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.     

Chronic Inhalation Toxicity and Carcinogenicity Testing of Respirable Fibrous Particles

On May 8–10, 1995, a workshop on chronic inhalation toxicity and carcinogenicity testing of respirable fibrous particles was held in Chapel Hill, North Carolina. The workshop was sponsored by the Office of Pollution Prevention and Toxics, U.S. Environmental Protection Agency (EPA), in collaboration with the National Institute of Environmental Health Sciences (NIEHS), the National Institute for Occupational Safety and Health (NIOSH), and the Occupational Safety and Health Administration (OSHA). The goal of the workshop was to obtain input from the scientific community on a number of issues related to fiber testing. Major issues for discussion were: (i) the optimal design and conduct of studies of the health effects of chronic inhalation exposure of animals to fibers; (ii) preliminary studies which would be useful guides in designing the chronic exposure study; (iii) mechanistic studies which would be important adjuncts to the chronic exposure study to enable better interpretation of study results and extrapolation of potential effects in exposed humans; and (iv) available screening tests which can be used to develop a minimum data set for (a) making decisions about the potential health hazard of the fibers and (b) prioritizing the need for further testing in a chronic inhalation study. After extensive discussion and debate of the workshop issues, the general consensus of the expert panel is that chronic inhalation studies of fibers in the rat are the most appropriate tests for predicting inhalation hazard and risk of fibers to humans. A number of guidances specific for the design and conduct of prechronic and chronic inhalation studies of fibers in rodents were recommended. For instance, it was recommended that along with other information (decrease in body weight, systemic toxicity, etc.), data should be obtained on lung burdens and bronchoalveolar lavage fluid analysis to assist in establishing the chronic exposure levels. Lung burden data are also important for quantifying aspects of risk assessment related to dosimetric adjustments before extrapolation. Although mechanistic studies are not recommended as part of the standard chronic inhalation studies, the expert panel stressed the need for obtaining mechanistic information as far as possible during the course of subchronic or chronic inhalation studies. At present, no single assay and battery of short-term assays can predict the outcome of a chronic inhalation bioassay with respect to carcinogenic effects. Meanwhile, several short-termin vitroandin vivostudies that may be useful to assess the relative potential of fibrous substances to cause lung toxicity/carcinogenicity have been identified.     

Embryotoxicity Study of Monomeric 4,4'-Methylenediphenyl Diisocyanate (MDI) Aerosol after Inhalation Exposure in Wistar Rats

One of the uses of MDI is as an alternative to formaldehydein the manufacture of furniture, its main route of exposureto humans being by inhalation. There have been no previous studieson the potential prenatal toxic effects of this compound. Toclose this gap in information, gravid Wistar rats, Crl:(WI)BR,were exposed by whole-body inhalation to clean air (control)and to 1, 3, and 9 mg/m3 MDI, respectively, for 6 hr per dayfrom Days 6 to 15 post conception (p.c). Rats were killed onDay 20 p.c. and the following results were obtained: Treatmentcaused a dose-dependent decrease in food consumption in allsubstance-treated groups during exposure, returning to normalvalues after cessation of treatment. The lung weights in thehigh-dose group were significantly increased compared to thesham-treated control animals. Treatment did not influence anyother maternal and/or fetal parameters investigated (maternalweight gain, number of corpora lutea, implantation sites, pre–and postimplantation loss, fetal and placental weights, grossand visceral anomalies, degree of ossification), although aslight but significant increase in litters with fetuses displayingasymmetric sternebra(e) was observed after treatment with thehighest dose of 9 mg/m³. Although the relevance of an increaseof this minor anomaly in doses which cause toxic effects indams (reduced food consumption, increased lung weights) is limitedand the number observed is within the limits of biological variability,a substance-induced effect in the high-dose group cannot beexcluded with certainty. Consequently, a no embryotoxic effectlevel of 3 mg/m³ was determined.     

