Evaluation of personal exposure of workers to indium concentrations in total dust and its respirable fraction at three Japanese indium plants.

This study aimed to evaluate personal exposures of 27 workers to indium compounds as "total" dust and its "respirable" fraction in their breathing zones at 3 Japanese indium plants. Eight-hour time-weighted average (TWA) indium concentrations of personal exposure to dust collected in sampling periods of 6 h or longer were determined by ICP-MS. The arithmetic means of exposure concentrations were 0.095 mg indium (In)/m3, when sampled as total dust, and 0.059 mg In/m3, as respirable fraction. ACGIH's TLV-TWA of 0.1 mg In/m3 for total particulate matter and Acceptable Exposure Concentration Limit (AECL) of 3×10-4 mg In/m3 for the respirable fraction notified by the Japanese Ministry of Health, Labour and Welfare were used to evaluate the exposure concentrations. Twenty-five out of 27 workers were exposed to indium concentrations lower than TLV-TWA, while all of the workers were exposed to the indium concentrations higher than AECL. We noted that there was a large discrepancy between the two occupational exposure limits referred to in this report, and these differences were attributed to the sampling strategies and health effects used as the prevention targets. Carcinogenicity of the respirable fraction of indium-containing particulates was considered in setting AECL, whereas it was not in ACGIH's TLV.

Quantitative assessment of occupational exposure to total indium dust in Japanese indium plants.

This study quantitatively assessed personal exposure of 86 workers to indium compounds as total dust at 11 Japanese indium plants. The personal exposures to indium concentrations in the breathing zone during an 8 h work-shift were determined by ICP-MS. The arithmetic mean indium concentration of all the workers was 0.098 mg Indium (In)/m3, with individual values ranging from 0.0001 to 1.421 mg In/m3. There were 11 workers whose exposure to indium concentrations exceeded the American Conference of Governmental Industrial Hygienists' Threshold Limit Value-Time Weighted Average (TLV-TWA) of 0.1 mg In/m3. Based on the condition TLV-TWA

Control banding assessment of workers' exposure to indium and its compounds in 13 Japanese indium plants.

OBJECTIVES: This study aimed to assess workers' exposure to indium and its compounds in 55 indium-handling operations among 13 Japanese plants. The surveyed plants were selected from indium-manufacturing plants whose annual indium production exceeded 500 kg. METHODS: The Control of Substances Hazardous to Health (COSHH) Essentials control banding toolkit, which contains simple scales for hazard levels, quantities in daily use, and "dustiness" characteristics, was used to assess generic risks of indium-handling operations. The operations were then classified into one of four Control Approaches (CAs). RESULTS: There were 35 indium-handling operations classified into CA4 (requires expert advice) and 16 grouped into CA3 (requires containment). There were three operations classified into CA2 (requires engineering controls) and only one into CA1 (requires good general ventilation (GV) and working practices). Of the 51 operations classified as CA4 and CA3, 36 were found to be improperly equipped with local exhaust ventilation, and the remaining 15 operations solely relied on GV practices. Respiratory protective equipment (RPE) used in the 13 indium plants was examined with reference to the recommendations of the COSHH Essentials and Japan's Technical Guidelines. CONCLUSIONS: Our findings suggest that stringent engineering control measures and respiratory protection from indium dust are needed to improve indium-handling operations. Our results show that the most common control approach for Japanese indium-handling operations is to require expert advice, including worker health checks for respiratory diseases and exposure measurement by air sampling.

Assessment of workplace air concentrations of formaldehyde during and before working hours in medical facilities.

Workplace air concentrations of formaldehyde (FA) in medical facilities where FA and FA-treated organs were stored and handled were measured before and during working hours and assessed by the official method specified by Work Environment Measurement Law. Sixty-percent of the total facilities examined were judged as inappropriately controlled work environment. The concentrations of FA before working hours by spot sampling were found to exceed 0.1 ppm in some facilities, and tended to increase with increasing volume of containers storing FA and FA-treated materials. Regression analysis revealed that logarithmic concentrations of FA during working hours by the Law-specified analytical method were highly correlated with those before working hours by spot sampling, suggesting the importance for appropriate storing methods of FA and FA-treated materials. The concentrations of FA during working hours are considered to be lowered by effective ventilation of FA-contaminated workplace air and appropriate storage of FA and FA-treated materials in plastic containers in the medical facilities. In particular, such improvement by a local exhaust ventilation system and tightly-sealed containment of FA-treated material were urgently needed for the dissecting room where FA-treated cadavers were prepared and handled for a gross anatomy course in a medical school.

