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.     

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.     

Pulmonary Fibrosis Produced in F-344 Rats by Subchronic Inhalation of Aerosols of a 4000 Molecular Weight Ethylene Oxide/Propylene Oxide Polymer

Pulmonary Fibrosis Produced in F-344 Rats by Subchronic Inhalationof Aerosols of a 4000 Molecular Weight Ethylene Oxide/PropyleneOxide Polymer. KLONNE, D. R., DODD, D. E., Losco, P. E., TROUP,C. M., AND TYLER, T. R. (1988), Fundam Appl. Toxicol 10, 682–690.Inhalation of aerosols of the ethylene oxide/propylene oxidepolymer (U-5100) evaluated in this study has previously beenshown in acute and 2-week studies to produce toxicologic effectson the lungs, with increased lung weights and microscopic findingsof congestion and hemorrhage of pulmonary alveolar capillariesand necrosis of alveolar epithelial cells (D. R. KLONNE, D.J. NACHREINER, D. E. DODD, P. E. Losco, AND T. R. TYLER, 1987,Fundam. Appl. Toxicol. 9, 7737–784). In the present studies,F-344 rats were exposed 6 hr/day, 5 day/week for 2 weeks toaerosols at mean concentrations of 0,0.9, or 5.0 mg/m³ or for13 weeks to mean concentrations of 0, 0.3, 1.1, or 5.2 mg/m³.Following the 2-week study, minimal multifocal hemorrhage andeosinophilic proteinaceous debris in alveoli were observed inthe 0.9 mg/m³ group; similar lesions plus alveolar cell necrosiswere found in the 5 mg/m³ group. In the 13-week study, the 5.2mg/m³ group had a slight decrease in body weight gain, whileincreases in absolute and/or relative lung weights occurredfor both the 1.1 and 5.2 mg/m³ groups at the end of the exposureregimen and at the end of a 5-week recovery period. Histologiclesions of the lungs occurred in all U-5100-exposed groups andconsisted of hemorrhage, alveolar histiocytosis, interstitialpneumonia, and multifocal fibrosis. The incidence and severityof the pulmonary lesions were concentration related. At theend of the 5-week recovery period, there was little change inthe severity or incidence of the pulmonary lesions in the 1and 5 mg/m³ groups when compared to rats killed the day afterthe termination of exposures. In conclusion, exposure to aerosolsof U-5100 for 13 weeks produced generally slight but biologicallysignificant pulmonary fibrosis in rats at all the exposure concentrationstested in this study.     

Use of Lung Toxicity and Lung Particle Clearance to Estimate the Maximum Tolerated Dose (MTD) for a Fiber Glass Chronic Inhalation Study in the Rat

Short–term toxicity and lung clearance were assessed inrats exposed by inhalation to size-selected fibrous glass (FG)for 13 weeks. Results from this study and from a recent FG chronicinhalation study are presented here as guidelines for the selectionof a maximum tolerated dose (MTD) for chronic inhalation studiesof fibers. Fischer 344 rats were exposed using nose–onlyinhalation chambers, 6 hr/day, 5 days/week, for 13 weeks toone of five concentrations of FG (36, 206, 316, 552, or 714fibers/cc; expressed gravirnetrically, 3, 16, 30, 45, or 60mg/m³) or to filtered air. Rats were then held for an additional10 weeks of postexposure recovery. Test fiber was size–selectedfrom glass wool having a chemical composition representativeof building insulation. Rats were terminated at 7, 13, 19, and23 weeks after the onset of exposure to evaluate pulmonary pathology,lung epithelium cell proliferation, lung fiber burden, and lunglavage cells and chemistry. The effect of fiber inhalation onlung clearance of innocuous microspheres was also evaluated:following fiber exposure, six rats/group were exposed to ⁸⁵Sr–labeled3.0-µm polystyrene microspheres by intratracheal inhalationand then monitored for whole–body radioactivity duringthe 10–week recovery period. Data from the short–termstudy support the choice of 30 mg/m³ as the MTD for the previouschronic FG study and also provide indicators of long–termlung toxicity and functional impairment that can be used toestimate the MTD for future chronic fiber inhalation studies.     

