Journal of Occupational Health
Advance Publication Journal of Occupational Health
Accepted for Publication Aug 26, 2009 J-STAGE Advance Published Date: Oct 16, 2009 1 Title： Causal relationship between indium compound inhalation and effects on the lungs
2 Authors: Makiko Nakano1, Kazuyuki Omae1, Akiyo Tanaka2, Miyuki Hirata2, Takehiro
3 Michikawa1, Yuriko Kikuchi1, Noriyuki Yoshioka1, Yuji Nishiwaki1, and Tatsuya Chonan3
4 1) Department of Preventive Medicine and Public Health, School of Medicine, Keio
5 University
6 2) Department of Hygiene, Graduate School of Medical Sciences, Kyushu University.
7 3) Department of Medicine, Nikko Memorial Hospital
8 Correspondence to: Makiko Nakano, MD
9 e-mail: [email protected]
10 phone: +81-3-5363-3758
11 fax: +81-3-3359-3686
12
13 Type of contribution: Originals
14 Running title: Indium-induced respiratory effects
15 The number of words in abstract and the text: (271 words, 3853 words)
16 The number of tables and figures: 5 tables and 1 figure
17
18 Keywords: indium, interstitial pneumonitis, HRCT, KL-6, SP-D, cross-sectional study
19 1
1 Abstract:
2 Background: Recent case reports and epidemiological studies suggest that inhalation of
3 indium dust induces lung damage
4 Objectives: To elucidate the dose-dependent effects of indium on the lungs and to prove a
5 causal relationship more clearly.
6 Methods: A baseline observation was conducted on 465 workers currently exposed to
7 indium, 127 workers formerly exposed to indium and 169 workers without indium exposure
8 in 12 factories and 1 research laboratory from 2003 to 2006. Indium in serum (In-S) was
9 determined as an exposure parameter, and its effects on the lungs were examined.
10 Results: The means of In-S in the current, former and no exposure workers were 8.35, 9.63
11 and 0.56 ng/ml, respectively. The current and former exposure workers had significantly
12 higher levels of KL-6, and showed significant dose-dependent increases in KL-6, SP-D, and
13 SP-A. Current exposure workers with In-S of 3 ng/ml or above demonstrated a significant
14 increase of KL-6 in both GM and prevalence exceeding the reference value. Approximately
15 a quarter of the former exposure workers had interstitial changes as seen on chest HRCT.
16 In-S of exposed workers who had been working before improvements of the working
17 environment (Group Bef) and those who started working after improvements (Group Aft)
18 were 12.29 and 0.81 ng/ml, respectively. Adjusted odds ratios indicated 87%, 71% and 43%
2
1 reductions among Group Aft workers who exceeded the reference values of KL-6, SP-D and
2 SP-A, respectively.
3 Conclusion: Dose-dependent lung effects due to indium exposure were shown, and a
4 decrease of indium exposure reduced the lung effects. An In-S value of 3 ng/ml may be a
5 cut-off value which could be used to prevent early effects on the lungs.
6 (271 words)
7
3
1 INTRODUCTION
2
3 Due to the rapid expansion of flat panel displays and solar cells, indium demand
4 has increased every year, and in 2007, Japan consumed over 90% of the indium in the
5 world.1)
6 Until the early 1990’s, there was little information on the toxic effects of indium on
7 humans or animals. In the mid 1990’s, intra-tracheal instillation studies of particles of
8 compound semiconductors such as indium phosphide, indium arsenide and indium
9 trichloride revealed that metal compounds containing indium had a strong potential to
10 induce severe lung damage.2-6) In 2003, Homma et al.7) disclosed a case of interstitial
11 pneumonia in a 27-year-old male worker engaged in the wet surface polishing process of
12 indium-tin oxide (ITO) target plates, high-density plates made of very hard ceramics
13 composed of indium oxide and tin oxide, which are used to laminate transparent
14 electro-conductive thin-film on flat displays and solar cells. The worker started this job in
15 1994, and at the beginning of 1998 was admitted to a hospital with the complaint of
16 increasing dry cough and breathlessness. After a detailed medical examination, he was
17 diagnosed with interstitial pneumonia, possibly caused by the inhalation of ITO particles.
18 Up to the end of 2008, seven indium-induced cases of lung injury were disclosed7-11). After
4
1 the first case was found, two epidemiological studies were performed in two different
2 populations of indium-exposed workers12,13). Both studies suggested strong relationships
3 between indium in serum (In-S) and effects on the lungs.
4 After the first cross-sectional study12), we continued to make efforts to contact
5 companies manufacturing indium products in order to inform them of the health risk of
6 indium compounds to their indium-exposed workers and to ask them to join our
7 epidemiological survey. By the end of 2006, 13 factories and 1 research laboratory had
8 agreed to join our epidemiological study.
9
5
1 SUBJECTS and METHODS
2 Study subjects
3 Among the 13 factories that participated, 1 factory studied by Chonan et al.13) and
4 4 factories studied by Hamaguchi et al.12) were included. Because the results of a
5 pre-analysis of the remaining factories and the participating laboratory were compatible
6 with the results of the two studies, we combined the data and analyzed all of them together.
7 We informed all study candidates about the health risks of indium exposure and the purpose
8 of the epidemiological study, and obtained their informed consent before they participated.