The Relationship between Attitudes toward Suicide and Family History of Suicide in Nagano Prefecture, Japan.

Certain attitudes toward suicide may be a risk factor for suicide among the bereaved. To explore this possibility, we examined the relationship between attitudes toward suicide and family history of suicide. We focused on two specific attitudes indicating resignation in a survey: #1 "When a person chooses to die by suicide, the suicide is inevitable" (i.e., inevitability belief); and #2 "A suicide cannot be stopped by any person, because suicide is unpreventable" (i.e., unpreventable belief). The data of 5117 fully completed questionnaires were analyzed. Logistic regression analysis revealed that the two attitudes of resignation were significantly associated with a family history of suicide. The adjusted odds ratio for #1 was 1.39 (95% CI, 1.07-1.79) for individuals having experienced suicide by a family member or relative, while that for #2 was 1.57 (95% CI, 1.27-1.95) for experiencing a suicide by a family member or relative and 1.25 (95% CI, 1.05-1.49) for experiencing a suicide by a friend, business associate, partner or other. These two attitudes of resignation toward suicide were significantly associated with a family history of suicide. These attitudes might increase suicide risk among the bereaved.

Control banding assessment of exposure of offset printing workers to organic solvents.

OBJECTIVES: We aimed to assess the exposure of offset printing workers to hazardous substances in the rinsing processes of small-sized companies using a control banding method. METHODS: We obtained half-year amounts of hazardous substances purchased through a questionnaire survey and the hazardous information from the safety data sheets (SDSs) and related literature. RESULTS: The amount of petroleum kerosine and carbon hydride markedly increased in 2013 compared with that in 2010. In contrast, the amount of dichloromethane (DCM) decreased in 2013, and 1,2-dichloropropane (DCP) was not used in either 2010 or 2013. Mineral oil and xylene were allocated to Hazard Group D and judged to require Control Approach 3. In addition to DCM with Global Harmonization System's carcinogenic category 1, mildly treated mineral oil and solvent naphtha, allocated into Hazard Group E, are carcinogenic to humans and were judged to require Control Approach 4. There are two limitations of the control banding assessment: first, only limited and scarce hazard information could be obtained from SDSs, and second, safe-sided judgment for control technology for industrial hygiene. CONCLUSION: Small-sized enterprises are encouraged to implement control banding assessment for hazardous substances and to access expert advice available from Regional Industrial Health Centers. Easy access to appropriate expert advice is important to compensate for the limited and scarce hazard information and safe-sided judgment for control technology for Control Approaches 3 and 4.

Relationships between suicidal ideation and psychosocial factors among residents living in Nagano Prefecture of Japan.

OBJECTIVES: Feeling ashamed for seeking help when distressed is known to be a critical factor promoting suicidal behaviors. The objective of this study was to examine the relationship between suicidal ideation and psychosocial factors, including worries or anxieties, having a person to confide in, feeling ashamed for seeking help when distressed, and K6 score. METHODS: Fourteen out of 77 municipalities from Nagano Prefecture participated in this questionnaire survey. Participants of both sexes over 20 years of age were randomly selected according to age distribution in each municipality. Association between suicidal ideation and sociodemographic and psychosocial factors, including "feeling ashamed for seeking help", were determined by multiple logistic regression analysis. RESULTS: Among a total of 11,100 participants, 7394 (66.6%) returned the questionnaire. 2147 participants responded properly to essential study parameters and were submitted to the final analyses. The adjusted odds ratio of suicidal ideation was 2.09 (95% CI 1.49-2.94) among participants feeling ashamed for seeking help, compared to those not feeling ashamed. Although the rate of "no person to confide in" was 4.4%, participants who responded with "no person to confide in" had significantly increased odds ratio of suicidal ideation compared with those who responded with "having a person to confide in" (OR 1.97, 95% CI 1.12-3.47). CONCLUSIONS: Our findings suggest a need for tailored intervention targeting individuals at risk by gatekeepers to encourage individuals at risk to overcome feeling ashamed for seeking help and to cultivate an appropriate person to confide in.