Chronic Inhalation Toxicity and Carcinogenicity Study on Potassium Octatitanate Fibers (TISMO) in Rats

A chronic inhalation toxicity/carcinogenicity study of potassium octatitanate fibers (TISMO) was conducted in male Fischer 344 rats. Groups of 135 rats were exposed via whole-body inhalation to 0, 20, 60, or 200 WHO fibers/cc of TISMO, 6 h/day, 5 days/w for 24 mo. Six of 30 subgroup rats were killed after 3, 6, 12, 18, and 24 mo of exposure for lung burden evaluations. Another 30 subgroup rats were removed from the exposure chambers after 6 mo of exposure, placed in clean air, and from this group 6 rats were killed at 3, 6, 9, 12, and 18 mo later to study lung clearance. The remaining 75 rats in each group were subjected to 24 mo of exposure for chronic toxicity and carcinogenicity study. Rats exposed to HEPA-filtered air (chamber control) were used as a negative control in each study. The lung burden results indicated that a time point of equilibrium between lung burden and lung clearance at 20 WHO fibers/cc exposure was attained after approximately 18 mo of exposure. There was no difference in the number of WHO fiber from the lungs between 18 and 24 mo at 20 WHO fibers/cc exposure. But disproportional rapid increase in lung burden at 200 WHO fibers/cc exposure appeared to be saturation of lung clearance mechanism resulting from lung overloading. At 200 WHO fibers/cc exposure, approximately 22.9 and 70.5 million WHO fibers were retained in the lung after 3 and 6 mo of exposure, respectively, but lungs revealed normal in appearance. However, alveolar walls enclosing aggregated TISMO-laden alveolar macrophages (AMs) showed fibrotic thickening and approximately 197.3 million WHO fibers were retained in the lungs after 18 mo of exposure. Inhaled fibers were rapidly cleared during 3- and 6-mo recovery periods, and thereafter gradually progressive fiber reduction was observed throughout 18 mo of recovery. The number of WHO fibers decreased by approximately 72%, 74%, and 79% in the 200, 60, and 20 WHO fibers/cc groups, respectively, at the end of the 18-mo recovery period following 6 mo of exposure. Although inhaled TISMO fibers in the 20 WHO fibers/cc exposure group were phagocytized by alveolar macrophages (AMs) the lung morphology appeared normal throughout 24 mo of exposure. At 60 WHO fibers/cc exposure, a slight dose- and time-dependent increase in TISMO-laden AMs was observed throughout 3, 6, and 12 mo of exposure and some alveoli containing aggregated TISMO-laden AMs showed alveolar wall thickening at 18 mo of exposure and minimal alveolar fibrosis at 24 mo of exposure. The exposure concentration is interpreted as a borderline effect level. At 200 WHO fibers/cc exposure, lungs preserved normal architecture at 3 and 6 mo of exposure. Some alveolar walls enclosing aggregates of TISMO-laden AMs were slightly thickened after 12 mo of exposure and revealed slight alveolar fibrosis after 18 and 24 mo of exposure. Neither exposure related-pulmonary neoplasm nor mesothelioma was observed in 24 mo of exposure. The 20 WHO fibers/cc exposure concentration is considered to be a no-observable-adverse-effect level (NOAEL). TISMO exposure limits of 1 WHO fiber/cc would not impose a significant health hazard to humans in the workplace based on the animal experiments and medical surveys on workers.     

Chronic Inhalation Toxicity/Carcinogenicity Study in Rats Exposed to Fluorocarbon 113 (FC-113)

Chronic Inhalation Toxicity/Carcinogenicity Study in Rats Exposedto Fluorocarbon 113 (FC-113). Trochimowicz, H. J., Rusch, G.M., Chiu, T., and Wood, C. K. (1988). Fundam Appl. Toxicol.11, 68–75. Groups of 100 male and 100 female CitCDBR ratswere exposed by whole-body inhalation to FC-113(1,1,2-trichloro-1,2,2-trifluoroethane)for 6 hr a day, 5 days a week for 24 months. Average exposureconcentrations (? 1 SD) were 0.0 (control), 2000 ? 100, 10,000? 500, and 20,000 ? 1000 ppm (v/v), respectively. Body weightswere consistently lower in both male and female rats in the20,000 ppm exposure group after approximately 1 and 4 months'exposure, respectively, and in female rats after 12 months'exposure at 10,000 ppm. Observations of appearance and behavior,mortality, and clinical laboratory measurements were unremarkableduring the 24-month exposure period. Despite exposure levelsas high as 20,000 ppm, only occasional slight increases in urinaryfluoride were seen. Microscopic examination of tissues fromrats examined during and at the end of the 24-month study revealedno evidence of compound-related toxicity or carcinogenicity.Based mainly on a 5 to 10% decrease in body weight gain at the10,000 and 20,000 ppm exposure levels, the no-observed-effectlevel for FC-113 in this study was 2000 ppm.     