9 The study was approved by the Ethical Committee, School of Medicine, Keio University. A
10 total of 889 subjects gave their informed consent. We excluded one factory (n=93) from the
11 analysis because In-S was determined by the factory’s laboratory using a different detection
12 limit. We obtained no data from 35 workers regarding their indium exposure or In-S. In
13 total, 128 workers were excluded, and 761 workers at 5 ITO manufacturing factories, 4
14 indium recycling factories, 3 indium oxide manufacturing factories, and 1 research
15 laboratory consisting of 465 current indium exposure workers, 127 former indium exposure
16 workers, and 169 no indium exposure workers were analyzed. The no exposure workers
17 worked at a factory that did not process indium or were office workers in indium-processing
18 factories. The participation rate was 85.6 % (761/889).
6
1 Table 1 shows the characteristics of the study subjects. The majority of the
2 subjects were male. The current exposure workers were significantly younger than the no
3 exposure workers. The mean length of indium exposure was 55.1 months (range: 0.25 -
4 455) in the current exposure workers and 60.4 months (1 - 252) in the former exposure
5 workers. The mean duration from the end of indium exposure in the former exposure
6 workers was 58.3 months (range 2-201). There were no significant differences in smoking
7 histories among the three groups. Thirty-seven workers (14 current exposure, 10 former
8 exposure, and 13 no exposure workers) had a history of asthma.
9
10 Exposure assessment
11 Most of the current and former exposure workers were exposed to multiple indium
12 compound dusts such as ITO, indium trioxide, indium hydroxide, indium chloride, indium
13 nitrate, and indium metal. Because information about the differences in the health effects
14 of each indium compound is very limited, and the indium concentrations at the work sites
15 could not be measured, we did not stratify the current and former workers by the species of
16 indium compounds. We selected In-S as a quantitative biological marker of indium
17 exposure14). In-S was determined by inductively coupled plasma mass spectrometry
18 (ICP-MS) at the Center of Advanced Instrumental Analysis, Kyushu University and the
7
1 Japan Industrial Safety and Health Association. The detailed procedure has been reported
2 elsewhere12, 13). If the level of In-S was below the detection limit, 0.05 ng/ml was used for
3 the statistical analysis.
4 As shown in Table 1, the means of In-S in the current exposure, former exposure
5 and no exposure workers were 8.35, 9.63 and 0.56 ng/ml, and the maximal concentrations
6 were 116.9, 126.8, and 3.0 ng/ml, respectively. In-S in the current exposure and former
7 exposure workers was significantly higher than in the no exposure workers.
8 To assess the dose-effect and dose-response relationships, the current and former
9 exposure workers were classified into 6 groups by In-S referring to Chonan et al. and
10 Hamaguchi et al.; namely, workers with an In-S of 0.9 or below were assigned to Group 1,
11 1.0 – 2.9 to Group 2, 3.0 – 4.9 to Group 3, 5.0 – 9.9 to Group 4, 10.0 – 19.9 to Group 5, 20.0 or
12 above to Group 6.
13
14 Medical examinations
15 Respiratory symptoms and smoking habit were assessed using the Japanese
16 version of the ATS-DLD questionnaire15, 16) with some supplementary questions regarding
17 past history of respiratory diseases and history of exposure to indium and other hazardous
18 substances such as zinc, cadmium, lead, copper, gallium, selenium, etc.
8
1 Spirometry was performed using electronic spirometers (HI-701 or HI-801; Chest
2 MI, Tokyo, Japan). Age- and height-adjusted predicted values of forced vital capacity
3 (FVC) and forced expiratory volume in one second (FEV1.0) were determined by the
4 regression formula recommended by the Japanese Respiratory Society (JRS)17), and the
5 rates (%) of observed/predicted values (%FVC, %FEV1.0) were calculated. Statistical
6 analysis was performed only for males because sex differences in pulmonary function are not
7 negligible, and the number of female subjects was small.
8 Serum KL-6 (Krebs von den Lungen-6) was measured in all study subjects18).
9 Lung surfactant protein D (SP-D), lung surfactant protein A (SP-A), white blood cell count
10 (WBC) and C-reactive protein (CRP) were measured for almost all subjects. For 44 subjects
11 with high indium exposures (see p14), serum biochemical tests for liver function (AST, ALT,
12 γ-GTP, LDH), immunological function (IgE, IgG, IgM, IgA), and collagen disease (ANA, RF,
13 ACE) were performed because some cases with indium-exposed lungs have shown mild liver
14 dysfunction, and hypersensitive pneumonitis and collagen diseases are well known to cause
15 interstitial change in the lungs. All tests were done at the Special Reference Laboratory,
16 Tokyo, Japan, which is a nationwide clinical laboratory. Urinary
17 8-hydroxy-2′-deoxyguanosine(8-OH-dG) was measured by high performance liquid
18 chromatography (HPLC) to assess oxidative stress on DNA in consideration of potential
9
1 carcinogenicity19).
