Time- and concentration-dependent genomic responses of the rat airway to inhaled nickel sulfate

While insoluble nickel subsulfide (Ni3 S2 ) was carcinogenic in the lung in a 2-year rat bioassay, soluble nickel sulfate hexahydrate (NiSO4* 6H2 O) was not. To investigate whether differences in the cellular responses to these two nickel compounds could underlie their differential activities, we conducted parallel studies to determine the gene expression changes in micro-dissected lung distal airway cells from Fischer 344 rats following inhalation of the two compounds for one and four weeks (6 hr per day, 5 days per week). The results of the Ni3 S2 study have been reported previously; this paper reports the results for NiSO4 and provides a comparative analysis. The cellular responses to NiSO4 were highly similar to those previously reported for Ni3 S2 , and a set of genes was identified whose expression could be used as biomarkers for comparing cellular nickel effects from in vitro or in vivo studies with soluble NiSO4 and particulate Ni3 S2 . Evaluation of the genomic concentration-responses for the two compounds suggests that the highest inhaled concentration in the tumor bioassay for NiSO4 , which was limited by toxicity, may not have achieved the Ni concentrations at which tumors were observed in the Ni3 S2 bioassay. However, several key differences in the immune responses to NiSO4 and Ni3 S2 were identified that may result from the differential intracellular disposition of Ni from NiSO4 entering the cell as an ion rather than as a slowly soluble Ni3 S2 particle. These differences may also contribute to the observation of tumors in the bioassay for Ni3 S2 but not NiSO4 . Environ. Mol. Mutagen. 58:607-618, 2017. © 2017 The Authors Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Transcriptional responses in the rat nasal epithelium following subchronic inhalation of naphthalene vapor

Male and female Fischer 344 rats were exposed to naphthalene vapors at 0 (controls), 0.1, 1, 10, and 30ppm for 6h/d, 5 d/wk, over a 90-day period. Following exposure, the respiratory epithelium and olfactory epithelium from the nasal cavity were dissected separately, RNA was isolated, and gene expression microarray analysis was conducted. Only a few significant gene expression changes were observed in the olfactory or respiratory epithelium of either gender at the lowest concentration (0.1ppm). At the 1.0ppm concentration there was limited evidence of an oxidative stress response in the respiratory epithelium, but not in the olfactory epithelium. In contrast, a large number of significantly enriched cellular pathway responses were observed in both tissues at the two highest concentrations (10 and 30ppm, which correspond to tumorigenic concentrations in the NTP bioassay). The nature of these responses supports a mode of action involving oxidative stress, inflammation and proliferation. These results are consistent with a dose-dependent transition in the mode of action for naphthalene toxicity/carcinogenicity between 1.0 and 10ppm in the rat. In the female olfactory epithelium (the gender/site with the highest incidences of neuroblastomas in the NTP bioassay), the lowest concentration at which any signaling pathway was significantly affected, as characterized by the median pathway benchmark dose (BMD) or its 95% lower bound (BMDL) was 6.0 or 3.7ppm, respectively, while the lowest female olfactory BMD values for pathways related to glutathione homeostasis, inflammation, and proliferation were 16.1, 11.1, and 8.4ppm, respectively. In the male respiratory epithelium (the gender/site with the highest incidences of adenomas in the NTP bioassay), the lowest pathway BMD and BMDL were 0.4 and 0.3ppm, respectively, and the lowest male respiratory BMD values for pathways related to glutathione homeostasis, inflammation, and proliferation were 0.5, 0.7, and 0.9ppm, respectively. Using a published physiologically based pharmacokinetic (PBPK) model to estimate target tissue dose relevant to the proposed mode of action (total naphthalene metabolism per gram nasal tissue), the lowest transcriptional BMDLs from this analysis equate to human continuous naphthalene exposure at approximately 0.3ppm. It is unlikely that significant effects of naphthalene or its metabolites will occur at exposures below this concentration.

Time- and concentration-dependent genomic responses of the rat airway to inhaled nickel subsulfide

OBJECTIVE

To provide insights into the mode of action for Ni3S2 lung carcinogenicity by examining gene expression changes in target cells after inhalation exposure.

METHODS

Gene expression changes were determined in micro-dissected lung broncho-alveolar cells from Fischer 344 rats following inhalation of Ni3S2 at 0.0, 0.04, 0.08, 0.15, and 0.60 mg/m(3) (0.03, 0.06, 0.11, and 0.44 mgNi/m(3)) for one and four weeks (6h/day, 5 days/week).

RESULTS

Broncho-alveolar lavage fluid evaluation and lung histopathology provided evidence of inflammation only at the two highest concentrations, which were similar to those tested in the 2-year bioassay. The number of statistically significant up- and down-regulated genes decreased markedly from one to four weeks of exposure, suggesting adaptation. Cell signal pathway enrichment at both time-points primarily reflected responses to toxicity, including inflammatory and proliferative signaling. While proliferative signaling was up-regulated at both time points, some inflammatory signaling reversed from down-regulation at 1 week to up-regulation at 4 weeks.

CONCLUSIONS

These results support a mode of action for Ni3S2 carcinogenicity driven by chronic toxicity, inflammation and proliferation, leading to mis-replication, rather than by direct genotoxicity. Benchmark dose (BMD) analysis identified the lowest pathway transcriptional BMD exposure concentration as 0.026 mgNi/m(3), for apoptosis/survival signaling. When conducted on the basis of lung Ni concentration the lowest pathway BMD was 0.64 μgNi/g lung, for immune/inflammatory signaling.

IMPLICATIONS

These highly conservative BMDs could be used to derive a point of departure in a nonlinear risk assessment for Ni3S2 toxicity and carcinogenicity.

Acute, 2-week, and 13-week inhalation toxicity studies on dimethylethoxysilane vapor in Fischer 344 rats

Dimethylethoxysilane (DMES), a volatile liquid, is used by NASA to waterproof the heat-protective silica tiles and blankets on the Space Shuttle. Acute, 2-wk, and 13-wk inhalation exposures to DMES vapor were conducted in male and female Fischer 344 rats. In the acute study, rats were exposed to 4000, 2000, 1000, 500, or 0 (control) ppm DMES for 4 h and observed for 14 days. There were no deaths. Narcosis and ataxia were observed in rats of the two highest concentrations only. These signs disappeared within 1 h following exposure. There were no DMES-related gross or microscopic tissue lesions in rats of all exposure groups. In the 2-wk study, rats were exposed for 6 h/day, 5 days/wk to 3000, 1000, 300, 100, or 0 ppm DMES. During exposure, narcosis was observed in rats of the 3000 and 1000 ppm groups. There was a mild decrease in body weight gain in rats of the 3000 ppm group. A decrease in platelet count, an increase in bile acids, and reduced weights of the thymus, testis, and liver were observed in rats of the 3000 ppm group. Microscopically, hypospermatogenesis and spermatid giant cells were observed in the seminiferous tubules of the testes of rats exposed to 3000 ppm DMES. In the 13-wk study, rats were exposed 6 h/day, 5 days/wk to 2000, 600, 160, 40, or 0 ppm DMES. During exposure, rats of the 2000 ppm group exhibited mild narcosis and loss of startle reflex. Recovery from these central nervous system signs was rapid. Body weights were mildly decreased for rats of the 2000 ppm group. There were no exposure-related effects in hematology, serum chemistry, or urinalysis. Female rats of the 2000 ppm group had delayed estrous cycles (6 days compared to 5 days in control rats). Noteworthy organ weight changes in rats of the 2000 ppm group included decreases in thymus, liver, and testicular weights; however, pathologic lesions were observed in the testes only. Sperm motility, epididymal sperm count, and testicular spermatid count were dramatically reduced. Microscopic lesions included degeneration of the seminiferous tubular cells, pyknosis or absence of germ cells, and hypospermia in the epididymis. Rats of the 600 ppm group had a slight decrease in thymic weight and a transient decrease in body weight. Results of the acute, 2-wk, and 13-wk inhalation studies indicate DMES concentrations of 1000 ppm and higher produce narcosis that rapidly disappears following exposure. Repeated exposure of rats to DMES at either 3000 ppm for 2 wk or 2000 ppm for 13 wk caused testicular atrophy and hypospermia in male rats. Female rats exposed to 2000 ppm for 13 wk had delayed estrous cycles. Toxicological effects in rats of the 600 ppm group were minimal and equivocal. The 160 ppm concentration was a no-observable-effect level (NOEL) for 13 wk of exposure to DMES.