Pulmonary response to inhaled Kevlar aramid synthetic fibers in rats

Groups of male rats were exposed to specially prepared ultrafine Kevlar pulp fibers (du Pont's registered trademark for certain aramid fibers) at atmospheric concentrations of either 0.1, 0.5, 3.0, or 18 mg/m3 for 2 weeks. Rats were killed at 0 and 2 weeks and 3 and 6 months postexposure (PE) except the rats exposed to 18 mg/m3, which were killed 0, 4, and 14 days and 1, 3, and 6 months PE. Another group of male rats was exposed to 18 mg/m3 (respirable dust approximately 2.5 mg/m3) of commercial Kevlar fibers for 2 weeks and were killed at 0 and 2 weeks and 3 and 6 months PE. Inhaled ultrafine Kevlar fibers were mostly phagocytized by alveolar macrophages (dust cells) in the alveolar ducts and adjoining alveoli after exposure to either 0.1 or 0.5 micrograms/m3. Most dust cells had disappeared and lungs showed a normal appearance throughout 6 months PE. The pulmonary response almost satisfied the biological criteria for a nuisance dust. Rats exposed to 3 mg/m3 ultrafine Kevlar fibers revealed occasional patchy thickening of alveolar ducts with dust cells and inflammatory cells but with no collagen fibers deposited throughout 6 months PE. After exposure to 18 mg/m3 ultrafine Kevlar, the respiratory bronchioles, alveolar ducts, and adjoining alveoli showed granulomatous lesions with dust cells by 2 weeks PE. The granulomatous lesions converted to patchy fibrotic thickening with dust cells after 1 month PE. The fibrotic lesions were markedly reduced in cellularity, size, and numbers from 3 to 6 months PE but revealed networks of reticulum fibers with slight collagen fiber deposition.     

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.     

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.     

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.     

Pulmonary Retention of Inhaled Diesel Particles after Prolonged Exposures to Diesel Exhaust

Pulmonary Retention of Inhaled Diesel Particles after ProlongedExposures to Diesel Exhaust CHAN, T. L., LEE, P. S., AND HERING,W. E. (1984). Fundam. Appl. Toxicol. 4, 624–631. The effectof continuous exposure to diluted diesel exhaust on the pulmonaryretention of inhaled diesel particles was studied in male Fischer344 rats. Test animals were first exposed to clean air or diluteddiesel exhaust in exposure chambers at nominal particulate concentrationsof 250 µg/m³ or 6 mg/m³ for 20 hr/day, 7 days/week, forperiods lasting from 7 to 112 days, followed by a nose-onlyexposure to ^l4C-tagged diesel particles for 45 min. At preselectedtime intervals after the radioactive exposure, the ¹⁴C-activitiesin the lungs of groups of four animals were measured to determinethe clearance of the ^l4C-diesel particles up to 1 year. Thepulmonary retention of the radioactive diesel particles wasgreater in animals which had been preexposed to diesel exhaustThe slower alveolar clearance of particle-laden macrophagesand leukocytes can be described by a normal Diphasic clearancemodel. Since some of the macrophages were found sequesteredas aggregates in the pulmonary region, a slow-clearing residualcomponent was included in a modified lung retention model. Whenthese residual fractions were determined and excluded from theactive particulate transport within the lungs, normal alveolarclearance rates were calculated for the animals with a preexposurediesel particulate dose less than 0.8 mg. Slower clearance wasobserved at a dose of 6.5 mg and no clearance was evident ata dose of 11.8 mg in their lungs. In effect, the greater retentionof inhaled particles can be interpreted as-a sign of impairedlung clearance attributable to the prolonged exposures to highconcentrations of diesel exhaust gases and/or the presence ofaccumulated carbonaceous particles residing in sequestered macrophageaggregates in the lungs.     