A cross-sectional analysis of dioxins and health effects in municipal and private waste incinerator workers in Japan.

This cross-sectional study was intended to examine health effects of 678 male workers employed during an 8-yr period from 2000 to 2007 at 36 municipal and private waste incineration plants in Japan. Blood samples were obtained for analysis of concentrations of dioxins including coplanar polychlorinated biphenyls (coplanar PCBs) and evaluation of health effects. Health effects including diabetes were surveyed via a physician's interview or clinical data from blood samples. There was a certain difference in serum concentrations of polychlorinated dibenzofurans (PCDFs) between the incinerator workers and Japanese general population, although no differences in the concentrations of total dioxins or polychlorinated dibenzo-p-dioxins (PCDDs) were found between the two groups. A few positive correlations between serum levels of PCDDs and PCDFs and the results of laboratory and physiological tests were found, but coplanar PCBs showed significant relations with 14 parameters of the tests. The background serum levels of PCDDs, PCDFs and total dioxins were significantly associated with the prevalence of diabetes. No essential differences in serum concentrations of total dioxins and in prevalence of diabetes between our subjects and the general population suggested that the incinerator workers were marginally exposed to dioxins in the workplace without any recognizable adverse health effects.

Isomer pattern and elimination of dioxins in workers exposed at a municipal waste incineration plant.

The aim of this study was to clarify patterns of serum concentrations of dioxins in the employees of a waste incineration plant and to estimate elimination rates and half-lives of serum dioxin isomers, and the maximum serum concentrations of dioxin isomers at the time of plant shutdown. Sixteen subjects participating 3 times or more in annual health examinations during an 8-yr period from 2000 to 2007 were recruited for this study. Serum concentrations of dioxins expressed as TEQ/g lipid decreased gradually after plant shutdown with the highest decrease observed in polychlorinated dibenzofurans (PCDFs) followed by polychlorinated deibenzo-p-dioxins (PCDDs) and then coplanar PCBs. The serum toxic equivalency (TEQ) concentrations of PCDF and PCDD congeners in the employees were higher than those in the general population survey by the Ministry of the Environment, Japan, whereas the serum concentrations of coplanar PCBs were similar to those in the general population. The estimated half-lives and elimination rates of PCDDs and PCDFs in the highly exposed workers increased compared with the moderately exposed workers. The estimated geometric mean serum concentrations of PCDDs, PCDFs and total dioxins at the time of plant shutdown were 35, 53 and 107 pg TEQ/g lipid, respectively.

Occupational exposure to N,N-dimethylformamide in the summer and winter.

We evaluated total body burden of N,N-dimethylformamide (DMF) taken through the lung and skin by personal exposure of workers to DMF and urinalysis of N-methylformamide (NMF) and N-acetyl-S(N-methylcarbamoyl)-cysteine (AMCC). A total of 270 workers were engaged in four different jobs in a workplace distant from main production lines emanating high levels of DMF. They were not required to wear any personal protective equipment including respirators or gloves. We found that log-transformed urinary levels of NMF and AMCC increased with an increase in log-transformed concentrations of exposure to DMF. Urinary levels of NMF and AMCC were significantly higher in the summer than the winter, although there was no significant seasonal difference in the concentrations of exposure to DMF. Our findings suggested that the increased urinary levels of NMF and AMCC in the summer resulted in increased skin absorption of DMF due to an increased amount of DMF absorbed by the moisturized skin under humid and hot conditions. Seasonal changes in the relative internal exposure index confirmed the present finding of enhanced summertime skin absorption of DMF. AMCC is thought to be a useful biomarker for assessments of cumulative exposure to DMF over a workweek and for evaluations of workers' health effects.