A 90-day drinking water toxicity study in rats of the environmental contaminant ammonium perchlorate

Perchlorate (ClO(4)(-)), the dissociated anion of perchlorate salts such as ammonium, potassium, and sodium perchlorate, has been recently recognized as a persistent and pervasive contaminant of drinking water supplies in a number of metropolitan areas. Perchlorate is of concern because of uncertainties in the toxicological database available to address the potential human health effects of low-level exposure. The purpose of this study was to evaluate the subchronic toxicity of perchlorate when administered to Sprague-Dawley rats as ammonium perchlorate (AP) for 14 or 90 days. The study consisted of an untreated control group and five treatment groups that received continuous exposure to AP via the drinking water at dosage levels of 0.01, 0.05, 0.2, 1.0, and 10.0 mg/kg/day. The study design included a nontreatment recovery period of 30 days to evaluate the reversibility of any AP-induced effects at the 0.05, 1.0, and 10.0 mg/kg/day levels. The study also investigated the potential effects of AP on male sperm parameters, female estrous cyclicity, bone marrow micronucleus formation, and serum hormone levels, i.e., triiodothyronine (T(3)), thyroxine (T(4)), and thyroid stimulating hormone (TSH). No toxicologically meaningful differences were observed between the control and AP-treated groups with respect to survival, clinical observations, body weights, food consumption, water consumption, ophthalmology, hematology, clinical chemistry, estrous cycling, sperm parameters, or bone marrow micronucleus formation. A target organ effect was produced by AP in the thyroids of male and female rats at the 10 mg/kg/day level after 14 and 90 days of exposure. The effect was characterized by significantly increased thyroid weights and thyroid histopathology consisting primarily of follicular cell hypertrophy with microfollicle formation and colloid depletion. These changes were reversible after a nontreatment recovery period of 30 days. Statistically significant changes in TSH and thyroid hormones were observed at all AP dosage levels tested; however, no thyroid organ weight or histopathological effects were observed at AP dosage levels < or = 1.0 mg/kg/day. In the absence of thyroid organ weight and histopathological effects, the toxicological significance of TSH and thyroid hormone changes at AP dosage levels < or = 1.0 mg/kg/day remains to be determined.

Developmental toxicity evaluation of inhaled toluene diisocyanate vapor in CD rats

Mated female CD (Sprague-Dawley) rats, 25/group, were exposed to toluene diisocyanate (TDI) vapor, for six h/day on gestational days (gd) 6 through 15, at 0.00, 0.02, 0.10, or 0.50 p.p.m.. Maternal clinical signs, body weights, and feed and water consumption were recorded throughout gestation. At termination (gd 21), maternal body, gravid uterine, and liver weights were recorded. Corpora lutea were counted, and implantation sites were identified: resorptions and dead and live fetuses. All live fetuses were examined for external alterations. One-half of the live fetuses/litter were examined for visceral (including craniofacial) alterations. The remaining intact fetuses/litter were stained with alizarin red S and examined for ossified skeletal alterations. Maternal toxicity at 0.50 ppm consisted of reduced body weights, body weight gains, feed consumption, and clinical signs of toxicity. Water consumption was unaffected. Gestational parameters exhibited no significant treatment-related changes, including pre- and postimplantation loss, sex ratio/litter, or fetal body weights/litter. Incidences of individual malformations, malformations by category (external, visceral, and skeletal), total malformations, individual external and visceral variations, variations by category, and total variations were unaffected. Of 111 skeletal variants observed, only 1, incidence of poorly ossified cervical centrum 5, was increased at 0.50 ppm, indicating possible minimal fetotoxicity, although it occurred in the absence of any other indications of developmental toxicity. Therefore, exposure to TDI vapor by inhalation, during major organogenesis in CD rats, resulted in maternal toxicity and minimal fetotoxicity at 0.50 ppm no observed adverse effect level (NOAEL) for maternal and developmental toxicity was 0.10 ppm. No treatment-related embryotoxicity or teratogenicity was observed.

Two-generation reproductive toxicity study of inhaled toluene diisocyanate vapor in CD rats

Twenty-eight 42-day-old pups/sex/group (F0) were exposed to toluene diisocyanate vapor (TDI; 80% 2,4-TDI, 20% 2,6-TDI) by inhalation at 0.0, 0.02, 0.08, or 0.3 ppm, 6 h/day, 5 days/week, for 10 weeks, then mated within groups for 3 weeks, with exposure 7 days/week during mating, gestation, and lactation. F0 maternal animals were not exposed from gestational day (gd) 20 through postnatal day (pnd) 4; maternal exposures resumed on pnd 5. Twenty-eight weanlings/sex/group continued exposure for 12 weeks (starting on pnd 28) and were bred as described above. F0 and F1 parents and ten F1 and F2 weanlings/sex/group were necropsied, and adult reproductive organs, pituitary, liver, kidneys, and upper respiratory tract (target organs) were evaluated histologically in ten/sex/group. Adult toxicity was observed in both sexes and generations at 0.08 and 0.3 ppm, including occasional reductions in body weights and weight gain, clinical signs of toxicity at 0.08 and 0.3 ppm, and histologic changes in the nasal cavities at 0.02, 0.08, and 0.3 ppm (including rhinitis, a nonspecific response to an irritating vapor, at all concentrations). There was no reproductive toxicity, reproductive organ pathology, or effect on gestation or lactation at any exposure concentration. Postnatal toxicity and reduced body weights and weight gains during lactation occurred only in F2 litters at 0.08 and 0.3 ppm. Therefore, under the conditions of this study, a no observed adverse effect level (NOAEL) was not determined for adult toxicity; the NOAEL for reproductive toxicity was at least 0.3 ppm, and the NOAEL for postnatal toxicity was 0.02 ppm.

Reproductive toxicity screen of trifluoroiodomethane (CF(3)I) in Sprague-Dawley rats

CF(3)I is being considered by the U.S. Air Force as a replacement for Halon 1301 for fire-extinguishing requirements in unoccupied spaces. The purpose of this study was to determine and evaluate the potential for CF(3)I to produce reproductive toxicity and to provide additional information on the effect of CF(3)I exposure on the thyroid. Groups of 16 male and 16 female rats were exposed (6 h/day) to CF(3)I vapor at concentrations of 0 (control), 0.2, 0.7, and 2.0% using whole-body inhalation chambers. Prior to mating, rats were exposed to CF(3)I for 4 wk (5 days/wk). Exposures were 7 days/wk during the periods of mating (2 wk), gestation (3 wk), and lactation (3 wk). First-generation pups were not exposed to CF(3)I vapor. In parental animals, there were no clinical signs of toxicity except for a minimal decrease in mean body weight in female rats at 2.0% CF(3)I. At necropsy, gross findings, mean serum chemistry levels, mean hematology values, mean bone marrow micronuclei scores, and mean organ weights were similar for all exposure groups, including the air control group. Statistically significant differences did not show a pattern and/or were considered incidental. There were no treatment-related microscopic tissue findings, including the thyroid organ. Analysis of reproductive indices and parameters indicates CF(3)I is not a reproductive toxicant. Results of serum thyroid hormone levels (e.g., T(3), T(4), rT(3), and TSH), showed concentration-related increases in TSH, T(4), and rT(3). T(3) levels were decreased. First-generation pup survival and mean body weights were similar in all exposure groups, including the control. Exposure of 2.0% CF(3)I vapor for approximately 14 wk produced minimal general toxicity and no reproductive toxicity in Sprague-Dawley rats. On the basis of reproductive indices and parameters, the NOAEL for this study is 2.0% CF(3)I.

Cardiac sensitization testing of the halon replacement candidates trifluoroiodomethane (CF3I) and 1,1,2,2,3,3,3-heptafluoro-1-iodopropane (C3F7I)

Trifluoroiodomethane (CF3I) and 1,1,2,2,3,3,3-heptafluoro-1-iodopropane (C3F7I) have been considered as replacement candidates for halon fire suppressants due to their excellent fire extinguishant capabilities and low ozone depletion potential compared to halon fire extinguishants in use currently. As part of the process to develop environmental and health effects criteria for halon substitutes, a cardiac sensitization test was conducted in beagle dogs. Cardiac sensitization to adrenaline is a phenomenon associated with the inhalation of a number of unsubstituted and halogenated hydrocarbons. Adrenaline was administered by intravenous injection before and during inhalation of the test substance. CF3I was administered to dogs at concentrations in air of 0.1, 0.2, 0.4 or 1% v/v. At each of 0.4 and 1.0% CF3I, the first dog exposed developed fatal ventricular fibrillation, and no further dogs were exposed at these concentrations. There was no cardiac sensitization at 0.1 or 0.2% CF3I. For the C3F7I experiment, dogs were exposed to concentrations in air of 0.1, 0.2 or 0.4% v/v. At each of 0.1 and 0.4% C3F7I, one dog responded with multifocal ventricular ectopic beats. Thus, CF3I and C3F7I are potent cardiac sensitizers in the adrenaline-challenged dog model.

Short-term and subchronic repeated exposure studies with 5-ethylidene-2-norbornene vapor in the rat

5-Ethylidene-2-norbornene (ENB) is an industrial chemical whose physical properties indicate a likelihood for vapor exposure to humans. The potential for target organ or cumulative toxicity was investigated in rats exposed for 6 h per day for 9 days over an 11-day period, or 66 or 67 days over 14 weeks; 4- week recovery animals were added to the 14-week study. Mean analytically measured ENB vapor concentrations (+/-SD) were 52 +/- 1.5, 148 +/- 2.3 and 359 +/- 4.2 ppm for the 9-day study and 4.9 +/- 0.14, 24.8 +/- 1.23 and 149 +/- 4.40 ppm for the subchronic study. There were no mortalities, and clinical signs were limited to periocular swelling and/or encrustation, and urogenital area wetness. Body weight gain was decreased in the 9-day 359 ppm females and in the subchronic 24.8 and 149 ppm males. A minimal macrocytic anemia was present in subchronically exposed males, which resolved during the recovery period. In the 9-day study increased liver weight was associated with minimal centrilobular hepatocytomegaly and cytoplasmic basophilia with no degenerative or serum biochemical liver function changes, suggesting an adaptive response. Only relative liver weights were increased in the subchronic 149 ppm males, and no histopathological findings were observed. Principal target organ effects were to the thyroid gland, which showed an exposure concentration-related, but not exposure time-related, depletion of follicular colloid that resolved during the recovery period, together with light microscopic evidence for a hypertrophic and hyperplastic response in the follicular epithelium that resolved more slowly. The thyroid colloid depletion was a graded effect without a clear no-effect concentration, but was not accompanied by any clinical or clear biochemical evidence for thyroid dysfunction. A no-effect concentration of 4.9 ppm was established for the follicular cytological effects.

