Lung Toxicity after 13-Week Inhalation Exposure to Nickel Oxide, Nickel Subsulfide, or Nickel Sulfate Hexahydrate in F344/N Rats and B6C3F1 Mice

Lung Toxicity after 13-Week Inhalation Exposure to Nickel Oxide,Nickel Subsulfide, or Nickel Sulfate Hexahydrate in F344/N Ratsand B6C3F₁ Mice. DUNNICK, J. K., ELWELL, M. BENSON, J. M., HOBBS,C. H., HAHN, F. F., HALY, P. J., CHENG, Y. S., AND EIDSON, A.F. (1989). Fundam. Appl. Toxicol. 12, 584–594. The relativetoxicity of nickel oxide (NiO), nickel sulfate hexahydrate (NiSO₄6H₂O)and nickel subsulfide (Ni₃S₂) was studied in F344/N rats andB6C3F₁ mice after inhalation exposure for 6 hr/day, 5 days/week,for 13 weeks. Exposure concentrations used (as mg Ni/m³ were0.4–7.9 for NiO, 0.02–0.4 for NiSO₄ 6H₂O and 0.11–1.8for Ni₃S₂. No exposure-related effects on mortality and onlyminor effects on body weight gain were seen in rats or mice.The most sensitive parameter for nickel toxicity was histopathologic change in the lungs of exposed animals where chronic activeinflammation, fibrosis, and alveolar macrophage hyperplasiawerez associated with nickel exposure. There was an exposure-related increase in lung weight in rats and mice. Equilibriumlevels of nickel in the lung were reached by 13 weeks of nickelsulfate and nickel subsulfide exposure, whereas lung levelsof nickel continued to increase throughout exposure to nickeloxide. Additional exposure-related histopathologic lesions intreated animals included atrophy of the olfactory epitheliumafter nickel sulfate and nickel subsulfide exposure. No nasallesions were seen after nickel oxide expo sure. Lymphoid hyperplasiaof the bronchial lymph nodes developed in animals exposed toall three nickel compounds. The order oftoxicity correspondedto the water solubility of the nickel compounds, with nickelsulfate being most toxic, followed by nickel subsulfide andnickel oxide.     

Two-Week, Repeated Inhalation Exposure of F344/N Rats and B6C3F Mice to Ferrocene

Two-Week, Repeated Inhalation Exposure of F344/N Rats and B6C3F¹Mice to Ferrocene. SUN, J. D., DAHL, A. R., GILLETT, N. A.,BARR, E. B., CREWS, M. L., EIDSON, A. F., BECHTOLD, W. E., BURT,D. G., DIETER, M. P., AND HOBBS, C. H. (1991). Fundam. ApplToxicol. 17, 150-158. Ferrocene (dicyclopentadienyl iron; CASNo. 102-54-5) is a relatively volatile, organometallic compoundused as a chemical intermediate, a catalyst, and as an antiknockadditive in gasoline. It is of particular interest because ofits structural similarities to other metallocenes that havebeen shown to be carcinogenic. F344/N rats and B6C3F, mice wereexposed to 0, 2.5, 5.0, 10, 20, and 40 mg ferrocene vapor/m3,6 hr/day for 2 weeks. During these exposures, there were nomortality and no observable clinical signs of ferrocene-relatedtoxicity in any of the animals. At the end of the exposures,male rats exposed to the highest level of ferrocene had decreasedbody-weight gains relative to the weight gained by filteredair-exposed control rats, while body-weight gains for all groupsof both ferrocene- and filtered air-exposed female rats weresimilar. Male mice exposed to the highest level of ferrocenealso had decreased body-weight gains, relative to controls,while female mice had relative decreases in body-weight gainsat the three highest exposure levels. Male rats had a slightdecrease in relative liver weight at the highest level of exposure,whereas no relative differences in organ weights were seen infemale rats. Male mice had exposure-relative decreases in liverand spleen weights, and an increase in thymus weights, relativeto controls. For female mice, relative decreases in organ weightswere seen for brain, liver, and spleen. No exposure-relatedgross lesions were seen in any of the rats or mice at necropsy.Histopathological examination was done only on the nasal turbinates,lungs, liver, and spleen. The only exposure-related findingwas histopathologic lesions in the nasal turbinates of bothspecies. These lesions were primarily centered in the olfactoryepithelium and were morphologically diagnosed as subacute, necrotizinginflammation. Nasal lesions were observed in all ferrocene-exposedanimals and differed only in severity, which was dependent onthe exposure concentration. In vitro metabolism studies of ferroceneshowed that nasal tissue, particularly the olfactory epithelium,had 10 times higher "ferrocene hydroxylating" activity thandid liver tissue from the same animals. These results suggestthat the mechanism of ferrocene toxicity may be the intracellularrelease of ferrous ion through ferrocene metabolism, followedby iron-catalyzed lipid peroxidalion of cellular membranes.     

Comparative Inhalation Toxicity of Nickel Subsulfide to F344/N Rats and B6C3F1 Mice Exposed for 12 Days

