A 90-Day Inhalation Toxicity Study with Benomyl in Rats

A 90-Day Inhalation Toxiaty Study with Benomyl in Rats. WARHEIT,D. B., KELLY, D. P., CARAKOSTAS, M. C., AND SINGER, A. W. (1989).Fundam Appl Toxicol./ 12, 333-345. Benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate,CAS Registry No. 17804-35-2] is a fungicide and the possibilityfor inhalation exposure exists for field workers. To assessthe toxicity of benomyl, groups of 20 male and 20 female CDrats were exposed nose-only 6 hr a day, 5 days a week, to concentrationsof 0, 10, 50 or 200 mg/m³ of a benomyl atmosphere. At the midpoint(approximately 45 days on test) and at the end of the exposureperiod, blood and urine samples for clinical evaluation werecollected from 10 rats/group/sex, and these animals were sacrificedfor pathological examination. Similar evaluations were performadon all remaining rats at the end of the 90-day test period.After approximately 45 days on test, compoundrelated degenerationof the olfactory epithelium was observed in all males and in8 of 10 female rats exposed to 200 mg/m³ benomyl. Two male ratsexposed to 50 mg/m³ had similar, although less severe, areasof olfactory epithelial degeneration. After approximately 90days of exposure, the remaining 10 rats/group/sex were sacrificedand examined. Of these rats, all of the males and females exposedto 200 mg/m³ had olfactory degeneration, along with 3 malesexposed to 50 mg/m³ of benomyl. No other observed lesions wereinterpreted to have been caused by the benomyl exposure. Inaddition, male rats exposed to 200 mg/m³ benomyl had depressedmean body weights compared to controls and this finding correlatedwith a reduction in food consumption. Based on pathologicalobservations, 10 mg/m³ represents the no-observable-effect level(NOEL) for the male rats, and 50 mg/m³ is the NOEL for the femalerats.     

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.     

Thirteen-Week, Repeated Inhalation Exposure of F344/N Rats and B6C3F1 Mice to Ferrocene

Ferrocene (dicyclopentadienyl iron; CAS No. 102-54-5) is a relativelyvolatile compound used as a chemical intermediate, a catalyst,and an antiknock additive in gasoline. This organometallic chemicalis of particular interest because of its structural similaritiesto other metallocenes, some of which are carcinogenic. F344/Nrats and B6C3F₁ mice were exposed to 0, 3.0, 10, and 30 mg ferrocenevapor/m³, 6 hr/day, 5 days/week, for 13 weeks. During theseexposures, no rats or mice died, nor were any clinical signsof ferrocene-related toxicity observed. At the end of the exposures,male rats exposed to the lowest and highest level of ferrocenehad decreased body weight gains compared to filtered-air-exposedcontrol male rats, while body weight gains for all groups ofboth ferrocene- and filtered-air-exposed female rats were similar.Male mice exposed to ferrocene had no differences in body weightgains, compared to controls, but female mice had decreases inbody weight gains at the 10 and 30 mg/m³ exposure levels. Therewere exposure concentration- and exposure-time-related increasesin lung burdens of iron. The mean iron lung burden in rats exposedto 30 mg ferrocene vapor/m³ for 90 days was four times greaterthan the burden in control rats. No exposure-related changesin respiratory function, lung biochemistry, bronchoalveolarlavage cytology, total lung collagen, clinical chemistry, andhematology parameters were observed. This suggests that theaccumulations of iron in lung did not cause an inflammatoryresponse nor any functional impairment of the lung. There wereno indications of developing pulmonary fibrosis nor of any hematologictoxicity. No exposure-related gross lesions were seen in anyof the rats or mice at necropsy. Exposure-related histopathologicalterations, primarily pigment accumulations, were observedin the nose, larynx, trachea, lung, and liver of both species,and in the kidneys of mice. Lesions were most severe in thenasal olfactory epithelium where pigment accumulation, necrotizinginflammation, metaplasia, and epithelial regeneration occurred.Nasal lesions were observed in all ferrocene-exposed animalsand differed only in severity, which was dependent on the exposureconcentration. Histochernical stains of these target tissuesshowed the presence of iron ions. The results suggest that themechanism of ferrocene toxicity may be the intracellular releaseof ferrous ion through ferrocene metabolism, followed by eitheriron-catalyzed lipid peroxidation of cellular membranes or theiron-catalyzed Fenton reaction to form hydroxyl radicals thatdirectly react with other key cellular components, such as proteinor DNA.     