Evaluation of 13-week inhalation toxicity study on methyl t-butyl ether (MTBE) in Fischer 344 rats

Methyl-t-butyl ether (MTBE) is widely used as an octane enhancing agent in gasoline. A 13-week inhalation study was conducted in Fischer 344 rats to provide information on potential target organs and toxicity of MTBE, and to ascertain a no-observed-adverse-effect level (NOAEL) for MTBE. Male and female Fischer 344 rats were exposed to target doses of MTBE vapor of 0, 800, 4000 and 8000 ppm for 6 h a day, 5 days per week for 13 weeks: MTBE produced no mortalities. At 8000 ppm, males and females showed a decrease in body weights compared to controls. The only notable effect on clinical observation was ataxia at 8000 ppm, which was apparent during the first 4 weeks of treatment. Mild hematological and clinical chemistry changes were observed in the 8000 ppm group. At 8000 ppm, animals showed increased serum levels of corticosteroids, which suggest some stress-like effect. At necropsy, there were no treatment-related gross lesions. Absolute and relative organ weights (liver, adrenals and kidneys) were increased in both sexes at 4000 and 8000 ppm, but there were no microscopic lesions in these tissues with the exception of the kidney. Microscopic examination of other tissues revealed no effects with the exception that at 8000 ppm, male rats showed: mild increased size of hyaline droplets within the kidney, mild increase in hemosiderosis in the spleen and higher incidence of hyperplasia in the lymph nodes. The highest NOAEL was judged at 800 ppm.

Acute and subchronic inhalation studies on trifluoroiodomethane vapor in Fischer 344 rats

Trifluoroiodomethane (CF3I) is being considered as a replacement compound for halon fire suppressants. Its structure is similar to that of Halon 1301 (CF3Br), but it has very low ozone depletion potential compared to CF3Br. As part of the process of developing environmental and health effects criteria, acute, 2-week, and 13-week nose-only inhalation toxicity studies were conducted in Fischer 344 rats. In the acute study, three groups of 30 male rats each were exposed to 0 (control), 0.5, or 1.0% (v/v) CF3I for 4 hr and euthanized immediately following exposure, 3 days postexposure, or 14 days postexposure. There were no deaths and no clinical signs of toxicity throughout the study. Histopathologic examination of select tissues showed no lesions of pathologic significance. In the 2-week study, four groups of 5 male rats each were exposed for 2 hr/day, 5 days/week to 0, 3, 6, or 12% CF3I. No deaths were observed, though lethargy and slight incoordination were noted in rats of the 6 and 12% groups at the conclusion of each daily exposure. Mean body weight gains were depressed in rats of the 6 and 12% groups. Serum thyroglobulin and reverse T3 (rT3) values were increased at all exposure levels. At necropsy, no gross lesions or differences in absolute or relative organ weights were noted. Histopathologic examination of the thyroid and parathyroid glands indicated no morphological abnormalities in the CF3I-exposed rats. In the 13-week study, four groups of 15 male and 15 female rats were exposed to 0, 2, 4, or 8% CF3I 2 hr/day, 5 days/week for 13 weeks. Rats exposed to 4 or 8% CF3I had lower mean body weights than the controls. Deaths observed in the 2 and 8% groups were attributed to accidents resulting from the restraint system employed. Hematologic alterations were minimal and considered insignificant. Increases in the frequency of micronucleated bone marrow polychromatic erythrocytes were observed in rats of all three CF3I groups. Serum chemistry alterations observed in rats of all CF3I exposure groups included decreases in T3 and increases in thyroglobulin, rT3, T4, and TSH. Relative organ weight increases (8% CF3I group) occurred in the brain, liver, and thyroid glands; decreases were observed in the thymus and testes. A decrease in relative thymus weights and an increase in relative thyroid weights were observed also in rats of the 2 and 4% groups. Histopathological findings included a mild inflammation in the nasal turbinates of rats exposed to 4 or 8% CF3I, mild atrophy and degeneration of the testes (4 and 8% CF3I groups), and a mild increase in thyroid follicular colloid content in rats of all CF3I exposure groups. Though NOAELs were observed for select target organs (e.g., nasal turbinates, testes), NOAELs were not apparent in all target organs examined (e.g., thyroid glands, bone marrow).

Central neurotoxicity induced by subchronic exposure to 2,4-pentanedione vapour

1. Male and female Fischer 344 rats were exposed to 2,4-pentanedione (2,4-PD) vapour acutely (4 h) at 1265 or 1811 ppm, or for 6 h day-1, 5 days a week for 14 weeks to 0, 101, 307 or 650 ppm. 2. Mortality occurred during or within a few hours of the acute exposures (10% at 1265 ppm; 70% at 1811 ppm). No animal had gross or microscopic brain lesions. 3. All female rats (20) and 10 of 30 male rats exposed to 650 ppm 2,4-PD vapour died by the 38th study day (29 exposures); there were no subsequent male deaths. Twenty-five of the 30 animals that died, and seven of the 15 males that survived, had light microscopical evidence of degenerative lesions, principally within the caudate/putamen nuclei, nuclei of the cerebellar medulla, and vestibular nuclei. Less frequently involved, in animals that died, were various regions of the cerebral cortex. The early histopathological lesions, seen from the 16th study day (12 exposures) to the 38th study day (28 exposures) were characterised by malacia. When present, lesions in male rats surviving the 14-weeks of 650 ppm 2, 4-PD exposure were characterised by malacia and gliosis. No peripheral nerve lesions were seen by light or transmission electron microscopy. 4. Neither mortality nor neuropathology were seen in rats subchronically exposed to 101 or 307 ppm, 2,4-PD vapour.

Evaluation of the developmental toxicity of ethylene glycol aerosol in CD-1 mice by nose-only exposure

Ethylene glycol (EG; CAS No. 107-21-1) is teratogenic to mice by whole-body (WB) exposure to aerosol (1000-2500 mg/m3). The WB results were confounded by possible exposure from ingestion after grooming and/or from percutaneous absorption. Therefore, CD-1 mice were exposed to EG aerosol (MMAD 2.6 +/- 1.7 microns) on Gestational Days (GD) 6 through 15, 6 hr/day, by nose-only (NO) (0, 500, 1000, or 2500 mg/m3) or WB exposures (0 or 2100 mg/m3, as positive control), 30/group. Five additional "satellite" females each at 2500 mg/m3 NO and 2100 mg/m3 WB were exposed on GD 6 for measurement of EG on fur. Control environments were water aerosol (4200 mg/m3 for NO; 2700 mg/m3 for WB). Females were weighed and evaluated for clinical signs and water consumption throughout gestation. On GD 18, maternal uterus, liver, and kidneys (2) were weighed, with kidneys examined microscopically. Corpora lutea and implantation sites were recorded. Live fetuses were weighed, sexed, and examined for structural alterations. For NO dams, kidney weights were increased at 1000 and 2500 mg/m3; no renal lesions and no other treatment-related maternal toxicity were observed. There were no effects on pre- or postimplantation loss; fetal body weights/litter were reduced at 2500 mg/m3. At 2500 mg/m3, incidences of fused ribs and skeletal variations were increased. The 2500 mg/m3 NO satellite animals had approximately 330 mg/kg extractable EG. The WB group exhibited maternal and developmental toxicity including increased fetal skeletal malformations and variations, confirming previous results, with 1390 mg/kg extractable EG on fur. Therefore, exposure of CD-1 mice to a respirable EG aerosol during organogenesis by NO inhalation resulted in minimal maternal toxicity at 1000 and 2500 mg/m3 and developmental toxicity at 2500 mg/m3. The NOAEL was 500 mg/m3 NO for maternal and 1000 mg/m3 NO for developmental toxicity. This study supports the interpretation of the initial EG WB results as due to systemic exposure from noninhalation routes since limiting noninhalation routes prevented almost all of the effects (including teratogenicity) observed in mice after WB exposure.