Inhalation Carcinogenicity and Chronic Toxicity of Carbon Tetrachloride in Rats and Mice

Carcinogenicity and chronic toxicity of carbon tetrachloride were examined by inhalation exposure of 50 F344 rats and 50 BDF1 mice of both sexes to carbon tetrachloride at 0 (clean air), 5, 25, or 125 ppm (v/v) for 6 h/day, 5 days/wk, for 104 wk. Incidences of hepatocellular adenomas and carcinomas in rats and mice of both sexes and of adrenal pheochromocytomas in mice of both sexes were significantly increased dose-dependently. Hepatocellular carcinomas and cirrhosis significantly occurred in the 125-ppm-exposed rats of both sexes, and 3 cases of hepatocellular carcinomas and increased incidences of hepatic altered cell foci were noted in the 25-ppm-exposed female rats. Hepatocellular carcinomas were induced in mice of both sexes at 25 and 125 ppm, and hepatocellular adenomas occurred in females at 5 ppm without any degenerative or necrotic change in hepatocytes. Hepatocellular carcinomas metastasized to the lung. The chronic hepatotoxicity was characterized by cirrhosis, fibrosis, and fatty change in rats, and ceroid deposition, bile-duct proliferation, and hydropic change in mice. Survival rates were decreased in the 125-ppm-exposed rats and mice of both sexes and in the 25-ppm-exposed female mice, in association with decreased body weights. The decreased survival rates were considered to be causally related to both various tumors including hepatocellular carcinomas and severe chronic progressive nephropathy in rats and to hepatocellular carcinomas in mice. This study provided clear evidence of carcinogenicity for carbon tetrachloride in rats and mice. A cytotoxic-proliferative and genotoxic mode of action for carbon tetrachloride-induced hepatocarcinogenesis was suggested.     

Chronic Toxicity and Carcinogenicity Study of Erythritol in Rats

The potential toxicity and carcinogenicity of erythritol, a low-calorie sugar substitute, were examined in Wistar Crl:(WI) WU BR rats. Groups of 50 rats of each sex consumed diets with 0, 2, 5, or 10% erythritol, or 10% mannitol, for a period of 104–107 weeks. To each of these main groups, two satellite groups of 20 males each were attached for interim kills after 52 and 78 weeks of treatment. At start of the study, the rats were 5–6 weeks old. The average intakes of erythritol in the 2, 5, and 10% groups were 0.9, 2.2, and 4.6 g/kg body wt/day for males and 1.0, 2.6, and 5.4 g/kg body wt/day for females, respectively. Mannitol intakes were 4.4 and 5.2 g/kg body wt/day in males and females, respectively. All treatments were well tolerated without diarrhea or other side effects. Body weights were significantly below control levels during most of the study in males of the 5% erythritol group and in males and females of the 10% erythritol and 10% mannitol groups. Survival of the animals was not adversely affected by the treatments. Hematological and clinicochemical examinations did not reveal noticeable changes which could be attributed to treatment. Analysis of urine samples collected during five 48-hr periods, from rats of the satellite groups in Weeks 26, 42, 50, and 78 and from rats of the main groups in Week 102, showed that about 60% of ingested erythritol was excreted unchanged. The urine volumes increased with increasing dietary erythritol levels. In line with previous observations on other polyols, erythritol and mannitol ingestion led to an increased excretion of urinary calcium and citrate. The urinary excretions of sodium, potassium, phosphate,N-acetylglucosaminidase (NAG), γ-glutamyltransferase (GGT), low-molecular-weight protein (LMP), and total protein (TP) were slightly elevated in the 10% erythritol group. Increased GGT and NAG excretions also were seen occasionally at the 5% dose. Significantly increased relative cecum weights were seen in rats of either sex in the 10% mannitol and, somewhat less pronounced, 10% erythritol groups. Some cecal enlargement also was seen in the 5% erythritol group. The relative weight of the kidneys was highest in the 10% erythritol group, the difference from controls reaching statistical significance at interim kills (males) and termination (females). Except for more frequent pelvic nephrocalcinosis in female rats of all erythritol dose groups, the histopathological examinations did not reveal any nonneoplastic, preneoplastic, or neoplastic changes that could be attributed to the ingestion of erythritol. In male and female rats of the 10% mannitol group, pelvic nephrocalcinosis, which in females was associated occasionally with pelvic hyperplasia, was the only remarkable finding. The incidence and progression of nephrosis, which is commonly seen in aging rats of this strain, were not influenced by the treatments. In the absence of morphological alterations in the kidneys or other signs of nephrotoxicity, the increased excretions of NAG, GGT, LMP, and TP are regarded as innocuous, functional sequelae of the renal elimination of erythritol. In conclusion, the toxicological profile of erythritol in rats resembles that of other polyols in several respects. Except for nephrocalcinosis, which is commonly seen in polyol-fed rats, no other treatment-related, morphological changes were observed in the kidneys. Evidence for a tumor-inducing or tumor-promoting effect of erythritol was not seen.     