Comparative Inhalation Toxicity of Nickel Subsulfide to F344/NRats and B6C3F₁ Mice Exposed for 12 Days. BENSON, J. M., CARPENTER,R. L., HAHN, F. F., HALEY, P. J. HANSON, R. L., HOBBS, C. H.,PICKRELL, J. A., AND DUNNICK, J. K. (1987). Fundam Appl. Toxicol.9, 251–265. Groups of F344/N rats and B6C3F₁ mice wereexposed to aerosols of nickel subsulfide (Ni₃S₂) 6 hr/day for12 days not including weekends. Actual exposure concentrationswere within 3% of target (target 10.0, 5.0, 2.5, 1.2, 0.6,and 0.0 mg Ni₃S₂/m³). Nickel lung burdens of exposed rats andmice increased linearly with exposure concentration. Two malerats and all mice exposed to 10.0 mg Ni₃S₂/m³ died before theend of the exposures. Exposure to Ni₃S₂ had no elfect on thenatural killer cell activity of mouse spleen cells. Lesionsin rats and mice related to inhalation of Ni₃S₂ were found inthe nasal epithelium, lung, and bronchial lymph nodes. The mostextensive lesions were found in the lung and included necrotizingpneumonia. Emphysema developed in rats exposed to 5.0 or 10.0mg Ni₃S₂/m³ while fibrosis developed in mice exposed to 5.0mg Ni₃S₂/m³ Degeneration of the respiratory epithelium and atrophyof the olfactory epithelium of the nose occurred in rats exposedto as low as 0.6 mg Ni₃S₂/m³ and mice exposed to 1.2 mg/m³ Resultsindicate that inhalation exposure of rats and mice to Ni₃S₂/aerosol concentrations near the current threshold limit value(TLV) for nickel compounds (1 mg/m³ for Ni metal and roastingfume and dust and 0.1 mg/m³ as Ni for soluble compounds) canproduce lesions in the respiratory tract. Atrophy of lymphoidtissues (spleen, thymus, and bronchial lymph nodes) was foundin animals of the highest exposure concentration. Degenerationof the testicular germinal epithelium was also observed in miceand rats that survived 5.0 or 10.0 mg/m³ exposure concentrations.     

Comparative Inhalation Toxicity of Nickel Sulfate to F344/N Rats and B6C3F1 Mice Exposed for Twelve Days

Comparative Inhalation Toxicity of Nickel Sulfate to F344/NRats and B6C3F₁ Mice Exposed for Twelve Days. BENSON, J. M.,BURT, D. G., CARPENTER, R. L., EIDSON, A. F., HAHN, F. F., HALEY,P. J., HANSON, R. L., HOBBS, C. H., PICKRELL, J. A., AND DUNNICK,J. K. (1988). Fundam. Appl. Toxicol 10, 164-178. Groups of F344/Nrats and B6C3F, mice were exposed to aerosols of nickel sulfatehexahydrate (NiSO₄-6H₂O) 6 hr/day for 12 days to determine theshort-term inhalation toxicity of this compound. Target exposureconcentrations were 60, 30, 15, 7, 3.5, and 0 mg NiSO₄.6H₂O/m³.Endpoints evaluated included clinical signs, mortality, quantitiesof Ni in selected tissues, effect on mouse resistance to tumorcells, and pathological changes in tissues of both rats andmice. All mice exposed to 7 mg NiSO₄ 6H2O/m³ or greater and10 rats exposed to 15 mg NiSO₄ 6H2O/m³ or greater died beforethe termination of exposures. Quantities of Ni remaining inlungs of rats at the end of the exposure were independent ofexposure concentration. Lung burdens of Ni in mice were approximatelyone-half that in lungs of rats. Exposure of female mice to 3.5mg NiSO₄ 6H2O/m³had no effect on resistance to tumor cells asdetermined by spleen natural killer cell activity. Histopathologicalchanges were seen in tissues of rats and mice exposed to aslow as 3.5 mg NiSO₄ 6H2O/m³. Lesions related to NiSO₄ 6H2O/m³exposureoccurred in lung, nose, and bronchial and mediastinal lymphnodes. Results indicated that exposure of rats and mice to amountsof NiSO₄ 6H2O/m³aerosols resulting in Ni exposure concentrationsonly eight times greater than the current threshold limit valuefor soluble Ni (0.1 mg/m³) for as little as 12 days can causesignificant lesions of the.     

Particle Clearance and Histopathology in Lungs of F344/N Rats and B6C3F1 Mice Inhaling Nickel Oxide or Nickel Sulfate

The goals of this study were to (1)determine the effects ofrepeated inhalation of relatively insoluble nickel oxide (NiO)and highly soluble nickel sulfate hexahydrate (NiSO₄ 6H₂O) onlung particle clearance, (2)investigate the effects of repeatedinhalation of NiO or NiSO₄ on the pulmonary clearance of subsequentlyinhaled ⁸⁵Sr-labeled microspheres, (3)correlate the observedeffects on clearance with accumulated Ni lung burden and associatedpathological changes in the lung, and (4)compare responses inF344 rats and B6C3F₁, mice. Male F344/N rats and B6C3F₁ micewere exposed whole-body to either NiO or NiSO₄ 6H₂O 6 hr/day,5 days/week for up to 6 months. NiO exposure concentrationswere 0, 0.62, and 2.5 mg NiO/m for rats and 0, 1.25, and 5.0mg NiO/ m for mice. NiSO₄ 6H₂O/m³ exposure concentrations were0, 0.12, and 0.5 mg NiSO₄ 6H₂ for rats and 0, 0.25, and 1.0mg NiSO₄ 6H₂O/m³ for mice. After 2 and 6 months of whole-bodyexposure, groups of rats and mice were acutely exposed nose-onlyto 63 (NiO-exposed animals only), ⁶³NiSO₄ 6H₂O (Ni SO₄ 6H₂Oanimals only), or to ⁸⁵Sr-labeled polystyrene latex (PSL) microspheres(both NiO- and NiSO₄ 6H₂O-exposed animals) to evaluate lungclearance. In addition, groups of rats and mice were euthanizedafter 2 and 6 months of exposure and at 2 and 4 months afterthe whole-body exposures were completed to evaluate histopathologicalchanges in the left lung and to quantitate Ni in the right lung.Repeated inhalation of NiO results in accumulation of Ni inlungs of both rats and mice, but to a greater extent in lungsof rats. During the 4 months after the end of the whole-bodyexposures, some clearance of the accumulated Ni burden occurredfrom the lungs of rats and mice exposed to the lower, but notthe higher NiO exposure concentrations. Clearance of acutelyinhaled ⁶³NiO was also impaired in both rats and mice, withthe extent of impairment related to both exposure concentrationand duration. However, the clearance of acutely inhaled ⁸⁵SrPSL microspheres was not impaired. The repeated inhalation ofNiO resulted in alveolar macrophage (AM) hyperplasia with accumulationof NiO particles in both rats and mice, chronic alveolitis inrats, and interstitial pneumonia in mice. These lesions persistedthroughout the 4-month recovery period after the NiO whole-bodyexposures were terminated. In contrast, repeated inhalationof NiSO₄ 6H₂O did not result in accumulation of Ni in lungsof either rats or mice and did not affect the clearance of ⁶³NiSO₄6H₂Oinhaled after either 2 or 6 months of NiSO₄ 6H₂O exposure. Clearanceof the ⁸⁵Sr-labeled microspheres was significantly impairedonly in rats exposed to the microspheres after 2 months of exposureto NiSO₄ 6H₂O Histopathological changes in rats were qualitativelysimilar to those seen in NiO-exposed rats. Only minimal histopathologicalchanges were observed in NiSO₄ 6H₂O mice. These results suggestthat repeated inhalation of NiO at levels resulting in AM hyperplasiaand alveolitis may impair clearance of subsequently inhaledNiO. The potential effects of repeated inhalation of solubleNiSO₄ 6H₂O on the clear ance of subsequently inhaled poorlysoluble particles are less clear.     

