A chronic inhalation toxicity/oncogenicity study of methylethylketoxime in rats and mice.

To evaluate the oncogenic potential of methylethylketoxime (MEKO), CD-1 mice (50/sex/group) and F-344 rats (50/sex/group) were coexposed 6 h/day, 5 days/wk for 18 mo (mice) or 26 mo (rats) via whole-body inhalation exposures to target vapor concentrations of 0, 15, 75, and 375 ppm (actual concentrations of 0, 15 +/- 1, 75 +/- 2, or 374 +/- 10 ppm). Satellite groups of rats and mice (10/sex/group/interval) were exposed for 12 mo (mice) and 3, 12, or 18 mo (rats) to evaluate chronic toxicity. Methyl ethyl ketone (MEK), a possible hydrolysis product of MEKO, was present at less than 1%. Treatment-related effects included increased body weight (male rats only), methemoglobin formation, hematology and clinical chemistry changes, increased liver weight, and increased spleen and testes weights (rats only). A high incidence of cataracts and corneal dystrophy occurred in both control and MEKO-exposed rats, with an earlier appearance and slightly higher incidence for these ocular lesions in MEKO-exposed animals compared to controls. Degenerative and reparative changes of the olfactory epithelium in the nasal turbinates, primarily limited to the dorsal meatus, occurred in both rats (75 and 374 ppm) and mice (15, 75, and 374 ppm). In addition, in the mice, liver changes included increased incidences of pigment in reticuloendothelial cells, centilobular hypertrophy, granulomatous inflammation, and a slightly increased incidence of necrosis (75 and 374 ppm). An increase in hepatocellular carcinomas occurred in male mice at 374 ppm. Additional MEKO-related findings in the rat included congestion of the spleen with pigment in reticuloendothelial cells and extramedullary hematopoiesis and a decreased incidence of lymphoreticular mononuclear cell leukemia. Effects observed in the liver of the rats included decreases in the incidence of both peribiliary fibrosis and hyperplasia/proliferation of the biliary duct, an increase of spongiosis hepatis in males, and an increase in the incidence of intracytoplasmic vacuoles and hepatocellular basophilic foci. The effects on the liver were generally most profound in the high-exposure groups and, with the exception of the spongiosis hepatis, occurred in both sexes. An increase in hepatocellular adenomas occurred in the male rats at 75 and 374 ppm, and hepatocellular carcinomas in the male rats at 374 ppm. In both species, the liver tumors appeared relatively late in the life of the animals, with no significant increase in tumors at 12 mo of exposure in mice and at 18 mo of exposure in rats. Lifespan shortening was not observed, as MEKO-exposed animals survived generally as well as, or slightly better than, the controls.

Methyl bromide 1-year dietary study in dogs.

Average human exposure resulting from consumption of methyl I bromide (MB)-fumigated food has been estimated to be 0.00125 mg/kg/day. A 1-yr feeding study in beagle dogs was conducted as a safety study in which the high-dose diet was intended to yield a methyl bromide dose of at least 100 times the calculated human dietary exposure. Diets were fumigated with MB and fed to the dogs daily, except for weekends and holidays. MB consumption each feeding day was calculated as a time weighted average (TWA) that accounted for the rate of degassing from the fumigated diet and the rate of feed consumption during the feeding period. TWA compound consumption in the loss-, mid- and high-dose groups, respectively, averaged 0.06 ¿ 0.02, 0.13 ¿ 0.03 and 0.28 ¿ 0.08 mg/kg/day in males and 0.07 ¿ 0.03, 0.12 ¿ 0.03 and 0.27 ¿ 0.09 mg/kg/day in females. Clinical observations, body weight and feed consumption, ophthalmology, clinical pathology, urinalysis, organ weights and macroscopic and microscopic pathology were comparable in control and MB-treated dogs. Under the conditions of this study. the no-observed-effect level (NOEL) for MB was at least 0.28 mg/ kg/day, or approximately 200 times the expected average human dietary exposure.

A 2-year inhalation study of phosphine in rats.

