Inhalation Toxicity Studies Research Articles

Identification of the appropriate dose metric for pulmonary inflammation of silver nanoparticles in an inhalation toxicity study

A number of studies have shown that induction of pulmonary toxicity by nanoparticles of the same chemical composition depends on particle size, which is likely in part due to differences in lung deposition. Particle size mostly determines whether nanoparticles reach the alveoli, and where they might induce toxicity. For the risk assessment of nanomaterials, there is need for a suitable dose metric that accounts for differences in effects between different sized nanoparticles of the same chemical composition. The aim of the present study is to determine the most suitable dose metric to describe the effects of silver nanoparticles after short-term inhalation. Rats were exposed to different concentrations (ranging from 41 to 1105 µg silver/m3 air) of 18, 34, 60 and 160 nm silver particles for four consecutive days and sacrificed at 24 h and 7 days after exposure. We observed a concentration-dependent increase in pulmonary toxicity parameters like cell counts and pro-inflammatory cytokines in the bronchoalveolar lavage fluid. All results were analysed using the measured exposure concentrations in air, the measured internal dose in the lung and the estimated alveolar dose. In addition, we analysed the results based on mass, particle number and particle surface area. Our study indicates that using the particle surface area as a dose metric in the alveoli, the dose–response effects of the different silver particle sizes overlap for most pulmonary toxicity parameters. We conclude that the alveolar dose expressed as particle surface area is the most suitable dose metric to describe the toxicity of silver nanoparticles after inhalation.

Histopathological analysis of the respiratory tract.

The basic anatomy of the mouse respiratory system is similar to that of other mammals and can be usefully examined under the light microscope in phenotyping studies, inhalation toxicity studies, and studies involving mouse models of human disease. In many studies, however, only the lungs are examined, leaving the possibility that phenotypic information from the majority of the conducting airways is lost. This unit provides standard approaches for tissue collection at necropsy and subsequent selection of a range of respiratory tissues for histological and pathological analysis. The major anatomical features to be found in each section are highlighted, and potential artifacts and methods to avoid them are discussed.

Derivation of occupational exposure levels (OELs) of low-toxicity isometric biopersistent particles: How can the kinetic lung overload paradigm be used for improved inhalation toxicity study design and OEL-derivation?

BackgroundConvincing evidence suggests that poorly soluble low-toxicity particles (PSP) exert two unifying major modes of action (MoA), in which one appears to be deposition-related acute, whilst the other is retention-related and occurs with particle accumulation in the lung and associated persistent inflammation. Either MoA has its study- and cumulative dose-specific adverse outcome and metric. Modeling procedures were applied to better understand as to which extent protocol variables may predetermine any specific outcome of study. The results from modeled and empirical studies served as basis to derive OELs from modeled and empirically confirmed directions.ResultsThis analysis demonstrates that the accumulated retained particle displacement volume was the most prominent unifying denominator linking the pulmonary retained volumetric particle dose to inflammogenicity and toxicity. However, conventional study design may not always be appropriate to unequivocally discriminate the surface thermodynamics-related acute adversity from the cumulative retention volume-related chronic adversity. Thus, in the absence of kinetically designed studies, it may become increasingly challenging to differentiate substance-specific deposition-related acute effects from the more chronic retained cumulative dose-related effects.ConclusionIt is concluded that the degree of dissolution of particles in the pulmonary environment seems to be generally underestimated with the possibility to attribute to toxicity due to decreased particle size and associated changes in thermodynamics and kinetics of dissolution. Accordingly, acute deposition-related outcomes become an important secondary variable within the pulmonary microenvironment. In turn, lung-overload related chronic adversities seem to be better described by the particle volume metric. This analysis supports the concept that ‘self-validating’, hypothesis-based computational study design delivers the highest level of unifying information required for the risk characterization of PSP. In demonstrating that the PSP under consideration is truly following the generic PSP-paradigm, this higher level of mechanistic information reduces the potential uncertainty involved with OEL derivation.

