Acute Respiratory Effects of Endotoxin-Contaminated Machining Fluid Aerosols in Guinea Pigs

Exposure to machining fluid aerosols in the automotive industryis associated with a variety of respiratory symptoms includingcross-shift changes in pulmonary function, cough, asthma, andphlegm. Lubricating and cooling fluids used in machining operationsare predominantly water and thus are susceptible to microbialgrowth. In the present study, the role of endotoxin in the acutepulmonary injury produced by machining fluid aerosols was examinedin guinea pigs. Animals were exposed to nebulized water, unusedmachining fluid, or used machining fluid. At the end of a 3-hrexposure, specific airway conductance (SGaw) was not affectedby exposure to the vehicle water, but was decreased in a dose-dependentmanner by exposure to aerosols of the used machining fluid.SGaw decreased from preexposure baseline values by 0, 7, and40% in animals exposed to 1, 10, and 100 mg/m³ used machiningfluid, respectively. These exposure levels also produced acutelung injury as evidenced by changes in cellular and biochemicalindices in lavage fluid. These adverse respiratory effects mayhave been due to microbial contamination of the used machiningfluid as the aerosol exposures were associated with airborneendotoxin concentrations of 0.3, 1.9, and 5.3 µg/rn³,respectively. Animals exposed to aerosols of the endotoxin-freeunused machining fluid had no statistically significant adversefunctional, cellular, or biochemical effects except for a fourfoldincrease in neutrophils at 100 mg/m³. These results suggestthat contamination of machining fluid during use or storagemay lead to the adverse respiratory effects of aerosolized machiningfluids. To examine whether contaminating endotoxin was responsiblefor these respiratory effects, animals were exposed to 10 or100 mg/m³ unused machining fluid to which endotoxin was addedto provide airborne endotoxin concentrations similar to thosedetermined in the used machining fluid studies. Endotoxin-contaminatedunused machining fluid produced significant decrements in SGaw(14 and 38% for 0.9 and 8.2 µg/m³ endotoxin, respectively)as well as significant increases in cellular and biochemicalparameters of acute lung injury in lavage fluid. Thus, endotoxinmay play a significant role in the adverse respiratory effectsof aerosolized machining fluids.     

Six-Month Exposure of Strain A/J Mice to Cigarette Sidestream Smoke: Cell Kinetics and Lung Tumor Data

Male strain A/J mice were exposed to sidestream smoke (SS) generatedfrom burning Kentucky 1R4F reference cigarettes. Chamber concentrationswere 4 mg/m³ of total suspended respirable particulate matter(TSP). Animals were exposed 6 hr a day, 5 days a week. One-weekcumulative labeling indices were significantly increased inthe large intrapulmonary airways during the 1st week and inthe respiratory epithelium of the nasal and maxillar turbinatesduring the first 3 weeks of exposure and then returned to controlvalues. Subsequently, signs of increased cell proliferationwere again found in the nasal and maxillar turbinates duringthe 9th and 16th exposure weeks. The experiment was terminatedafter 6 months. The number of animals bearing lung tumors wasthe same in smoke-exposed as in filtered airexposed animalsas was the average number of tumors per lung. Analysis of theDNA of individual tumors obtained from exposed and control micefor K-ras mutations suggested that exon 2 might be a specifictarget for SS. It was concluded that (1) duration of exposurewas too short or (2) concentration of TSP was too low to reveala possible carcinogenic potential of SS in strain A/J mice orthat (3) SS is not carcinogenic in strain A mice.     

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.     

Acute Inhalation Toxicopathology of Lithium Combustion Aerosols in Rats

Acute Inhalation Toxicopathology of Lithium Combustion Aerosolsin Rats. Rebar, A. H., Greenspan, B. J., and Allen, M. D. (1986).Fundam. Appl. Toxtcol. 7, 58-67. Male and female F344/Lov ratswere exposed to aerosols produced by burning lithium metal underconditions, designed to stimulate a fire in the containmentbuilding of a fusion reactor. Lithium combustion aerosols weregenerated by sweeping lithium vapor into air atmospheres withcontrolled CO₂ and H₂O concentrations. Chemical analyses ofthe aerosols produced indicated a dependence of the chemicalform of carbon dioxide concentrations and relative humidity.Under conditions of low CO₂ concentration and low relative humidity(<25%), the aerosol was predominantly lithium monoxide withsome lithium hydroxide and about 12% lithium carbonate. Underconditions of high relative humidity (>75%), the aerosolwas primarily lithium hydroxide with about 23% A lithium carbonate.Although these two aerosols might be expected to have differentacute toxicities based on their differing alkalinities, the14-day LC50 values (with 95% confidence limits) determined after4-hr exposures were 940 (730-1200) mg/m³ for the lithium oxideand hydroxide mixture and 960 (830-1200) mg/m³ for the lithiumhydroxide aerosols. Histopathologic lesions were observed inthe nasal turbinates, larynx, and occasionally in the lungswith both aerosols. The most prominent lesions were necrotizinglaryngitis and ulcerative rhinitis. Pulmonary lesions representeda secondary extension of the upper respiratory tract lesionsrather than a primary manifestation of lithium toxicity. Thesimilarities in the LC50 valus and also in the histopathologiclesions observed suggest that any Li2O in the aerosol reactedrapidly with water vapor in the respiratory tract to form LiOHprior to deposition.     

