Investigation of the Effects of Benomyl on Rat Nasal Mucosa

Benomyl [methyl 1-(butylcarbamoyl)-2-benzimidazolecarbamate,CAS Registry No. 17804-35-2] is a widely used agricultural fungicide.Previously, olfactory epithelial lesions were produced followinga 45-day inhalation exposure to 50 and 200 mg/m³ benomyl. Thepresent study, part of a range-finding study for a two-generationreproduction study, was conducted to determine if the previouslyreported effects on the nasal mucosa are the result of systemictoxicity or attributable to the inhalation route of exposure.Groups of 10 7-week-old male Crl:CD BR rats were fed diets containing0, 5000, 10000, or 15000 ppm benomyl for 32 days. Individualbody weights and food consumption were determined weekly andon the last day of the study. After 32 days on test, rats wereeuthanatized by pentobarbital anesthesia and exsanguinationand were examined for gross alterations. The nasal cavity wasprocessed for pathological examination. Mean body weight gainwas statistically significantly decreased during the first weekof treatment and the overall test period (Days 0–32) atthe two highest dose levels. A significant decrease in foodconsumption also was seen during test interval Days 0–7for the two highest dose groups. In addition, statisticallysignificant decreases in food consumption were observed at theDay 7–14 interval for the 15,000 ppm dose group and atthe 21–28 and 28–32 intervals for the two highestdose groups compared with controls. No histopathological lesionswere noted in the nasal epithelium of any of the control orbenomyl-treated rats. These results suggest that the nasal cavityis not a target following dietary administration of benomyland the olfactory epithelial damage reported following inhalationexposure is specific to the route of 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.     

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

The chemical constituents of cigarette smoke are greatly dilutedin environmental tobacco smoke (ETS). In the typical indoorenvironment where cigarettes are smoked, the mean value of respirablesuspended particles is approximately 0.1 mg/m³. In this study,we used aged and diluted sidestream smoke (ADSS) of 1R4F Universityof Kentucky research cigarettes as a surrogate for ETS and exposedSprague-Dawley rats nose-only to 0, 0.1, 1.0, and 10 mg wettotal particulate matter (WTPM)/m³ for 6 hr per day for 14 consecutivedays. DNA from lung, heart, larynx, and liver was tested foradduct formation after 7 and 14 days of exposure and after 14days of recovery. In addition, alveolar macrophages from animalsexposed for 7 days were examined for chromosomal aberrations.Exposure-related DNA adducts were not observed in any of theanimals at 0.1 or 1.0 mg WTPM/ m³, which represent ambient and10-fold exaggerated ETS concentrations, respectively. Slightdiagonal radioactive zones, characteristic of adducts observedin human smokers and in animals exposed to mainstream smoke,were observed, but only in lung and heart DNA of animals exposedto the highest concentration of ADSS (10 mg WTPM/m³), a 100-foldexaggeration of typical field measurements of ETS. The meanrelative adduct labeling values (±SE) were 8.7 (±0.2)adducts per 10' nucleotides for lung DNA and 5.7 (±0.7)adducts per 10' nucleotides for heart DNA after 14 days of exposure.No elevation in chromosomal aberrations was observed in alveolarmacrophages. These results indicate a no-observed-effect-level(NOEL) of 1.0 mg/m³ for DNA adduct formation in lung and heartand a NOEL of at least 10 mg/m³ for the induction of chromosomeaberrations in alveolar macrophages under the conditions ofthis study.     

Subchronic Inhalation Toxicity of Hexamethylenediamine in Rats

Four groups of 15 male and 15 female Sprague-Dawley-derived(CD) rats each were exposed to aqueous hexamethylenediamine(HMD) aerosols for 6 hr/thy, 5 days/week for 13 weeks at meananalytical concentrations of 0, 12.8, or 51 mg/m³ Because ofexposure-related deaths in a group of male and female rats similarlyexposed to 215 mg/m³ HMD, this group was terminated during theseventh week of the study. Signs of respiratory and conjunctivalirritation were observed in rats at both the 51 and 215 mg/m³HMD test levels. Body weight gain was significantly reducedin both sexes exposed to 215 mg/m³ HMD. At the 5-week studyinterval, slight hemopoietic stimulation of peripheral bloodparameters was observed in rats of both sexes exposed to 215mg/m³ HMD. Treatment-related microscopic lesions were seen onlyin rats exposed to 215 mg/m³ MD and were confined to the trachea,nasal passages, and lungs. The noeffect level in this studyis considered to be 12.8 mg/m³ HMD.     

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.     

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.     

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.     