The sub-chronic toxicity of regular White Spirit in rats

Hydrocarbon solvents are mostly complex substances (UVCB) with carbon numbers in the range of approximately C5–C20. One of the most common types is a C9–C14 aliphatic solvent containing approximately 20% aromatics and commonly known as White Spirit in Europe and mineral spirits in the US. In previous repeated inhalation toxicity studies, White Spirit was reported to cause minimal systemic effects in most animal species with few effects other than male rat-specific kidney changes at levels up to approximately 2000mg/m3. In the present study male and female rats were exposed to White Spirit vapors, 6h/day, 5days/week for 13weeks at levels of approximately 2000, 4000, or 8000mg/m3 to assess the potential for effects at higher exposure levels. All of the rats survived the treatment period. In life observations were largely restricted to acute central nervous system (CNS) effects in the high exposure group. Terminal body weights of high exposure groups animals were significantly below control values. Statistically significant differences in the clinical and hematological observations were small and within normal physiological limits. Weights of some organs including liver, spleen and kidneys were elevated, but microscopic examination indicated that the only pathological effects were changes in the kidneys of the male rats, consistent with an α2u-globulin-mediated process, which is gender and species-specific and not relevant to humans. The overall no observed adverse effect level (NOAEC) was 4000mg/m3.

A short-term inhalation study protocol: designed for testing of toxicity and fate of nanomaterials.

The Short-Term Inhalation Toxicity Study Design described here was specifically developed for the testing of nanoparticles. It consists of a 5-day inhalation exposure with a subsequent 3-week exposure-free period. The protocol has been optimized for the detection of toxic effects in the respiratory tract by incorporation of additional endpoints like collection of bronchoalveolar lavage and measurement of biomarkers indicative for pro-inflammatory and inflammatory changes. Analytical determination of the test compound concentrations in the lung and other organs can be included in the study design for the determination of organ burden and fate of the tested nanomaterial. Over 20 nanomaterials have been tested with this method. In case of those compounds, where data of 90-day inhalation studies were available, the qualitative effects were comparable in both study types. Likewise, the No Observed Adverse Effect Levels were similar between the two study types, showing that the short-term design is suitable for a first risk assessment.

Comparison of inhalation toxicity studies of gentamicin in rats and dogs

Nebulized gentamicin solution was administered to rats (nose-only) and dogs (face mask) for 14 days with a 14-day recovery period. Control groups of each were exposed to saline aerosols. Mean estimated inhaled lung doses of gentamicin were 39, 123 and 245 mg/kg for rats (deposited doses 6, 17 and 34 mg/kg) over 30, 90 and 180 min, respectively. Since dogs do not tolerate exposures as long as rats, inhaled lung doses were limited to 7, 14 and 41 mg/kg (deposited doses of 1, 3 and 8 mg/kg) over 15, 30 and 60 min. Comparable doses were achieved at the low dose for rats and high dose for dogs. Serum AUCs (14 ± 2 µg/mL*h (mean ± SD) at 6 mg/kg in rats and 11 ± 7 µg/mL*h at 8 mg/kg in dogs) showed comparable exposure between the two, implying similar absorbed doses and confirming similar deposited lung doses. Rat exposures resulted in dose-related lung pathology (including low dose) manifested as upper respiratory tract irritant reactions with alveolar histiocytosis, inflammation, airway epithelial metaplasia and lymphomegaly in lung tissue. This was associated with high lung tissue gentamicin levels 24 h post-dose on Day 14 (375 ± 33 µg/g at deposited dose of 6 mg/kg). Dose-related kidney tubular necrosis (a well-known toxicity of parenteral gentamicin) was observed, but no test-article related effects on lung histopathology in dogs (even at highest deposited dose of 8 mg/kg) and low levels of lung tissue gentamicin (42 ± 11 µg/g) 24 h post-dose on Day 14.

