Jeong Hee Han

Subchronic Inhalation Toxicity of Silver Nanoparticles

The subchronic inhalation toxicity of silver nanoparticles was studied in Sprague-Dawley rats. Eight-week-old rats, weighing approximately 253.2 g (males) and 162.6 g (females), were divided into four groups (10 rats in each group): fresh-air control, low dose (0.6 x 10(6) particle/cm(3), 49 microg/m(3)), middle dose (1.4 x 10(6) particle/cm(3), 133 microg/m(3)), and high dose (3.0 x 10(6) particle/cm(3), 515 microg/m(3)). The animals were exposed to silver nanoparticles (average diameter 18-19 nm) for 6 h/day, 5 days/week, for 13 weeks in a whole-body inhalation chamber. In addition to mortality and clinical observations, body weight, food consumption, and pulmonary function tests were recorded weekly. At the end of the study, the rats were subjected to a full necropsy, blood samples were collected for hematology and clinical chemistry tests, and the organ weights were measured. Bile-duct hyperplasia in the liver increased dose dependently in both the male and female rats. Histopathological examinations indicated dose-dependent increases in lesions related to silver nanoparticle exposure, including mixed inflammatory cell infiltrate, chronic alveolar inflammation, and small granulomatous lesions. Target organs for silver nanoparticles were considered to be the lungs and liver in the male and female rats. No observable adverse effect level of 100 microg/m(3) is suggested from the experiments.

Monitoring multiwalled carbon nanotube exposure in carbon nanotube research facility.

With the increased production and widespread use of multiwalled carbon nanotubes (MWCNTs), human and environmental exposure to MWCNTs is inevitably increasing. Therefore, this study monitored the possible exposure to MWCNT release in a carbon nanotube research laboratory. To estimate the potential exposure of researchers and evaluate the improvement of the workplace environment after the implementation of protective control measures, personal and area monitoring were conducted in an MWCNT research facility where the researchers handled unrefined materials. The number, composition, and aspect ratio of MWCNTs were measured using scanning transmission electron microscopy with an energy-dispersive x-ray analyzer. The gravimetric concentrations of total dust before any control measures ranged from 0.21 to 0.43 mg/m3, then decreased to a nondetectable level after implementing the control measures. The number of MWCNTs in the samples obtained from the MWCNT blending laboratory ranged from 172.9 to 193.6 MWCNTs/cc before the control measures, and decreased to 0.018–0.05 MWCNTs/cc after the protective improvements. The real-time monitoring of aerosol particles provided a signature of the MWCNTs released from the blending equipment in laboratory C. In particular, the number size response of an aerodynamic particle sizer with a relatively high concentration in the range of 2 to 3 μ m in aerodynamic diameter revealed the evidence of MWCNT exposure. The black carbon mass concentration also increased significantly during the MWCNT release process. Therefore, the present study suggests that the conventional industrial hygiene measures can significantly reduce exposure to airborne MWCNTs and other particulate materials in a nano research facility.

Lung Function Changes in Sprague-Dawley Rats After Prolonged Inhalation Exposure to Silver Nanoparticles

The antimicrobial activity of silver nanoparticles has resulted in their widespread use in many consumer products. However, despite the continuing increase in the population exposed to silver nanoparticles, the effects of prolonged exposure to silver nanoparticles have not been thoroughly determined. Accordingly, this study attempted to investigate the inflammatory responses and pulmonary function changes in rats during 90 days of inhalation exposure to silver nanoparticles. The rats were exposed to silver nanoparticles (18 nm diameter) at concentrations of 0.7 × 106 particles/cm3 (low dose), 1.4 × 106 particles /cm3 (middle dose), and 2.9 × 106 particles /cm3 (high dose) for 6 h/day in an inhalation chamber for 90 days. The lung function was measured every week after the daily exposure, and the animals sacrificed after the 90-day exposure period. Cellular differential counts and inflammatory measurements, such as albumin, lactate dehydrogenase (LDH), and total protein, were also monitored in the acellular bronchoalveolar lavage (BAL) fluid of the rats exposed to the silver nanoparticles for 90 days. Among the lung function test measurements, the tidal volume and minute volume showed a statistically significant decrease during the 90 days of silver nanoparticle exposure. Although no statistically significant differences were found in the cellular differential counts, the inflammation measurements increased in the high-dose female rats. Meanwhile, histopathological examinations indicated dose-dependent increases in lesions related to silver nanoparticle exposure, such as infiltrate mixed cell and chronic alveolar inflammation, including thickened alveolar walls and small granulomatous lesions. Therefore, when taken together, the decreases in the tidal volume and minute volume and other inflammatory responses after prolonged exposure to silver nanoparticles would seem to indicate that nanosized particle inhalation exposure can induce lung function changes, along with inflammation, at much lower mass dose concentrations when compared to submicrometer particles.