Phosphine is a highly toxic gas used as a fumigant, a dopant in semiconductor manufacturing, and in the production of organophosphines. In a chronic toxicity and oncogenicity study of phosphine, 60 male and female F344 rats per group were exposed via whole-body inhalation for 6 h/day, 5 days/wk for up to 104 wk to mean concentrations of 0, 0.3, 1, or 3 ppm phosphine. Three parts per million was considered the maximum exposure level because of lethality seen at higher exposure levels in previous repeat dose studies. Ten rats per sex per group were sacrificed after 52 wk of exposure. Survivors were sacrificed after 104 wk of exposure. There were no phosphine-related effects seen on clinical observations, body weight, food consumption, hematology, clinical chemistry, urinalysis, or ophthalmology. There were no phosphine-related macroscopic findings or effect on absolute or relative organ weights. No histomorphologic alterations attributable to phosphine exposure were seen. In conclusion, under the conditions of this study, there were no treatment-related changes suggestive of a toxic or carcinogenic effect seen in rats following 52 wk or 2 yr of whole-body inhalation exposure to 0.3, 1, or 3 ppm phosphine.

Methyl bromide: 1-year dietary study in dogs.

Average human exposure resulting from consumption of methyl bromide (MB)-fumigated food has been estimated to be 0.00125 mg/kg/day. A 1-yr feeding study in beagle dogs was conducted as a safety study, in which the high-dose diet was intended to yield a methyl bromide dose of at least 100 times the calculated human dietary exposure. Diets were fumigated with MB and fed to the dogs daily, except for weekends and holidays. MB consumption each feeding day was calculated as a time weighted average (TWA) that accounted for the rate of degassing from the fumigated diet and the rate of feed consumption during the feeding period. TWA compound consumption in the low-, mid- and high-dose groups, respectively, averaged 0.06 +/- 0.02, 0.13 +/- 0.03 and 0.28 +/- 0.08 mg/kg/day in males and 0.07 +/- 0.03, 0.12 +/- 0.03 and 0.27 +/- 0.09 mg/kg/day in females. Clinical observations, body weight and feed consumption, ophthalmology, clinical pathology, urinalysis, organ weights and macroscopic and microscopic pathology were comparable in control and MB-treated dogs. Under the conditions of this study, the no-observed-effect level (NOEL) for MB was at least 0.28 mg/kg/day, or approximately 200 times the expected average human dietary exposure.

Subchronic and chronic inhalation toxicity of antimony trioxide in the rat.

Fischer 344 rats were exposed by inhalation to Sb2O3 (antimony trioxide) dust at exposure levels of 0, 0.25, 1.08, 4.92, and 23.46 mg/m3 for 6 hr/day, 5 days/week for 13 weeks followed by a 27-week observation period. Subsequently, an inhalation oncogenicity study was conducted at exposure levels of 0, 0.06, 0.51, and 4.50 mg/m3 for 12 months followed by a 12-month observation period. The Sb2O3 in the subchronic study had a mass median aerodynamic diameter (MMAD) of 3.05 +/- 0.21 microns (mean +/- SD) with a geometric standard deviation (GSD) of 1.57 +/- 0.06. In the chronic study, the MMAD was 3.76 +/- 0.84 and the GSD was 1.79 +/- 0.32. Except for the eyes, no adverse clinical observations were attributed to Sb2O3 in either study. In the subchronic study, corneal irregularities were seen after about 2 weeks of exposure and did not abate during the observation period. In the chronic study, ophthalmoscopic evaluation at 24 months revealed a dose-related increase in cataracts of 11, 24, 28, and 32% (both sexes combined) for each group, respectively. Body weights were significantly lower (6%) than the control group's weights in the 23.46 mg/m3 males in the subchronic study. These rats did not recover this weight during the 27-week observation period. Body weights of the females in both studies and males in the chronic study were unaffected. There were no Sb2O3 effects on clinical chemistry or hematology in either study. Mean absolute and relative lung weights were significantly increased in the 4.92 and 23.46 mg/m3 groups in the subchronic study. The 23.46 mg/m3 group's lung weights did not recover to control levels during the 27-week observation period. Lung weights for rats in the chronic study were unaffected. Microscopic changes in the lungs in the subchronic and chronic study were limited to subacute-chronic interstitial inflammation, increased numbers of alveolar-intraalveolar macrophages, foreign material in the alveolar-intraalveolar macrophages in the peribronchial and perivascular (chronic study only) lymphoid aggregates and in the peribronchial lymph nodes, granulomatous inflammation/granulomas, and fibrosis. In the chronic study, any observed neoplasms occurred with comparable incidence among all groups and were within the historical range for controls. Clearance of Sb2O3 from the lung was burden dependent and was reduced by 80% in the 4.50 mg/m3 group in the chronic study. The previously reported studies, which found Sb2O3 to be a carcinogen, were run at higher lung burdens. Under the exposure conditions of the current study, Sb2O3 was not a carcinogen.

