages and lung epithelial cells in vitro further suggesting that ionic indium is the primary cytotoxic component of InP.

[Health effects of solar cell component material. Toxicity of indium compounds to laboratory animals determined by intratracheal instillations]

Owing to the increasing interest being paid to the issue of the global environment, the production of solar cells has increased rapidly in recent years. Copper indium gallium diselenide (CIGS) is a new efficient thin film used in some types of solar cell. Indium is a constitutive element of CIGS thin-film solar cells. It was thought that indium compounds were not harmful until the beginning of the 1990s because there was little information regarding the adverse health effects on humans or animals arising from exposure to indium compounds. After the mid-1990s, data became available indicating that indium compounds can be toxic to animals. In animal studies, it has been clearly demonstrated that indium compounds cause pulmonary toxicity and that the dissolution of indium compounds in the lungs is considerably slow, as shown by repeated intratracheal instillations in experimental animals. Thus, it is necessary to pay much greater attention to human exposure to indium compounds, and precautions against possible exposure to indium compounds are paramount with regard to health management.

Studies on the toxicity and distribution of indium compounds according to particle size in sprague-dawley rats

OBJECTIVES

The use of indium compounds, especially those of small size, for the production of semiconductors, liquid-crystal panels, etc., has increased recently. However, the role of particle size or the chemical composition of indium compounds in their toxicity and distribution in the body has not been sufficiently investigated. Therefore, the aim of this study was to examine the effects of particle size and the chemical composition of indium compounds on their toxicity and distribution.

METHODS

Male Sprague-Dawley rats were exposed to two different-sized indium oxides (average particle sizes under 4,000 nm [IO_4000] and 100 nm [IO_100]) and one nano-sized indium-tin oxide (ITO; average particle size less than 50 nm) by inhalation for 6 hr daily, 5 days per week, for 4 weeks at approximately 1 mg/m(3) of indium by mass concentration.

RESULTS

We observed differences in lung weights and histopathological findings, differential cell counts, and cell damage indicators in the bronchoalveolar lavage fluid between the normal control group and IO- or ITO-exposed groups. However, only ITO affected respiratory functions in exposed rats. Overall, the toxicity of ITO was much higher than that of IOs; the toxicity of IO_4000 was higher than that of IO_100. A 4-week recovery period was not sufficient to alleviate the toxic effects of IO and ITO exposure. Inhaled indium was mainly deposited in the lungs. ITO in the lungs was removed more slowly than IOs; IO_4000 was removed faster than IO_100. IOs were not distributed to other organs (i.e., the brain, liver, and spleen), whereas ITO was. Concentrations of indium in the blood and organ tissues were higher at 4 weeks after exposure.

CONCLUSIONS

The effect of particle size on the toxicity of indium compounds was not clear, whereas chemical composition clearly affected toxicity; ITO showed much higher toxicity than that of IO.

Cytotoxicity and characterization of particles collected from an indium-tin oxide production facility

Occupational exposure to indium compound particles has recently been associated with lung disease among workers in the indium-tin oxide (ITO) industry. Previous studies suggested that excessive alveolar surfactant and reactive oxygen species (ROS) may play a role in the development of pulmonary lesions following exposure to indium compounds. However, toxicity at the cellular level has not been comprehensively evaluated. Thus, the aim of this study was to assess which, if any, compounds encountered during ITO production are toxic to cultured cells and ultimately contribute to the pathogenesis of indium lung disease. The compounds used in this study were collected from eight different processing stages at an ITO production facility. Enhanced dark field imaging showed 5 of the compounds significantly associated with cells within 1 h, suggesting that cellular reactions to the compound particles may be occurring rapidly. To examine the potential cytotoxic effects of these associations, ROS generation, cell viability, and apoptosis were evaluated following exposures in RAW 264.7 mouse monocyte macrophage and BEAS-2B human bronchial epithelial cell lines. Both exhibited reduced viability with exposures, while apoptosis only occurred in RAW 264.7 cells. Our results suggested that excessive ROS production is likely not the predominant mechanism underlying indium-induced lung disease. However, the effects on cell viability reveal that several of the compounds are cytotoxic, and therefore, exposures need to be carefully monitored in the industrial setting.