Chronic Inhalation Toxicity and Carcinogenicity Study of Respirable Polymeric Methylene Diphenyl Diisocyanate (Polymeric MDI) Aerosol in Rats

Four groups of 60 Wistar rats of each sex were exposed by inhalationto 0, 0.2, 1.0, or 6.0 mg/m³ respirable polymeric methylenediphenyl diisocyanate (polymeric MDI) aerosol (93.5% < 4.2µm)for 6 hr a day, 5 days a week for up to 24 months. In addition,satellite groups of 10 rats/sex/group received the same treatmentfor 12 months. There was no adverse effect on general health,survival, body weight, or hematological or clinical chemistryparameters. Lung weights were increased in both males and femalesexposed to 6.0 mg polymeric MDI/m³ for 12 or 24 months. Grossexamination at autopsy of males exposed to 6.0 mg polymericMDI/m³ for 24 months revealed an increased incidence of spottedand discolored lungs. Increased incidences of degeneration andbasal cell hyperplasia of the nasal olfactory epithelium, oftenaccompanied by hyperplasia of Bowman's glands, were found inthe 1.0 and 6.0 mg/m³ groups. Light and electron microscopicstudies of the lungs revealed accumulations of alveolar macrophagescontaining polymeric MDI-associated refractile yellowish materialat the level of the alveolar duct in all exposed groups. Alveolarduct epithelialization as well as fibrosis of tissues surroundingthe macro phage accumulations occurred at the 1.0 and 6.0 mg/m³exposure levels. In addition, increased incidences of calcareousdeposits and localized alveolar bronchiolization were seen inthe 6.0 mg/m³ group. Moreover, eight pulmonary adenomas (sixin males and two in females) and one pulmonary adenocarcinoma(in a male) were observed in the 6.0 mg/m³ exposure group. Thetime sequence of the spectrum of pulmonary changes indicatesthat recurrent alveolar wall damage by polymeric MDI and/orpolymeric MDI-containing alveolar macrophages leads to alveolarbronchiolization and ultimately to bronchioloalveolar tumors.No lung tumors were found in the lower concentration groupsand in the control group. The incidence and distribution ofother types of tumors were not influenced by polymeric MDI.It was concluded that in the present study, the "no-observed-adverse-effectlevel" of polymeric MDI was 0.2 mg/m³ and that chronic exposureto polymeric MDI at a level of 6.0 mg/m³ was related to theoccurrence of pulmonary tumors. It was also concluded that exposureto polymeric MDI at concentrations not leading to recurrentlung tissue damage will not produce pulmonary tumors.     

Phenyl Isocyanate-Induced Asthma in Rats Following a 2-Week Exposure Period

This study was conducted to assess the toxic effects of repeatedinhalation exposures to phenyl isocyanate vapor in male Wistarrats. Rats were exposed to design concentrations of 0, 1, 4,7, or 10 mg/m³ phenyl isocyanate air for 2 weeks (6 hr/day,5 days/week). The rats were assessed for normal toxicologicparameters, and pulmonary function tests, blood gas measurements,and analysis of bronchoalveolar lavage fluid (BALF) parameterswere utilized shortly after exposures as well as 2 months postexposure.The results indicated that rats exposed to 7 and 10 mg/m³ experienceddecreased body weights, hypoactivity, hypothermia, signs ofrespiratory tract irritation, delayed onset of mortality, andchanges in organweights. In addition, pulmonary function testsdemonstrated decreased forced expiratory flow rates and quasistaticlung compliance. Arterial blood gases showed an arterial hypoxemiaand changes consistent with a pronounced venous-admixture-likeperfusion, suggesting severe mismatch of the ventilation/perfusionrelationship. Delayed onset of mortality appeared to be associatedwith respiratory acidosis and hypoxernia. Biochemical and cellularcomponents in BALF complemented the results of the functionalalterations. Remarkable changes were indicated by increasedactivities of the BALF parameters, -GPT, protein, and sialicacid. Histopathological findings provided evidence of increasedsecretory cell activity and a concentration-dependent increasein goblet cell hyperplasia at concentrations of 4 mg/m³ andabove. In rats exposed to 7 mg/m³ further findings consistedof intraluminal inflammation of airways, hypertrophia of bronchialsmooth muscle, epithelial desquamation, and eosinophilia ofthe airways. A complete regression of morphological lesionswas not found in the animals exposed to 4 mg/m³ and above atthe 2-month postexposure time period. In conclusion, the damageto the airways comprise most of the features characteristicof chronic airway inflammation or asthma.     