Exposure assessment of workplaces manufacturing nanosized TiO2 and silver

With the increased production and widespread use of nanomaterials, human and environmental exposure to nanomaterials is inevitably increasing. Therefore, this study monitored the possible exposure to nanoparticles at workplaces that manufacture nano-TiO2 and nano-silver. To estimate the potential exposure of workers, personal sampling, area monitoring, and real-time monitoring using a scanning mobility particle sizer (SMPS) and dust monitor were conducted at workplaces where the workers handle nanomaterials. The gravimetric concentrations of TiO2 ranged from 0.10 to 4.99 mg/m3, which were lower than the occupational exposure limit 10 mg/m3 set by the Korean Ministry of Labor or American Conference of Governmental Industrial Hygienists (ACGIH). Meanwhile, the silver metal concentrations ranged from 0.00002 to 0.00118 mg/m3, which were also lower than the silver dust 0.1 mg/m3 and silver soluble compound 0.01 mg/m3 occupational exposure limits set by the ACGIH. The particle number concentrations at the nano-TiO2 manufacturing workplaces ranged from 11,418 to 45,889 particles/cm3 with a size range of 15–710.5 nm during the reaction, although the concentration decreased to 14,000 particles/cm3 when the reaction was stopped. The particle concentrations at the TiO2 manufacturing workplaces increased during the reactor and vacuum pump operations, and during the collection of the synthesized TiO2 particles. Similarly, the particle concentrations at the silver nanoparticle manufacturing workplaces increased when the sodium citrates were weighed or reacted with the silver nitrates, and during the cleaning of the workplace. The number of silver nanoparticles in the samples obtained from the workplace manufacturing silver nanoparticles using induced coupled plasma ranged from 57,789 to 2,373,309 particles/cm3 inside the reactor with an average size of 20–30 nm and 535–25,022 particles/cm3 with a wide range of particle sizes due to agglomeration or aggregation after the release of nanoparticles into the workplace air. In contrast, the silver nanoparticles manufactured by the wet method ranged from 393 to 3526 particle/cm3 with an average size of 50 nm. Thus, when taken together, the TiO2 and silver nanoparticle concentrations were relatively lower than existing occupational exposure limits.

Manganese Distribution in Brains of Sprague Dawley Rats after 60 Days of Stainless Steel Welding-Fume Exposure

Welders working in a confined space, as in the shipbuilding industry, are at risk of being exposed to high concentrations of welding fumes and developing pneumoconiosis or other welding-fume exposure related diseases. Among such diseases, manganism resulting from welding-fume exposure remains a controversial issue, as the movement of manganese into specific brain regions has not yet been clearly established. Accordingly, to investigate the distribution of manganese in the brain after welding-fume exposure, male Sprague-Dawley rats were exposed to welding fumes generated from manual metal arc-stainless steel (MMA-SS) at concentrations of 63.6 +/- 4.1 mg/m(3) (low dose, containing 1.6 mg/m(3) Mn) and 107.1 +/- 6.3 mg/m(3) (high dose, containing 3.5 mg/m(3) Mn) total suspended particulate (TSP) for 2 h per day in an inhalation chamber over a 60-day period. Blood, brain, lung, and liver samples were collected after 2 h, 15, 30, and 60 days of exposure and the tissues analyzed for their manganese concentrations using an atomic absorption spectrophotometer. Although dose- and time-dependent increases in the manganese concentrations were found in the lungs and livers of the rats exposed for 60 days, only slight manganese increases were observed in the blood during this period. Major statistically significant increases in the brain manganese concentrations were detected in the cerebellum after 15 days of exposure and up until 60 days. Slight increases in the manganese concentrations were also found in the substantia nigra, basal ganglia (caudate nucleus, putamen, and globus pallidus), temporal cortex, and frontal cortex, thereby indicating that the pharmacokinetics and distribution of the manganese inhaled from the welding fumes were different from those resulting from manganese-only exposure.