The sub-chronic toxicity in rats of isoparaffinic solvents

Results from a 13-week inhalation study in rats on a C10–C12 isoparaffinic solvent are compared to the results of repeated inhalation and oral toxicity studies of four other isoparaffinic hydrocarbon solvents. Statistically significant findings which were consistent across all studies included: nephropathy and small but significant changes in hematological parameters in male rats and liver enlargement in both male and female rats. The male rat kidney changes were due to an alpha 2u globulin process and not relevant for human health or risk assessment. The liver enlargement without pathologic changes or elevations in liver enzyme markers was considered to be an adaptive response. The reason for the reductions in hematological parameters that were observed in males only is not clear, but it is suggested that these were either due to normal variation or a secondary consequence of the nephropathy. The overall No Observed Adverse Effect Concentration (NOAEC) was the highest concentration tested in the study, >10,000mg/m3. Because of the overall pattern of response, this solvent is considered to be representative of low aromatic C9–C14 aliphatic solvents in general. The data are useful for risk assessment and other purposes including the development of occupational exposure recommendations.

Human inhalation exposure to iron oxide particles

AbstractIn the past decade, many studies have been conducted to determine the health effects induced by exposure to engineered nanomaterials (NMs). Specifically for exposure via inhalation, numerous in vitro and animal in vivo inhalation toxicity studies on several types of NMs have been published. However, these results are not easily extrapolated to judge the effects of inhaling NMs in humans, and few published studies on the human response to inhalation of NMs exist. Given the emergence of more industries utilizing iron oxide nanoparticles as well as more nanomedicine applications of superparamagnetic iron oxide nanoparticles (SPIONs), this review presents an overview of the inhalation studies that have been conducted in humans on iron oxides. Both occupational exposure studies on complex iron oxide dusts and fumes, as well as human clinical studies on aerosolized, micron-size iron oxide particles are discussed. Iron oxide particles have not been described to elicit acute inhalation response nor promote lung disease after chronic exposure. The few human clinical studies comparing inhalation of fine and ultrafine metal oxide particles report no acute changes in the health parameters measured. Taken together existing evidence suggests that controlled human exposure to iron oxide nanoparticles, such as SPIONs, could be conducted safely.

Comparative hazard identification of nano- and micro-sized cerium oxide particles based on 28-day inhalation studies in rats

There are many uncertainties regarding the hazard of nanosized particles compared to the bulk material of the parent chemical. Here, the authors assess the comparative hazard of two nanoscale (NM-211 and NM-212) and one microscale (NM-213) cerium oxide materials in 28-day inhalation toxicity studies in rats (according to Organisation for Economic Co-operation and Development technical guidelines). All three materials gave rise to a dose-dependent pulmonary inflammation and lung cell damage but without gross pathological changes immediately after exposure. Following NM-211 and NM-212 exposure, epithelial cell injury was observed in the recovery groups. There was no evidence of systemic inflammation or other haematological changes following exposure of any of the three particle types. The comparative hazard was quantified by application of the benchmark concentration approach. The relative toxicity was explored in terms of three exposure metrics. When exposure levels were expressed as mass concentration, nanosized NM-211 was the most potent material, whereas when expression levels were based on surface area concentration, micro-sized NM-213 material induced the greatest extent of pulmonary inflammation/damage. Particles were equipotent based on particle number concentrations. In conclusion, similar pulmonary toxicity profiles including inflammation are observed for all three materials with little quantitative differences. Systemic effects were virtually absent. There is little evidence for a dominant predicting exposure metric for the observed effects.

In vivo lung deposition and sub-acute inhalation toxicity studies of nano-sized alendronate sodium as an antidote for inhaled toxic substances in Sprague Dawley rats

IntroductionAlendronate sodium is a bisphosphonate agent used for the treatment of osteoporosis and other bone diseases. It has a strong chelating property to bind or, to some extent, counteract the effects of substances, such as magnesium, calcium citrate, ferrous fumarate, carbonyl iron, as well as the zinc gluconate, sulfate and acetate salts. The objective of the present study was to evaluate lung deposition and sub-acute inhalation toxicity of the alendronate sodium respiratory formulation. MethodsParticle dimension of aerosols of alendronate was measured using a particle size analyzer. Alendronate was radiolabeled using Technetium-99m for in vitro and in vivo biodistribution studies. Alendronate at doses, 0.5%, 1.0%, and 1.5% in ethanol-saline respiratory formulation was inhaled twice a day up to 5 weeks for inhalation toxicity investigations. Hematological, biochemical and lung toxicity biomarkers in bronchoalveolar lavage (BAL) fluid were determined at the end of the experiment. Histopathological analysis of lung tissues was carried out to observe any microscopic changes ResultsParticle size analysis revealed the size within 300–500nm. Anderson cascade impactor results showed that the particles exhibited higher respirable fraction (55.52%) with MMAD of 4.66μm. Hematology, serum biochemistry and lung toxicity biomarkers in BAL fluid performed in the sub-acute toxicity studies indicated no adverse effects of alendronate sodium inhalation except for a significant increase in cholesterol levels and marginal increase in BAL fluid protein. At autopsy, no histopathological changes in major organs were observed. ConclusionsThe lung deposition and safety evaluation data observed from these studies suggested that aerosolized nanosized alendronate sodium by the inhalation route could be a new and promising route of administration as an antidote to radioactive substances through an increase in the bioavailability of the drug as well as a decrease in side effects on systemic delivery.