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.     

The Chronic Toxicity and Oncogenicity of Inhaled Technical-Grade 1,3-Dichloropropene in Rats and Mice

The Chronic Toxicity and Oncogenicity of Inhaled Technical-Grade1,3-Dichloropropene in Rats and Mice. LOMAX, L, G., STOTT, W.T., JOHNSON, K. A., CALHOUN, L. L., YANO, B. L., AND QUAST,J. F. (1989). Fundam. Appl. Toxicol. 12, 418–431. Maleand female Fischer 344 rats and B6C3F1 mice were exposed byinhalation to target concentrations of 0, 5, 20, or 60 ppm (0,22.7, 90.8, or 272 mg/m³) technical-grade 1,3-dichloropropene(DCPT) 6 hr/day, 5 days/week, for upto 2 years. Ancillary groupsof rats and mice were exposed for 6- and 12- month periods.Significant treatment-related nonneoplastic changes followingexposure for 2 years were morphological alterations in the nasaltissues of rats exposed to 60 ppm and mice exposed to 20 or60 ppm DCPT. In addition, mice exposed to 20 or 60 ppm had hyperplasiaof the transitional epithelium lining the urinary bladder. Survivalof male and female rats and mice exposed to DCPT was similarto that of the corresponding controls. No statistically increasedtumor incidence was observed in treated rats. The only neoplasticresponse observed in mice was an increased incidence of benignlung tumors (bronchioloalveolar adenomas) in male mice exposedto 60 ppm DCPT (22/50 versus 9/50 in controls).     

Inhalation Fertility and Reproduction Studies with O,O'- Dimethylphosphorodithioate in Sprague-Dawley Rats

Inhalation Fertility and Reproduction Studies with O,O'-Dimethylphosphorodithioatein Sprague-Dawley Rats. HEYDENS, W. F., AND KRONENBERG, J. M.(1989). Fundam. Appl Toxicol. 12, 62–69. Groups of 15male and 35 female Sprague-Dawley rats were exposed to 0,0'-dimethylphosphorodithioate(DMPDT) 6 hr/day, 5 days/week for 11 weeks. Initial target concentrationswere 0, 4, 25, and 200 mg/m³ However, because of excessive toxicity,the high exposure level was reduced to 125 mg/m³ after 8 weeks.Exposed males were cohoused with two unexposed females immediatelyfollowing the exposure period and later mated to an additionaltwo unexposed females following a 16-week recovery period. Exposedfemales were cohoused with untreated males, and exposures wereresumed after mating and continued during gestation. Some femaleswere terminated at midgestation to assess fertility, while otherswere allowed to deliver their pups. F₁ animals were terminatedfor histological examination or mated to assess fertility. High-exposurelevel F₀ males were infertile after exposures, and there waslittle or no recovery. The fertility of low-exposure level maleswas not affected, but equivocal results were obtained at themid-exposure level. In this study, testicular lesions were observedonly in high level F₀ males. However, testicular lesions werealso noted in a few males exposed to 4 and 25 mg/³ in a concurrentsubchronic toxicity study. Female fertility was apparently unaffectedby exposure, and no treatment-related effects were noted inmales or females exposed in utero     

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 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     