2 High-resolution computed tomography (HRCT) of the lungs without a contrast
3 agent was performed at the three levels of the lungs recommended by the JRS20, 21), namely,
4 the superior border of the aortic arch (upper lung field), the tracheal bifurcation (middle
5 lung field), and 1-3 cm above the right diaphragm (lower lung field). HRCT was performed
6 mainly using a multi-slice CT scanner (Asteion 4, Toshiba Medical Systems Co., Tochigi) at
7 120 kV, 200 mA, and a slice thickness of 1 mm or a multi-slice CT scanner at hospitals near
8 the factories. The scores of interstitial changes and emphysematous changes of the upper,
9 middle, and lower lung fields of the right and left sides were assessed by two pulmonologists
10 according to modified JRS guidelines for the diagnosis and management of chronic
11 obstructive pulmonary disease (COPD)21). Namely, a score of 0 to 5 was given to each of the
12 6 lung fields when the area of interstitial or emphysematous changes occupied 0%, 1-9%,
13 10-24%, 25-49%, 50-74%, or more than 75% of each lung field assessed20). To estimate the
14 prevalence of interstitial or emphysematous changes, a score of 2 or above in at least one of
15 the 6 lung fields was analyzed, because the quality of the HRCT photographs was not
16 sufficiently uniform due to differences in the CT equipment.
17
18 Statistical Analysis
10
1 For continuous data, the data distribution was examined, and an appropriate
2 transformation was performed to approximate a normal distribution before the analysis.
3 The mean values of the variables were compared using the non-paired Student’s t-test,
4 Welch’s t-test, or analysis of variance followed by Dunnett’s test, if necessary, for adjusting
5 multiple comparisons. Wilcoxon’s rank sum test or the Mann-Whitney U test was applied
6 when an appropriate transformation, such as interstitial change scores or emphysematous
7 change scores, could not be applied. For categorical data, proportions were compared by
8 the χ2 test or Fisher's exact method followed by Bonferroni’s method, if necessary, for
9 adjusting multiple comparisons. Testing for trend was performed using a multiple
10 regression model for continuous data and a logistic regression model for binary data. Age-,
11 exposure time-, and smoking-adjusted odds ratios were calculated according to exposure
12 category by applying the logistic regression model. To assess statistical significance,
13 two-tailed p <0.05 was used throughout the analyses. All statistical analyses were
14 performed using SPSS version 15.0 J (SPSS Inc., Chicago, IL, USA).
15
11
1 RESULTS
2 Table 2 shows the outcomes of the medical examinations according to exposure
3 status. The geometric mean of KL-6 was significantly higher in the current exposure and
4 former exposure workers than in the no exposure workers. The highest KL-6 levels of the
5 current exposure and former exposure workers were 6,950 U/ml and 4,150 U/ml, respectively,
6 which were 14 times and 8 times higher than the clinically applied reference value of KL-6
7 (<500 U/ml). Approximately a quarter of the current exposure and one-fifth of the former
8 exposure workers exceeded the reference value, and the prevalences of KL-6 in the current
9 exposure and former exposure workers were significantly higher than that in the no
10 exposure workers. The prevalence of SP-D was also significantly higher in the current
11 exposure workers than in the no exposure workers. SP-A was not significantly different
12 among the three groups. Spirometry did not show any exposure-related changes in the
13 current and former exposure workers, even after adjusting for smoking status. The former
14 exposure workers showed a significantly higher prevalence rate of interstitial changes than
15 the no exposure workers, and approximately a quarter of the former exposure workers
16 showed evident interstitial changes. On the other hand, the emphysematous scores were
17 not different among the current exposure, former exposure, and no exposure workers. The
18 prevalence rates of cough and/or sputum in the current exposure and former exposure
12
1 workers were significantly higher than in the no exposure workers. The results for the
2 current exposure workers were very similar when workers with a history of asthma were
3 excluded from the analysis, and when smoking status was stratified by current smokers and
4 non-smokers. The current, former and no exposure workers showed prevalence rates of
5 cough and/or sputum of 26.5%, 20.8%, and 10.4% in nonsmokers, and 29.6%, 28.4%, and
6 17.0% in smokers, respectively.
7 Figures 1a-1d show scatter diagrams of log10(In-S) vs. KL-6 and SP-D for current
8 and former exposure workers. Sharp dose-dependent increases in KL-6 and SP-D were
9 seen in both the current and former exposure workers.
10 Tables 3 and 4 show the means, prevalence of abnormal findings, and adjusted odds
11 ratios (AOR) by In-S level in the current (Table 3) and former (Table 4) exposure workers.
12 In the current exposure workers, the geometric mean, prevalence and AOR of KL-6 were
13 significantly higher in groups with an In-S of 3.0 ng/ml or above than in no exposure
14 workers, and the dose-dependent trend was statistically significant when a multiple
15 regression model or a multiple logistic regression model was applied. The mean and
16 prevalence of SP-D were also higher in groups with an In-S of 5.0 ng/ml or above than in no
17 exposure workers, and the dose-dependent trend was also statistically significant. SP-A
18 also increased dose-dependently, and the geometric mean, prevalence and AOR were
13
1 significantly higher in workers with an In-S of 5.0 ng/ml or above. Pulmonary function
2 tests did not show a clear dose-dependent decrease, but the AOR of %FVC (5.51, 95%CI
3 1.53-19.86) and %FEV1.0 (3.71, 95%CI 1.32-10.48) increased in groups with an In-S of 20 or
4 above. Smoking status did not affect pulmonary function outcomes. HRCT findings did
5 not reveal dose-dependent trends, but the AOR of emphysematous changes increased in
6 Group 6 (AOR 4.42, 95%CI 0.95-20.60). Symptoms of cough and/or sputum did not show a
7 dose-dependent trend.