Inhalation Toxicity of 1,6-Hexanediamine Dihydrochloride in F344/N Rats and B6C3F1 Mice

1,6-Hexanediamine (HDA) is a high production volume chemicalwhich is used as an intermediate in the synthesis of paints,resins, inks, and textiles and as a corrosion inhibitor in lubricants.Two- and 13-week studies of the toxicity of the dihydrochloridesalt of HDA (HDDC) were conducted in male and female Fischer344/N rats and B6C3F₁ mice using whole-body inhalation exposure.Both species were evaluated for histopatho-logic and reproductiveeffects, and rats were examined for clinical chemistry and hematologicchanges. In the 2-week inhalation studies, animals were exposedto 10–800 mg HDDC/m³, 6 hr per day. All rats, all femalemice, and two of five male mice in the high-exposure group diedbefore the end of the study. Surviving mice in this group hada dose-dependent depression in body weight gain. Clinical signswere primarily related to upper respiratory tract irritationand included dyspnea and nasal discharge in both species. Treatment-relatedhistopathologic lesions included inflammation and necrosis ofthe laryngeal epithelium of both species and the tracheal epitheliumof mice, as well as focal inflammation and ulceration of therespiratory and olfactory nasal mucosa. In the 13-week inhalationstudies, animals were exposed to HDDC at concentrations of 1.6–160mg/ m³ for 6 hr per day, 5 days per week. In addition to thebase study groups, a supplemental group of rats at each exposurelevel was included to assess the effect of HDDC on reproduction.No treatment-related changes in organ weights or organ-to-body-weightratios occurred in rats, and no treatment-related clinical signsor gross lesions were seen in either species. Chemical-relatedmicroscopic lesions were limited to the upper respiratory tract(larynx and nasal passages) in the two highest exposure groupsand were similar in both species. These lesions included minimalto mild focal erosion, ulceration, inflammation, and hyperplasiaof the laryngeal epithelium, in addition to degeneration ofthe olfactory and respiratory nasal epithelium. HDDC causedno significant changes in sperm morphology or vaginal cytologyand no significant adverse effects on reproduction in rats ormice. Hematologic and clinical chemistry changes in rats wereminor and sporadic and were not accompanied by related histologicfindings. HDDC did not increase the frequency of micronucleatederythrocytes in mice. In summary, the toxicity of HDDC to ratsand mice was a result of the irritant properties of the chemical,was limited primarily to the nasal passages and upper airways,and was consistent with the effects of other irritant chemicalsadministered by inhalation.     

Effect of Inhaled Azodicarbonamide on F344/N Rats and B6C3F1 Mice with 2-Week and 13-Week Inhalation Exposures

Effect of Inhaled Azodicarbonamide on F344/N Rats and B6C3F,Mice with 2-Week and 13-Week Inhalation Exposures. MEDINSKY,M. A., BECHTOLD, W. E., BIRNBAUM, L. S., BOND, J. A., BURT,D. G., CHENG, Y. S., GILLFTT, N. A., GULATI, D. K., HOBBS, C.H., AND PICK-RELL, J. A. (1990). Fundam. Appl. Toxicol 15, 308/319.Azodicarbonamide (ADA), a compound used in the baking and plasticsindustries, has been reported to cause pulmonary sensiti-zationand dermatitis in people. Two-week repeated and 13-week subchronicinhalation exposures of F344/N rats and B6C3F, mice to ADA wereconducted to determine the toxicity of inhaled ADA. The meanair concentrations of ADA in the 2-week studies were 207, 102,52, 9.4, or 2.0 mg/m3. No exposure-related mortality nor abnormalclinical signs were observed in rats or mice during or afterexposure. The terminal body weights were slightly depressedin the highest exposure group. Liver weights were lower in malerats exposed to 200 mg ADA/m3. No significant lesions were notedon either gross or histologic evaluation of rats or mice. Inthe 13-week subchronic study, the mean air concentrations ofADA were 204, 100, or 50 mg/m3. No mortality or clinical signsrelated to exposure were observed. The terminal body weightsof exposed rats were not significantly different from thoseof control rats but were significantly depressed in mice exposedto 100 or 200 mg ADA/m3. No histopathological lesions were notedin mice. Lung weights were increased and enlarged mediastinaland/or tracheobronchial lymph nodes were noted in rats exposedto 50 mg ADA/m3. No exposure-related lesions were observed microscopicallyin rats exposed to 100 or 200 mg ADA/m3. All rats in the 50mg ADA/m3 exposure group only had lung lesions that consistedof perivascular cuffing with lymphocytes and a multifocal typeII cell hyperplasia, suggesting a possible immune reaction toan antigen in the lung. Viral titers for rats exposed to 50mg ADA/m3 were negative for Sendai virus and pneumonia virusof mice, which produce similar lesions. The possibility of anunknown viral antigen causing this lesion cannot be eliminated.Lung tissue from male rats was analyzed for ADA and biurea,the major metabolite of ADA. No ADA was detected. The amountof biurea in the lungs increased nonlinearly with increasingexposure concentration, suggesting that clearance was somewhatimpaired with repeated exposures. However, even at the highestexposure concentration, this amount of biurea was less than1 % of the estimated total ADA deposited over the exposure period.In summary, ADA is rapidly cleared from the lungs, even wheninhaled at concentrations up to 200 mg/m3. Exposure to ADA forup to 13 weeks did not appear to be toxic to rodents     