Macrophage solubilization and cytotoxicity of indium-containing particles in vitro

Indium-containing particles (ICPs) are used extensively in the microelectronics industry. Pulmonary toxicity is observed after inhalation exposure to ICPs; however, the mechanism(s) of pathogenesis is unclear. ICPs are insoluble at physiological pH and are initially engulfed by alveolar macrophages (and likely airway epithelial cells). We hypothesized that uptake of ICPs by macrophages followed by phagolysosomal acidification results in the solubilization of ICPs into cytotoxic indium ions. To address this, we characterized the in vitro cytotoxicity of indium phosphide (InP) or indium tin oxide (ITO) particles with macrophages (RAW cells) and lung-derived epithelial (LA-4) cells at 24h using metabolic (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide) and membrane integrity (lactate dehydrogenase) assays. InP and ITO were readily phagocytosed by RAW and LA-4 cells; however, the particles were much more cytotoxic to RAW cells and cytotoxicity was dose dependent. Treatment of RAW cells with cytochalasin D (CytoD) blocked particle phagocytosis and reduced cytotoxicity. Treatment of RAW cells with bafilomycin A1, a specific inhibitor of phagolysosomal acidification, also reduced cytotoxicity but did not block particle uptake. Based on direct indium measurements, the concentration of ionic indium was increased in culture medium from RAW but not LA-4 cells following 24-h treatment with particles. Ionic indium derived from RAW cells was significantly reduced by treatment with CytoD. These data implicate macrophage uptake and solubilization of InP and ITO via phagolysosomal acidification as requisite for particle-induced cytotoxicity and the release of indium ions. This may apply to other ICPs and strongly supports the notion that ICPs require solubilization in order to be toxic.

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.

Indium lung disease

BACKGROUND

Reports of pulmonary fibrosis, emphysema, and, more recently, pulmonary alveolar proteinosis (PAP) in indium workers suggested that workplace exposure to indium compounds caused several different lung diseases.

METHODS

To better understand the pathogenesis and natural history of indium lung disease, a detailed, systematic, multidisciplinary analysis of clinical, histopathologic, radiologic, and epidemiologic data for all reported cases and workplaces was undertaken.

RESULTS

Ten men (median age, 35 years) who produced, used, or reclaimed indium compounds were diagnosed with interstitial lung disease 4-13 years after first exposure (n = 7) or PAP 1-2 years after first exposure (n = 3). Common pulmonary histopathologic features in these patients included intraalveolar exudate typical of alveolar proteinosis (n = 9), cholesterol clefts and granulomas (n = 10), and fibrosis (n = 9). Two patients with interstitial lung disease had pneumothoraces. Lung disease progressed following cessation of exposure in most patients and was fatal in two. Radiographic data revealed that two patients with PAP subsequently developed fibrosis and one also developed emphysematous changes. Epidemiologic investigations demonstrated the potential for exposure to respirable particles and an excess of lung abnormalities among coworkers.

CONCLUSIONS

Occupational exposure to indium compounds was associated with PAP, cholesterol ester crystals and granulomas, pulmonary fibrosis, emphysema, and pneumothoraces. The available evidence suggests exposure to indium compounds causes a novel lung disease that may begin with PAP and progress to include fibrosis and emphysema, and, in some cases, premature death. Prospective studies are needed to better define the natural history and prognosis of this emerging lung disease and identify effective prevention strategies.

Occupational exposure to indium: what does biomonitoring tell us?

BACKGROUND

The industrial uses of indium, a rare metal with no known physiological role in humans, have increased dramatically over the past 15 years. The results of animal toxicity studies showing pulmonary and systemic effects as well as some reports in workers have created a growing concern about the possible occurrence of toxic effects in exposed workers. Validated biomarkers to assess exposure to indium are not available.