Additional Histopathologic Examination of the Lungs from a 3-Month Inhalation Toxicity Study with Multiwall Carbon Nanotubes in Rats

For hazard assessment of multiwalled carbon nanotubes (MWCNTs), a 90-day inhalation toxicity study has been performed with Nanocyl NC 7000 in accordance with OECD 413 test guideline. MWCNTs produced no systemic toxicity. However, increased lung weights, multifocal granulomatous inflammation, diffuse histiocytic and neutrophilic infiltrates, and intra-alveolar lipoproteinosis were observed in lung and lung-associated lymph nodes at 0.5 and 2.5mg/m(3). Additional investigations of the lungs were performed, including special stains for examination of connective tissue, and electron microscopy was performed to determine the location of the MWCNTs. The alveolar walls revealed no increase of collagen fibers, whereas within the microgranulomas a slight increase of collagen fibers was observed. The pleura did not reveal any increase in collagen fibers. Only a slight increase in reticulin fibers in the alveolar walls in animals of the 0.5 and 2.5mg/m(3) concentration group was noted. In the 0.1mg/m(3) group, the only animal revealing minimal granulomas exhibited a minimal increase in collagen within the granuloma. No increase in reticulin was observed. Electron microscopy demonstrated entangled MWCNTs within alveolar macrophages. Occasionally electron dense particles/detritus were observed within membrane-bound vesicles (interpreted as phagosomes), which could represent degraded MWCNTs. If so, MWCNTs were degradable by alveolar macrophages and not persistent within the lung. Inhalation of MWCNTs caused granulomatous inflammation within the lung parenchyma but not the pleura in any of the concentration groups. Thus, there are some similarities to effects caused by inhaled asbestos, but the hallmark effects, namely pleural inflammation and/or fibrosis leading to mesotheliomas, are absent.

Derivation of a chronic reference concentration for decalin

Decalin is found naturally in crude oil and as a product of combustion. It is used commercially as a solvent due to its ability to solubilize oils and fats. Despite its widespread occurrence in consumer products and the environment that lead to inhalation exposures, an inhalation toxicity value is not currently available for decalin. To derive a reference concentration (RfC) for decalin, inhalation toxicity studies were reviewed using a weight-of-evidence approach. A 2-year mouse inhalation study was chosen as the critical study for the derivation of the chronic RfC. Benchmark dose modeling was utilized to derive a point of departure for hepatic necrosis, syncytial alteration, eosinophilic focus, and erythrophagocytosis. A BMDL10 of 44mg/m3 was modeled for the most sensitive adverse effect, syncytial alteration. A chronic RfC for decalin of 0.08mg/m3 was calculated by conversion of the BMDL10 to a human equivalent continuous inhalation dose of 7.9mg/m3 and application of a total uncertainty factor of 100. Future research is needed to better characterize the toxicity associated with the chronic inhalation of decalin and refine the development of toxicity values.