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 to be teratogenic at high doses by gavage in rodents. Since one route 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 microns) on Gestational Days (GD) 6 through 15 for 6 hr per day at target exposure concentrations of 0, 150, 1000, or 2500 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. Clinical observations and maternal body weights were documented throughout gestation for both species. Maternal food and water consumption was measured in rats only throughout gestation. At scheduled necropsy (GD 21 for rats, GD 18 for mice), maternal animals were evaluated for body weight, liver weight, kidney weight, gravid uterine weight, number of ovarian corpora lutea, and status 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 skeletal malformations and variations. All rat dams survived to scheduled termination. Minimal maternal toxicity was indicated by a significant increase in absolute and relative liver weight at 2500 mg/m3. Food and water consumption, maternal body weights and weight gain, and maternal organ weights (other than liver) were unaffected by 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-related increase in the incidence of any individual malformation, in the 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 visceral variations. Evidence of fetotoxicity, expressed as reduced ossification in the humerus, the zygomatic arch, and the metatarsals and proximal phalanges of the hind-limb, was observed at 1000 and 2500 mg/m3. All mouse dams survived to scheduled termination. One dam at 2500 mg/m3 was carrying a totally resorbed litter at termination. Maternal toxicity was observed at 1000 and 2500 mg/m3, expressed as reduced body weight and weight gain during and after the exposure period, and reduced gravid uterine weight. (Maternal effects may have been due, in part or whole, to effects on the conceptuses; see below.)(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of exposure to water aerosol or air by nose-only or whole-body inhalation procedures for CD-1 mice in developmental toxicity studies

This study was performed to evaluate the effects of nose-only restraint versus whole-body exposure procedures in the absence of test chemical, and to determine the appropriate control environment (water aerosol or air) for subsequent developmental toxicity studies of test materials administered as aerosols. Timed-pregnant CD-1 mice, 30/group, were exposed to high concentrations of water aerosol or to air by whole-body or nose-only inhalation procedures on Gestational Days (GD) 6 through 15 for 6 hr per day. The group exposed to air by whole-body procedures was designated as the control group. Clinical observations and maternal body weights were recorded throughout gestation. At scheduled necropsy on GD 18, maternal animals were evaluated for body weight, gravid uterine weight, liver weight, number of ovarian corpora lutea, and status of uterine implantation sites. Fetuses were counted, weighed, and sexed and were examined for external, visceral (including craniofacial), and skeletal alterations. Indices of maternal toxicity were affected in both nose-only groups. Maternal body weights were reduced during and after the exposure period; maternal weight gain was reduced during the exposure period. Clinical signs observed, from animals struggling during restraint, were resolved by GD 18. At sacrifice on GD 18, maternal body weights and maternal gestational weight gains (both corrected for gravid uterine weights) and absolute liver weights were reduced in both nose-only groups. Four females died (13.3%, all pregnant) in the air nose-only group, and maternal liver weight (relative to body weight) was reduced in the aerosol nose-only group. Gestational parameters were unaffected by any of the treatments. There were no statistically significant differences in the incidences of any individual malformations or malformations by category (external, visceral, or skeletal) or of total malformations. However, exencephaly, low set ears, cleft palate and ventricular septal defect were observed only in both aerosol-exposed groups (whole-body and nose-only exposed). The incidences of individual external or visceral variations or of variations by category or of total variations were unaffected. The incidence of one skeletal variation, poorly ossified supraoccipital skull bone, was significantly increased in the aerosol nose-only group relative to the air whole-body controls. There were also increased incidences (not statistically significant) of extra (14th) ribs in both aerosol groups. Therefore, maternal restraint (in both nose-only groups) during organogenesis produced indications of maternal toxicity, but restraint did not appear to affect normal embryo/fetal morphologic development.(ABSTRACT TRUNCATED AT 400 WORDS)

Hepatotoxicity in guinea pigs following acute inhalation exposure to 1,1-dichloro-2,2,2-trifluoroethane

Groups of 10 male Hartley guinea pigs were exposed to 3.0, 2.0, 1.0, or 0.1% (v/v) 1,1-Dichloro-2,2,2-trifluoroethane (HCFC-123) or 1.0% (v/v) halothane by inhalation for 4 hr. A sixth group of 10 guinea pigs received only air. All animals were sacrificed 48 hr postexposure. Gross and histopathologic examination of the liver, heart, and kidney and routine hematology and clinical chemistry analyses [including isocitrate dehydrogenase (ICDH)] were done on all guinea pigs. Lesions related to HCFC-123 and halothane exposure were limited to the liver and included centrolobular vacuolar (fatty) change, multifocal random degeneration and necrosis, and centrolobular degeneration and necrosis. These lesions were observed in 90-100% of the exposed animals and were absent in the air-only controls. There was significant individual animal variation in susceptibility to both HCFC-123 and halothane, resulting in a spectrum of histologic lesions and clinical chemistry values within each exposure group. Alanine aminotransferase, aspartate aminotransferase, and ICDH were the most significant predictors of hepatocellular damage. Similarities in the response between halothane and HCFC-123 in this guinea pig model suggests that humans susceptible to halothane-induced hepatitis may be susceptible to HCFC-123 by a common mechanism of toxicity.

Metabolism and pharmacokinetics of selected halon replacement candidates

Metabolism studies were conducted using Fischer 344 and Sprague-Dawley rats following inhalation exposure to 1.0% (v/v) air atmospheres of 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123), 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124), 1-chloro-1,1-difluoroethane (HCFC-142b), bromochlorodifluoromethane (Halon 1211), and perfluorohexane (PFH) for 2 h. There were no remarkable differences in results between the two strains of rats. Animals exposed to HCFC-123 or HCFC-124 excreted trifluoroacetic acid in their urine. Urinary fluoride concentrations were increased in rats exposed to HCFC-124, and urinary bromide levels were increased in rats exposed to Halon 1211. Small quantities of volatile metabolites 2-chloro-1,1,1-trifluoroethane (HCFC-133a) and 2-chloro-1,1-difluoroethylene were observed in the livers of rats exposed to HCFC-123. Rats exposed to HCFC-142b excreted chlorodifluoroacetic acid in their urine; no volatile metabolites were detected in tissue samples. For PFH studies, no metabolites were detected in the urine or tissues of exposed animals. These results are consistent with proposed oxidative and reductive pathways of metabolism for these chemicals. Pharmacokinetic studies were carried out in rats exposed by inhalation to 1.0%, 0.1%, or 0.01% of HCFC-123. Following exposure, blood concentrations of HCFC-123 fell sharply, whereas trifluoroacetic acid levels rose for approx. 5 h and then declined gradually. Using a physiologically based pharmacokinetic model, saturation of HCFC-123 metabolism was estimated to occur at approx. 0.2% (2000 ppm) HCFC-123.

Air Force approach to risk assessment for halon replacements

Finding safe, environmentally acceptable, and effective replacements for Halon fire-extinguishing agents and other chemicals banned by the Montreal Protocol is a formidable task for Air Force research and development organizations. One factor that makes this task a challenge is the uncertainty in relating toxicology studies in laboratory animals to the human situation. This uncertainty from toxicology studies affects the risk assessment process by calling for very conservative decisions. Because of this uncertainty, public pressure and politics also impact the regulatory process. The Air Force approach to assessing health hazards for Halon replacements is to provide scientific information that directly applies to the parts of the extrapolation process that are responsible for the most uncertainty. Most regulatory agencies readily incorporate scientific information, when it is available, which can reduce uncertainty. These Air Force studies will be used to provide realistic exposure levels for replacement chemicals which will allow mission accomplishment and provide safety for the worker and the populace.

Subchronic toxicity study of dicyclopentadiene vapor in rats

Fischer 344 rats were exposed by inhalation to 0, 1, 5 or 50 ppm dicyclopentadiene (DCPD) vapor 6 hr/day, 5 days/week for 13 weeks, followed by a 13-week recovery period. Animals were euthanized following completion of exposure at 2, 6, or 13 weeks and at postexposure weeks 4 or 13. No mortality, overt signs, body weight changes, hematologic or clinical chemistry values were related to DCPD exposure. In the high-exposure male rats, relative liver weights were significantly increased but with no accompanying histopathologic changes. Exposure to DCPD produced adverse kidney effects in male, but not female, rats as evidenced by the excretion of epithelial cells in the urine. Histologic changes were localized to the proximal tubules of the kidney and included increased accumulation of protein droplets, regenerative epithelium, and the presence of intraluminal proteinaceous material. In addition, several alterations in renal function were observed. Urinary Na+ excretion rates were decreased and urinary K+ excretion rates were increased throughout the exposure period; however, glucose was not present in the urine, and creatinine clearance was normal. The ability of the kidney to concentrate urine was also impaired. After the recovery period, many of the treatment-related kidney effects were not observed, including the presence of hyaline droplets in the proximal tubules and epithelial cells in the urine. These findings indicate an overall low degree of systemic toxicity following subchronic inhalation exposure of dicyclopentadiene at exposure levels up to 50 ppm. The only effect that was observed was a male rat-specific nephropathy that is characteristic of the hyaline droplet nephropathy produced by a diverse group of compounds.

Acute vapour inhalation toxicity of acrolein and its influence as a trace contaminant in 2-methoxy-3,4-dihydro-2H-pyran

1. The LC50 values for acrolein (AC) vapour to Sprague-Dawley rats (combined sexes) were determined to be 26 ppm (1 h) and 8.3 ppm (4 h). Signs of severe irritancy were present, and death was due to lung injury. 2. Exposure of rats to a 2-methoxy-3,4-dihydro-2H-pyran (MDP) saturated vapour atmosphere statistically generated from liquid MDP containing 0.037% AC, caused severe irritancy and death from accumulation of AC vapour. Sparging the impure material with nitrogen gas before atmosphere generation significantly reduced or abolished lethal toxicity. 3. Dynamically generated MDP vapour atmosphere produced transient respiratory and ocular irritancy, but no mortalities. The intrinsic acute vapour inhalation toxicity of MDP is low. 4. The presence of highly volatile toxic impurities in a material may confer a significant acute inhalation toxicity and hazard under conditions of low air movement. Assessment of potential inhalation hazards from liquid mixtures may require investigation by static and dynamic methods for vapour generation.