8 In the former exposure workers, sharp dose-effect relationships of the biomarkers
9 of interstitial changes were observed that were similar to those in the current exposure
10 workers, and the dose-dependent trend was also statistically significant, although the
11 former exposure workers had left their indium jobs for a period of 58.3 months on average.
12 Significant irreversible lung interstitial changes were seen in Groups 3, 5, and 6, so the
13 trend of the interstitial changes was admitted.
14 For 44 workers with high indium exposure, serum biochemical tests for liver
15 function, immunological function, and collagen disease and urinary 8-OH-dG were
16 performed. We did not find any significant differences in these indices among the current,
17 former and no exposure workers.
18 After we had intensively disseminated health risk information to the factories, they
14
1 all began improving their working environments and using dust-protective masks to reduce
2 indium inhalation. We asked them to report when they had finished implementing the first
3 improvement in working conditions, and we were able to obtain this information from 12
4 factories. We categorized the current and former exposure workers in the 12 factories into
5 2 groups, one consisting of 379 workers who had been working before the improvements
6 were implemented (Group Bef), and 109 workers who started working in a job involving
7 indium after the improvements had been implemented (Group Aft). Average exposure
8 durations were 67.1 months and 17.3 months in the Bef and Aft groups, respectively; mean
9 ages were 37.6 years and 33.0 years in the Bef and Aft groups, respectively; and the male
10 proportions were 94.2% and 83.3% in the Bef and Aft groups, respectively. These
11 differences between the groups were all statistically significant. The smoking rate was not
12 different between the Bef and Aft groups (71.2 and 66.1%). Table 5 shows the In-S and
13 medical examination results for both groups. In-S was significantly lower in Group Aft
14 than in Group Bef. KL-6, SP-D and SP-A were also significantly lower, and their
15 prevalence rates were significantly lower in Group Aft than in Group Bef. Adjusted odds
16 ratios indicated 87%, 71% , and 43% reductions of Group Aft workers exceeding the
17 reference values of KL-6, SP-D , and SP-A, respectively. The pulmonary function and
18 HRCT findings did not show differences between Groups Bef and Aft.
19 15
1 DISCUSSION
2 We combined 3 populations, i.e. those reported by Hamaguchi et al.12), Chonan et
3 al13) , and newly enrolled workers, because all 3 populations showed essentially the same
4 dose-dependent effects of indium on the respiratory system. Consequently, the internal
5 validity of this study may have been improved in terms of assessing the causal relationships
6 between indium exposure and its effects on the lungs.
7 The geometric means and the prevalence of serum biomarkers of interstitial lung
8 changes (KL-6, SP-D) were significantly higher in current exposure workers than in no
9 exposure workers. The markers of inflammation such as the CRP and WBC count did not
10 show any differences among the groups of current, former and no exposure workers. These
11 findings were compatible with the results of two epidemiological studies12, 13) and 5 clinical
12 case reports7-9). As shown in Table 3 and Figures 1a and 1c, the dose-effect and
13 dose-response relationships between indium exposure and the biological effect indices of
14 interstitial lung changes were very similar. KL-6 showed the sharpest dose-effect and
15 dose-response relationships, and significantly increased in In-S Groups 3 to 6. Based on
16 these relationships, we believe that the concentration of In-S should be kept at less than 3
17 ng/ml to prevent interstitial damage to the lungs from indium exposure.
18 Other occupational toxicants inducing interstitial lung damage may be potential
16
1 candidates for inducing high KL-6. There are only two previous articles evaluating the
2 association between occupational diseases and KL-6. Inoue et al. showed that serum KL-6
3 in 26 patients with chronic pulmonary berylliosis was significantly higher than in 15
4 beryllium-sensitized workers with no berylliosis or 32 control workers22). Abe et al.
5 compared the KL-6 levels of asbestos-exposed workers with or without pleural plaque, and
6 stated that KL-6 was higher in 17 workers with pleural plaque than in 16 workers without
7 pleural plaque, although the difference was not statistically significant23). Thus, exposure
8 to beryllium and asbestos may be a potential cause of high KL-6, but no former or current
9 exposure workers had an occupational history of asbestos or beryllium exposure.
10 Hamaguchi et al. disclosed that no difference in KL-6 was seen between indium no exposure
11 workers with and without an occupational history of exposure to non-ferrous metals other
12 than indium12). Therefore, it is unlikely that exposure to occupational toxicants other than
13 indium was a cause of the interstitial changes observed in this study.
14 KL-6 was significantly higher in non-smoking current exposure workers than in
15 smoking current exposure workers (data not shown). The former exposure workers showed
16 a similar trend, but the difference was not significant. However, no difference in KL-6 was
17 found between non-smoking and smoking no exposure workers, and Kobayashi et al.24)
18 reported that KL-6 was unaffected by smoking status. If smoking is a potential suppresser
17
1 of KL-6 release from type II alveolar pneumocytes and bronchiolar epithelial cells, KL-6 in
2 smoking workers with indium exposure might be underestimated.