An improved dispersion method of multi-wall carbon nanotube for inhalation toxicity studies of experimental animals

A multi-wall carbon nanotube (MWCNT) product Mitsui MWNT-7 is a mixture of dispersed single fibers and their agglomerates/aggregates. In rodents, installation of such mixture induces inflammatory lesions triggered predominantly by the aggregates/agglomerates at the level of terminal bronchiole of the lungs. In human, however, pulmonary toxicity induced by dispersed single fibers that reached the lung alveoli is most important to assess. Therefore, a method to generate aerosol predominantly consisting of dispersed single fibers without changing their length and width is needed for inhalation studies. Here, we report a method (designated as Taquann method) to effectively remove the aggregate/agglomerates and enrich the well-dispersed singler fibers in dry state without dispersant and without changing the length and width distribution of the single fibers. This method is base on two major concept; liquid-phase fine filtration and critical point drying to avoid re-aggregation by surface tension. MWNT-7 was suspended in Tert-butyl alcohol, freeze-and-thawed, filtered by a vibrating 25 µm mesh Metallic Sieve, snap-frozen by liquid nitrogen, and vacuum-sublimated (an alternative method to carbon dioxide critical point drying). A newly designed direct injection system generated well-dispersed aerosol in an inhalation chamber. The lung of mice exposed to the aerosol contained single fibers with a length distribution similar to the original and the Taquann-treated sample. Taquann method utilizes inexpensive materials and equipments mostly found in common biological laboratories, and prepares dry powder ready to make well-dispersed aerosol. This method and the chamber with direct injection system would facilitate the inhalation toxicity studies more relevant to human exposure.

Ten-week Whole-body Inhalation Toxicity Study of Chlorine Dioxide Gas in Rats

Chlorine dioxide (ClO2) gas can protect against influenza virus infection at a concentration of 0.03 parts par million (volume/volume), which is believed to be nontoxic in humans. This suggests an opportunity for the development of a novel protective method against airborne infectious diseases. This method is especially applicable to the highly pathogenic H5N1 influenza virus, as there is currently no safe and effective protection against H5N1. However, concerns remain regarding the safety of ClO2 gas for protection against virus infection, especially whether a concentration of 0.03 parts per million is really non-toxic when it is used for humans in closed or semiclosed spaces. In view of the importance of the usefulness and necessity of low concentration ClO2 gas treatment, it is critical to determine the “no observed adverse effect level” (NOAEL) of ClO2 gas. In 1972 Paulet and Desbrousses reported that the “lowest observed adverse effect level” (LOAEL) of ClO2 gas was 1 part per million. We attempted to confirm their data under carefully designed experimental conditions. Here, we performed a rat hole-body inhalation toxicity study, where rats were exposed to 1 part per million ClO2 gas for 5 hours per day and 5 days per week over a period of 10 weeks. The rats were exposed to a meticulously controlled low-concentration ClO2 gas. No adverse effect was observed under these experimental conditions in contrast to the study by Paulet and Desbrousses. We conclude that the no observed adverse effect level of ClO2 gas at these experimental conditions is 1 ppm. We hope this result will help develop a preventive method against airborne microbial infectious diseases of humans.

Toxicologic evaluation of tungsten: 28-day inhalation study of tungsten blue oxide in rats

The toxicity and toxicokinetics of tungsten blue oxide (TBO) were examined. TBO is an intermediate in the production of tungsten powder, and has shown the potential to cause cellular damage in in vitro studies. However, in vivo evidence seems to indicate a lack of adverse effects. The present study was undertaken to address the dearth of longer-term inhalation toxicity studies of tungsten oxides by investigating the biological responses induced by TBO when administered via nose-only inhalation to rats at levels of 0.08, 0.325, and 0.65 mg TBO/L of air for 6 h/day for 28 consecutive days, followed by a 14-day recovery period. Inhaled TBO was absorbed systemically and blood levels of tungsten increased as inhaled concentration increased. Among the tissues analyzed for tungsten levels, lung, femur and kidney showed increased levels, with lung at least an order of magnitude greater than kidney or femur. By exposure day 14, tungsten concentration in tissues had reached steady-state. Increased lung weight was noted for both terminal and recovery animals and was attributed to deposition of TBO in the lungs, inducing a macrophage influx. Microscopic evaluation of tissues revealed a dose-related increase in alveolar pigmented macrophages, alveolar foreign material and individual alveolar foamy macrophages in lung. After a recovery period there was a slight reduction in the incidence and severity of histopathological findings. Based on the absence of other adverse effects, the increased lung weights and the microscopic findings were interpreted as nonadverse response to exposure and were not considered a specific reaction to TBO.