Effects of Inhaled Chromium Dioxide Dust on Rats Exposed for Two Years

Effects of Inhaled Chromium Dioxide Dust on Rats Exposed forTwo Years. LEE, K. P., ULRICH, C. E., GEIL, R. G., AND TROCHIMOWICZ,H. J. (1988). Fundam. Appl. Toxicol 10, 125–145. Ratswere exposed by inhalation to chromium dioxide (C1O2) dust atdesign concentrations of 0, 0.5 mg/m³(stabilized and unstabilized,respectively), or 25 mg/m³ (stabilized) for 6 hr/day, 5 days/weekfor 2 years. No dust-exposure-related pathological changes otherthan lung lesions were observed in all exposed rats. There wereno significant differences in pulmonary responses between unstabilizedand stabilized CrC>2 at the 0.5 mg/m³ exposure level. Thelungs showed minute dust deposition in the alveoli adjacentto the alveolar ducts, but maintained an intact general architecture.The pulmonary responses satisfied the biological criteria fora nuisance dust. At 25 mg/m³, dust deposition was sharply confinedto the alveoli in the alveolar duct region. Alveolar walls enclosingdust-laden macrophage (dust cell) aggregates were thickenedwith hyperplastic Type II pneumocytes and slightly collagenizedfibrosis. Alveoli adjacent to the terminal bronchioles werelined with bronchiolar epithelium (alveolar bronchiolar-ization).In addition, lungs showed foamy macrophage response, cholesterolgranulomas, alveolar protoeinosis, and minute fibrotic pleurisy.These pulmonary lesions occurred predominantly in female rats.Of 108 female rats, 6 developed keratin cysts and 2 had cystickeratinizing squa-mous cell carcinoma (CKSCC). None of 106 malerats had either a keratin cyst or a CKSCC. The lung tumors developedfrom metaplastic squamous cells in the areas of alveolar bronchio-larizationat the alveolar duct region. The lung tumors were well differentiatedand devoid of characteristics of true malignancy. The CKSCCis an experimentally induced, unique tumor type and is differentfrom the type of spontaneous lung tumor seen in man or animals.The relevance to man of this type of lung tumor appears to benegligible.     

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     

Effect of Chronic Cigarette Smoke Exposure on Lung Clearance of Tracer Particles Inhaled by Rats

Cigarette smoking can influence the pulmonary disposition ofother inhaled materials in humans and laboratory animals. Thisstudy was undertaken to investigate the influence of cigarettesmoke exposures of rats on the pulmonary clearance of inhaled,relatively insoluble radioactive tracer particles. Following13 weeks of whole-body exposure to air or mainstream cigarettesmoke for 6 hr/day, 5 days/week at concentrations of 0, 100,or 250 mg total particulate matter (TPM)/m³, rats were acutelyexposed pernasally to ⁸⁵Sr-labeled fused aluminosilicate (⁸⁵Sr-FAP)tracer particles, then air or smoke exposures were resumed.A separate group of rats was exposed to the ⁸⁵Sr-FAP then seriallyeuthanized through 6 months after exposure to confirm the relativeinsolubility of the tracer particles. We observed decreasedtracer particle clearance from the lungs that was smoke concentration-dependent.By 180 days after exposure to the tracer aerosol, about 14,20, and 40% of the initial activity of tracer was present incontrol, 100 mg TPM/m³, and 250 mg TPM/m³ groups, respectively.Body weight gains were less in smoke-exposed rats than in controls.Smoke exposure produced lung lesions which included increasednumbers of pigmented alveolar macrophages distributed throughoutthe parenchyma and focal collections of enlarged alveolar macrophageswith concomitant alveolar epithelial hyperplasia and neutro-philicalveolitis. The severity of the lesions increased with smokeexposure duration and concentration to include interstitialaggregates of pigmented macrophages and interstitial fibrosis.Our data confirm previous findings that exposure to cigarettesmoke decreases the ability of the lungs to clear inhaled materials.We further demonstrate an exposure-concentration related magnitudeof effect, suggesting that the cigarette smoke-exposed rat constitutesa useful model for studies of the effects of cigarette smokeon the disposition of inhaled particles.     