3 Improvement of the working conditions caused a reduction of In-S and of the effects
4 on the lung interstitium, as shown in Table 5. This improvement may be evidence of the
5 specificity of a causal association between indium exposure and its effects on the lungs. We
6 did not assess intra-individual changes of exposure and effect indices in the current and
7 former exposure workers between the periods before and after the improvement of working
8 conditions because we judged it unreasonable to assess the efficacy of the improvement
9 based on the findings that the In-S concentration was still higher and the effects on the
10 lungs were prolonged in the former exposed workers, and based on an animal experiment
11 indicating a long biological half-life for indium in the lungs19).
12 In addition to the current exposure workers, the former exposure workers also
13 showed significantly higher In-S, KL-6 and interstitial lung changes than the no exposure
14 workers, and the dose-dependent effects on the lungs were significant. Approximately a
15 quarter of the former workers had irreversible interstitial changes in the lungs and
16 symptoms of cough and/or sputum. These findings indicate that the indium burden in the
17 lungs may slowly decrease after indium exposure stops, but that indium accumulated in the
18 lungs actively and continuously generates effects in the lungs. These findings are
18
1 consistent with the prolonged pulmonary inflammation and slow elimination of indium from
2 the lungs that were seen in rats and mice exposed to 0.1 or 0.3 mg/m3 of indium phosphide
3 for 21 or 22 weeks and to room air for approximately 80 weeks19). A long-term follow-up of
4 the former exposure workers is needed to determine the as-yet-unknown prognosis of the
5 effects of indium on the lungs.
6 This study had several limitations. It is likely that workers who were eligible for
7 participation, but who had left or retired from indium jobs due to indium-induced
8 respiratory effects, could not participate in our epidemiological study, because the existence
9 of indium-induced respiratory effects was not known until our first epidemiological study12).
10 Though this limitation may lead our study to produce results that are underestimated, we
11 believe that the survival selection bias was small because the dose-effect and dose-response
12 relationships between indium exposure and interstitial lung effects were evident in both
13 current exposure and former exposure workers.
14 Additionally, there was some information bias due to differences in where and when
15 the first cross-sectional observation was conducted at each factory. In-S was measured at
16 two different laboratories, and the chest HRCT was taken at a hospital near each factory.
17 The resolving power of the CT scanner was different at each hospital. Although unified
18 instructions for performing chest CT were given to the hospitals, and two pulmonologists
19
1 read all of the HRCT films, some measurement bias may have been unavoidable. The
2 serum biochemical indices were determined in one nationwide clinical laboratory, and
3 pulmonary function tests were performed by trained staff at our research unit. Therefore,
4 measurement bias in the serum biochemistry and pulmonary function test is likely to have
5 been small.
6 In 1964, the advisory committee to the US Surgeon General on “Cigarette Smoking
7 and Lung Cancer” established the “Criteria for causal association in epidemiology”, which
8 included 5 criteria: “Temporal relationship”, “Strength of association”, “Consistency of
9 association”, “Coherence of association”, and “Specificity of association”.
10 The first criterion, “Temporal relationship”, i.e. “Exposure always precedes the
11 outcome”, must be absolutely fulfilled to show a causal association. Indium exposure in the
12 general environment is negligible, and occupational exposure is the only source of indium
13 exposure. Thus, the temporal relationship was adequately fulfilled. The strength of
14 association is very clear. Exposed workers showed higher levels of indium with a higher
15 prevalence of outcome indices related to interstitial changes of the lungs, such as KL-6 and
16 SP-D. The dose-effect and dose-response relationships between In-S and the outcome
17 indices were also significant, and pronounced. In this study, we combined three sets of
18 baseline data, namely data reported by Hamaguchi et al.12), those reported by Chonan et
20
1 al.13), and other newly collected unpublished data, because all three sets of data showed the
2 same consequences. Seven indium lung cases have been discovered7-11). Therefore, the
3 consistency of association criterion seems to be fulfilled. The data were obtained only in
4 Japan, because indium demand in countries other than Japan is small1). It may not be
5 possible to measure the incidence of indium lung effects or to conduct an epidemiological
6 study in the USA or European countries. It is well known that the inhalation of hardly
7 soluble hazardous particles, such as crystalline silica, asbestos, and so on, induces
8 pneumoconiosis. In animal experiments, intra-tracheal instillation of indium compounds
9 induces pneumonitis, proliferation of fibrous tissues, pulmonary fibrosis, and other lung
10 diseases3-6). The results of our study are consistent with this information. Thus, the
11 coherence of association criterion seems to be fulfilled. In newly exposed workers who
12 started working after changes in working conditions were made (Group Aft), the indium
13 exposure level was considerably reduced, and the interstitial effects on the lungs were
14 reduced. Therefore, we think that specificity of association may have been established.
15 In a strict sense, the causal association between indium exposure and effects on the
16 lungs has not been completely proven, but the results of the present study strongly support
17 the causal association between indium exposure and effects on the lungs, and we think it
18 has been substantially established.
21
1 In conclusion, the concentration of In-S should be kept at less than 3 ng/ml to
2 prevent interstitial lung damage from indium exposure. Follow-up observations are now in
3 progress to elucidate the biological kinetics of In-S and the prognosis of the effects on the
4 lungs.