Methylene Chloride: A 2-Year Inhalation Toxicity and Oncogenicity Study in Rats

Methylene Chloride: A 2-Year Inhalation Toxicity and OncogenicityStudy in Rats. Nit-schke, K. D. Burek, J. D., Bell, T. J., Kociba,R. J., Rampy, L. W. and McKenna, M. J. (1988). Fundam. Appl.Toxicol. 11, 48-59. Male and female Sprague-Dawley rats wereexposed to 0, 50, 200, or 500 ppm methylene chloride for 6 hr/day,5 days/week for 2 years. Blood carboxyhemoglobin levels wereelevated in a dose-dependent (less than linear) manner in ratsexposed to 50–500 ppm methylene chloride Histopathologiclesions related to methylene chloride exposure were confinedto the liver and mammary tissue of rats. An increased incidenceof hepatocellular vacuolization was observed in male and femalerats exposed to 500 ppm methylene chloride. Female rats exposedto 500 ppm methylene chloride also had an increased incidenceof multinucleated hepatocytes and number of spontaneous benignmammary tumors/ tumor-bearing rat (adenomas, fibromas, and fibroadenomaswith no progression toward malignancy); the incidence of benignmammary tumors in female rats exposed to 50 or 200 ppm methylenechloride was comparable to historical control values. No increasein the number of any malignant tumor type was observed in ratsexposed to concentrations as high as 500 ppm methylene chloride.Additional groups of female rats were exposed to 500 ppm methylenechloride for the first 12 months or the last 12 months of the24-month study. The response observed in female rats exposedto 500 ppm for the first 12 months was the same as that observedin female rats exposed to 500 ppm for 2 years. Conversely, theresponse observed in female rats exposed to 500 ppm during thelast 12 months of the study was similar to that observed incontrol animals. Based upon the results of this study, the no-adverse-effectlevel for chronic inhalation exposure of Sprague-Dawley ratswas judged to be 200 ppm methylene chloride.     

Methylene Chloride: A Two-Year Inhalation Toxicity and Oncogenicity Study in Rats and Hamsters

Methylene Chloride: A Two-Year Inhalation Toxicity and OncogenicityStudy in Rats and Hamsters. BUREK, J. D., NITSCHKE, K. D., BELL,T. J., WACKERLE, D. L., CHILDS, R. C., BEYER, J. E., DITTENBER,D. A., RAMPY, L. W., AND MCKENNA, M. J. (1984). Fundam. Appl.Toxicol. 4, 30–47. A long-term study was conducted todetermine the possible chronic toxicity and oncogenicity ofmethylene chloride. Rats and hamsters were exposed by inhalationto 0, 500, 1500, or 3500 ppm of methylene chloride for 6 hrper day, 5 days a week, for 2 years. No exposure-related cytogeneticeffects were present in male or female rats exposed to 500,1500, or 3500 ppm. Females rats exposed to 3500 ppm had an increasedmortality rate while female hamsters exposed to 1500 or 3500ppm had decreased mortality rates. Carboxyhemoglobin valueswere elevated in rats and hamsters exposed to 500, 1500, or3500 ppm with the percentage increase in hamsters greater thanin rats. Minimal histopathologic effects were present in thelivers of rats exposed to 500, 1500, or 3500 ppm. Decreasedamyloidosis was observed in the liver and other organs in hamstersexposed to 500, 1500, or 3500 ppm. While the number of femalerats with a benign tumor was not increased, the total numberof benign mammary tumors was increased in female rats in anexposure-related manner. This effect was also evident in malerats in the 1500- and 3500-ppm exposure groups. Finally, malerats exposed to 1500 or 3500 ppm had an increased number ofsarcomas in the ventral neck region located in or around thesalivary glands. Therefore, in this 2-year study, some effectswere observed in male and female rats exposed to 500, 1500,or 3500 ppm of methylene chloride. In contrast, hamsters exposedto the same exposure concentrations had less extensive spontaneousgeriatric changes, decreased mortality (females), and lackedevidence of definite target organ toxicity.     