Subchronic Inhalation and Oral Toxicity of Hydrogenated Terphenyls in Rats

The subchronic toxicity of a commercial blend of partially hydrogenatedterphenyl was evaluated in rats by inhalation and oral routesof exposure. Animals were exposed to target concentrations of0, 10, 100, or 500 mg/m³ for 6 hr/day, 5 days/week or were offereddiets daily with concentrations of 0, 50, 200, or 2000 ppm.Each study lasted approximately 14 weeks. The study designsincluded observations for clinical signs, body weights, ophthalmicexams, hematology and clinical chemistry, major organ weights,and gross and histopathology. No treatment-related effects werenoted in the ophthalmic exams. Body weights were slightly depressedin high-dose males from the inhalation study and high-dose femalesin the dietary study. Liver and liver/body weights were increasedin high-dose animals of both sexes and high-and mid-dose malesin the dietary and inhalation studies, respectively. In thehigh-dose females of the dietary study, kidney and kidney/bodyweights were increased with increased adrenal and adrenal/bodyweights were also observed. No compound-related gross lesionsnor pathological correlates to the organ weight changes wereobserved in either study. The no-adverse effect levels wereconsidered to be 100 mg/m³ and 200 ppm (15.9 mg/kg) for theinhalation and dietary studies, respectively. These data indicatethat a wide margin of safety exists for hydrogenated terphenylworkplace exposure.     

Ninety-Day Inhalation Study in Rats, Using Aged and Diluted Sidestream Smoke from a Reference Cigarette: DNA Adducts and Alveolar Macrophage Cytogenetics

To study the genotoxic effects of subchronic exposure to environmentaltobacco smoke, Sprague-Dawley rats were exposed to 0, 0.1, 1.0,and 10 mg total particulate matter (TPM)/m³ of aged and dilutedsidestream smoke (ADSS) from 1R4F reference cigarettes 6 hrper day, 5 days a week for 13 weeks. DNA from lung, heart, larynx,bladder, and liver was tested for adduct formation by the ³²P-postlabelingassay after 28 (except bladder) and 90 days of exposure and90 days after cessation of exposure. In addition, alveolar macrophagesfrom animals exposed for 28 or 90 days were examined for chromosomalaberrations. Exposure-related DNA adducts were not observedin any tissue in any of the animals exposed to 0.1 or 1.0 mgTPM/m³. However, increased levels of DNA adducts with diagonalradioactive zones were observed in lung, heart, and larynx DNAof animals exposed to the highest concentration of ADSS (10mg TPM/m³). Adduct analyses with varying amounts of DNA fromlungs of mid-and high-exposure animals clearly indicate thatthe dose-response for DNA adduct formation is nonlinear. Theadduct levels were highest after 90 days of exposure and weresignificantly reduced in all target tissues 90 days after cessationof exposure. Chromosomal aberrations in alveolar macrophageswere not elevated in any group after 28 or 90 days of exposure.These results indicate a no-observed-effect-level (NOEL) ofat least 1.0 mg/m³ for DNA adduct formation in lung, heart,and larynx, and a NOEL of at least 10 mg/m³ for the inductionof chromosome aberrations in alveolar macrophages, under theconditions of this study.     

Development of α2u-Globulin Nephropathy and Adrenal Medullary Pheochromocytomas in Male Rats Following Exposure to Stoddard Solvent IIC

Stoddard solvent IIC is widely used as a solvent in paints and varnishes, and for dry cleaning and other grease removal applications. Because concern exists regarding the long-term effects of occupational exposure in industrial settings, the toxicity and carcinogenicity of Stoddard solvent IIC were evaluated in male and female F344/N rats and B6C3F₁ mice. Rats and mice were exposed to 0, 138, 275, 550, 1100, or 2200 mg/m³ Stoddard solvent IIC by whole-body inhalation for 3 mo, and to 0, 138 (male rats), 550, 1100, or 2200 (female rats and male and female mice) mg/m³ for 2 yr. The kidney, liver, and adrenal medulla were targets of Stoddard solvent IIC toxicity in rats. After 3 mo of exposure, male rats developed lesions characteristic of α_2u-globulin nephropathy. Male and female rats displayed increased liver weights and/or clinical pathology changes suggestive of hepatic injury, although no accompanying histopathologic changes were observed. After 2 yr, increased incidences of adrenal medullary pheochromocytomas provided some evidence of carcinogenicity in male rats. Renal tubule adenomas were slightly increased in male rats after 2 yr, and may have been related to exposure. In mice, there was no chemical-related toxicity after 3 mo, with the exception of increased liver weights in male mice exposed to 2200 mg/m³. After 2 yr, the incidences of hepatocellular adenomas were increased in female mice exposed to 2200 mg/m³; however, these increases were marginal and associated with increases in body weight. There was no evidence of Stoddard solvent IIC carcinogenicity in female rats or male mice. In summary, inhalation exposures of Stoddard solvent IIC resulted in renal toxicity and adrenal medullary pheochromocytomas in male rats. The liver also appeared to be a site of toxicity in male and female rats and mice.     