Metallothionein Induction and Pulmonary Responses to Inhaled Cadmium Chloride in Rats and Mice

Inhaled CdCl₂ is a pulmonary carcinogen in rats but not in mice.We hypothesized that pulmonary metallothionein (MT) inductionmay be different in both species and thereby may lead to differentlevels of protection from Cd-induced lung injury. Fisher-344rats and B6C3F₁ mice were exposed for 4 weeks to CdCl₂ aerosolsof 0, 30, 50, and 150 µg/m³ air or 0, 10, 30, and 100µg/m³ air, respectively. Animals from each exposure groupwere terminated at 1, 30, and 133 days after the end of exposure.The lungs were lavaged for cell and biochemical analyses. Cadmiumand MT in lavagate and lung tissue were measured. The retentionhall-time of pulmonary Cd was greater in mice (290 vs 90 days,p<0.05). Cd exposure provoked an inflammatory response whichwas dose-dependent in both species, and while it was only short-livedin rats, it persisted throughout the observation period in miceat the high exposure concentrations. Mice were found to havea greater baseline level of MT (18.046.96 vs 11.71.98 µgMT/g control lung, p<0.05). Mice showed greater inducibilityof MT for a given CdCl₂ exposure concentration; however, bothspecies had a similar relationship between retained pulmonaryCd and MT induction though mice maintained increased MT levelsfor a longer period of time. The greater pulmonary baselineMT together with the longer presence of Cd-induced pulmonaryMT may result in greater protection from Cd carcinogenicityin spite of the greater pulmonary Cd-induced inflammation inmice.     

The Immunotoxicity of Three Nickel Compounds following 13-Week Inhalation Exposure in the Mouse

The Immunotoxicity of Three Nickel Compounds following 13-WeekInhalation Exposure in the Mouse. HALEY, P. J. SHOPP, G. M.,BENSON, J. M, CHENG, Y.-S., BICE, D. E., LUSTER, M. I., DUNNICK,J. K., AND HOBBS, C. H. (1990). Fundam. Appl. Toxicol 15, 476–487.Groups of B6C3F₁, mice were exposed to aerosols of nickel subsulfide(Ni₃S₂), nickel oxide (NiO), or nickel sulfate hexahydrate (NiSO₄6H₂O)6 hr/day, 5 days per week for 65 days to determine the immunotoxicityof these compounds. Exposure concentrations were 0.11, 0.45,and 1.8 mg Ni/m³ for Ni₃S₂, 0.47, 2.0, and 7.9 mg Ni/m³ forNiO; and 0.027, 0.11, and 0.45 mg Ni/m³ for NiSO₄. Thymic weightswere decreased only in mice exposed to 1.8 mg Ni/m³ Ni₃S₂. Increasednumbers of lung-associated lymph nodes (LALN), but not spleennucleated cells, were seen with all compounds. Nucleated cellsin lavage samples were increased in mice exposed to the highestconcentrations of NiSO₄ and NiO and to 0.45 and 1.8 mg Ni/m³Ni₃S₂. Increased antibody-forming cells (AFC) were seen in LALNof mice exposed to 2.0 and 7.9 mg Ni/m³ NiO and 1.8 mg Ni/m³Ni₃S₂. Decreased AFC/10⁶ spleen cells were observed in miceexposed to NiO, and decreased AFC/spleen were seen for miceexposed to 1.8 mg Ni/m³ Ni₃S₂. Only mice exposed to 1.8 mg Ni/m³Ni₃S₂ had a decrease in mixed lymphocyte response. All concentrationsof NiO resulted in decreases in alveolar macrophage phagocyticactivity, as did 0.45 and 1.8 mg Ni/m³ Ni₃S₂. None of the nickelcompounds affected the phagocytic activity of peritoneal macro-phages.Only 1.8 mg Ni/m³ Ni₃S₂ caused a decrease in spleen naturalkiller cell activity. Results indicate that inhalation exposureof mice to nickel can result in varying effects on the immunesystem, depending on dose and physicochemical form of the nickelcompound. These nickel-induced changes may contribute to significantimmunodysfunction.     