Influence of exposure mode on vinyl chloride action

Rats were subjected to 4 h continuous or intermittent exposure to vinyl chloride (VC) at different time-weighted average concentrations (15, 50, 150, 500 and 15,000 mg/m³). Hepatic non-protein sulfhydryl content (NPSH) and excretion of thiodiglycolic acid (TdGA) in urine were determined. VC at concentrations from 50 mg/m³ to 15,000 mg/m³ caused a dose-dependent depression of NPSH, but no difference in the magnitude of this depression induced by continuous or intermittent exposure at the same average concentration of VC was noted. At average concentrations of 50 mg/m³ and 150 mg/m³, the urinary excretion of TdGA under continuous exposure did not differ from that under intermittent exposure, whereas at VC concentrations of 500 mg/m³ and 15,000 mg/m³ it was higher following continuous exposure.     

INHALATION TOXICITY OF POTASSIUM OCTATITANATE FIBERS (TISMO) IN RATS FOLLOWING 13 WEEKS OF AEROSOL EXPOSURE

One hundred and forty male and 140 female rats were divided into 1 control and 3 test groups of 35 rats each, per sex, and exposed by whole-body inhalation to test compound at target concentrations of 0, 1 mg/m³ (1700 fibers/cm³, 123 WHO fibers/cm³), 10 mg/m³ (5900 fibers/cm³, 952 WHO fibers/cm³), and 100 mg/m³ (112,700 fibers/cm³, 7440 WHO fibers/cm³) for 6 h/day, 5 days/wk for 13 wk. Ten rats from each group were killed after 13 wk of exposure and 13 wk of recovery, respectively, for histopathological evaluation. The other 15 rats from each group were killed to study lung clearance after 91 days of exposure, and approximately 1.5 and 3 mo of recovery following the end of the 13 wk of exposure. The mean fiber length of the chamber atmosphere was 2.8, 2.7, and 2.8 µm, while the mean fiber width was 0.48, 0.48, and 0.45 µm for the 1-, 10-, and 100-mg/m³ chambers, respectively. In the 1-mg/m³ (123 WHO fibers/cm³) exposure group, inhaled particles were mostly retained in a few fiberladen alveolar macrophages (AMs) within the alveoli adjacent to alveolar ducts without any adverse tissue response throughout 13 wk of exposure and following 13 wk of recovery. This exposure concentration was considered to be a no-observable-adverse-effect level (NOAEL), since the alveoli containing fiber-laden AMs preserved normal structure. After 13 wk of exposure to 10 mg/m³ (952 WHO fibers/cm³), fiber-laden AMs were mainly retained at the alveoli adjacent to the alveolar ducts. Infrequently, slight fibrotic thickening was observed in the alveolar ducts and adjoining alveoli, with proliferating fibroblasts and hyperplastic Type II pneumocytes, and microgranulomas. Occasionally, trace amounts of collagenous material were deposited in the thickened alveolar ducts and adjoining alveolar walls. In addition, minimal alveolar bronchiolarization was occasionally found in the alveoli adjacent to the terminal bronchioles. The peribronchial lymphoid tissue and thymic lymph nodes contained migrated fiber-laden AMs. After 13 wk of recovery, fiber-laden AMs had mostly disappeared from alveoli located in the peripheral acini, but they localized in the alveolar ducts region, suggesting there was active lung clearance of fibers by the AMs via airways. Thickened alveolar ducts and adjacent alveoli were decreased in thickness, a reversible change manifested by reduction of proliferating Type II pneumocytes and fibroblasts. Collagenized fibrosis was slightly more pronounced in the thickened alveolar ducts and adjoining alveoli. The lung response following 13 wk of exposure to 100 mg/m³ (7440 WHO fibers/cm³) and after 13 wk of recovery was similar to those findings of the 952 WHO fibers/cm³ group but more pronounced, demonstrating a clear concentration-related response. Alveolar ducts and adjoining alveolar walls in the central acini were irregularly thickened with more frequent evidence of minimal collagenized fibrosis. The lung burden and clearance of fibers were estimated by measuring the total content of titanium (Ti) in the lungs, but high variability of Ti content in control and exposed groups prevented meaningful lung clearance analysis.     