Toxicity and occupational exposure assessment for hydroprocessed esters and fatty acids (HEFA) alternative jet fuels

ABSTRACT

The U.S. Air Force (USAF) has pursued development of alternative fuels to augment or replace petroleum-based jet fuels. Hydroprocessed esters and fatty acids (HEFA) renewable jet fuel is certified for use in commercial and USAF aircraft. HEFA feedstocks include camelina seed oil (Camelina sativa, HEFA-C); rendered animal fat (tallow, HEFA-T); and mixed fats and oils (HEFA-F). The aim of this study was to examine potential toxic effects associated with HEFA fuels exposures. All 3 HEFA fuels were less dermally irritating to rabbits than petroleum-derived JP-8 currently in use. Inhalation studies using male and female Fischer-344 rats included acute (1 day, with and without an 11-day recovery), 5-, 10- or 90-day durations. Rats were exposed to 0, 200, 700 or 2000 mg/m³ HEFA-F (6 hr/day, 5 days/week). Acute, 5 – and 10-day responses included minor urinalysis effects. Kidney weight increases might be attributed to male rat specific hyaline droplet formation. Nasal cavity changes included olfactory epithelial degeneration at 2000 mg/m³. Alveolar inflammation was observed at ≥700 mg/m³. For the 90-day study using HEFA-C, no significant neurobehavioral effects were detected. Minimal histopathological effects at 2000 mg/m³ included nasal epithelium goblet cell hyperplasia and olfactory epithelium degeneration. A concurrent micronucleus test was negative for evidence of genotoxicity. All HEFA fuels were negative for mutagenicity (Ames test). Sensory irritation (RD₅₀) values were determined to be 9578 mg/m³ for HEFA-C and greater than 10,000 mg/m³ for HEFA-T and HEFA-F in male Swiss-Webster mice. Overall, HEFA jet fuel was less toxic than JP-8. Occupational exposure levels of 200 mg/m³ for vapor and 5 mg/m³ for aerosol are recommended for HEFA-based jet fuels.     

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.     

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.     

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.     

The inhalation toxicity of sulfolane (tetrahydrothiophene-1,1-dioxide)

The mean survival time (MST) of rats exposed to 11,000 mg of aerosolized sulfolane/m³ was 19.4 hr and all rats convulsed during the exposure. The sulfolane concentration expected to yield a MST of 24 hr was calculated to be 4700 mg/m³. After less than 24 hr of exposure, leukopenia and convulsions were observed in rats (3600 mg/m³) or squirrel monkeys (4850 mg/m³) exposed to high concentrations of aerosolized sulfolane. Six subacute exposures were conducted: one repeated exposure to 495 mg/m³ for 8 hr/day, 5 days/week for 27 exposure days and five 23 hr/day, continuous exposures of approximately 90-day duration to 200, 159, 20, 4.0, and 2.8 mg/m³. Squirrel monkeys convulsed, vomited, and died during the exposures to 495 and 200 mg/m³. Dogs convulsed, vomited, and were unusually aggressive during continuous exposure to 200 mg/m³, but not during repeated exposures to 495 mg/m³. Rodents did not convulse in any of these subacute exposures. Leukopenia and increased plasma transaminase activity were found in guinea pigs exposed to 200 mg/m³, but not those exposed to 159 mg/m³. Hemorrhagic, inflamed lungs were also observed in most animals exposed to the two highest concentrations. In this study, no overt toxic effects were noted during exposure of rats, guinea pigs, squirrel monkeys, or dogs to 20, 4.0, or 2.8 mg of sulfolane/m³.     

Inhalation toxicity study of disk-shaped potassium octatitanate particles (Terracess TF) in rats following 90 days of aerosol exposure