Comparison of High MRI T1 Signals with Manganese Concentration in Brains of Cynomolgus Monkeys After 8 Months of Stainless Steel Welding-Fume Exposure

Several pharmacokinetic studies on inhalation exposure to manganese (Mn) have already demonstrated that Mn readily accumulates in the olfactory and brain regions. However, a shortening of the magnetic resonance imaging (MRI) T1 relaxation time or high T1 signal intensity in specific sites of the brain, including the globus pallidus and subcortical frontal white matter, as indicative of tissue manganese accumulation has not yet been clearly established for certain durations of known doses of welding-fume exposure in experimental animals. Accordingly, to investigate the movement of manganese after welding-fume exposure, six cynomolgus monkeys were acclimated and assigned to three dose groups: unexposed, low dose (31 mg/m3 total suspended particulate [TSP], 0.9 mg/m3 of Mn), and high dose (62 mg/m3 TSP, 1.95 mg/m3 of Mn) of total suspended particulate. The primates were exposed to manual metal arc stainless steel (MMA-SS) welding fumes for 2 h per day in an inhalation chamber system equipped with an automatic fume generator. Magnetic resonance imaging (MRI) studies were conducted before the initiation of exposure and thereafter every month. The tissue Mn concentrations were then measured after a plateau was reached regarding the shortening of the MRI T1 relaxation time. A dose-dependent increase in the Mn concentration was found in the lungs, while noticeable increases in the Mn concentrations were found in certain tissues, such as the liver, kidneys, and testes. Slight increases in the Mn concentrations were found in the caudate, putamen, frontal lobe, and substantia nigra, while a dose-dependent noticeable increase was only found in the globus pallidus. Therefore, the present results indicated that a shortening of the MRI T1 relaxation time corresponded well with the Mn concentration in the globus pallidus after prolonged welding-fume exposure.

Gene-expression profiling using suppression-subtractive hybridization and cDNA microarray in rat mononuclear cells in response to welding-fume exposure:

Welders with radiographic pneumoconiosis abnormalities have shown a gradual clearing of the X-ray identified effects following removal from exposure. In some cases, the pulmonary fibrosis associated with welding fumes appears in a more severe form in welders. Accordingly, for the early detection of welding-fume-exposure-induced pulmonary fibrosis, the gene expression profiles of peripheral mononuclear cells from rats exposed to welding fumes were studied using suppression-subtractive hybridization (SSH) and a cDNA microarray. As such, Sprague-Dawley rats were exposed to a stainless steel arc welding fume for 2 h/day in an inhalation chamber with a 107.59 / 2.6 mg/m3 concentration of total suspended particulate (TSP) for 30 days. Thereafter, the total RNA was extracted from the peripheral blood mononuclear cells, the cDNA synthesized from the total RNA using the SMARTTM PCR cDNA method, and SSH performed to select the welding-fume-exposure-regulated genes. The cDNAs identified by the SSH were then cloned into a plasmid miniprep, sequenced and the sequences analysed using the NCBI BLAST programme. In the SSH cloned cDNA microarray analysis, five genes were found to increase their expression by 1.9-fold or more, including Rgs 14, which plays an important function in cellular signal transduction pathways; meanwhile 36 genes remained the same and 30 genes decreased their expression by more than 59%, including genes associated with the immune response, transcription factors and tyrosine kinases. Among the 5200 genes analysed, 256 genes (5.1%) were found to increase their gene expression, while 742 genes (15%) decreased their gene expression in response to the welding-fume exposure when tested using a commercial 5.0k DNA microarray. Therefore, unlike exposure to other toxic substances, prolonged welding-fume exposure was found to substantially downregulate many genes.

Recovery from Welding-Fume-Exposure-Induced MRI T1 Signal Intensities after Cessation of Welding-Fume Exposure in Brains of Cynomolgus Monkeys

The shortening of the MRI T1 relaxation time, indicative of a high signal intensity in a T1-weighted MRI, is known as a useful biomarker for Mn exposure after short-term welding-fume exposure. A previous monkey experimental study found that the T1 relaxation times decreased time-dependently after exposure, and a visually detectable high signal intensity appeared after 150 days of exposure. The nadir for the shortening of the T1 relaxation time was also previously found to correspond well with the blood Mn concentration in welders, suggesting a correlation between a prolonged high blood Mn concentration and shortened T1 relaxation time. Accordingly, to clarify the clearance of the brain Mn concentration after the cessation of welding-fume exposure, cynomolgus monkeys were assigned to 3 groups—unexposed, low dose (31 mg/m3 total suspended particulate (TSP), 0.9 mg Mn/m3), and high dose (62 mg/m3 TSP, 1.95 mg Mn/m3)—and exposed to manual metal-arc stainless steel (MMA-SS) welding fumes for 2 h per day for 8 mo in an inhalation chamber system equipped with an automatic fume generator. After reaching the peak MRI T1 signal intensity (shortest T1 relaxation time), the monkeys were allowed to recover by ceasing the welding-fume exposure. Within 2 mo, the MRI T1 signal intensities for the exposed monkeys returned to nearly the same level as those for the unexposed monkeys, indicating the potential for recovery from a high MRI T1 signal intensity induced by welding-fume exposure, even after prolonged exposure. Clearance of the Mn tissue concentration was also demonstrated in the globus pallidus, plus other tissues from the brain, liver, spleen, and blood. In contrast, there was no clearance of the lung concentrations of Mn, indicating that a soluble form of Mn was transported to the blood and brain. Therefore, the solubility of Mn in welding fumes would appear to be an important determinant as regards the retention of blood Mn levels and brain tissue Mn concentrations in welders.