5
22
1 Acknowledgements: The authors thank staff members and participants at all factories for
2 their helpful and cordial cooperation. This study was supported in part by Grants-in-aid
3 for Scientific Research (Project No 15390191, 17390179) from the Ministry of Education,
4 Culture, Sports, Science and Technology of Japan (2003-4, 2005-6).
5 Competing interests: None declared
6
23
1 REFERENCES
2 1. Minami H. Demand, supply, and price trend etc. of indium. UIRTUAL Mineral
3 Resources Information Center - Metallic resource report -. 2007;37:171-6.(in Japanese)
4 2. Tanaka A, Hisanaga A, Hirata M, et al. Chronic toxicity of indium arsenide and
5 indium phosphide to the lungs of hamsters. Fukuoka Igaku Zasshi. 1996;87:108-15.(in
6 Japanese)
7 3. Kabe I, Nakashima H, Nomiyama T, et al. In Vitro Solubility and In Vivo Toxicity of
8 Indium Phosphide. Journal of Occupational Health. 1996;38:6-12.
9 4. Uemura T, Omae K, Takebayashi T, et al. Effects of Intratracheally Administered
10 Indium Phosphide on Male Fischer 344 Rats. Journal of Occupational Health.
11 1997;39:205-10.
12 5. Blazka ME, Tepper JS, Dixon D, Winsett DW, O'Connor RW, Luster MI. Pulmonary
13 response of Fischer 344 rats to acute nose-only inhalation of indium trichloride. Environ Res.
14 1994;67:68-83.
15 6. Blazka ME, Dixon D, Haskins E, Rosenthal GJ. Pulmonary toxicity to
16 intratracheally administered indium trichloride in Fischer 344 rats. Fundam Appl Toxicol.
17 1994;22:231-9.
18 7. Homma T, Ueno T, Sekizawa K, Tanaka A, Hirata M. Interstitial pneumonia
24
1 developed in a worker dealing with particles containing indium-tin oxide. Journal of
2 Occupational Health. 2003;45:137-9.
3 8. Homma S, Miyamoto A, Sakamoto S, Kishi K, Motoi N, Yoshimura K. Pulmonary
4 fibrosis in an individual occupationally exposed to inhaled indium-tin oxide. Eur Respir J.
5 2005;25:200-4.
6 9. Taguchi O, Chonan T. Three cases of indium lung. Nihon Kokyuki Gakkai Zasshi.
7 2006;44:532-6.(in Japanese)
8 10. Nakano M, Omae K. A case of indium lung diagnosed by worker’s health
9 examination. Occupational Health journal. 2007;30:25-9.(in Japanese)
10 11. Takeuchi H, Morikawa T, Uchikoshi A, et al. Center type interstitial pneumonia on
11 upprer lungs due to Indium inhalation. Nihon Kokyuki Gakkai Zasshi.
12 2006;44(suppl):274.(in Japanese)
13 12. Hamaguchi T, Omae K, Takebayashi T, et al. Exposure to hardly soluble indium
14 compounds in ITO production and recycling plants is a new risk for interstitial lung damage.
15 Occup Environ Med. 2008;65:51-5.
16 13. Chonan T, Taguchi O, Omae K. Interstitial pulmonary disorders in
17 indium-processing workers. Eur Respir J. 2007;29:317-24.
18 14. Miyaki K, Hosoda K, Hirata M, et al. Biological monitoring of indium by means of
25
1 graphite furnace atomic absorption spectrophotometry in workers exposed to particles of
2 indium compounds. Journal of Occupational Health. 2003;45:228-30.
3 15. Research on method of mesuring influence on health due to air pollution. Japan
4 Public Health Association. Tokyo(Japan) 1984. p3-69.
5 16. Ferris BG. Epidemiology Standardization Project (American Thoracic Society). Am
6 Rev Respir Dis. 1978;118:1-120.
7 17. Clinical Pulmonary Functions Committee of the Japanese Respiratory Society.
8 Standard values of spirogram and arterial blood gas partial pressure among Japanese.
9 Nihon Kokyuki Gakkai Zasshi. 2001;39(3).(in Japanese)
10 18. Ohnishi H, Yokoyama A, Kondo K, et al. Comparative study of KL-6, surfactant
11 protein-A, surfactant protein-D, and monocyte chemoattractant protein-1 as serum markers
12 for interstitial lung diseases. Am J Respir Crit Care Med. 2002;165:378-81.
13 19. Toxicology and carcinogenesis studies of indium phosphide (CAS No. 22398-80-7) in
14 F344/N rats and B6C3F1 mice (inhalation studies). Natl Toxicol Program Tech Rep Ser.
15 2001;(499):7-340.
16 20. Goddard PR, Nicholson EM, Laszlo G, Watt I. Computed tomography in pulmonary
17 emphysema. Clin Radiol. 1982;33:379-87.