Four-Week Inhalation Toxicity Study with Ludox Colloidal Silica in Rats: Pulmonary Cellular Responses

Four-Week Inhalation Toxicity Study with Ludox Colloidal Silicain Rats: Pulmonary Cellular Responses. WARHEIT, D. B., CARAKOSTAS,M. C, KELLY, D. P., AND HARTSKY, M. A. (1991). Fundam. Appl.Toxicol. 16, 590–601. This study was designed to complementa traditional subchronic inhalation toxicity study with Ludoxcolloidal silica. CD rats were exposed nose-only for 2 or 4weeks at concentrations of 0, 10, 50, and 150 mg/m³ Ludox (driedSiO₂). Additional groups of rats exposed for 4 weeks were givena 3-month recovery period. Following exposure and/or recovery,fluids and cells were recovered from the lungs by bronchoalveolarlavage (BAL) and measured for cellular and biochemical parameters.Additional groups of animals were processed for cell labelingstudies or lung deposition studies. Inhaled doses of Ludox colloidalsilica were measured after 4-week exposures and were found tobe 489 µg/lung (10 mg/m³ group), 2418 µg/lung (50mg/m³), and 7378 µg/lung (150 mg/m³), respectively. Resultsshowed that exposures to 150 mg/m³ Ludox for 2 or 4 weeks producedpulmonary inflammation along with increases in BAL protein,LDH, and alkaline phosphatase values (p<0.05) and reducedmacrophage phagocytosis. Inflammatory responses, evidenced byincreased numbers of neutrophils, were also measured in thelungs of the 50 mg/m³ group following 2 and/or 4 weeks of exposure.Most biochemical parameters for all groups returned to controlvalues following a 3-month recovery period. Autoradiographicstudies demonstrated that the labeling indices of terminal bronchiolarand lung parenchymal cells were generally increased in the 50and 150 mg/m³ groups after 2 and 4 weeks of exposure but, withone exception, returned to normal levels following a 3-monthpostexposure period. No significant alterations in any measuredparameters were detected in rats exposed to 10 mg/m³ Ludox atany time postexposure. The determination of a no-observable-effectlevel (NOEL) of 10 mg/m³ was consistent with results obtainedby conventional toxicology methods and affirms the utility ofthese biochemical, cellular, and autoradiographic techniquesfor providing a predictive screen to assess the toxicity ofinhaled particles.     

Prechronic Inhalation Toxicity Studies of 2-Mercaptobenzimidazole (2-MBI)in F344/N Rats

2-Mercaptobenzimidazole (2-MBI), used in rubber processing,is a suspect carcinogen structurally related to ethylene thiourea.The inhalation toxicity of 2-MBI was evaluated in male and femaleF344/N rats exposed 6 hr/day, 5 days/week to respirable aerosolsgenerated by spray atomization of aqueous suspensions of the2-MBI powder and subsequent drying of the resulting aerosols.Twelve exposures at target concentrations of 0, 6.3, 12.5, 25.0,50.0, or 100 mg/m³ of 2-MBI produced a dose-related reductionin body weight gains, thyroid follicular cell hyperplasia, adrenalcortex fatty change, and pituitary atrophy. Sub-chronic exposureswere conducted at target concentrations of 0, 3.1, 6.2, 12.5,25.0, and 50.0 mg/m³ of 2-MBI. Rats at 25 mg/m³ displayed hunchedposture, hypoactivity, and reduced body weight gain, with compoundrelated mortality at the highest exposure level. Anemia; increasedSGPT, SGOT, alkaline phosphatase, sorbitol dehydrogenase, BUN,and cholesterol; and reduced free fatty acid were seen in ratsat 25 mg/m³. Increased thyroid weight and thyroid follicularcell hyperplasia were noted in both sexes at 6.2 mg/m³, withreduced triiodothyronine and thyroxine levels in both sexesat > 12.5 mg/m³. Thyroid follicular cell hyperplasia wasalso seen in rats at 3.1 mg/m³. Thymus weights were significantlyreduced in both sexes at all exposure levels with liver weightincreases at 6.2 mg/m³. Exposure-related histopathologic changesincluded pituitary cytoplasmic vacuolization, adrenal cortexnecrosis, lymphoid depletion, thymic atrophy, liver cell hypertrophy,renal mineralization and tubular atrophy, and hypocellularityof the bone marrow.     

The Pulmonary Response and Clearance of Ludox Colloidal Silica after a 4-Week Inhalation Exposure in Rats

Rats were exposed to Ludox colloidal silica (CS) at concentrationsof 0, 10, 50, and 150 mg/m³ for 6 hr/day, 5 days/week for 4weeks. Rats were killed after 4 weeks of exposure and 10 daysor 3 months post exposure (PE). The exposure concentration of10 mg/m³ Ludox CS is considered to be the no-effect concentration.There were no exposure-related clinical signs in any group.After 4 weeks exposure, lung weights were increased significantlyin rats exposed to 50 and 150 mg/m³ Ludox CS, but lung weightswere similar to those of controls at 3 months PE. After 4 weeksexposure to 50 mg/m³ Ludox CS, a slight alveolar macrophageresponse, polymorphonuclear leukocytic infiltration, and TypeII pneumocyte hyperplasia in alveolar duct regions were present.After 3 months PE, these pulmonary lesions had almost disappearedwith removal of most dust-laden alveolar macrophages (AMs).The pulmonary response to 150 mg/m³ Ludox CS was similar incharacter but increased in magnitude from that seen at 50 mg/m³At 3 months PE, most particleladen AMs had disappeared and theremaining AMs were aggregated and sharply demarcated. A fewaggregates of particle-laden AMs appeared to transform intosilicotic nodules comprising macrophages, epithelioid cells,and lymphocytic infiltration in some animals. Some silicoticnodules showed reticular fiber networks with minute collagenfiber deposition. Tracheobronchial lymph nodes were enlargedwith aggregates of particle-laden AMs and hyperplastic histiocyticcells. Lung-deposited Ludox cleared rapidly from the lungs withhalf-times of approximately 40 and 50 days for the 50 and 150mg/m³ groups, respectively.     