Studies on the Chronic Toxicity (Inhalation) of Wollastonite in Fischer 344 Rats

Abstract

Wollastonite is a naturally occurring calcium metasilicate acicular mineral that is used in a variety of commercial applications and has been proposed as an asbestos substitute for selected products. Male Fischer 344 rats were exposed by inhalation to 10 mg/m³ (360 fibers/cm³) wollastonite (NYAD-G) for 6 h/d, 5 d/wk for 12 or 24 mo. They were compared to untreated chamber controls and positive controls [chrysotile asbestos, 70 mg/m³ (-7000 fibers/cm³) for 12 mo]. Six rats from each exposure group were killed after 3, 12, and 24 mo. The remaining rats were held for lifetime observation (until 90% mortality). The results of this study showed that wollastonite was slightly toxic to the lung, producing an alveolar macrophage response that resolved after exposure ceased. There was no evidence of wohstonite-induced neoplasms, although the chrysotile asbestos administered under similar conditions produced a high incidence of bronchoalveolar carcinomas.     

Inhalation Toxicity Study of Formamide in Rats

Formamide is a widely used solvent for the manufacture and processingof plastics, and the possibility for inhalation exposure existsfor workers. To assess the toxicity of repeated inhalation ofsublethal concentrations of formamide, three groups of 10 maleCrl:CD BR rats each were exposed nose-only for 6 hr/day, 5 days/weekfor 2 weeks to design concentrations of 100, 500, or 1500 ppmof formamide vapor in air. A control group of 10 male rats wasexposed simultaneously to air only. At the end of the exposureperiod, blood and urine samples were collected for clinicalanalyses, and 5 rats per group were killed for pathologic examination.The remaining 5 rats per group were retained for a 14-day postexposureobservation (recovery) period and then subjected to the sameclinical and pathologic examinations. Male rats exposed to 1500ppm had significantly depressed body weights and body weightgains during the exposure and recovery periods compared to controls.Clinical pathologic examinations revealed that decreased plateletand/or lymphocyte counts were observed in rats exposed to 500or 1500 ppm of formamide. Pathologic examinations revealed compound-relatedmicroscopic changes in the kidneys of rats exposed to 1500 ppmformamide. Minimal to severe necrosis and regeneration of renaltubular epithelial cells were observed principally in the outerstripe of the outer medulla and in cortical medullary rays.Based upon the hematologic and clinical chemical parametersmeasured, the no-observed-effect exposure concentration forrepeated inhalation of formamide was considered to be 100 ppm,under the conditions of this study. The findings of treatment-relatedmicroscopic lesions in the kidneys as well as increases in meanabsolute kidney weights and kidney-to-body weight ratios reflectthe target organ toxicity.     

Methylene Chloride: Two-Generation Inhalation Reproductive Study in Rats

Methylene Chloride: Two-Generation Inhalation Reproductive Studyin Rats. Nitschke, K. D., Eisenbrandt, D. L., Lomax, L. G.,and Rao, K. S. (1988). Fundam Appl Toxicol. 11, 60–67.Reproductive parameters in Fischer 344 rats were evaluated followinginhalation of methylene chloride (MeCl₂) for two successivegenerations. Thirty male and female rats were exposed to 0,100, 500, or 1500 ppm MeCl₂ for 6 hr/day, 5 days/week for 14weeks and then mated to produce f, litters. After weaning, 30randomly selected f, pups/sex/group were exposed to MeCl₂ for17 weeks and subsequently mated to produce f2 litters. Reproductiveparameters examined included fertility, litter size and neonatalgrowth, and survival. All adults and selected weanlings wereexamined for grossly visible lesions. Tissues from selectedweanlings were examined histopathologically. No adverse effectson reproductive parameters, neonatal survival, or neonatal growthwere noted in animals exposed to methylene chloride in eitherthe f₀ or fE generations. Similarly, there were no treatment-relatedgross pathologic observations in fo or f, adults or f, and f²weanlings. Histopathologic examination of tissues from f, andf² weanlings did not reveal any lesions attributed to methylenechloride. Thus, exposure of rats to concentrations as high as1500 ppm methylene chloride, which has been shown in a 2-yearstudy to produce treatment-related effects, did not affect anyreproductive parameters.     

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.     