A Pilot Study on the Refinement of Acute Inhalation Toxicity Studies: The Isolated Perfused Rat Lung as a Screening Tool for Surface-active Substances

New surface-active agents in waterproofing sprays are frequently tested for acute inhalation toxicity in vivo according to OECD Test Guideline 403. In order to refine and reduce the number of acute inhalation tests performed, we propose a screening test that uses isolated lungs. The test consists of the exposure of isolated, ventilated and perfused rat lungs, to aerosolised formulations of waterproofing agents (mass median aerodynamic diameter = 1μm), and on-line monitoring of respiratory parameters and gross pathology analysis. A pilot evaluation of the isolated perfused rat lung model for use in a screening test was carried out by blind testing 12 surface-active substances. The results obtained compared well with data available from in vivo acute inhalation studies. Substances that triggered harmful effects, such as impaired lung compliance and atelectasis of the isolated perfused lung, were also found to cause changes in respiratory parameters, some of which would be severe enough to lead to death in in vivo tests with rats. The changes in respiratory parameters suggest that the mode-of-action is associated with impairment of the surfactant layer. Therefore, pre-testing in the isolated perfused rat lung allows the identification of surface-active substances with the potential for causing acute inhalation toxicity.

Safety evaluation of a lipase enzyme (BD29241 Palmitase) preparation, expressed in Pseudomonas fluorescens, intended for removing palmitic acid from triacylglycerol

The lipase enzyme, BD29241 Palmitase, can be used as a processing aid for removing palmitic acid from triacylglycerol in the production of refined oil. This enzyme was produced from a Pseudomonas fluorescens (P. fluorescens) production strain and was tested in acute, inhalation, and subchronic toxicity studies. In addition, this enzyme was also tested for its potential to induce genotoxicity. Dosages of the test article preparation ranged from 5000μg/plate for in vitro toxicity studies to 2000mg/kg/day for in vivo toxicity studies. The highest oral dose tested in vivo (NOAEL of 2000mg/kg/day) resulted in a safety margin of 2.442×103 based on a conservative estimate of the total human consumption of BD29241 Palmitase of 0.819mg/kg/day. There was no toxicity reported for any of these studies including additional safety studies. A review of the literature indicates that P. fluorescens fulfills recognized safety criteria pertinent to microbial production strains used in the manufacture of food enzyme preparations. The results of the toxicity studies presented herein attest to the safety of BD29241 Palmitase for its above-stated intended use.

Ninety-Day Inhalation Toxicity Study With A Vapor Grown Carbon Nanofiber in Rats

A subchronic inhalation toxicity study of inhaled vapor grown carbon nanofibers (CNF) (VGCF-H) was conducted in male and female Sprague Dawley rats. The CNF test sample was composed of > 99.5% carbon with virtually no catalyst metals; Brunauer, Emmett, and Teller (BET) surface area measurements of 13.8 m2/g; and mean lengths and diameters of 5.8 µm and 158 nm, respectively.Four groups of rats per sex were exposed nose-only, 6 h/day, for 5 days/week to target concentrations of 0, 0.50, 2.5, or 25 mg/m3 VGCF-H over a 90-day period and evaluated 1 day later. Assessments included conventional clinical and histopathological methods, bronchoalveolar lavage fluid (BALF) analysis, and cell proliferation (CP) studies of the terminal bronchiole (TB), alveolar duct (AD), and subpleural regions of the respiratory tract. In addition, groups of 0 and 25 mg/m3 exposed rats were evaluated at 3 months postexposure (PE). Aerosol exposures of rats to 0.54 (4.9 f/cc), 2.5 (56 f/cc), and 25 (252 f/cc) mg/m(3) of VGCF-H CNFs produced concentration-related small, detectable accumulation of extrapulmonary fibers with no adverse tissue effects. At the two highest concentrations, inflammation of the TB and AD regions of the respiratory tract was noted wherein fiber-laden alveolar macrophages had accumulated. This finding was characterized by minimal infiltrates of inflammatory cells in rats exposed to 2.5mg/m(3) CNF, inflammation along with some thickening of interstitial walls, and hypertrophy/hyperplasia of type II epithelial cells, graded as slight for the 25mg/m(3) concentration. At 3 months PE, the inflammation in the high dose was reduced. No adverse effects were observed at 0.54mg/m(3). BALF and CP endpoint increases versus controls were noted at 25mg/m(3) VGCF-H but not different from control values at 0.54 or 2.5mg/m(3). After 90 days PE, BALF biomarkers were still increased at 25mg/m(3), indicating that the inflammatory response was not fully resolved. Greater than 90% of CNF-exposed, BALF-recovered alveolar macrophages from the 25 and 2.5mg/m(3) exposure groups contained nanofibers (> 60% for 0.5mg/m(3)). A nonspecific inflammatory response was also noted in the nasal passages. The no-observed-adverse-effect level for VGCF-H nanofibers was considered to be 0.54mg/m(3) (4.9 fibers/cc) for male and female rats, based on the minimal inflammation in the terminal bronchiole and alveolar duct areas of the lungs at 2.5mg/m(3) exposures. It is noteworthy that the histopathology observations at the 2.5mg/m(3) exposure level did not correlate with the CP or BALF data at that exposure concentration. In addition, the results with CNF are compared with published findings of 90-day inhalation studies in rats with carbon nanotubes, and hypotheses are presented for potency differences based on CNT physicochemical characteristics. Finally, the (lack of) relevance of CNF for the high aspect ratio nanomaterials/fiber paradigm is discussed.