Changes in blood manganese concentration and MRI t1 relaxation time during 180 days of stainless steel welding-fume exposure in cynomolgus monkeys.

Welders are at risk of being exposed to high concentrations of welding fumes and developing pneumoconiosis or other welding-fume exposure-related diseases. Among such diseases, manganism resulting from welding-fume exposure remains a controversial issue, as although the movement of manganese into specific brain regions has been established, the similar movement of manganese presented with other metals, such as welding fumes, has not been clearly demonstrated as being similar to that of manganese alone. Meanwhile, the competition between Mn and iron for iron transporters, such as transferrin and DMT-1, to the brain has also been implicated in the welding-fume exposure. Thus, the increased signal intensities in the basal ganglia, including the globus pallidus and subcortical frontal white matter, based on T1-weighted magnetic resonances in welders, require further examination as regards the correspondence with an increased manganese concentration. Accordingly, to investigate the movement of manganese after welding-fume exposure, 6 cynomolgus monkeys were acclimated for 1 mo and assigned to 3 dose groups: unexposed, low dose of (total suspended particulate [TSP] 31 mg/m3, 0.9 mg/m3 of Mn), and high dose of total suspended particulate (62 mg/m3 TSP, 1.95 mg/m3 of Mn). The primates were exposed to manual metal-arc stainless steel (MMA-SS) welding fumes for 2 h/day in an inhalation chamber system equipped with an automatic fume generator for 6 mo. Magnetic resonance imaging (MRI) studies of the basal ganglia were conducted before the initiation of exposure and thereafter every month. During the exposure, the blood chemistry was monitored every 2 wk and the concentrations of metal components in the blood were measured every 2 wk and compared with ambient manganese concentrations. The manganese concentrations in the blood did not show any significant increase until after 2 mo of exposure, and then reached a plateau after 90 days of exposure, showing that an exposure period of at least 60 days was required to build up the blood Mn concentration. Furthermore, as the blood Mn concentration continued to build, a continued decrease in the MRI T1 relaxation time in the basal ganglia was also detected. These data suggested that prolonged inhalation of welding fumes induces a high MRI T1 signal intensity with an elevation of the blood manganese level. The presence of a certain amount of iron or other metals, such as Cr and Ni, in the inhaled welding fumes via inhalation was not found to have a significant effect on the uptake of Mn into the brain or the induction of a high MRI T1 signal intensity.

Tissue Distribution of Manganese in Iron-Sufficient or Iron-Deficient Rats After Stainless Steel Welding-Fume Exposure

Welders can be exposed to high levels of manganese through welding fumes. Although it has already been suggested that excessive manganese exposure causes neurotoxicity, called manganism, the pathway of manganese transport to the brain with welding-fume exposure remains unclear. Iron is an essential metal that maintains a homeostasis in the body. The divalent metal transporter 1 (DMT1) transports iron and other divalent metals, such as manganese, and the depletion of iron is known to upregulate DMT1 expression. Accordingly, this study investigated the tissue distribution of manganese in iron-sufficient and iron-deficient rats after welding-fume exposure. The feeding of an iron-deficient diet for 4 wk produced a depletion of body iron, such as decreased iron levels in the serum and tissues, and upregulated the DMT1 expression in the rat duodenum. The iron-sufficient and iron-deficient rats were then exposed to welding fumes generated from manual metal arc stainless steel at a concentration of 63.5 ± 2.3 mg/m3 for 2 h per day over a 30-day period. Animals were sacrificed on days 1, 15, and 30. The level of body iron in the iron-deficient rats was restored to the control level after the welding-fume exposure. However, the tissue distributions of manganese after the welding-fume exposure showed similar patterns in both the iron-sufficient and iron-deficient groups. The concentration of manganese increased in the lungs and liver on days 15 and 30, and increased in the olfactory bulb on day 30. Slight and heterogeneous increases of manganese were observed in different brain regions. Consequently, these findings suggest that the presence of Fe in the inhaled welding fumes may not have a significant effect on the uptake of Mn into the brain. Thus, the condition of iron deficiency did not seem to have any apparent effect on the transport of Mn into the brain after the inhalation of welding fumes.