Dominant lethal assay of 2,4-pentanedione vapor in Fischer 344 rats

2,4-Pentanedione (2,4-PD: CAS No. 123-54-6) is a volatile industrial chemical of moderate acute toxicity, centrally neurotoxic by repeated exposure to high vapor concentrations, fetotoxic, and clastogenic. Its wide use and known toxicology indicated the conduct of a dominant lethal assay. Male Fischer 344 rats, 20 per group, were exposed to 2,4-PD vapor concentrations (mean +/- SD) of 0, 99.1 +/- 2.2, 412 +/- 12.6 and 694 +/- 9.1 ppm, for 6 hr/day for 5 consecutive days. The day following the final exposure they were bred to unexposed female Fischer 344 rats, 2 per week for 8 consecutive weeks. Weight loss occurred with males during 2,4-PD exposure for the 412 and 694 ppm groups, with compensatory increased weight at 694 ppm, for the first two weeks postexposure. No histopathological change was seen in brain, testes or thymus from high concentration males sacrificed after eight weeks of mating. Minor transient reproductive and gestational effects were present at 412 and 694 ppm. At week 2 there was a reduction, not statistically significant, in the number of corpora lutea and total and viable implants per dam at 694 ppm, and a slight increase in preimplantation loss. At week 3 the number of pregnant females was slightly reduced at 412 and 694 ppm, causing a lowered female fertility index. At week 4 there was a slight reduction in the number of total and viable implants per litter and a significant preimplantation loss at 694 ppm. The dominant lethal factor (FL%) was increased slightly at 694 ppm for weeks 2 and 4. Thus, the "no observable effect" level for dominant lethal effects was 99 ppm. The results, although not statistically significant, are dose-related and compatible with a transient slight dominant lethal effect at the spermatid stage of spermatogenesis.

Two-week aerosol inhalation study on polyethylene glycol (PEG) 3350 in F-344 rats

PEGs in the 3000 to 4000 MW range are used in many pharmaceutical and cosmetic applications; they produce little ocular or dermal irritation and have extremely low acute and subchronic toxicity by oral and dermal routes of administration. However, little information exists on the potential of aerosols of these materials to produce adverse health effects. F-344 rats were exposed to aerosols of PEG 3350 (20% w:w in water) at 0, 109, 567, or 1008 (highest attainable) mg/m3 for 6 hr/d, 5 d/wk for 2 wk. No exposure-related toxicity was found with regard to clinical signs, ophthalmology, serum chemistry, urinalysis, or gross pathology. Exposure-related effects included: a 50% increase in the neutrophil count (males only) at 1008 mg/m3; decreased body weight gain (16%) for both the 567 and 1008 mg/m3 groups (males only); absolute lung weights of both sexes were increased 10 and 18% for the 567 and 1008 mg/m3 groups, respectively. A slight increase in the number of macrophages in the alveoli was the only change observed histologically in all PEG 3350-exposed groups. Therefore, inhalation of aerosols of PEG 3350 at concentrations up to 1008 mg/m3 produced relatively little toxicity in rats, the lung was the target organ, and the no-observable-effect-level was between 109 to 567 mg/m3.

The acute toxicity of tris(dimethylamino)silane

The acute handling hazards of tris(dimethylamino)silane [TDMAS] were investigated. The acute male rat peroral LD50 (with 95% confidence limits) was 0.71 (0.51-0.97) ml/kg, and the acute male rabbit percutaneous LD50 was 0.57 (0.35-0.92) ml/kg. The liquid was severely irritating to the rabbit eye and skin, and the vapor severely irritating to the rat eye. The dynamically generated saturated vapor Lt50 in female rats was 12 (9.7-15) min. The effect of varying the atmospheric concentration of vapor from TDMAS on acute inhalation toxicity was investigated by passing ordinary moist air countercurrent to liquid TDMAS metered into a slightly heated glass tube. Based on nominal concentrations, the 4 hr-LC50 for vapor from TDMAS was 734 (603-893) ppm in female rats by this procedure. Stoichiometrically, this accords with toxicity due to liberation of dimethylamine (DMA) from TDMAS. In a subsequent study designed to assess the influence of relative humidity on vapor toxicity, nitrogen was passed over heated liquid TDMAS and the resultant atmosphere was introduced into the air intake duct of the inhalation exposure chamber. Gas chromatographically measured TDMAS concentrations (+/- SD) were 395 +/- 111, 127 +/- 25, 62 +/- 8 and 23 +/- 21 ppm; the corresponding DMA vapor concentrations were 112 +/- 171, 31 +/- 43, 10 +/- 6 and 26 +/- 44 ppm. The 4-hr LC50 (males and females) was 38 (34-43) ppm TDMAS vapor. Thus, TDMAS is of moderate acute peroral and percutaneous toxicity, a severe primary skin and eye irritant, an aspiration hazard, and of high intrinsic acute inhalation toxicity, but in moist air conditions lethal toxicity may be reduced and in such circumstances DMA may be a significant factor in toxicity.

Pulmonary fibrosis produced in F-344 rats by subchronic inhalation of aerosols of a 4000 molecular weight ethylene oxide/propylene oxide polymer

Inhalation of aerosols of the ethylene oxide/propylene oxide polymer (U-5100) evaluated in this study has previously been shown in acute and 2-week studies to produce toxicologic effects on the lungs, with increased lung weights and microscopic findings of congestion and hemorrhage of pulmonary alveolar capillaries and 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, 773-784). In the present studies, F-344 rats were exposed 6 hr/day, 5 day/week for 2 weeks to aerosols at mean concentrations of 0, 0.9, or 5.0 mg/m3 or for 13 weeks to mean concentrations of 0, 0.3, 1.1, or 5.2 mg/m3. Following the 2-week study, minimal multifocal hemorrhage and eosinophilic proteinaceous debris in alveoli were observed in the 0.9 mg/m3 group; similar lesions plus alveolar cell necrosis were found in the 5 mg/m3 group. In the 13-week study, the 5.2 mg/m3 group had a slight decrease in body weight gain, while increases in absolute and/or relative lung weights occurred for both the 1.1 and 5.2 mg/m3 groups at the end of the exposure regimen and at the end of a 5-week recovery period. Histologic lesions of the lungs occurred in all U-5100-exposed groups and consisted of hemorrhage, alveolar histocytosis, interstitial pneumonia, and multifocal fibrosis. The incidence and severity of the pulmonary lesions were concentration related.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyalin droplet nephrosis in male Fischer-344 rats following inhalation of diisobutyl ketone

Four groups, each consisting of 10 male and 10 female Fischer-344 rats, were exposed 6 h/day, 5 days/week, for 9 days to diisobutyl ketone (DIBK) vapor at concentrations of 905, 300, 98, or 0 (control) ppm. An additional 10 rats/sex were assigned to the 905 and 0 ppm groups and allowed two weeks recovery prior to sacrifice. Rats exposed to 905 ppm had mild ocular irritation (lacrimation) and evidence of kidney toxicity, manifested as: 1) an increase in absolute and relative (as a percentage of body weight) kidney weights, 2) an increase in urine volume (and water intake) with a concomitant decrease in urine osmolality (males only), and 3) an increase in severity of hyalin droplet nephrosis in the proximal tubules (males only). Absolute and relative liver weights were also increased in both male and female rats of the 905 and 300 ppm groups. These effects either disappeared or lessened in severity following the 2-week recovery period. Male rats exposed to 300 ppm had similar renal alterations to the males of the 905 ppm group, although the alterations were fewer in number and smaller in magnitude. Kidney weights and renal histology of the males of the 98 ppm group were similar to the control male rats, although an increase in urine volume with a decrease in urine osmolality was observed. The kidney findings in this study were not surprising because of the chemical relationship of DIBK with other aliphatic ketones (e.g., methyl isobutyl ketone, methyl isoamyl ketone) which, after repeated inhalation exposure, cause hyalin droplet nephropathy in male rats. The significance of this male rat nephrosis with regard to human exposure is unknown.

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 evaluated in this study have previously been shown to have a low order of toxicity and/or irritancy by ocular, dermal, or oral routes of administration. These studies evaluated the acute inhalation toxicity 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% confidence limits) for U-660, U-2000, and U-5100 in Wistar albino rats were 4670 (4090-5320), 330 (227-480), and 106 (45-245) mg/m3. Occasionally, slight increases in respiration rate and slight hyperactivity were observed during the postexposure period. All deaths were delayed for 2-5 days postexposure. Body weight gains were transiently depressed in rats exposed to U-2000 and U-5100. Discolored lungs and livers occurred in animals which died during the 14-day postexposure period. Subsequently, a repeated-exposure study was conducted on U-5100 in F-344 rats exposed for 6 hr/day, 5 days/week, for 9 exposures at mean concentrations of 0, 5, 26, and 50 mg/m3. Portions of the control and 50 mg/m3 groups were maintained for an additional 2-week recovery period. Exposure-related effects included transient urogenital wetness in 50 mg/m3 group females; decreased body weight gain (7-29%) in all U-5100 groups except the 5 mg/m3 group females; increases in absolute (17-52%) and relative lung weights in all U-5100 groups; macroscopic red foci in the lungs; and microscopic findings of congestion and hemorrhage of pulmonary alveolar capillaries and necrosis of alveolar epithelial cells. Lung weights 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 inhalation in comparison to other routes of administration, vary considerably in their acute lethal toxicity as a function of chain length/molecular weight, and induce pulmonary hemorrhage, and possibly edema, following repeated aerosol exposures at concentrations as low as 5 mg/m3.