Toxicity of calcium sodium metaphosphate fiber. II. Chronic inhalation and oncogenicity study.

Male and female Fischer 344 rats (80/sex/group) were exposed to CSM fiber 6 hr/day, 5 days/week at target-exposure levels of 0, 1, 5, or 25 mg/m3 for 24 months, corresponding to 0, 27, 80, and 513 fibers/cc, respectively. Number and size of the airborne fibers were determined during the course of the study. At 3 and 12 months, 10 rats/sex/group were euthanized and at 18 and 24 months 5 rats/sex/group were euthanized. In addition, 5 rats/sex/group were removed from exposure at 18 months and maintained for a 6-month recovery period. All animals surviving at the completion of the exposure period were maintained in a clean environment for up to 5 additional months. Clinical laboratory examinations were performed on 10 animals/sex/group at 3, 12, and 24 months. The number of fibers in the lung were also determined at 3, 12, 18, and 24 months. Body weight and survival did not appear to be affected by treatment. There were no biologically significant effects on clinical parameters. There was a dose-related increase in lung weight during the exposure period which was generally reversible during the recovery periods. There also was a dose-related increase in the number of fibers/milligram of lung, but no increase in lung fiber burden after the first 3 months. The number of fibers in the lungs of animals exposed to CSM fiber for 18 months and allowed 6-month recovery period showed a decrease especially at the high dose. No increase in tumors (benign or malignant) was observed in this study. Microscopic changes considered reflective of an irritant response were observed in the nasal turbinates notably at the 5 and 25 mg/m3 levels. Histological changes were also observed in the lungs at the 5 and 25 mg/m3 levels. The incidence and/or severity of histopathological changes in the 1 mg/m3 group was considered to be essentially comparable to controls.

Acute inhalation toxicity studies in several animal species of an ethylene oxide/propylene oxide copolymer (UCON 50-HB-5100).

An acute inhalation toxicity study in several species of animals with an ethylene oxide/propylene oxide copolymer (EO/PO) having a molecular weight of 4000 [UCON-50-HB-5100, CAS #9038-95-3] was designed to determine if any species variation could be shown. Species tested included: rats, mice, hamsters, guinea pigs, and dogs. The test material was administered as a respirable liquid aerosol for 4 hours at target concentrations of 50, 100, 200, and 500 mg/m3. A vehicle control group was exposed to a distilled water aerosol. The 4 hours LC50's were calculated to be 147 mg/m3 [rats], 174 mg/m3 [mice], 293 mg/m3 [guinea pigs] and 511 mg/m [hamsters]. The dog LC50 was determined to be greater than 500 mg/m3 since all the test animals survived exposure to this concentration. These values show that rats and mice were the most sensitive species with a declining response in guinea pigs, hamsters and dogs. Lung weights were increased at all exposure concentrations in rats, mice and hamsters. Lung weights were increased in guinea pigs at exposure concentrations of 100 mg/m3 and above. Lung weights in dogs were increased only at the 500 mg/m3 exposure concentration. Significant pathological changes were limited to the lungs and were more common in animals which died prior to scheduled sacrifice. Grossly, these lung changes consisted of red discoloration, edema, emphysema, and surface irregularities. Microscopic findings in the lungs included acute congestion and hemorrhage and, less commonly, acute interstitial inflammation.

Measurement of the deposition and clearance of inhaled radiolabeled particles from rat lungs.