Since fibrous particles such as asbestos and some man-made fibers (MMF) have been known to produce carcinogenic or fibrogenic effects, disk-shaped potassium octatitanate (POT) particles (trade name: Terracess TF) were manufactured as nonfibrous particles. A 90-day inhalation toxicity study of Terracess TF was performed to evaluate comparative inhalation toxicity of the disk shape with a fibrous shape that was previously evaluated. Four groups of 20 male and 15 female rats each were exposed to Terracess TF aerosols at concentrations of 0, 2, 10, or 50?mg/m³ for 90 days. Ten male and 10 female rats per group were sacrificed at 90 days of exposure. After 90 days of exposure, 5 male rats per group were sacrificed at 3 wk of recovery period and 4–5 male rats per group or 5 female rats per group were sacrificed at 15?wk of recovery for lung clearance and histopathology. The mass median aerodynamic equivalent diameter (MMAED) of the aerosols of test materials ranged from 2.5 to 2.9?μm. There were no test-substance-related adverse effects on clinical observations. At the end of the 90-day exposure, a slight increase in lung-to-body weight ratios was observed at 50?mg/m³ in male but not in female rats. However, lung weights were within normal limits after 3- or 15-wk recovery periods. Microscopically, inhaled Terracess TF particles were mostly phagocytized by free alveolar macrophages (AMs) in the alveolar airspaces and alveolar walls maintained normal structure at 2 and 10?mg/m³. At 50?mg/m³, some alveoli were distended and filled with aggregates of particle-laden AMs. The alveolar walls showed slight type II pneumocyte hyperplasia, but neither proliferative inflammation nor alveolar fibrosis was present at 50?mg/m³. The clearance half-times for Terracess TF were estimated to be in the order of 6 to 9?mo for the 50-mg/m³ group and 2 to 3?mo for the 10- and 2-mg/m³ groups. The lung responses and lung clearance rate were comparable to those of “nuisance” type dusts at these concentrations. Based on interpretation that aggregated particle-laden AMs in alveoli was considered to be an early histopathological sign of lung overloading, an effect level was considered to be 50?mg/m³ and no-observed-adverse-effect level (NOAEL) was 10?mg/m³. This experiment clearly demonstrated that particle morphology was considered to be an important factor to determine inhaled particle toxicity.     

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.     

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).     

Mucous Cell Metaplasia in the Airways of Rats Exposed to Machining Fluids

Occupational exposure to microbial-contaminated machining fluidsis associated with a variety of adverse pulmonary effects includingchronic bronchitis and increased sputum production. We havepreviously demonstrated in F344 rats that inhaled endotoxincan increase the amount of stored intraepithelial mucosubstances(Vs) in the respiratory tract. The purpose of the present studywas to examine the effect of endotoxin-contaminated machiningfluid aerosols on mucous production. Rats were exposed to aerosolsof pyrogen-free water, 1 or 10 mg/m³ used machining fluid, or10 mg/m³ unused machining fluid for 3 hr/day for 3 days. Twenty-fourhours after the final exposure, right lung lobes were lavagedand the nasal cavity and left lung were fixed in formalin. Theamount of Alcian blue/periodic acid-Schiff-stained mucosubstanceswas determined by morphometry. Exposure to 10 mg/m³ used machiningfluid (equivalent to 0.8 µg/m³ endotoxin) produced a significantincrease in Vs in the epithelial lining of both the nasal septumand intrapulmonary airways. These changes in Vs were accompaniedby a significant increase in total cells and neutrophils inthe lavage fluid. No changes in stored mucosubstances or lavageparameters were found in animals exposed to 1 mg/m³ used machiningfluid aerosols. A significant increase in Vs was observed inthe nasal septum but not in the intrapulmonary airways of animalsexposed to 10 mg/m³ unused machining fluids (no measurable endotoxin).These results suggest that in addition to endotoxin, nonendotoxincomponents of machining fluids may contribute to the increasein sputum and chronic bronchitis reported for workers exposedto machining fluid aerosols.     

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.     

Toxicological evaluation of aerosols of a tobacco extract formulation and nicotine formulation in acute and short-term inhalation studies

Abstract

A formulation of tobacco extract containing 4% nicotine (TE) and similar nicotine formulation containing vehicle and 4% nicotine (NF) were evaluated using animal inhalation assays. Two 4-h inhalation exposures at 1 and 2?mg/L aerosol exposure concentrations, respectively, of the tobacco extract with 4% nicotine formulation showed that the LC₅₀ was greater than 2?mg/L, the maximum concentration tested. All inhalation exposures were conducted using the capillary aerosol generator (CAG). Increasing aerosol TPM concentrations (0, 10, 50, 200, 1000?mg/m³ TE and 0, 50, 200, 500, 1000?mg/m³ NF) were generated via the CAG and used to expose groups of male and female rats for 4-h per day for 14 days. In life monitors for potential effects included clinical observations, weekly body weights and food consumption. Post mortem evaluations included gross tissue findings, hematology, clinical chemistry, serum plasma and nicotine levels, absolute and normalized organ and tissue weights, and histopathology of target organs. Treatment-related changes were observed in body weights, hematology, clinical chemistry, organ weights and histopathological findings for TE at the 200 and 1000?mg/m³ exposure levels, and in the 500 and 1000?mg/m³ exposure groups for NF. Under the conditions of these studies, the no-observed-adverse-effect level in the rat was approximately 50?mg/m³ for the TE aerosol-exposed groups, and approximately 200?mg/m³ in the NF aerosol-exposed groups.     

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.