Dimethylethanolamine: acute, 2-week, and 13-week inhalation toxicity studies in rats

Dimethylethanolamine (DMEA) is a volatile, water-soluble amine that has applications in the chemical and pharmaceutical industries. These studies evaluated the acute and subchronic inhalation toxicity of DMEA. Acute (4-hr) exposures of Wistar rats to DMEA vapor resulted in an LC50 value (95% confidence limits) of 1641 (862-3125) ppm. Clinical signs of nasal and ocular irritation, respiratory distress, and body weight loss were observed in rats exposed to 1668 ppm DMEA and higher. In the 2-week study, F-344 rats exposed to 98, 288, or 586 ppm DMEA for 9 days (6 hr/day) during an 11-day period also exhibited signs of respiratory and ocular irritation (except the 98 ppm group). All animals of the 586 ppm group and 4 of 15 male rats of the 288 ppm group died. Body weight values for the 288 ppm group were reduced to about 75% of preexposure values, while the 98 ppm group gained 35% less weight than controls. Statistically significant differences in clinical pathology parameters (288 ppm group) and in organ weight values (288 and 98 ppm groups) probably resulted from the decreased food consumption and not from specific target organ toxicity. In the groups evaluated histologically (the 98 and 288 ppm groups) the eye and nasal mucosa were the primary target organs. In the 13-week subchronic study, F-344 rats were exposed to 0, 8, 24, or 76 ppm DMEA for 6 hr/day, 5 days/week for 13 weeks. The principal exposure-related changes were transient corneal opacity in the 24 and 76 ppm groups; decreased body weight gain for the 76 ppm group; and histopathologic lesions of the respiratory and olfactory epithelium of the anterior nasal cavity of the 76 ppm group and of the eye of several 76 ppm group females. Rats maintained for a 5-week recovery period only exhibited histological lesions of the nasal tissue, with the lesions being decreased in incidence and severity. DMEA acts primarily as an ocular and upper respiratory tract irritant and toxicant at vapor concentrations of 76 ppm, while 24 ppm or less produced no biologically significant toxicity in rats. Thus, 24 ppm was considered to be the no-observable-effect level.

A 14-week vapor inhalation toxicity study of methyl isobutyl ketone

In a 2-week probe study male and female Fischer-344 rats and B6C3F1 mice were exposed 6 hr/day to 2000, 500, 100, or 0 ppm methyl isobutyl ketone (MIBK). At 2000 ppm there was a slight increase in male rat liver weight (absolute and relative). The only changes observed histologically were increases in regenerative tubular epithelia and hyalin droplets in kidneys of male rats exposed to 2000 or 500 ppm. Exposure levels for a subchronic study were 0, 50, 250, or 1000 ppm methyl isobutyl ketone vapors 6 hr/day, 5 days per week, for 14 weeks. The 14 weeks of exposure had no adverse effect on the clinical health or growth of rats or mice. Male rats and male mice exposed to 1000 ppm MIBK had a slight but statistically significant increase in liver weight and the liver weight/body weight ratio. Liver weight was also increased slightly in male mice exposed to 250 ppm. No gross or microscopic hepatic lesions related to MIBK exposure were observed. Furthermore, the only microscopic change observed was an increase in the incidence and extent of hyalin droplets within proximal tubular cells of the kidneys of male rats exposed to 250 and 1000 ppm of MIBK. The relevance of the male rat kidney tubular effect to humans is not known. In conclusion, other than the male rat kidney effect, exposure of male and female rats and mice to MIBK at levels up to 1000 ppm for 14 weeks was without significant toxicological effect.

Eighty-five day postexposure follow-up study in Fischer 344 rats after repeated exposures to methyl isocyanate vapor

The objectives of this study were to describe the microscopic lesions in the respiratory tract of Fischer 344 rats as a result of 4- or 8-days exposure (6 hr/day) of 3 ppm MIC and to characterize the postexposure development of these lesions up to day 85. All rats survived the exposure regimen, although significant decreases in body weight and encrustation of the eyes, nose, or mouth were observed. During the first 15 days of postexposure, the rats were hypoactive and had increased respiratory rates. Male mortality was as high as 63%; only 5% of the MIC-exposed females died. The cause of death was interpreted to be respiratory compromise complicated by anorexia and probably dehydration as well. During the next 28 postexposure days, 48% of the male survivors died, while only 3% of the female survivors died. Throughout the 85-day postexposure period, body weight gains in the MIC-treated groups were consistently below control values. Inflammatory and squamous metaplastic lesions of the respiratory tract, observed the day following completion of either the 4- or 8-day exposure regimen, decreased in both frequency and/or severity in survivors of the 85-day postexposure period, indicating recovery from the cytotoxic and irritating effects of MIC vapor. The squamous metaplastic epithelium was replaced by regenerative epithelium beginning in the deeper portion of the respiratory tract.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological effects of short-term, high-concentration exposure to methyl isocyanate. V. Morphologic evaluation of rat and guinea pig lungs

The morphologic changes induced in the lungs of rats and guinea pigs exposed to high concentrations of MIC vapor (100, 600, and 1000 ppm in the rat and 25, 125, 225, and 675 ppm in the guinea pig) for a short time (15 min) in a static exposure chamber were evaluated at varying postexposure periods (0, 1, 2, 4, and 16 hr). The 675 ppm-exposed guinea pigs were evaluated only immediately following removal from the chamber. Attention was primarily focused on the intrapulmonary conducting airways and the parenchyma (gas exchange region) of the lungs. The severity of morphologic changes observed by light microscopy was directly correlated with exposure concentration and time postexposure in both species. Specifically, degenerative changes were observed in the bronchial, bronchiolar, and alveolar epithelium in both species. Quantitative differences were observed; 100 ppm of MIC in the rat resulted in much less damage than did 125 ppm of MIC in the guinea pig. Morphologic evidence of sloughing of large sheets of conducting airway epithelium with fibrin buildup and increased mucus production resulted in plugging of major airways and atelectasis. These observations support the hypothesis that tissue hypoxia was a major contributing factor resulting in death.

Biological effects of short-term, high-concentration exposure to methyl isocyanate. VI. In vitro and in vivo complement activation studies

The ability of MIC to induce complement activation in vitro and in vivo was investigated. For the in vitro studies, both human and guinea pig serum or EDTA-plasma samples were exposed to 1167 to 1260 ppm MIC vapor for 15 min at room temperature. The human serum samples exposed to MIC showed significant reductions in Factor B, C2, C4, C3, C5, and total hemolytic complement CH50 activity levels. C6 functional activity was unaffected. The C3, C5, and CH50 functional activities in guinea pig serum (the only functional tests conducted on these samples) were more sensitive to MIC-mediated reduction than the corresponding activity reductions observed in the human serum samples. The human and single guinea pig EDTA-plasma samples exposed to MIC vapor showed no evidence of C3 consumption but did show significant reductions in CH50 levels. Thus, MIC vapor was able to activate, and thereby reduce serum complement C3 activity in vitro by a complement-dependent process. However, the data suggest at least one complement component other than C3 was inactivated in EDTA-plasma by a complement-independent mechanism. For the in vivo studies, five pairs of guinea pigs were exposed to 644 to 702 ppm MIC vapor until one of the pair died (11-15 min). MIC exposure was then discontinued, the surviving guinea pig was sacrificed, and EDTA-plasma was obtained from both animals and analyzed for complement consumption.(ABSTRACT TRUNCATED AT 250 WORDS)

Methyl isocyanate eight-day vapor inhalation study with Fischer 344 rats

Groups of ten male and ten female Fischer 344 rats were exposed by inhalation 3.1, 0.6, 0.15, or 0.0 (control) ppm of methyl isocyanate (MIC) vapor 6 hr per day for 8 days (two 4-day sessions separated by a 2-day rest). Evaluation of toxic effects included body weight, food consumption, organ weights, and selected hematologic, ophthalmic, neurologic, gross anatomic, and histologic examinations. There were no deaths during the study. Rats of the 3.1 ppm exposure group had decreased body weights, food consumption, and blood oxygen saturation (males only). An increase in hemoglobin concentration (males only) and in lung weights (absolute and as a percentage of body weight) were also observed in the 3.1 ppm rats. Ophthalmic or neurofunctional behavior evaluations were negative for all MIC exposure groups. Only 3.1 ppm of MIC vapor resulted in lesions in the respiratory tract, 0.6 or 0.15 ppm did not. The types of lesions observed were inflammation and squamous metaplasia in the nasal cavity, trachea, and bronchi; inflammation of the bronchioles and alveoli; and submucosal fibroplasia of the bronchioles. No significant lesions were observed in tissues other than those of the respiratory tract in all MIC exposure groups. The results of this study indicate the current 0.02 ppm threshold limit value for MIC is not too high regarding toxicity.

Biological effects of short-term, high-concentration exposure to methyl isocyanate. I. Study objectives and inhalation exposure design

Early reports from India indicated that humans were dying within minutes to a few hours from exposure to methyl isocyanate (MIC). Attempts to explain the cause(s) of these rapid mortalities is where Union Carbide Corporation concentrated its post-Bhopal toxicologic investigations. The MIC studies involving rats and guinea pigs focused primarily on the consequences of acute pulmonary damage. All MIC inhalation exposures were acute, of short duration (mainly 15 min), and high in concentration (ranging from 25-3506 ppm). MIC vapors were statically generated in a double chamber exposure design. Precautionary measures taken during exposures are discussed. Guinea pigs were more susceptible than rats to MIC exposure-related early mortality. A greater than one order of magnitude difference was observed between an MIC concentration that caused no early mortality in rats (3506 ppm) and an MIC concentration that caused partial (6%) early mortality in guinea pigs (225 ppm) for exposures of 10 to 15 min duration. For both species, the most noteworthy clinical signs during exposure were lacrimation, blepharospasm, and mouth breathing. Fifteen minute LC50 tests with 14-day postexposure follow-up were conducted, and the LC50 (95% confidence limit) values were 171 (114-256) ppm for rats and 112 (61-204) ppm for guinea pigs. Target exposure concentrations for the toxicologic investigations of MIC-induced early mortality were established. A short summary of pertinent results of Union Carbide Corporation's post-Bhopal toxicologic investigations is presented.