Acute, Subacute, and Subchronic Inhalation Toxicity Studies of Respirable Polymeric Methylene Diphenyl Diisocyanate (Polymeric MDI) Aerosol in Rats

Short-term inhalation toxicity studies with respirable polymericmethylene diphenyl diisocyanate (polymeric MDI) aerosol wereperformed in rats. The 4-hr LC50 was found to be 490 mg polymericMDI/m³ (95.5% <4.3 µm). Exposure of (4-week-old) ratsto 0, 2.2, 4.9, or 13.6 mg polymeric MDI/m³ (95% < 5 µm)for 2 weeks resulted in mortality, severe growth retardation,and elevated lung weights at 13.6 mg/m³ at 4.9 mg/m³ slightgrowth retardation and slightly elevated lung weights were observed.A 13-week study with 6-week-old rats exposed to 0.35, 1.4, or7.2 mg polymeric MDI/m³ (95% < 5 µm) revealed transientgrowth retardation and a slightly increased number of pulmonaryalveolar macrophages occasionally accompanied by increased numbersof mononuclear cells and fibroblasts in alveolar septa onlyat 7.2 mg/ m³ In a second 2-week study with 4 or 6-week-oldrats exposed to 14.1 mg polymeric MDI/m³ (95% < 5 µm),4-week-old rats died earlier and in greater numbers than 6-week-oldrats. In a second 13-week study with 6-week-old rats, usingexposure concentrations of 0, 4.1, 8.4, and 12.3 mg polymericMDI/ m³ (95% < 5 µm) and including a 4-week recoveryperiod, 12.3 mg/ m³ induced mortality, growth retardation, severerespiratory distress, increased lung weights, degeneration andhyperplasia of the nasal epithelium, accumulations of macrophagesin the lungs and mediastinal lymph nodes, and focal inflammatorychanges in the lungs. Rats exposed to 8.4 mg/ m³ showed respiratorydistress, lower body weights in males, increased lung weights,and similar, but much less severe, histopathological changesin the respiratory tract and mediastinal lymph nodes. Most ofthe histopathological changes seen at the higher concentrationswere also seen at 4.1 mg/m³ but to a very minor degree and ina few rats only. At the end of the 4-week posttreatment periodthe microscopical changes in nose, lungs, and mediastinal lymphnodes were still present but generally to a much less degreethan at the end of the exposure period. It was concluded thatthe dose-effect curve for repeated exposures of rats to respirablepolymeric MDI is very steep, and that the "no-observed-adverse-effectlevel" of polymeric MDI was 1.4 mg/m³ the actual no-adverse-effectlevel being lower than but most probably very close to 4.1 mg/m³.     

Thirteen-week study of toxicity of fiber-like multi-walled carbon nanotubes with whole-body inhalation exposure in rats

Abstract

Cancer development due to fiber-like straight type of multi-walled carbon nanotubes (MWCNTs) has raised concerns for human safety because of its shape similar to asbestos. To set concentrations of MWCNT for a rat carcinogenicity study, we conducted a 13-week whole body inhalation study. F344 male and female rats, 6-week-old at the commencement of the study, were exposed by whole-body inhalation to MWCNT at concentrations of 0, 0.2, 1 and 5?mg/m³ with a generation and exposure system utilizing the cyclone sieve method. Measured concentrations in the exposure chambers were 0.20?±?0.02, 1.01?±?0.11 and 5.02?±?0.25?mg/m³ for 13 weeks. The MMAD (GSD) of MWCNT were 1.4–1.6?μm (2.3–3.0), and mean width and length were 94.1–98.0?nm and 5.53–6.19?μm, respectively, for each target concentration. Lung weights were increased 1.2-fold with 1?mg/m³ and 1.3-fold with 5?mg/m³ in both sexes compared to the controls. In the bronchoalveolar lavage fluid (BALF) analyses, inflammatory parameters were increased concentration-dependently in both sexes from 0.2?mg/m³. Granulomatous changes in the lung were induced at 1 and 5?mg/m³ in females and even at 0.2?mg/m³ in males. Focal fibrosis of the alveolar wall was observed in both sexes at 1?mg/m³ or higher. Inflammatory infiltration in the visceral pleural and subpleural areas was induced only at 5?mg/m³. In conclusion, we determined 0.2?mg/m³ as the low-observed-adverse-effect level (LOAEL) for respiratory tract toxicity in the present inhalation exposure study of rats.     