Toxicity and Carcinogenicity of Chronic Exposure to Tris(2-chloroethyl)phosphate

Previous short-term studies of tris(2-chloroethyl)phosphate(TRCP), a flame retardant used in industrial and consumer products,demonstrated that repeated administration of 350 mg TRCP/kgbody wt by oral gavage resulted in necrosis of pyramidal neuronsin the CA1 region of the hippocampus of F344 rats, but not inB6C3F₁ mice. The 2-year studies reported here were designedto characterize the chronic toxicity and potential carcinogenicityof TRCP in each sex of F344 rats and B6C3F₁ mice. Groups of60 rats per sex received 0, 44, or 88 mg/kg by oral gavage,once per day, 5 days per week, for up to 103 weeks. Groups of60 mice per sex received 0, 175, or 350 mg/kg by oral gavageon the same dosing schedule. Each of these groups contained10 animals which were euthanized at 66 weeks. The principaltoxic effects of chronic exposure of rats to TRCP occurred inthe brain and kidney. In contrast to the findings in the 16-weekstudies, a hippocampal lesion was not observed in the brain,although degenerative lesions were widely distributed in thegray and white matter of the brain stem and cerebral cortexof high-dose female and, to a lesser extent, male rats. Thesefindings suggest that the hippocampal necrosis may be dependentupon the size of the individual doses or may have a pathogenesisdifferent from that of the lesions in the brain stem and cerebralcortex. The other primary effect of chronic exposure was a dose-dependentincreased incidence of renal tubule hyperplasia and adenoma.Renal tubule neoplasms, primarily adenomas, were observed in4% of control, 10% of low-dose, and 50% of high-dose male ratsand in 0% of control, 4% of low-dose, and 10% of high-dose femalerats. There were also marginal increases in mononuclear cellleukemia and in thyroid follicular neoplasms in dosed male andfemale rats that were not clearly related to TRCP administration.Mice were less sensitive to TRCP than rats and lesions attributableto chemical administration in mice were limited to a dose-dependentincreased incidence of karyomegaly (nuclear enlargement) inepithelial cells of proximal tubules in the inner cortex andouter stripe of the outer medulla of the kidneys both sexes.Marginal increases in the incidence of renal tubule neoplasmsin male mice and harderian gland neoplasms in female mice werenot considered clearly related to TRCP administration.     

Inhalation Toxicity of Methylglutaronitrile in Rats

Abstract

Methylglutaronitrile (MGN) is a high-boiling (263°C) solvent/intermediate used in the fiber industry. Twenty male rats per group were exposed nose-only to condensation aerosol/vapor concentrations of approximately either 5, 25, or 200 mg/m³ of MGN for 6 h/day, 5 days/week over a 4-week period. Ten rats/group were sacrificed one day after the final exposure and the remaining rats after a four-week recovery period. No effects were observed in clinical observations during the exposure period, but body-weight depression was observed in the 200 mg/m³ group. The 200 mg/m³ group showed minimal decreases in red blood cell count, hemoglobin, and hematocrit values accompanied by increases in reticulocytes. There were no other effects observed in clinical or pathologic evaluations in the study. A neurobehavioral battery of tests (including grip strength, functional observational battery, and motor activity tests) given at the end of the exposure and recovery periods showed no MGN effects. During the 4-week recovery, body weights in the 200 mg/m³ group returned to normal and the hematologic findings in all groups were normal. Based on the above findings of body weight depression at 200 mg/m³, the no-observed-adverse-effect level (NOAEL) for this study was considered to be 25 mg/m³.     

Chronic Toxicity/Oncogenicity of Dimethylformamide in Rats and Mice Following Inhalation Exposure