Biological effects of short-term, high-concentration exposure to methyl isocyanate. II. Blood chemistry and hematologic evaluations

Human, rat, and guinea pig packed erythrocytes exposed to 100, 500, or 1000 ppm of methyl isocyanate (MIC) vapor in vitro showed a concentration-related inhibition of cholinesterase (ChE) activity. Rat and guinea pig packed erythrocytes showed an almost complete inhibition of ChE activity at 2000 ppm. In vitro exposures of human and guinea pig blood to 1000 or 2000 ppm of MIC vapor resulted in qualitative alterations in the electrophoretic mobility of hemoglobin (Hb) as measured by citrated agar electrophoresis. In rats and guinea pigs, neither IV injection of liquid MIC nor in vivo exposure to 1000 ppm of MIC by inhalation resulted in any inhibition of erythrocyte ChE activity or alteration in Hb electrophoretic mobility. As a result of these observations, it was concluded that neither ChE inhibition nor structural alteration of Hb were major contributing factors to death resulting from MIC exposure. Rats and guinea pigs receiving IV injections of liquid MIC showed an increase in creatine kinase (CK) levels. This increase could not be attributed to a specific isoenzyme of CK by ion exchange chromatography. Rats exposed to 100, 600, or 1000 ppm of MIC and guinea pigs exposed to 25, 125, or 225 ppm of MIC and bled immediately following a 15-min exposure or at 1, 2, 4, or 16 hr postexposure had the following alterations in blood parameters: an increase in CK, increases in hemoglobin concentration and hematocrit, reticulocytosis (rats only), neutrophilia, a decrease in blood pH and PO2, and an increase in blood PCO2.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory tract changes in guinea pigs, rats, and mice following a single six-hour exposure to methyl isocyanate vapor

Groups of male and female Fischer 344 rats, B6C3F1 mice, and Hartley guinea pigs were exposed once for 6 hr to mean concentrations of 10.5, 5.4, 2.4, 1.0, or 0 (control) ppm of methyl isocyanate (MIC) vapor. Rats and mice were also exposed to 20.4 ppm of MIC. The majority of deaths occurred during postexposure days 1 through 3. The 6-hr LC50 values (with 95% confidence limits) were 6.1 (4.6 to 8.2) ppm for rats, 12.2 (8.4 to 17.5) ppm for mice, and 5.4 (4.4 to 6.7) ppm for guinea pigs. Notable clinical observations during and immediately following MIC exposure were lacrimation, perinasal/perioral wetness, respiratory difficulty (e.g., mouth breathing), decreased activity, ataxia, and hypothermia. Body weight losses were common in all species following MIC exposures of 2.4 ppm or greater. Microscopic lesions included acute necrosis of the epithelial lining throughout the respiratory tract in animals that died shortly after exposure, coupled with congestion, edema, and inflammation. A microscopic lesion that appeared unique to guinea pigs was bronchiolitis obliterans (where the products of necrosis and inflammation completely closed the bronchioles). Additional microscopic lesions observed in some animals that died or were sacrificed at the end of the study (postexposure day 14) consisted of squamous metaplasia of respiratory epithelium in the nasal cavity, which extended into the larynx, trachea, and in some cases, the bronchi.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological effects of short-term, high-concentration exposure to methyl isocyanate. III. Influence on gas exchange in the guinea pig lung

The influence of methyl isocyanate (MIC) inhalation on the gas exchange function of the lungs in guinea pigs was studied by measuring arterial blood gases, pH, and tracheal pressure during constant-volume, artificial ventilation with air or 100% O2 at 40 and 120 min after exposure. A 15 min exposure to MIC at concentrations of 240 to 628 ppm caused a marked reduction in PaO2 and pHa and an elevated tracheal pressure during artificial ventilation. The low PaO2 was only slightly elevated when the animals were ventilated with 100% O2. Although the dry-wet lung weight ratio was reduced at the highest exposure concentration, the effect was not severe and no significant increase in lung water was found at the lower concentrations. MIC inhalation caused severe pulmonary blood shunting and ventilation/perfusion imbalance. This, in turn, led to hypoxemia, metabolic acidosis, and tissue hypoxia, which could produce death. The pulmonary gas exchange deficit likely resulted from bronchial and bronchiolar obstruction caused by sloughed epithelium and other debris from intra- and extrapulmonary airways.

Reproduction and fertility evaluations in CD rats following nitrobenzene inhalation

A two-generation reproduction study was performed by exposure of Sprague-Dawley CD rats to concentrations of 40, 10, 1, or 0 (control) ppm of nitrobenzene (NB) vapor. No NB-related effects on reproduction were observed at 10 or 1 ppm. At 40 ppm, a decrease in the fertility index of the F0 and F1 generations occurred, which was associated with alterations in the male reproductive organs. Specifically, weights of testes and epididymides were reduced and seminiferous tubule atrophy, spermatocyte degeneration, and the presence of giant syncytial spermatocytes were observed. The only significant finding in the litters derived from rats exposed to 40 ppm was an approximate 12% decrease in the mean body weight of F1 pups on Postnatal Day 21. Survival indices were unaltered. To examine the reversibility of this selective effect on male gonads, the F1 males from the 40-ppm group were allowed a 9-week nonexposure period and mated to naive females. An almost fivefold increase in the fertility index was observed, indicating at least partial functional reversibility upon removal from NB exposure. Also, the numbers of giant syncytial spermatocytes and degenerated spermatocytes were greatly reduced. The results of this study support the selection of 10 ppm of NB as the no-observable-effect level for reproduction and fertility effects in rats.

Development toxicity evaluation of inhaled nitrobenzene in CD rats

Pregnant CD (Sprague-Dawley) rats were exposed to nitrobenzene vapor (CAS Registry No. 98-95-3) at 0, 1, 10, and 40 ppm (mean analytical values of 0.0, 1.06, 9.8, and 39.4 ppm, respectively) on gestational days (gd) 6 through 15 for 6 hr/day. At sacrifice on gd 21, fetuses were evaluated for external, visceral, and skeletal malformations and variations. Maternal toxicity was observed: weight gain was reduced during exposure (gd 6-9 and 6-15) to 40 ppm, with full recovery by gd 21, and absolute and relative spleen weights were increased at 10 and 40 ppm. There was no effect of treatment on maternal liver, kidney, or gravid uterine weights, on pre- or postimplantation loss including resorptions or dead fetuses, on sex ratio of live fetuses, or on fetal body weights (male, female, or total) per litter. There were also no treatment-related effects on the incidence of fetal malformations or variations. In summary, during organogenesis in CD rats, there was no developmental toxicity (including teratogenicity) associated with exposure to nitrobenzene concentrations that produced some maternal toxicity (10 and 40 ppm) or that produced no observable maternal toxicity (1 ppm).

Acute, 9-day, and 13-week vapor inhalation studies on ethylene glycol monohexyl ether

At ambient conditions, the low vapor pressure of ethylene glycol monohexyl ether (EGHE) allows for a maximum vapor concentration of approximately 85 ppm. In an acute inhalation study on Wistar albino rats, a 4-hr exposure to 83 ppm EGHE produced no clinical signs, body weight effects, mortality, or macroscopic lesions in thoracic or abdominal organs. Fischer 344 rats exposed for 9 days (6 hr/day) over an 11-day period, to 0 (control), 19, 41, or 84 ppm EGHE had decreased body weight gains and increased liver to body weight values at 84 ppm EGHE. No alterations of the hematology parameters or the morphology of the testes or liver were observed. In a subsequent study, rats were exposed to mean EGHE concentrations of 0 (control), 20, 41, or 71 ppm for 6 hr/day, 5 days/week, for 13 weeks. Urogenital wetness was observed in all EGHE-exposed groups of females and in males of the 71-ppm group. Decreased body weight gains were observed in both sexes of the 71-ppm group, and a slight decrease was also observed in females of the 41-ppm group. Increased absolute and/or relative liver weights were observed in both sexes of the 71-ppm group and to a lesser extent in the 41-ppm group. Possibly related to these findings in the liver were decreases in serum transaminases (aspartate and alanine aminotransferase) and sorbitol dehydrogenase, with an increase in alkaline phosphatase observed in the 71-ppm group of female rats. However, there were no gross or histopathologic lesions found to indicate impairment of the liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Methyl isocyanate subchronic vapor inhalation studies with Fischer 344 rats

Groups of Fischer 344 rats were exposed to 3.1, 0.6, 0.15, or 0.0 (control) ppm of methyl isocyanate (MIC) vapor 6 hr per day for two 4-day sessions separated by a 2-day rest. There were no deaths during the study. The rats were killed the morning following the last exposure day. The 3.1-ppm-exposed rats had decreased body weight, food consumption, and blood oxygen saturation (males only). Increased hemoglobin concentration (males only) and lung weights were also observed in this group of rats. Multiple histologic lesions, limited to the respiratory tract, were observed in rats of the 3.1-ppm group only. The lesions consisted of necrosis, suppurative inflammation, squamous metaplasia, and intraluminal and submucosal fibroplasia (bronchi and bronchioles only) which extended from the anterior nasal cavity to the terminal bronchioles. In a second study, rats were exposed to 3.0 ppm MIC, 6 hr per day, for either one or two 4-day sessions and sacrificed on postexposure Days 1, 15, 43, and 85. All rats survived the 4- or 8-day exposure regimen, although significant decreases in body weight and encrustation of the eyes, nose, or mouth area were observed. During the first 15 days postexposure, male mortality was 63%; only 6% of the MIC-exposed females died. The cause of death was interpreted to be a combination of pulmonary vascular and inflammatory changes coupled with anorexia. For survivors, recovery from the necrotizing and irritating effects of MIC vapor was observed. Squamous metaplasia of respiratory epithelium, observed in rats sacrificed at the end of the exposure period, was replaced by tall pseudostratified columnar (regenerative) epithelium beginning in the bronchi and bronchioles as well as the distal trachea. Collagen maturation and condensation of the intraluminal and submucosal fibroplasia occurred during the postexposure period. The results of these investigations support the current threshold limit value for MIC of 0.02 ppm.