Short-Term Effects of Sidestream Smoke on Respiratory Epithelium in Mice: Cell Kinetics

Male strain A/J and C57BL/6 mice were exposed on five consecutivedays, for 6 hr a day, to sidestream smoke generated from Kentucky1R4F reference cigarettes. Chamber concentrations were 1 mg/m³of total suspended particulate matter and 528 to 549 µg/m³of nicotine. Cumulative labeling indices in the airways andin the pulmonary parenchyma were measured following 1, 3, or5 days exposure to unfiltered or filtered sides tream smoke.A significantly increased labeling index was found in A/J micein the epithelium lining large intrapulmonary airways and terminalbronchioles after 3 and 5 days exposure to unfiltered smoke,whereas following exposure to filtered smoke labeling indicesremained normal. The alveolar labeling index was not increasedfollowing smoke exposure. In C57BL/6 mice, sidestream smokedid not produce signs of increased cell proliferation in therespiratory tract. It is concluded that the response to sidestreamsmoke inhalation in mice may depend upon the strain of miceexamined.     

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.     

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.     

Irritative effects of fumes and aerosols of bitumen on the airways: results of a cross-shift study

Possible health hazards of fumes and aerosols of bitumen are in discussion, and data on their adverse effects on human airways under current exposure conditions are limited. To assess the irritative effects of exposure to fumes and aerosols of bitumen on the airways, a cross-sectional cross-shift study was conducted including external and internal exposure measurements, spirometry and especially non-invasive methods like nasal lavage collection and induction of sputum in order to identify and evaluate more precisely inflammatory process in the upper and lower airways. The cross-shift study comprised 74 mastic asphalt workers who were exposed to fumes and aerosols of bitumen and 49 construction workers without this exposure as reference group. Questionnaire, spirometry, ambient monitoring and urinary analysis were performed. Humoral and cellular parameters were measured in nasal lavage fluid (NALF) and induced sputum. For data analysis, a mixed linear model was performed on the different outcomes with exposure group, time of measurement (pre-, post-shift), current smoking, German nationality and age as fixed factors and subjects as random factor. Based on personal exposure measurements during shift, mastic asphalt workers were classified into a low (< or =10 mg/m(3); n = 46) and a high (>10 mg/m(3); n = 28) exposure group. High exposure was accompanied by significant higher urinary post-shift concentrations of 1-hydroxypyrene and the sum of hydroxyphenanthrenes. Acute respiratory symptoms were reported more frequently in the high exposure group after shift. Significant cross-shift declines in lung function parameters (forced expiratory volume in 1 s [FEV(1) (% predicted)] and forced vital capacity [FVC (% predicted)]) were measured in mastic asphalt workers. Pre-shift FEV(1) (% predicted) and FVC (% predicted) were higher in the low exposure group. In pre- and post-shift NALF samples, interleukin (IL)-1beta-, IL-8- and total protein concentrations were lower in the low exposure group compared to the reference and the high exposure group. Pre- and post-shift neutrophil percentages in both nasal and sputum samples were also lower in the low exposure group. Significantly higher pre- and post-shift sputum concentrations of IL-8, IL-6, nitrogen oxide (NO) derivatives and total protein were detected especially in highly exposed workers. Irritative effects of exposure to fumes and aerosols of bitumen on the upper and lower airways were apparent, especially in mastic asphalt workers with exposure above 10 mg/m(3).     

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.     

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.     

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.     

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.     

Ozone exposure enhances endotoxin-induced mucous cell metaplasia in rat pulmonary airways.