The potential chronic toxicity and oncogenicity of dimethylformamide(DMF) was evaluated by exposing male and female rats and miceto 0, 25, 100, or 400 ppm DMF for 6 hr/day, 5 days/week for18 months (mice) or 2 years (rats). Clinical pathology was evaluatedat 3, 6, 12, 18, and 24 (rats only) months. An interim euthanasiafor rats occurred at 12 months and hepatic cell proliferationin rats and mice was examined at 2 weeks, 3 months, and 12 months.No compound-related effects on clinical observations or survivalwere observed. Body weights of rats exposed to 100 (males only)and 400 ppm were reduced. Conversely, body weights were increasedin 400 ppm mice. No hematologic changes were observed in eitherspecies. Serum sorbitol dehydrogenase activity was increasedin rats exposed to 100 or 400 ppm. There were no compound-relatedeffects on the estrous cycle of rats or mice at any concentration.Compound-related morphological changes were observed only inthe liver. In rats, exposure to 100 and 400 ppm produced increasedrelative liver weights, centrilobular hepatocellular hypertrophy,lipofuscin/hemosiderin accumulation in Kupifer cells, and centrilobularsingle cell necrosis (400 ppm only). In mice, increased liverweights (100 ppm males, 400 ppm both sexes), centrilobular hepatocellularhypertrophy, accumulation of lipofuscin/hemosiderin in Kupffercells, and centrilobular single cell necrosis were observedin all exposure groups. These observations occurred in a dose-responsefashion and were minimal at 25 ppm. No increase in hepatic cellproliferation was seen in mice or female rats. Slightly higherproliferation was seen in male rats exposed to 400 ppm at 2weeks and 3 months but not at 12 months. Dimethylformamide wasnot oncogenic under these experimental conditions in eitherthe rat or mouse.     

Evaluation of the Inhalation Toxicity of Diethylethanolamine (DEEA) in Rats

Diethylethanolamine (DEEA), an industrial anticorrosive additive,was evaluated in rats for its potential toxicity. A 2-week inhalationexposure to 10 ppm revealed no signs of toxicity. At 56 ppm,rats exhibited signs of nasal irritation and corneal opacities.Significant mortality (males, 90% females, 50%) occurred at301 ppm. Histopathology revealed inflammatory cell infiltrationsof the nasal turbinate mucosa and squamous metaplasia afterexposure to 56 ppm. In the 14-week subchronic study, rats wereexposed to 0, 11, 25, or 76 ppm. During exposure to DEEA, transientsigns of mild to moderate respiratory irritation (noises orrales) were observed with a frequency and severity that wasdose dependent. These signs usually cleared within 1 hr post-exposure.However, at 76 ppm some rats continued to exhibit these respiratorysigns overnight. There were no significant DEEA-induced changesin either blood chemistry or neurobehavioral parameters. Nasalcavities of rats exposed to 25 or 76 ppm revealed evidence ofinflammatory cell infiltration, focal hyperplasia, and squamousmetaplasia in the respiratory epithelium of the anterior nasalturbinates. Hypertrophic goblet cells, focal necrosis, and exudatein the nasal lumen were also seen at 76 ppm. DEEA vapors failedto produce persistent ocular or respiratory tract toxicity below26 ppm. The no-observed-effect-level in this study was 10 ppm.     

Chronic Toxicity/Oncogenicity of Dimethylacetamide in Rats and Mice Following Inhalation Exposure

The potential chronic toxicity and oncogenicity of dimethylacetamide(DMAC) was evaluated by exposing male and female rats and miceto 0, 25, 100, or 350 ppm DMAC for 6 hr/day, 5 days/week for18 months (mice) or 2 years (rats). Clinical pathology was evaluatedat 3, 6, 12, 18, and 24 (rats only) months. An interim euthanizationfor rats occurred at 12 months and hepatic cell proliferationin rats and mice was examined at 2 weeks and 3 and 12 months.No compound-related effects on survival were observed. Ratsexposed to 350 ppm had lower body weight and/or body weightgain. There were no compound-related effects on body weightor weight gain in mice at any concentration. There were no compound-relatedadverse effects on the incidence of clinical signs of toxicityin rats or mice. No hematologic changes were observed in eitherspecies. Serum sorbitol dehydrogenase activity was increasedin rats exposed to 350 ppm. Serum cholesterol and glucose concentrationswere significantly higher in 100 and 350 ppm female rats. Compound-relatedmorphological changes were observed in the liver. In rats, exposureto 100 or 350 ppm produced increased absolute and/or relativeliver weights, hepatic focal cystic degeneration, hepatic peliosis,biliary hyperplasia (350 ppm only), and lipofuscin/hemosiderinaccumulation in Kupffer cells. In mice, exposure to 100 or 350ppm produced increased absolute and relative liver weights (350ppm females only), accumulation of lipofuscin/hemosiderin inKupifer cells, and centrilobular single cell necrosis. Malerats exposed to 350 ppm also had significantly higher absoluteand relative kidney weights which correlated with the grossand microscopic changes resulting from a compound-related increasein severity of chronic progressive nephropathy. Female miceexposed to 350 ppm had an increased incidence of bilateral,diffuse retinal atrophy. No increase in hepatic cell proliferationwas seen in mice or rats at any exposure concentration. DMACwas not oncogenic under these experimental conditions in eitherthe rat or mouse. The NOAEL for male and female rats and miceis 25 ppm.     