2,4-Pentanedione: 9-day and 14-week vapor inhalation studies in Fischer-344 rats

Fischer-344 rats, in groups of 10 males and 10 females, were exposed for 9 days (6 hr/day) to 2,4-pentanedione (2,4-PD) vapor at mean concentrations of 805, 418, 197, and 0 (control) ppm. No deaths occurred, and the only adverse signs were of sensory irritation (partial closure of eyelids, periocular and perioral wetness) at 805 ppm. Also at 805 ppm were decreased body and organ weights, lymphocytosis, and moderate inflammation of the nasal mucosa. At 418 ppm there was a decrease in body weight gain and mild inflammation of the nasal mucosa. Apart from minimal nasal mucosal inflammation, there were no effects at 197 ppm. In the subchronic (14-week) study, rats were exposed (6 hr/day; 5 days/week) to 650, 307, 101, and 0 (control) ppm of 2,4-PD vapor, using groups containing 20 males and 20 females, with half being sacrificed at the end of the exposure period and the remainder kept for a 4-week postexposure recovery period. An additional 10 males were added to the 650 and 0 ppm groups for glutaraldehyde perfusion and subsequent electron microscopic examination of sciatic nerves. At 650 ppm, all females and 10 of 30 males died between the second and sixth weeks of exposure. These animals had acute degenerative changes in the deep cerebellar nuclei, vestibular nuclei and corpora striata, and acute lymphoid degeneration in the thymus. Seven of 15 male survivors of the 650 ppm group (combined 14-week and recovery sacrifices) had gliosis and malacia in the same brain regions, minimal squamous metaplasia in the nasal mucosa, decreased body and organ weights, lymphocytosis, and minor alterations in serum and urine chemistries. No ultrastructural evidence of peripheral neuropathy was observed. Except for central neuropathy, many of the adverse effects at 650 ppm were less marked in the 4-week recovery animals. No deaths occurred at 307 ppm, but females had slightly decreased body weight gains, and in both sexes there were minor alterations in hematology, serum chemistry, and urinalysis parameters, which were not present in the 4-week recovery animals. Rats exposed to 101 ppm showed no differences from the control rats. Subchronic exposure to 650 ppm of 2,4-PD vapor causes serious adverse biological effects. Under these study conditions, the minimum-effects concentration was 307 ppm, and the no-adverse effects concentration was 101 ppm.

Acute inhalation studies with methyl isocyanate vapor. I. Methodology and LC50 determinations in guinea pigs, rats, and mice

Groups of male and female Fischer 344 rats, B6C3F1 mice, and Hartley guinea pigs were exposed once for 6 hr to mean concentrations of 10.5, 5.4, 2.4, 1.0, or 0 (control) ppm of methyl isocyanate (MIC) vapor. Rats and mice were also exposed to 20.4 ppm of MIC. No deaths occurred in animals exposed to 2.4 or 1.0 ppm. The majority of deaths for the 20.4- and 10.5-ppm groups occurred during postexposure Days 1 through 3, while at 5.4 ppm deaths were observed throughout the 14-day postexposure period. The 6-hr LC50 values (with 95% confidence limits) were 6.1 (4.6 to 8.2) ppm for rats, 12.2 (8.4 to 17.5) ppm for mice, and 5.4 (4.4 to 6.7) ppm for guinea pigs. Notable clinical observations during and immediately following MIC exposure were lacrimation, perinasal/perioral wetness, respiratory difficulty (e.g., mouth breathing), decreased activity, ataxia, and hypothermia. The frequency of clinical signs decreased during the second postexposure week. Body weight losses were common in all species following MIC exposures of 2.4 ppm or greater. At 1.0 ppm, only female mice had body weight depression. Recovery of body weight loss was observed in the 5.4- (guinea pigs only), 2.4- and 1.0-ppm concentration groups. The lungs of all animals that died were discolored. Following microscopic examination of the respiratory tract, deaths were attributed to pulmonary edema and congestion. In a separate study, Fischer 344 rats and Hartley guinea pigs were exposed once for 4 hr to mean concentrations of 36.1, 25.6, 15.2, or 5.2 ppm of MIC vapor. In general, the results were similar to those of the single 6-hr exposure study.

Acute inhalation studies with methyl isocyanate vapor. II. Respiratory tract changes in guinea pigs, rats, and mice

Hartley guinea pigs, Fischer-344 rats, and B6C3F1 mice of both sexes were exposed to varying concentrations of methyl isocyanate (MIC) vapor with the highest concentration being 20.4 ppm for rats and mice and 10.5 ppm for guinea pigs. A control group for each species was exposed to air only. All animals were exposed for a duration of 6 hr, and survivors were sacrificed 14 days following exposure. The respiratory tract was removed and examined microscopically from all animals. Guinea pigs were more sensitive to the MIC vapor than were rats which were in turn more sensitive than mice. Gross lesions encountered in many of the animals that died consisted of nasal discharge, often blood tinged, and discoloration of the lungs. Microscopic lesions included acute necrosis of epithelial lining throughout the respiratory tract in animals that died shortly after exposure coupled with congestion, edema, and inflammation. A microscopic lesion which appeared unique to guinea pigs was bronchiolitis obliterans where the necrosis and inflammation had completely closed the bronchioles. Additional microscopic lesions observed in some animals that died or were sacrificed at the end of the study (postexposure Day 14) consisted of squamous metaplasia of respiratory epithelium in the nasal cavity, which extended into the larynx, trachea, and, in some cases, the bronchi. In addition, epithelial regeneration throughout the tract and submucosal fibroplasia in the trachea, bronchi, and bronchioles were observed, the latter lesion being primarily confined to rodents. No animals exposed to 2.4 or 1.0 ppm of MIC vapor died following exposure. There were minimal microscopic lesions at sacrifice in the 2.4 ppm-exposed animals from all three species. Only in guinea pigs were there lesions in the 1.0-ppm group attributed to MIC vapor exposure.

The acute toxicity and primary irritancy of 2,4-pentanedione

2,4-Pentanedione was found to have acute peroral LD50 values (with 95% confidence limits) in the rat of 0.78 (0.66-0.91) ml/kg for males and 0.59 (0.51-0.70) ml/kg for females, and acute percutaneous LD50 values by 24 hr occluded contact on the rabbit of 1.41 (0.80-2.49) ml/kg for males and 0.81 (0.59-1.12) for females. Lt50 values for exposure of rats to saturated vapor atmospheres were 52 min (7060 ppm) for males and 55 min (7912 ppm) for females. The 4 hr LC50 value for rats was 1224 (1063-1409) ppm for combined male and female data. A 4 hr occluded contact with 0.5 ml produced mild local erythema and edema. Instillation of 0.1 ml into the inferior conjunctival sac, produced mild conjunctivitis of less than 24 hr duration without corneal injury.

Monochlorodiisobutylene vapor: acute and 9-day inhalation studies in Fischer-344 rats and B6C3F1 mice

Acute and 9-day repeated exposures to monochlorodiisobutylene (CDIB) were conducted in male and female Fischer-344 rats and B6C3F1 mice. The 4-hr LC50 values for these animals ranged between 1400 and 2100 ppm. Animals in the 9-day study were exposed at a mean concentration of 478, 97, or 25 ppm of CDIB for 6 hr per day. Treatment-related effects differed between species in this study. Body weight change was decreased in rats. Morphologic changes in the kidneys with accompanying polyuria and hematuria/hemoglobinuria were observed in male rats. The only effect observed at 25 ppm was a low incidence of hematuria/hemoglobinuria in male rats. Mice appeared unaffected by exposure to CDIB at levels as high as 478 ppm.

The acute toxicity and primary irritancy of N-benzyl-N,N-dimethylamine

N-Benzyl-N,N-dimethylamine (BDMA), a polyester foam catalyst, was determined to have LD50 values of 0.65 (0.48-0.88) ml/kg perorally in the rat, and 1.66 (1.35-2.04) ml/kg by 24-hr occluded dermal contact in rabbits. The Lt50 for saturated vapor atmosphere exposure of rats was 35.4 min, and the 4-hr LC50 was 373 (311-447) ppm for rats and mice. Histological examination of the respiratory tract of animals exposed to BDMA concentrations of 277 ppm or higher revealed acute inflammatory changes in the nasal mucosa and pulmonary congestion. Unoccluded skin contact with 0.01 ml undiluted BDMA in rabbits produced moderate local erythema and edema. A 4-hr occluded contact resulted in local necrosis. Severe eye irritancy was produced by 0.005 ml undiluted BDMA and 0.5 ml 5% BDMA in propylene glycol; 1% BDMA was nonirritant to the eye. BDMA should be regarded as an acutely hazardous material by all routes of exposure.