Seasonal difference in percutaneous absorption of N,N-dimethylformamide as determined using two urinary metabolites.

OBJECTIVE: We evaluated the percutaneous absorption of N,N-dimethylformamide (DMF) in DMF-exposed workers in the summer and winter by assessing their urinary levels of DMF metabolites. METHODS: Breathing-zone concentrations of DMF and workers' urinary levels of N-methylformamide (NMF) and N-acetyl-S-(N-methylcarbamoyl)-cysteine (AMCC) were simultaneously measured in the summer and winter in 193 male workers wearing a respirator and chemical protective gloves. RESULTS: The mean breathing-zone concentrations of DMF in both seasons were below the occupational exposure limit of 10 ppm. Although there was no significant seasonal difference in the breathing-zone concentrations of DMF, workers' urinary levels of NMF and AMCC were significantly higher in the summer than in the winter. Log-transformed urinary levels of the metabolites were significantly correlated with log-transformed breathing-zone concentrations of DMF in the summer, whereas no significant correlation between AMCC and DMF was found in the winter. The urinary levels of AMCC were dispersed more widely than those of NMF, suggesting that urinary AMCC reflected the cumulative exposure to DMF over a workweek. CONCLUSIONS: Percutaneous absorption was the principal route of exposure to DMF for the respirator-wearing workers. Increased urinary levels of NMF and AMCC in the summer were attributed to increased percutaneous absorption of DMF resulting from the increased amount of water-soluble DMF absorbed by sweaty skin caused by the increased summertime room temperature and humidity.

Assessment of workplace air concentrations of indium dust in an indium-recycling plant.

OBJECTIVES: Suspended indium dust in an indium-recycling plant was quantified, in order to improve the work environment and to reduce workers' exposure to the dust. METHODS: Assessment of indium dust in the workplace air by multipoint area sampling and personal breathing zone sampling was conducted twice in 2004 and 2008. RESULTS: In 2004, all recycling processes except for purity analysis were classified into control class III according to the 2004 Notification. Two out of 5 workers were exposed to total dust with indium concentrations exceeding the ACGIH's TLV-TWA of 0.1 mg In/m(3). In 2008, the indium-contaminated workplace air was improved by local exhaust ventilation systems installed in some processes, resulting in control class I. According to the 2010 Technical Guideline, however, all the processes were classified into stage II or III, indicating that the first assessment value or Measurement B-based concentrations exceeded the acceptable exposure concentration limit of 0.0003 mg In/m(3) of respirabe dust. Exposure of almost all the workers to indium dust was below the TLV-TWA. CONCLUSIONS: The first field survey showed that almost all workplaces were classified into control class III, and that some workers were exposed to dust with indium concentrations exceeding the TLV-TWA. It was found in the second survey that workplace air contamination was improved by the local exhaust ventilation system, but was not reduced sufficiently to a level that meets the new Guideline.

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.

Pulmonary toxicity in mice by 2- and 13-week inhalation exposures to indium-tin oxide and indium oxide aerosols.

OBJECTIVES: Inhalation toxicities of indium-tin oxide (ITO) and indium oxide (IO) in mice were characterized in comparison with those previously reported in rats. METHODS: B6C3F(1) mice of both sexes were exposed by inhalation to ITO or IO aerosol for 6 h/day, 5 day/wk for 2 wk at 0, 0.1, 1, 10 or 100 mg/m(3) or 13 wk at 0, 0.1or 1 mg/m(3). RESULTS: ITO and IO particles were deposited in the lung, mediastinal lymph node (MLN) and nasal-associated lymphoid tissue. Alveolar proteinosis, infiltrations of alveolar macrophages and inflammatory cells and increased lung weight were induced by 2- and 13-week exposures to ITO and IO, while alveolar epithelial hyperplasia occurred only in the 2-week exposures. Thickened pleural wall, hyperplastic MLN, extramedullary hematopoiesis in the spleen and increased levels of erythrocyte parameters were induced by 13-week exposure to ITO. The ITO- and IO-induced pulmonary lesions were milder in mice than those previously reported in rats, and the fibrotic lesions were different between these two species. Indium levels in the lung and pooled blood were analyzed in the mice exposed to ITO and IO for 13 wk. In the 13-week inhalation exposure of mice to ITO, alveolar proteinosis and significantly increased lung weight were induced at the same exposure concentration as the current threshold limit value for indium and its compounds.