Inhalation Toxicity of Cyclododecatriene in Rats

ABSTRACT

Cyclododecatriene (CDDT, CAS No. 4904-61-4) was tested for its inhalation toxicity in rats following repeated exposures. Male rats were exposed nose-only to CDDT for 6 hr/day, 5 days/wk for a total of 9 exposures over 2 weeks. Particular attention was paid to neurotoxicologic endpoints. Concentrations of 0 (control), 5, 50, and 260 ppm were studied. The 260 ppm chamber contained both vapor and aerosol while the 5 and 50 ppm chambers were vapor only. Four groups of 10 rats each were used to measure standard clinical signs and growth, clinical pathology (including hematology, biochemistries, and urine analysis), and tissue pathology. Another 4 groups of similar size were used for neurotoxicity testing. In the standard toxicity groups, 1/2 of the rats were sacrificed 1 day following the 9th exposure; the other half underwent a 2-week recovery period prior to being sacrificed (recovery group). During the exposures rats inhaling 260 ppm had a diminished or absent response to an alerting stimulus. Irregular respiration and lethargy were observed in these rats immediately following exposure. These signs were rapidly reversible and were not seen prior to the subsequent exposure. Body weights in rats exposed to either 50 or 260 ppm were significantly lower than the corresponding controls. No compound-related clinical pathology changes were seen in any of the test groups and tissue pathology effects only occurred in the nasal tissue. In rats exposed to 260 ppm, minimal degeneration/necrosis of nasal olfactory epithelium was observed in rats examined immediately following the exposure period. This change was not seen in the recovery rats. Functional observational battery (FOB) assessments and motor activity (MA) evaluations conducted after the 4th and 9th exposures on rats from all test groups, and specific neuropathologic evaluation on perfused brain, spinal cord, and skeletal muscle from rats exposed to 260 ppm failed to demonstrate any specific neurotoxicity. Outward signs of sedation were seen at the top level tested. Under the conditions of this test, the no-observed-adverse-effect level (NOAEL) was determined to be 5 ppm based upon a reduced rate of body weight gain in the 50 ppm group. No specific neurotoxicity was detected and the histopathologic response was limited to reversible changes in the nasal epithelia in rats exposed to 260 ppm.     

Two-Year Inhalation Toxicity Study in Rats with Hydrochlorofluorocarbon 123

The potential chronic toxicity and oncogenicity of hydrochlo-rofluorocarbon123 (HCFC-123) was evaluated by exposing male and female ratsto 0, 300, 1000, or 5000 ppm HCFC-123 for 6 hr/day, 5 days/week,for 2 years. Clinical pathology was evaluated at 6, 12, 18,and 24 months. An interim termination and measurements of hepaticcell proliferation and beta-oxidation activity were conductedat 12 months. The terminal euthani-zation occurred at 24 months.Males and females exposed to 5000 ppm and females exposed to300 or 1000 ppm had lower body weights and body weight gains.Serum triglyceride and glucose concentrations were significantlydecreased at all exposure concentrations in both sexes. Serumcholesterol was also lower in 300, 1000, and 5000 ppm femalesand in 5000 ppm males. Alterations in serum protein concentrationsoccurred at 300, 1000, and 5000 ppm. Survival was higher in1000 and 5000 ppm males and females. At 24 months, increasedrelative liver weight occurred in 5000 ppm males, and decreasedabsolute kidney weight occurred in 5000 ppm males and in 1000and 5000 ppm females. Benign hepatocellular adenomas were increasedin 5000 ppm males and in all test groups of females. Hepaticcholangiofibromas were also increased in 5000 ppm females. Pancreaticacinar cell adenomas were increased in all test groups of males,and acinar cell hyperplasia was increased in the 1000 and 5000ppm males and females. Benign testicular interstitial adenomasand focal interstitial cell hyperplasia were also increasedin all male test groups compared to controls. Diffuse retinalatrophy was increased in all male and female test groups, butit was considered to be an indirect compound-related effect.Hepatic beta-oxidation activity (peroxisome proliferation) washigher in 300, 1000 and 5000 ppm males and 1000 and 5000 ppmfemales. Compound-related differences in the rate of hepaticcell proliferation were not observed at any exposure concentration.Decreased incidences of a variety of age-related lesions occurredat 1000 and 5000 ppm.