18 21. Guideline for COPD diagnosis and treatment (the second edition). Japan Public
26
1 Health Association. Tokyo(Japan) 2004.
2 22. Inoue Y, Barker E, Daniloff E, Kohno N, Hiwada K, Newman LS. Pulmonary
3 epithelial cell injury and alveolar-capillary permeability in berylliosis. Am J Respir Crit
4 Care Med. 1997;156:109-15.
5 23. Abe T, Oda J, Takizawa Y, Suzuki E, Gejyo F. Evaluation of serum fibrosis markers
6 in asbestos-exposed workers. Nihon Kokyuki Gakkai Zasshi. 2008;46:875-9.(in Japanese)
7 24. Kobayashi H, Kanoh S, Motoyoshi K. Serum surfactant protein-A, but not
8 surfactant protein-D or KL-6, can predict preclinical lung damage induced by smoking.
9 Biomarkers. 2008;13:385-92.
10
27
1 FIGURE LEGENDS
2 Table 1: Characteristics of study population and concentrations of indium in serum.
3 Table 2: The mean and prevalence of respiratory effect indices by exposure status.
4 Table 3: Dose-dependent relationships between In-S and respiratory effects for workers
5 with current indium exposure.
6 Table 4: Dose-dependent relationships between In-S and respiratory effects for workers
7 with former indium exposure.
8 Table 5: Effectiveness of the work environment improvements on indium exposure and
9 respiratory effects.
10 Figure 1a-d: Dose-effect relationships between KL-6 and SP-D, and In-S for workers with
11 current and former indium exposure.
12
28
Table 1. Characteristics of study population and concentrations of indium in serum
No exposure Former exposure Current exposure n 169 127 465 Male (%) 81.9 91.1 ** 91.6 ** Age ( years ): Mean ± SD 40.9 ± 10.89 39.1 ± 9.61 35.9 ± 11.30 ** Smokers (%) 116 ( 67.8 ) 76 ( 60.8 ) 278 ( 72.8 ) In-S ( ng/ml ): Mean (range ) 0.56 ( n.d. - 3.0 ) 9.63 ( n.d - 126.8 ) ** 8.35 (n.d. - 116.9) ** Exposure duration (mo): Mean (range) - 60.4 ( 1 - 252 ) 55.1 ( 0.25 - 455 ) Duration after the end of indium - 58.3 ( 2 - 201 ) - exposure (mo): Mean (range)
**; p< 0.01 by Dunnett test (reference = non-exposed workers) or χ2 test. 1
29
Table 2. The mean and prevalence of respiratory effect indices by exposure status.
No exposure Former exposure Current exposure Mean or Mean or Mean or n Range n Range n Range Prevalence Prevalence Prevalence Mean and range KL-6 ( U/ml )$ 142 226 92-523 125 295 ** 95-4150 424 337 ** 108-6950 SP-D ( ng/ml )$ 142 49.1 17.2-197 96 51.1 17.2-415 342 54.8 17.2-311 SP-A ( ng/ml )$ 142 33.1 10.8-109 93 35.3 12.6-86.4 305 33.0 10-117 CRP ( mg/dl )$ 114 0.05 0.01-3.81 46 0.05 0.01-1.27 119 0.04 0.01-1.99 WBC ( x102/mm3 ) 21 66.0 44-96 53 67.8 33-114 168 65.1 29-122 %FVC (%)& 109 98.5 71.8-138.4 78 98.4 72.3-121.7 225 99.4 66.6-137.4 & FEV1.0 / FVC (%) 109 80.6 65.7-95.6 108 81.4 49.1-95.5 338 82.5 59.9-99.6 & %FEV1.0 (%) 109 91.7 63.8-132.4 78 92.0 69.5-116.9 225 93.5 62.5-123.8
Prevalence (%) KL-6 ( >500 ) 142 0.7 125 16.8 ** 424 24.3 ** SP-D ( >110 ) 142 9.2 96 11.5 342 16.4 * SP-A ( >43.2 ) 142 22.5 93 33.3 305 26.9 %FVC ( <80 ) 109 5.5 78 3.8 225 4.0
FEV1.0 / FVC ( <70 ) 109 10.1 108 6.5 338 3.6
％FEV1.0 ( <80 ) 109 15.6 78 15.4 225 12.0 Interstitial change on HRCT 114 9.6 44 27.3 * 99 5.1 Emphysematous changes on HRCT 114 4.4 44 9.1 99 5.1 Cough or/and sputum 142 14.8 122 25.4 376 28.7 ** **; p< 0.01 by Dunnett test (reference = non-exposed workers) or χ2 test. $: Geometric mean. &: Only male data was analyzed 1 because of potential sex diffefences in spirometry.
30
Table 3. Dose-dependent relationships between In-S and respiratory effects in see p28.