Two- and 13-week inhalation toxicities of indium-tin oxide and indium oxide in rats.

OBJECTIVES: Two- and 13-week inhalation toxicities of indium-tin oxide (ITO) and indium oxide (IO) were characterized for risk assessments of workers exposed to ITO. METHODS: F344 rats of both sexes were exposed by inhalation to ITO or IO aerosol for 6 h/day, 5 day/wk for 2 wk at 0, 0.1, 1, 10 or 100 mg/m(3) or 13 wk at 0, 0.1 or 1 mg/m(3). An aerosol generator and inhalation exposure system was constructed. RESULTS: Blood and lung contents of indium were elevated in a dose-related manner in the ITO- and IO-exposed rats. ITO and IO particles were deposited in the lung, mediastinal lymph node and nasal-associated lymphoid tissue. Exposures to ITO and IO induced alveolar proteinosis, infiltrations of alveolar macrophages and inflammatory cells and alveolar epithelial hyperplasia in addition to increased lung weight. ITO affected the lung more severely than IO did. Fibrosis of alveolar wall developed and some of these lesions worsened at the end of the 26-week post-exposure period. CONCLUSIONS: Persistent pulmonary lesions including alveolar proteinosis and macrophage infiltration occurred after 2- and 13-week inhalation exposures of rats to ITO and IO. Fibrosis of alveolar wall developed later. These lesions occurred after ITO exposure at the same concentration as the current occupational exposure limit in the USA and at blood indium levels below the biological exposure index in Japan for indium.

Inhalation carcinogenicity and toxicity of 1,2-dichloropropane in rats.

The toxicity and carcinogenicity of 1,2-dichloropropane (DCP) were examined by inhalation exposure of male and female F344 rats to DCP for either 13 wk or 2 years. In the 13-wk study, the DCP concentrations used were 125, 250, 500, 1000, or 2000 ppm (v/v), and in the 2-year study the DCP concentrations were 80, 200, or 500 ppm (v/v). Thirteen-week exposure to DCP induced hyperplasia in the respiratory epithelium and atrophy of the olfactory epithelium at 125 ppm and above. At the higher levels of exposure, hemolytic anemia and lesions of liver and adrenal gland were observed. Two-year exposure to DCP significantly increased incidences of papilloma in the nasal cavity of male and female rats exposed to 500 ppm DCP. In addition, three cases of esthesioneuroepithelioma were observed in the DCP-exposed male rats. Total nasal tumors increased in a concentration-dependent manner. Hyperplasia of the transitional epithelium and squamous cell hyperplasia, both of which were morphologically different from the hyperplasia of the respiratory epithelium observed in the 13-wk exposure study, occurred in a concentration-dependent manner; these lesions are considered to be preneoplastic lesions. Atrophy of the olfactory epithelium, inflammation of the respiratory epithelium, and squamous cell metaplasia were also seen in the 2-year study. These results demonstrate that DCP is a nasal carcinogen in rats. Lifetime cancer risks for humans exposed to DCP in the ambient air and work environment were quantitatively estimated, using both nonthreshold and threshold approaches, with the data obtained from the 2-year study.

Characteristics of multiwall carbon nanotubes for an intratracheal instillation study with rats.