Coexposure to different airborne pollutants can be more toxic to airway epithelium than an inhalation exposure to a single pollutant. We have previously reported that coexposure to ozone, the primary oxidant gas in photochemical smog, and unique inflammatory biogenic substances such as allergens or bacterial endotoxin, results in augmented epithelial and inflammatory responses in rat nasal airways (M. V. Fanucchi et al., 1998, Toxicol. Appl. Pharmacol. 152, 1-9; J. G. Wagner et al., 2002a, Toxicol. Sci.67, 284-294). In the present study, we investigated the toxic interaction of ozone and endotoxin on the respiratory epithelium in the pulmonary airways of laboratory rodents. F344 rats were intranasally instilled with 0, 2, or 20 microg endotoxin dissolved in sterile saline (150 microl/nasal passage). Six h after instillation rats were exposed to air or 1 ppm ozone for 8 h. One day later, endotoxin and ozone exposures were repeated. Three days after the last exposure, rats were sacrificed, the lungs were lavaged with saline, and the collected bronchoalveolar lavage fluid (BALF) was analyzed for inflammatory cells and secreted mucosubstances (mucin 5AC). Lung tissues were processed for light microscopic examination and morphometric analysis of numeric density of epithelial cell populations and volume densities of intraepithelial mucosubstances (IM). Conducting airways were microdissected and analyzed by quantitative RT-PCR to determine steady-state mucin gene (rMuc5AC) mRNA levels in respiratory epithelium. Endotoxin instillation caused a dose-dependent increase in BALF neutrophils that was further increased twofold in ozone-exposed rats given 20 microg endotoxin. Mucin glycoprotein 5AC was elevated in BALF from rats exposed to 20 microg, but not 2 microg endotoxin. Exposure to ozone alone did not cause mucus hypersecretion, but ozone potentiated mucus secretion in rats given 2 or 20 microg endotoxin. Airways of rats exposed to air or ozone alone had scant amounts of IM. Endotoxin instillation induced a dose-dependent increase in IM in airway epithelium that was significantly increased (twofold) in rats that were also exposed to ozone. Expression of rMuc5AC was induced in axial pulmonary airways by 2 and 20 microg endotoxin, and was increased further by ozone-exposure in rats instilled with 20 microg endotoxin. These data demonstrate that ozone exposure potentiates neutrophilic inflammation and mucus production and secretion elicited by a biogenic substance in rat pulmonary airways.     

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.     

Evaluation of the Acute Respiratory Effects of Aerosolized Machining Fluids in Mice

Using a previously developed bioassay, the sensory and pulmonaryirritating properties of a group of 10 aerosolized machiningfluids were evaluated in mice. Single, 3-hr inhalation exposureswere conducted with the fluids at exposure concentrations-rangingfrom 20 to 2000 mg/m³. The results have shown that all 10 werecapable of inducing sensory and pulmonary irritation, with littleor no change in pulmonary histopathology. A concentration-responserelationship was developed for each fluid which revealed that,for the 10 fluids studied here, the synthetic/semisyntheticand soluble fluids were more potent irritants than the straightoils. Also, 3 of the 10 fluids which had been collected fromworkplace operations (i.e., "in use" fluids) were found to besimilar in potency to the same fluids prior to their introductioninto the workplace (i.e., "neat" fluids). From concentration-responserelationships, the RD50 value (i.e., concentration inducinga 50% response) was obtained for each of the 10 fluids. TheRD50 values ranged from 100 to 1000 mg/m³ for all fluids exceptthe straight oils whose RD50 values were over 100,000 mg/m³.Using these values, exposure limits were then suggested forworkers in industry to prevent irritation. This bioassay maybe a good first step in evaluating new machining fluids whoseformulations may change depending upon the current industrialneeds.     

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

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

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.     

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.     

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.     

Cell Proliferation in the Respiratory Tract of Hamsters Continuously Exposed During 4 Weeks to 0.8 PPM Ozone

Abstract

Male Syrian golden hamsters were exposed to 0.8 ppm ozone, 24 h/day for 4 wk. Cumulative labeling indices were measured during each week of exposure in the lung, the intrapulmonary airways, the trachea, and the nasal passages. In the alveolar zone, ozone did not affect labeling indices beyond the centriacinar region. In the terminal bronchioles and large intrapulmonary airways, labeling indices were significantly higher than in controls throughout exposure to ozone. The largest increase was seen during wk I. In the trachea and the nasal passages, a significant increase in cell labeling was only seen during wk I; thereafter the values returned to control levels. It was concluded that exposure to 0.8 ppm ozone produces signs of proliferative activity during a 4-wk continuous exposure in the epithelium of the intrapulmonary airways, but not in other sites.