In-S levels of workers with current indium exposure p for Unexposed Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 trend workers In-S 0.9 or below 1.0 - 2.9 3.0 - 4.9 5.0 - 9.9 10.0 - 19.9 20.0 or above Mean and standard deviation or range KL‐6 n 142 166 68 35 52 50 53 GM 226 220 255 333 ** 450 ** 511 ** 943 ** <0.001 GSD 1.42 1.47 1.42 1.60 1.73 1.70 1.95
SP‐D n 142 158 54 29 37 34 30 GM 49.1 40.3 58.9 54.9 67.9 ** 78.8 ** 121.4 ** <0.001 GSD 1.78 1.67 1.62 1.74 1.73 1.73 1.74
SP‐A n 142 136 52 24 30 33 30 GM 33.1 28.1 29.8 37.5 43.6 ** 35.3 51.3 ** <0.001 GSD 1.51 1.46 1.48 1.65 1.54 1.51 1.54
Prevalence (%) of abnormal finding and age-, exposure length- and smoking-adjusted odds KL‐6 Prev 0.7 3.6 2.9 17.1# 36.5# 50.0# 84.9# <0.001 AOR 1 2.5 2.6 21.3 49.1 94.3 526 95%CI 0.5-18.5 0.3-22.1 4.5-155 12.8-328 24.3-634 125-3770
SP‐D Prev 9.2 4.4 9.3 13.8 24.3# 32.4# 66.7# <0.001 AOR 1 0.4 1 2.1 3.7 5.7 26.0 95%CI 0.1-1.1 0.3-3 0.5-6.7 1.4-9.9 2.2-15.1 9.5-77.9
SP‐A Prev 22.5 13.2 15.4 41.7 50.0# 33.3 66.7# <0.001 AOR 1 1.0 0.9 4.2 4.5 3.0 10.1 95%CI 0.5-2.0 0.3-2.1 1.5-12 1.8-11.5 1.2-7.6 3.9-28.3
n 114 8 27 10 11 20 23 HRCT-I Prev 9.6 0.0 3.7 0.0 0.0 0.0 17.4 0.946 HRCT-E Prev 4.4 0.0 0.0 0.0 9.1 0.0 17.4# 0.110 GM, GSD, Prev: geometric mean, geometric standard deviation, and prevalence. AOR, 95%CI: sex-, age-, and smoking- adjusted odds ratio applying logistic regression model and 95% confidence interval. HRCT-I, HRCT-E: Interstitial or emphysematous changes in lung HRCT. *,**: p <0.05, 0.01 by Dunnet's test . #: p < 0.05 after adjusting for multiple comparison by the Bonferroni method. Trend p was analyzed by applying a multiple logistic regression model or a 1 multiple regression model adjusting for sex, age and smoking.
31
Table 4. Dose-dependent relationships between In-S and respiratory effects in see p28.
Unexposed In-S levels of workers with former indium exposure p for trend workers Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 In-S 0.9 or below 1.0 - 2.9 3.0 - 4.9 5.0 - 9.9 10.0 - 19.9 20.0 or above Mean and standard deviation or range n 142 50 21 9 16 14 15 KL‐6 GM 226 206 216 318 285 392 ** 1083 ** <0.001 GSD 1.42 1.42 1.23 1.42 1.56 1.83 1.94
n 142 48 16 4 11 9 8 SP‐D GM 49.1 36.5 55.9 29.5 73.9 85.7 * 146.2 ** <0.001 GSD 1.78 1.66 1.85 1.42 1.47 2.61 2.17
n 142 46 15 4 11 9 8 SP‐A GM 33.1 29.9 32.1 39.1 42.1 44.3 56.5 ** <0.001 GSD 1.51 1.56 1.37 1.30 1.53 1.61 1.38
Prevalence (%) of abnormal finding and age-, exposure length- and smoking-adjusted odds ratio KL‐6 Prev 0.7 0.0 0.0 11.1 12.5# 28.6# 93.3# <0.001 SP‐D Prev 9.2 0.0 12.5 0.0 9.1 44.4# 50.0# <0.001 SP‐A Prev 22.5 19.6 13.3 50.0# 54.5# 66.7# 75.0# <0.001 n 114 12 8 3 8 8 5 HRCT-I Prev 9.6 8.3 12.5 66.7# 25.0 50.0# 40.0# <0.001 HRCT-E Prev 4.4 8.3 0.0 33.3# 0.0 25.0# 0.0 0.617
Abbreviations and symbols: see Table 3. 1
2
32
Table 5. Effectiveness of the work environment improvements on indium exposure and respiratory effects
Group Aft# Group Bef# Prevalence (%) AOR 95%CI n Mean Range n Mean Range Group Aft Group Bef In-S 109 0.81 ** n.d.-11.2 379 12.29 n.d.-126.8 KL-6 $ 105 216 ** 95-698 379 380 124-6950 3.8 ** 29.6 0.13 0.05-0.37 SP-D $ 105 41.7 ** 17.2-184 268 61.7 17.2-350 5.7 ** 20.5 0.29 0.12-0.74 SP-A $ 100 28.6 ** 12.4-94.1 233 37.7 12.7-117 16.0 ** 37.3 0.56 0.28-1.09 Cough and/or sputum 108 369 26.9 27.4 0.90 0.53-1.53
#: See text. $: Geometric mean. **: p < 0.01 by Student's t-test or χ2 test. AOR, 95%CI: Sex-, age- and smoking- adjusted odds ratio of Group Aft for Group Bef and 95% confidence interval applying logistic regression model. 1
2
33
Figure 1a-d Dose-effect relationships between KL-6 and SP-D, and In-S. see p28
Figure 1a Figure 1b
Figure 1c Figure 1d
Fig. 1a and 1c are satter diagrams of Iog10(In-S) vs. KL-6 and SP-D for workers
with current indium exposure. Fig. 1b and 1d are scatter diagrams of Iog10(In- S) vs. KL-6 and SP-D for workers with former indium exposure. KL-6, SP-D: 1 cut-off values are 500 U/ml and 110 ng/ml, respectively.
34