Six-month low level chlorine dioxide gas inhalation toxicity study with two-week recovery period in rats

BackgroundChlorine dioxide (CD) gas has a potent antimicrobial activity at extremely low concentration and may serve as a new tool for infection control occupationally as well as publicly. However, it remains unknown whether the chronic exposure of CD gas concentration effective against microbes is safe. Therefore, long-term, low concentration CD gas inhalation toxicity was studied in rats as a six-month continuous whole-body exposure followed by a two-week recovery period, so as to prove that the CD gas exposed up to 0.1 ppm (volume ratio) is judged as safe on the basis of a battery of toxicological examinations.MethodsCD gas at 0.05 ppm or 0.1 ppm for 24 hours/day and 7 days/week was exposed to rats for 6 months under an unrestrained condition with free access to chow and water in a chamber so as to simulate the ordinary lifestyle in human. The control animals were exposed to air only. During the study period, the body weight as well as the food and water consumptions were recorded. After the 6-month exposure and the 2-week recovery period, animals were sacrificed and a battery of toxicological examinations, including biochemistry, hematology, necropsy, organ weights and histopathology, were performed.ResultsWell regulated levels of CD gas were exposed throughout the chamber over the entire study period. No CD gas-related toxicity sign was observed during the whole study period. No significant difference was observed in body weight gain, food and water consumptions, and relative organ weight. In biochemistry and hematology examinations, changes did not appear to be related to CD gas toxicity. In necropsy and histopathology, no CD gas-related toxicity was observed even in expected target respiratory organs.ConclusionsCD gas up to 0.1 ppm, exceeding the level effective against microbes, exposed to whole body in rats continuously for six months was not toxic, under a condition simulating the conventional lifestyle in human.

Estimation of human equivalent exposure from rat inhalation toxicity study of silver nanoparticles using multi-path particle dosimetry model

Respiratory tract dosimetry is a useful tool to estimate the exposure concentrations of an inhaled substance that will produce the same result at a target site of the respiratory tract in both rats and humans. Thus, to enable the results of animal inhalation studies to be extrapolated to human equivalent exposure levels, the MPPD (multi-path particle dosimetry) model was used to estimate the differences in the respiratory dosimetry of rats and humans. In our previous study, when animals were subchronically exposed to silver nanoparticles over a period of 90 days, a no observable adverse effect level (NOAEL) of 100 μg m−3 was suggested. Therefore, this study used results from a previous animal study, including the test aerosol information and estimated clearance rate of silver nanoparticles after a 90 day inhalation toxicity test. As a result, the human equivalent workplace exposure concentration of silver nanoparticles was estimated as 59 μg m−3 compared to the rat NOAEL of 100 μg m−3.