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.     

Deposition of Cigarette Smoke Particles in the Rat

The fractional deposition of cigarette smoke particles in therespiratory tracts of rats was studied. Male and female ratswere conditioned in nose-only exposure tubes 25 min/day for2 days, exposed to cigarette smoke at mass concentrations of95 or 341 mg/m³ 25 min/day for 3 days, and then exposed to smokeat mass concentrations of 212 and 657 mg/m³, 25 min/day for5 days. Mainstream cigarette smoke was generated by a modifiedWalton smoking machine from two 1R3 research cigarettes burnedsequentially for each exposure. Deposition studies were conductedby placing the rats in plethysmograph tubes to allow respiratoryminute volume measurements during exposure, then exposing themto [¹⁴C] cigarette smoke at mass concentrations of 202 or 624mg/m³ for 25 min, using the same smoking machine. Size distribution,real-time concentration, and ¹⁴C activity of the smoke particleswere determined using a multijet Mercer impactor, a real-timeaerosol monitor, and filter samples, respectively. Immediatelyafter the exposure, the rats were terminated to determine thedistribution of the ¹⁴C. Individual lung lobes, trachea andlobar bronchi, head, larynx, kidneys, liver, gastrointestinal(GI) tract, blood, and depelted carcass of each rat were analyzedfor ¹⁴C content. Results showed that the GI tract contained16–31% of the total activity, indicating significant clearancefrom the large airways and nose to the GI tract during the exposureand during the 10–15 min between the cessation of theexposure and the removal ofthe organs. Total deposition of theinhaled ¹⁴C activity was 20.1 ? 1.6% for both exposure concentrations.The intrapulmonary deposition fractions (lung lobes plus airwaysbelow the lobar bronchi) were 12.4 ? 0.9 and 15.9 ? 1.4% forconcentrations of 202 and 624 mg/m³ respectively, suggestinga slight enhancement in upper airway deposition for animalsexposed to the higher smoke concentration.     

Toxicity of Calcium Sodium Metaphosphate Fiber: II. Chronic Inhalation and Oncogenicity Study

Male and female Fischer 344 rats (80/sex/group) were exposedto CSM fiber 6 hr/day, 5 days/week at target-exposure levelsof 0, 1, 5, or 25 mg/m³ for 24 months, corresponding to 0, 27,80, and 513 fibers/cc, respectively. Number and size of theairborne fibers were determined during the course of the study.At 3 and 12 months, 10 rats/sex/group were euthanized and at18 and 24 months 5 rats/sex/group were euthanized. In addition,5 rats/ sex/group were removed from exposure at 18 months andmaintained for a 6-month recovery period. All animals survivingat the completion of the exposure period were maintained ina clean environment for up to 5 additional months. Clinicallaboratory examinations were performed on 10 animals/sex/groupat 3, 12, and 24 months. The number of fibers in the lung werealso determined at 3, 12, 18, and 24 months. Body weight andsurvival did not appear to be affected by treatment. There wereno biologically significant effects on clinical parameters.There was a dose-related increase in lung weight during theexposure period which was generally reversible during the recoveryperiods. There also was a dose-related increase in the numberof fibers/ milligram of lung, but no increase in lung fiberburden after the first 3 months. The number of fibers in thelungs of animals exposed to CSM fiber for 18 months and allowed6-month recovery period showed a decrease especially at thehigh dose. No increase in tumors (benign or malignant) was observedin this study. Microscopic changes considered reflective ofan irritant response were observed in the nasal turbinates notablyat the 5 and 25 mg/m³ levels. Histological changes were alsoobserved in the lungs at the 5 and 25 mg/m³ levels. The incidenceand/ or severity of histopathological changes in the 1 mg/m³group was considered to be essentially comparable to controls.     

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.     

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.