Subchronic and Chronic Inhalation Toxicity of Antimony Trioxide in the Rat

Fischer 344 rats were exposed by inhalation to Sb₂O₃ (antimonytrioxide) dust at exposure levels of 0, 0.25, 1.08, 4.92, and23.46 mg/m³ for 6 hr/day, 5 days/week for 13 weeks followedby a 27-week observation period. Subsequently, an inhalationon-cogenicity study was conducted at exposure levels of 0, 0.06,0.51, and 4.50 mg/m³ for 12 months followed by a 12-month observationperiod. The Sb₂O₃ in the subchronic study had a mass medianaerodynamic diameter (MMAD) of 3.05 ± 0.21 microns (mean± SD) with a geometric standard deviation (GSD) of 1.57± 0.06. In the chronic study, the MMAD was 3.76 ±0.84 and the GSD was 1.79 ± 0.32. Except for the eyes,no adverse clinical observations were attributed to Sb₂O₃ ineither study. In the subchronic study, corneal irregularitieswere seen after about 2 weeks of exposure and did not abateduring the observation period. In the chronic study, ophthalmoscopicevaluation at 24 months revealed a dose-related increase incataracts of 11, 24, 28, and 32% (both sexes combined) for eachgroup, respectively. Body weights were significantly lower (6%)than the control group's weights in the 23.46 mg/m³ males inthe subchronic study. These rats did not recover this weightduring the 27-week observation period. Body weights of the femalesin both studies and males in the chronic study were unaffected.There were no Sb₂O₃ effects on clinical chemistry or he-matologyin either study. Mean absolute and relative lung weights weresignificantly increased in the 4.92 and 23.46 mg/m³ groups inthe subchronic study. The 23.46 mg/m³ group's lung weights didnot recover to control levels during the 27-week observationperiod. Lung weights for rats in the chronic study were unaffected.Microscopic changes in the lungs in the subchronic and chronicstudy were limited to subacute-chronic interstitial inflammation,increased numbers of alveolar-in-traalveolar macrophages, foreignmaterial in the alveolar-in-traalveolar macrophages in the peribronchialand perivascular (chronic study only) lymphoid aggregates andin the peribronchial lymph nodes, granulomatous inflammation/granulomas,and fibrosis. In the chronic study, any observed neoplasms occurredwith comparable incidence among all groups and were within thehistorical range for controls. Clearance of Sb₂O₃ from the lungwas burden dependent and was reduced by 80/ in the 4.50 mg/m³group in the chronic study. The previously reported studies,which found Sb₂O₃ to be a carcinogen, were run at higher lungburdens. Under the exposure conditions of the current study,Sb₂O₃ was not a carcinogen.     

Isobutyraldehyde Administered by Inhalation (Whole Body Exposure) for up to Thirteen Weeks or Two Years Was a Respiratory Tract Toxicant but Was Not Carcinogenic in F344/N Rats and B6C3F1 Mice

Isobutyraldehyde (a chemical structurally related to formaldehydeand used as a flavoring agent) was studied for toxicity andcarcinogenicity by exposing male and female F344/N rats andB6C3F₁ mice. Animals were exposed to isobutyraldehyde vapors6 h per day, 5 days per week for up to 13 weeks or 2 years.In the 13-week studies, groups of 10 male and 10 female F344/Nrats and B6C3F₁ mice were exposed to concentrations of 0, 500,1000, 2000, 4000, or 8000 ppm. Chemical-related body weightdepression and deaths occurred in rats and mice exposed to 4000and 8000 ppm. Necrosis of the epithelium accompanied with acuteinflammatory reaction was observed in the nasal turbinate, larynx,and trachea of rats exposed to 8000 ppm. Exposure of rats to4000 ppm resulted in metaplasia of the nasal respiratory epithelium,inflammation, degeneration of the olfactory epithelium, andosteodystrophy of the nasal turbinate bone. In the 13-week mousestudy, exposure to 8000 ppm or 4000 ppm resulted in necrosisof the epithelium lining of the nasal turbinates. Osteodystrophyof the nasal turbinate bone and squamous metaplasia of the nasalrespiratory epithelium were noted in mice exposed 4000 ppm.Degeneration of the olfactory epithelium was noted in malesexposed 2000 ppm and in females exposed to 4000 ppm. In the2-year studies, groups of 50 male and 50 male F344/N rats andB6C3F1 were exposed to concentrations isobutyraldehyde vaporsof 0, 500, 1000, or 2000 ppm 6 h per day, 5 days per week. Therewere no differences in survival rates or mean body weights betweenexposed groups and control rats. Survival of male mice exposedto 2000 ppm and mean body weights of female mice exposed to1000 or 2000 ppm were lower than those of the of the controls.No increase in neoplasm incidence was observed in rats and micein the 2-year studies that could be attributed to isobutyraldehydeexposure. Chemical-related nonneoplastic lesions were limitedto the nose of rats and mice. They included squamous metaplasiaof the respiratory epithelium (rats), suppurative inflammation(rats), and olfactory epithelial degeneration (rats and mice)at 1000 and 2000 ppm.     

Deposition and Fate of Inhaled Ethylene Glycol Vapor and Condensation Aerosol in the Rat

Deposition and Fate of Inhaled Ethylene Glycol Vapor and CondensationAerosol in the Rat. Marshall, T.C. and Cheng, Y.S. (1983). Fundam.Appl. Toxicol. 3:175-181. Fischer-344 rats were exposed by nose-onlyinhalation for 30 min to ethylene glycol-¹⁴C vapor at a concentrationof 32 mg/m³. A second group of rats was exposed for 17 min toan ethylene glycol-¹⁴C aerosol formed by condensation of theglycol on 0.1 m ⁶⁷Ga₂O₃ particles. The mass median aerodynamicdiameter (MMAD) of the condensation aerosol was 2.3 µm (g = 1.8) with an ethylene glycol concentration of 184 mg/m³. Initial radiocarbon body burdens were at glycol levels of0.7 mg/kg for the vapor exposure and 2.4 mg/kg for the aerosolexposure. Estimates indicated that at least 60% of the ethyleneglycol inhaled for both exposures was deposited in rats withthe highest concentration of radioactivity being in the nasalcavities. Distribution from the site of deposition was rapidsince 75 to 80% of the initial body burden was found throughoutthe bodies of rats sacrificed immediately after exposure. Thepredominant routes of elimination during the first 4 days followingexposure were via the expired air as ¹⁴CO₂ (63% for the vaporexposure and 70% for the aerosol exposure) and urine as theunchanged glycol (20% and 11%). The proportion of the dosesexcreted as ¹⁴CO₂ suggested more complete metabolism of ethyleneglycol following inhalation relative to that observed afterintravenous injections reported previously. The half-time forclearance of plasma radiocarbon was 39 and 34 hr for the vaporexposure and aerosol exposure, respectively. The studies suggestedthat ethylene glycol plasma levels following acute exposureto high airborne concentrations of ethylene glycol vapor and/oraerosol would not approach the toxic concentrations associatedwith known dose-dependent changes in the glycol's metabolism.     