Alterations in Particle Accumulation and Clearance in Lungs of Rats Chronically Exposed to Diesel Exhaust

Alterations in Particle Accumulation and Clearance in Lungsof Rats Chronically Exposed to Diesel Exhaust. WOLFF, R. K.,HENDERSON, R. F., SNIPES, M. B., GRIFFITH, W. C., MAUDERLY,J. L., CUDDIHY, R. G., AND MCCLELLAN, R. 0. Fundam Appl. Toxicol9, 154–166. F344 rats were chronically exposed to dieselexhaust at target soot concentrations of 0 (control, C), 0.35(low, L), 3.5 (medium, M), and 7.0 (high, H) mg/m³ Accumulatedlung burdens of diesel soot were measured after 6, 12, 18, and24 months of exposure. Parallel measurements of particle depositionand clearance were made to provide insight into the mechanismsof particle accumulation in lungs. The fractional depositionof inhaled ⁶⁷Ga₂O₃ particles after 6, 12, 18, and 24 monthsof exposure and of inhaled ¹³⁴Cs-fused aluminosilicate particlesafter 24 months were similar for all groups. Progressive increasesin lung burdens of soot particles were observed in M and H exposedrats, reaching levels of 11.5 ± 0.5 and 20.5 ±0.8 mg/lung (SE), respectively, after 24 months. Rats in theL group had smaller relative increases in lung burden, reachinglevels of 0.60 ± 0.02 mg/lung after 24 months. Trachealmucociliary clearance measurements, using ^99mTc-macroaggitatedalbumin deposited in the trachea, showed no changes at anytime.There were statistically significant increases inclearance half-timesof inhaled radiolabeled particles of ⁶⁷Ga₂O₃ as early as 6 monthsat the H level and 18 months at the M level; no significantchanges were seen at the L level. Rats inhaled fused aluminosilicateparticles labeled with ¹³⁴Cs after 24 months of diesel exhaustexposure to measure long-term components of pulmonary clearance.The long-term clearance half-times were 79 ± 5, 81 ±5, 264 ± 50, and 240 ± 50 days (± SE) forthe C, L, M, and H groups, respectively. Differences were significantbetween the C and both the M and H exposure groups (p <0.01).Lung burdens of diesel soot were more than expected at the Hand M levels and were also associated with impaired particleclearance while smaller responses were observed in both burdensand clearance at the L level.     

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.     

Acute and 2-Week Inhalation Toxicity Studies on Aerosols of Selected Ethylene Oxide/Propylene Oxide Polymers in Rats

The ethylene oxide/propylene oxide (EO/PO) polymers evaluatedin this study have previously been shown to have a low orderof toxicity and/or irritancy by ocular, dermal, or oral routesof administration. These studies evaluated the acute inhalationtoxicity of respirable aerosols of three EO/PO compounds (U-660,U-2000, and U-5100) that differ in chain length, molecular weight,and viscosity. The respective 4-hr LC50 values (95% confidencelimits) for U-660, U-2000, and U-S 100 in Wistar albino ratswere 4670 (4090–5320), 330 (227–480), and 106 (45–245)mg/m³. Occasionally, slight increases in respiration rate andslight hyperactivity were observed during the postexposure period.All deaths were delayed for 2–5 days postexposure. Bodyweight gains were transiently depressed in rats exposed to U-2000and U-5100. Discolored lungs and livers occurred in animalswhich died during the 14-day postexposure period. Subsequently,a repeated-exposure study was conducted on U-5100 in F-344 ratsexposed for 6 hr/day, 5 days/week, for 9 exposures at mean concentrationsof 0, 5, 26, and 50 mg/m³ Portions of the control and 50 mg/m³groups were maintained for an additional 2-week recovery period.Exposure-related effects included transient urogenital wetnessin 50 mg/m³ group females; decreased body weight gain (7–29%)in all U-5100 groups except the 5 mg/m³ group females; increasesin absolute (17–52%) and relative lung weights in allU-5100 groups; macroscopic red foci in the lungs; and microscopicfindings of congestion and hemorrhage of pulmonary alveolarcapillaries and necrosis of alveolar epithelial cells. Lungweights remained elevated after the 2-week recovery period,but the severity of the microscopic lesions was noticeably less,indicating partial reversibility of the lesions. In conclusion,EO/PO polymers have a higher order of toxicity by inhalationin comparison to other routes of administration, vary considerablyin their acute lethal toxicity as a function of chain length/molecularweight, and induce pulmonary hemorrhage, and possibly edema,following repeated aerosol exposures at concentrations as lowas 5 mg/m³.     