OBJECTIVES

This work aimed at investigating the kinetics of indium in urine (In-U) and plasma (In-Pl) in workers manufacturing In ingots and mainly exposed to hardly water-soluble In compounds. All nine workers from the In department of a large metallurgical concern participated in the study as well as 5 retired workers and 20 controls.

METHODS

Personal breathing zone air was collected throughout the work shift on Monday and Friday. Blood and urine samples were collected, before and after the shift, on the same day as the air sampling and on preshift the next Monday after a non-working week-end. Moreover, rats were given either InCl(3) by intraperitoneal injection or In(2)O(3) by pharyngeal aspiration, In was followed in plasma during 120 days and measured in tissues 120 days after exposure.

RESULTS

Higher In-Pl and In-U concentrations were found in both current (range 0.32-12.61 μg/L plasma; 0.22-3.50 μg/g creat) and former (0.03-4.38 μg/L plasma; 0.02-0.69 μg/g creat) workers compared with controls (<0.03 μg/L plasma; <0.02 μg/g creat). Both biological parameters were highly correlated but no correlation was found between In-air (10-1030 μg/m(3)) and In-Pl or In-U. Normalizing In-U by the urinary creatinine concentration reduced the inter- (from 90% to 70%) and intra-individual variability (from 54% to 35%). In-Pl remained remarkably stable along the working week (inter- and intra-individual variability: 89% and 10%, respectively). Neither In-U nor In-Pl significantly increased during the day or the week. A week-end without occupational exposure was not sufficient to reach the background In-Pl and In-U levels measured in controls. The results of the experimental investigations confirmed the hypothesis that inhalation of hardly soluble In compounds may cause accumulation of In in the body leading to a prolonged "endogenous exposure" from both a lung depot of "insoluble" particles that are progressively absorbed and from a retention depot in other internal organs.

CONCLUSION

This study shows that in workers exposed to hardly soluble In compounds, In-U and In-Pl are very sensitive to detect exposure and mainly reflect long-term exposure. In-Pl levels are particularly stable for a given individual. In-U might be more influenced than In-Pl by recent exposure. Both parameters remained high years after withdrawal from exposure, indicating a possible endogenous exposure and a prolonged risk of pulmonary and systemic diseases even after work exposure has ceased.

Inhalation carcinogenicity and chronic toxicity of indium-tin oxide in rats and mice

OBJECTIVES

Carcinogenicity and chronic toxicity of indium-tin oxide (ITO) were examined by inhalation exposure of rats and mice to ITO aerosol.

METHODS

Fifty mice of both sexes were exposed to ITO at 0 (control), 0.01, 0.03 or 0.1 mg/m(3) for 6 h/day, 5 day/wk for 104 wk, and 50 rats of both sexes were exposed to 0, 0.01 or 0.03 mg/m(3) ITO for the same time period. The repeated exposure of 50 rats of both sexes to 0.1 mg/m(3) ITO was discontinued at the 26th wk, followed by clean air exposure for the remaining 78 wk.

RESULTS

In rats, incidences of bronchiolo-alveolar adenomas and carcinomas, bronchiolo-alveolar hyperplasia, alveolar wall fibrosis and thickened pleural wall, alveolar proteinosis and infiltrations of alveolar macrophages and inflammatory cells were significantly increased. Combined incidences of malignant lung tumors in male rats and total lung tumors in male and female rats were significantly increased at exposure to 0.01 mg/m(3) ITO. In mice, no carcinogenic response occurred, but thickened pleural wall, alveolar proteinosis and alveolar macrophage infiltration were induced. Mice were less susceptible to ITO than rats. The lung content of indium was the greatest, followed by the spleen, kidney and liver. Blood indium levels increased dose-dependently.

CONCLUSIONS

There was clear evidence of carcinogenicity of inhaled ITO in male and female rats but not clear evidence in mice, together with occurrence of the chronic pulmonary lesions in both rats and mice.