Evaluation of the Developmental Toxicity of Ethylene Glycol Aerosol in the CD Rat and CD-1 Mouse by Whole-Body Exposure

Ethylene glycol (EG) is a major industrial chemical, shown tobe teratogenic at high doses by gavage in rodents. Since oneroute of industrial exposure is to the aerosol at high concentrations,timed-pregnant CD rats and CD-1 mice were exposed, whole-body,to a respirable aerosol of EG (mass median aerodynamic diameter,2.3 µm) on Gestational Days (GD) 6 through 15 for 6 hrper day at target exposure concentrations of 0, 150, 1000, or2500 mg/m³ (analytical concentrations of 0, 119 ± 13,888 ± 149, and 2090 ± 244 mg/m³, respectively),with 25 plug-positive animals per species per group. Clinicalobservations and maternal body weights were documented throughoutgestation for both species. Maternal food and water consumptionwas measured in rats only throughout gestation. At schedulednecropsy (GD 21 for rats, GD 18 for mice), maternal animalswere evaluated for body weight, liver weight, kidney weight,gravid uterine weight, number of ovarian corpora lutea, andstatus of implantation sites, i.e., resorptions, dead fetuses,live fetuses. Fetuses were dissected from the uterus, counted,weighed, sexed, and examined for external, visceral, and skeletalmalformations and variations. All rat dams survived to scheduledtermination. Minimal maternal toxicity was indicated by a significantincrease in absolute and relative liver weight at 2500 mg/m³.Food and water consumption, maternal body weights and weightgain, and maternal organ weights (other than liver) were unaffectedby exposure. Gestational parameters were unaffected by exposure,including pre- and post-implantation loss, live fetuses/litter,sex ratio, and fetal body weight/litter. There was no treatment-relatedincrease in the incidence of any individual malformation, inthe incidence of pooled external, visceral, or skeletal malformations,or in the incidence of total malformations by fetus or by litter.There were no increases in the incidence of external or visceralvariations. Evidence of fetotoxicity, expressed as reduced ossificationin the humerus, the zygomatic arch, and the metatarsals andproximal phalanges of the hind-limb, was observed at 1000 and2500 mg/m³. All mouse dams survived to scheduled termination.One dam at 2500 mg/m³ was carrying a totally resorbed litterat termination. Maternal toxicity was observed at 1000 and 2500mg/m³, expressed as reduced body weight and weight gain duringand after the exposure period, and reduced gravid uterine weight.(Maternal effects may have been due, in part or in whole, toeffects on the conceptuses; see below.) Embryo/fetal toxicitywas also observed at 1000 and 2500 mg/m³, expressed as an increasein nonviable implantations/litter, a reduction in viable implantations/litter,and reduced fetal body weights (male, female, and total)/litter.The incidences of individual and pooled external, visceral,and skeletal malformations were increased at 1000 and 2500 mg/m³,as was the incidence of total malformations. Malformations werefound in the head (exencephaly), face (cleft palate, foreshortenedand abnormal face, and abnormal facial bones), and skeleton(vertebral fusions, and fused, forked, and missing ribs). Theincidences of many fetal variations were also increased at 1000and 2500 mg/m³ (and only a few at 150 mg/m³). The no observableadverse effect level (NOAEL) for maternal toxicity in rats was1000 mg/m³ (analytical concentration 888 mg/m³) and in micewas 150 mg/m³ (analytical concentration 119 mg/m³). The NOAELfor development toxicity in rats was 150 mg/m³ and in mice wasat or below 150 mg/m³, under the conditions of this study. Analysisof EG on the fur of rats and mice during and after the exposureperiod at 2500 mg/m³ indicated that much of the EG "dose" (65–95%)was potentially derived from ingestion after grooming and/orpercutaneous absorption. This contribution of the ingested and/orabsorbed chemical could have been sufficient, per se, to producethe teratogenic effects observed in mice. The definitive evaluationof the possible role of inhaled EG aerosol alone in teratogenesisrequires an exposure regimen which limits or precludes exposureby any other route.     

Subchronic Inhalation Exposure of Dearomatized White Spirit and C10-C11 Isoparaffinic Hydrocarbon in Sprague-Dawley Rats