Chronic Inhalation Toxicity of Size-Separated Glass Fibers in Fischer 344 Rats

This study was initiated to determine the chronic biologicaleffects in Fisher 344 rats of inhaled size-separated respirablefractions of fibrous glass (FG) having compositions representativeof common building insulation wools. Rats were exposed usingnose-only inhalation chambers, 6 hr/day, 5 days/week, for 24months to three concentrations (3, 16, and 30 mg/m³) of twodifferent compositions of FG (designated MMVF 10 and MMVF 11),or to filtered air (negative control). Fibrous glass findingswere compared to those from a concurrent inhalation study ofchrysotile asbestos and refractory ceramic fiber (RCF). TheFGs used in this study were size selected to be largely respirablein the rat and the aerosol generation technique did not alterthe dimensions of the fibers. Interim euthanizations took placeat 3- to 6-month intervals to monitor progression of pulmonarychanges. Fibers were recovered from digested lung tissue fordetermination of changes in fiber number and morphology. Inanimals exposed to 30 mg/m³ of MMVF 10 or MMVF 11, 4.2±0.9x10⁵and 6.4±3.1x10⁵ fibers/mg dry lung tissue, respectively,were recovered after 24 months of exposure. Exposure to chrysotileasbestos (10 mg/m³) and to a lesser extent RCF (30 mg/m³) resultedin pulmonary fibrosis as well as mesothelioma and significantincreases in lung tumors. FG exposure was associated with anonspecific inflammatory response (macrophage response) in thelungs that did not appear to progress after 6–12 monthsof exposure. These cellular changes are reversible and are similarto the effects observed after inhalation of an inert dust. Nolung fibrosis was observed in the FG-exposed animals. Further,FG exposure resulted in no mesotheliomas and no statisticallysignificant increase in lung tumor incidence when compared tothat of the negative control group. These findings, along withprevious inhalation studies, suggest that respirable fibrousglass does not represent a significant hazard for fibrotic orneoplastic lung disease in humans.     

The Disposition of Coal Dusts in the Lungs and Tracheobronchial Lymph Nodes of Dogs

The Disposition of Coal Dusts in the Lungs and TracheobronchialLymph Nodes of Dogs. Morrow, P.E. and Yuile, C.L. (1982). Fundam.Appl. Toxicol. 2:300–305. The pulmonary disposition, histopathologyand lymphatic uptake of anthracite (Tamaqua) and bituminous(Lower Kittaning) coal dusts were measured as part of a pulmonaryretention study which revealed a mean half-time of 1.92 yearsin dogs (Morrow et al. 1981). After brief (1-2.5 hr) exposuresto either natural or neutron-activated coals having an averageairborne mass concentration of {small tilde}90 mg m^–3and a 1.8 µm mass median aerodynamic diameter (g 2.5),dogs (n=12) were serially sacrificed up to 52 weeks after exposure.Coal dusts were found only in the lungs and pulmonary lymphnodes. The coals were considered indistinguishable as to theirpulmonary clearance and disposition and lymphatic uptake. Allcoals in the lung were associated mainly with the peribronchiolarand perivascular lymphatics or connective tissue spaces, andsome were found in alveolar macrophages. The lymphatic uptakeof coal dusts followed the powder function 0.55 t^0.613 wheret is in weeks and uptake is expressed as percent of the initialalveolar burden. In terms of pulmonary dust clearance, only4 percent of the initial alveolar burden appeared to have beentranslocated to the tracheobronchial lymph nodes in the first50 weeks, but this constituted {small tilde}14 percent of thetotal alveolar clearance. Histopathologically, one distinctionwas found: animals exposed to the highest level of neutron-activatedanthracite showed patchy hyaline thickening of some small bloodvessels and alveolar septa. The response was low grade, probablyexposure-related, but otherwise unremarkable.