Much concern has been raised over the health consequences of workers exposed to carbon nanotubes. In order to characterize multi-wall carbon nanotubes (MWCNT) suspended in a phosphate-buffered saline containing 0.1% Tween 80 for an intratracheal instillation study. Length and width distributions of the MWCNT fibers, dispersion of MWCNT in the suspension and in the lung tissue and the MWCNT contents of metal impurities were investigated. Arithmetic mean length and width of the MWCNT fibers as measured on scanning electron microscope (SEM) photographs were 5.0 microm and 88 nm, respectively, and fibers longer than 5.0 microm were 38.9% of all fibers measured. Dynamic light scattering size measurement revealed that 5-min ultrasonication, together with addition of Tween 80 into the suspension, decreased the hydrodynamic diameters of the agglomerated MWCNT to those of finer particles below 1.0 microm. SEM observation showed good dispersion of MWCNT in the suspension, and in the alveoli on Day 1 after instillation. Concentration of iron, chromium and nickel in the MWCNT were 4,400, 48 and 17 ppm (wt/wt), respectively, all of which were below levels that would elicit positive pulmonary toxic responses to these metals. The results suggest that well-dispersed, long and thin MWCNT fibers exhibit asbestos-like pathogenicity in the lung.

Pulmonary toxicity of intratracheally instilled multiwall carbon nanotubes in male Fischer 344 rats.

In order to assess pulmonary toxicity of multiwall carbon nanotubes (MWCNT), male F344 rats were intratracheally instilled with MWCNT suspension at a dose of 40 or 160 µg/head or α-quartz particles as a positive control at a dose of 160 µg/head and sacrificed for lung histopathology and bronchoalveolar lavage (BAL) fluid analyses on Day 1, 7, 28 or 91 after instillation. Well-dispersed MWCNT brought about dose- or time-dependent changes in lung weight, total proteins, albumin, lactate dehydrogenase and alkaline phosphatase in the BAL fluid, and pulmonary lesions including inflammation, Type II cell hyperplasia, microgranulomas and fibrosis. Phagocytosed and free forms of MWCNT were found in both bronchiolar and alveolar spaces. MWCNT deposition in the bronchus-associated lymphoid tissue gradually increased after instillation. Persistent infiltration of macrophages, transient infiltration of inflammatory cells primarily composed of neutrophils, microgranulomas associated with macrophages engulfing MWCNT, Type II cell hyperplasia and fibrosis with alveolar wall thickening as well as number of multinucleated alveolar macrophages increased dose-dependently. The MWCNT-induced lesions were more potent on Day 91 than the α-quartz-induced ones at an equal mass dose. The present results for intratracheally instilled MWCNT were extrapolated to potential inhalation exposure of humans to MWCNT at workplaces based on several assumptions.

Genotoxicity and cytotoxicity of multi-wall carbon nanotubes in cultured Chinese hamster lung cells in comparison with chrysotile A fibers.

OBJECTIVES: The potential applications and industrial production of multi-wall carbon nanotubes (MWCNT) have raised serious concerns about their safety for human health and the environment. The present study was designed to examine the in vitro cytotoxicity and genotoxicity of MWCNT and UICC chrysotile A (chrysotile). METHODS: Cytotoxicity using both colony formation and lactate dehydrogenase (LDH) assays and genotoxicity including chromosome aberration, micronucleus induction and hgprt mutagenicity were examined by exposing cultured Chinese hamster lung (CHL/IU) cells to MWCNT or chrysotile at different concentrations. RESULTS: The in vitro cytotoxicity of MWCNT depended on the solvent used for suspension of MWCNT and ultrasonication duration of the MWCNT suspension. A combination of DMSO/culture medium and 3-minute ultrasonication resulted in a well-dispersed medium with dispersion and isolation of agglomerated MWCNT by ultrasonication which manifested the highest cytotoxicity. The cytotoxicity was more potent for chrysotile than MWCNT. The genotoxicity of MWCNT was characterized by the formation of polyploidy without structural chromosome aberration, and an increased number of bi- and multi-nucleated cells without micronucleus induction, as well as negative hgprt mutagenicity. Chrysotile exhibited essentially the same genotoxicity as MWCNT, except for marginal but significant induction of micronuclei. MWCNT and chrysotile were incompletely internalized in the cells and localized in the cytoplasm. CONCLUSIONS: MWCNT and chrysotile were cytotoxic and genotoxic in Chinese hamster lung cells, but might interact indirectly with DNA. The results suggest that both test substances interfere physically with biological processes during cytokinesis.