Subchronic Inhalation Exposure of Dearomatized White Spiritand C₁₀-C₁₁ Isoparaffin Hydrocarbon in Sprague-Dawley Rats.PHILLIPS, R. D., AND EGAN, G. F. (1984). Fundam. Appl. Toxicol.4, 808–818. Groups of 35 male and 35 female Sprague-Dawleyrats were exposed to either Dearomatized White Spirit (DAWS)vapor at concentrations of 1.97 and 5.61 g/m³ or C₁₀-C₁₁ IsoparaffinicHydrocarbon (IPH) vapor at concentrations of 1.91 and 5.62 g/m³.These concentrations were targeted for the recommended occupationalexposure limits and three times that value, respectively. Exposureswere 6 hr-day, 5 days/week for 12 weeks. Following Weeks 4,8. and 12 of exposure, a total of 10, 10, and 15 rats, respectively,from each group were sacrificed. Clinical chemistry and hematologyparameters were measured in blood samples taken immediatelyprior to sacrifice, and selected organs were removed and weighed.Twenty-three organs and tissues from each animal were examinedmicroscopically. There were no deaths during the course of thisstudy related to either DAWS or IPH. Mean body weights weresignificantly tower than controls in male rats following exposureto 5.61 g/m³ DAWS, and 5.62 or 1.91 g/m³ IPH. Body weights werenot affected in females. The primary effects from DAWS or IPHexposure were observed in the kidneys of male rats only fromboth exposure groups beginning at Week 4. Evidence of mild tubulartoxicity, such as regenerative tubular ephhelia and dilatedtubules containing proteinaceous casts, was observed at thecortieomedullary junction. The incidence and severity appearedto increase with increasing concentration and exposure duration.There were scattered instances of statistically significantincreases in liver and kidney weights in both males and females.With the exception of the mild male rat tubular nephrotoxiriry,other significant toxic effects were not observed at levelstested     

Peracute Toxic Effects of Inhaled Hydrogen Sulfide and Injected Sodium Hydrosulfide on the Lungs of Rats

Peracute Toxic Effects of Inhaled Hydrogen Sulfide and InjectedSodium Hydrosulfide on the Lungs of Rats. LOPEZ, A., PRIOR,M. G., REIFFENSEIN, R. J., AND GOODWIN, L. R. (1989). FundamAppl Toxicol. 12, 367–373. This study was designed totest whether intraperitoneally injected sodium hydrosulfide(NaHS) would mimic the pulmonary alterations induced by lethalperacute exposure to an atmosphere containing hydrogen sulfide.Groups of five Sprague- Dawley rats were exposed to an atmosphereof either 2317.6 ± 547.3 mg m^-3 H₂S (H₂S group) or noH₂S (air group), or were injected intraperitoneally with a solutioncontaining 30 mg kg^-1 sodium hydrosulfide (NaHS group) or salinesolution (vehicle control). Rats of the air and saline groupswere killed by cervical dislocation. All rats exposed to H²Sor injected with NaHS died within 3 min; however, only ratsexposed to H²S showed severe respiratory distress in the agonicphase preceding death. In addition, rats in the H²S group hada notable discharge of serous fluid from the mouth and nostrils.At necropsy, all rats in the H²S group had gross and histologicevidence of pulmonary edema characterized by massive extravasationof eosinophilic fluid into the bronchcalveolar space. In contrastthe lungs of rats injected with NaHS or saline or exposed toair were unaffected. It was concluded that the edematogeniceffect of H²S in the lungs cannot be reproduced by injectionof NaHS. The severity of lung edema induced by a peracute exposureto H² was extensive enough to account for death.     

Thirteen-Week Inhalation Toxicity of 2- and 4-Chloronitrobenzene in F344/N Rats and B6C3F1 Mice

Toxicity studies were performed by exposing F344/N rats andB6C3F₁ mice to 2- and 4-chloronitrobenzene (CNB) by whole bodyinhalation 6 hr/day, 5 days/week, for 13 weeks. Animals wereevaluated for clinical chemistry (rats), hematology (rats),histopathology, and body/organ weights. Exposure concentrationswere 0, 1.1, 2.3, 4.5, 9, and 18 ppm for 2-CNB and 0, 1.5, 3,6, 12, and 24 ppm for 4-CNB. All rats in the 2-CNB study surviveduntil the end of the study. Two male mice in the 18-ppm groupin the 2-CNB study, however, died during Week 12; no deathsattributable to 4-CNB exposure occurred in rats or mice. Inboth studies, the mean body weight gains of exposed animalswere similar to those of the respective controls. In rats, inhalationexposure to 2- or 4-CNB resulted in methemoglobinemia leadingto a regenerative anemia and a variety of tissue changes secondaryto the oxidative erythrocyte injury. In the 2-CNB study, methemoglobinemiaresulted in a normocytic, normochiomic, responsive anemia, whereaswith 4-CNB, the methemoglobinemia was more severe and resultedin a niacrocytic, hyperchromic, responsive anemia. Alterationsof erythrocyte morphology were observed in both studies; changesincluded Heinz bodies, poikilocytes, and polychromasia. In rats,both isomers caused increases in serum activities of alanineaminotransferase and sorbitol dehydrogenase and increased bileacid concentrations. Microscopic liver changes included hemosiderindeposition in Kupffer cells (rats and mice exposed to 4-CNB),hepatocytomegaly (mice), and cytoplasmic basophilia (rats).Hepatocellular necrosis and chronic inflammation observed inmice were rather specific to the 2-CNB isomer, as only slightevidence of focal necrosis in the liver was observed in miceexposed to 4-CNB. Splenic lesions included hemosiderin accumulation,capsular fibrosis, and increased hematopoietic cell proliferation.Increased bone marrow hemosiderin and hematopoietic cell proliferationand kidney tubule hemosiderin deposition were also observed.Other findings, attributed to chemical exposure but not to thehematotoxicity, were described. Lesions included hyaline dropletnephropathy and degeneration of the testis in male rats exposedto 4-CNB, inflammation of the harderian gland in rats exposedto 4-CNB, hyperplasia of the nasal cavity epithelium in ratsexposed to 2-CNB, and hyperplasia of the forestomach epitheliumin mice exposed to 4-CNB; these lesions have not been describedpreviously in studies with these chemicals. Based on the exposureconcentrations evaluated, A no-observed-adverse-effect level(NOAEL) for histopathological injury in mice was 4.5 ppm for2-chloronitrobenzene and 6 ppm for 4-chloronitrobenzene; a NOAELwas not determined for rats.