Immediately after a 20 min nose only exposure to 51Cr labeled polystyrene latex microspheres (1.4 MMAD, geometric standard deviation = 1.3, 2 micrograms m-3), 23% of the measured radioactivity was within the trachea-lungs of the exposed rats, 37% was within the gastrointestinal tract, 10% was within the defurred head, and 30% was on the fur. One hour after deposition these percentages had changed to 20, 64, 5 and 11%, respectively. As a result of this non-pulmonary particle load transiting the esophagus, external thoracic radioactivity measurements did not accurately reflect excised lung measurements until 30 h post-deposition. Consequently, it was necessary to combine excised lung ratioactivity data (0-30 h post deposition) with serial external thoracic measurements (30-934 h post-deposition) to measure the clearance of these microspheres. Use of an annulus shaped detector sufficiently increased sensitivity to allow measurements to be made through at least 934 h post-deposition. The lung radioactivity retention curve was biexponential with half times of 34.3 +/- 2.3 and 963 +/- 107 h. Simultaneous exposures to 5% CO2 increased deposition by 40% but failed to reduce deposition inhomogeneity and test variability.

Alterations in alveolar clearance after 4-ipomeanol-induced necrosis of Clara and ciliated cells in the terminal bronchiole of the rat.

The administration of 4-ipomeanol, [0, 10 (LD), and 25 (HD) mg/kg, ip], to rats resulted in dose-dependent degeneration and necrosis of the nonciliated (Clara) and ciliated epithelial cells of the terminal bronchioles. More extensive necrosis of the terminal bronchiolar epithelium, with exposure of the basement membrane, was produced in the HD group. Repair of the terminal bronchiolar epithelium was complete within 10 days. Alveolar clearance of 51Cr labeled polystyrene latex microspheres was analyzed through 40 days postinstillation by nonlinear regression for a double exponential model. Alveolar clearance during phase 1 (Days 2 to 6) was delayed and significantly decreased in both the LD and HD groups. Alveolar clearance during phase 2 (Days 10 to 40) was significantly decreased only in the HD group. The decreased alveolar clearance in HD subjects was long term and did not correlate with the return of morphologically normal appearing Clara and ciliated cell structure.

Measurement of ventilation using digitally filtered transthoracic impedance.

A seven-stage low-pass digital filter was used to remove the cardiac artifact and motion interference from a respiratory transthoracic impedance signal in human subjects. After removal of these artifacts, the mean difference from a conventional gasometer technique fell from 5% to 1.6%. When the impedance technique was used to measure ventilation during air breathing, the addition of a breathing valve with a mouthpiece and noseclip induced the following changes in ventilatory parameters: 7% drop in frequency, 24% increase in tidal volume, 49% increase in inspiratory time, 56% increase in expiratory time, 10% decrease in inspiratory flow rate, and 4% decrease in ratio of respiratory time to total breath duration. These alterations were not significant at elevated inspired CO2 levels. The digitally filtered transthoracic impedance technique provides an accurate technique for measuring ventilatory parameters without the perturbations induced by using a conventional breathing valve technique even when cardiac and motion artifacts were prominent.

Gas chromatographic determination of 1,2-propanediol dinitrate in blood.

A method is described for determination of 1,2-propanediol dinitrate in blood at concentrations ranging from 10 ng/ml up to 25,000 ng/ml. It used double ether extraction with manual shaking in order to complete sample preparation within 5 min. Samples are analyzed via gas chromatography-electron-capture detection using a column of 3% base deactivated SP-2250 on Supelcoport. This column provides excellent separation and little 1,2-propanediol dinitrate tailing.

Physiological response to aerosol propellants.

Acute exposures to isobutane, propane, F-12, and F-11 in concentrations of 250, 500, or 1000 ppm for periods of 1 min to 8 hr did not produce any untoward physiological effects as determined by the methods employed which included serial EKG's and continuous monitoring of modified V5 by telemetry during exposure. Repetitive exposures to these four propellants were also without measurable untoward physiological effect with the exception of the eight male subjects repetitively exposed to 1000 ppm, F-11, who did show minor decrements in several of the cognitive tests. Of particular importance is the observation that none of the subjects showed any decrement in pulmonary function or alteration in cardiac rhythm as the result of exposure to concentrations of the gases or vapors far greater than encountered in the normal use of aerosol products in the home.

Acute and repetitive human exposure to isobutane.

Eight adult volunteers of both sexes were exposed to isobutane in a controlled-environment chamber for the purpose of monitoring their physiological responses to a series of gas concentrations ranging from 250 to 1,000 ppm. First, the response to exposure periods of 1 min, 2 min, 1 h, 2 h, and 8 h were studied. There being no untoward responses to these acute exposures, the eight volunteers were exposed repetitively to isobutane at concentrations of 500 ppm, 1, 2 or 8 h per day, five days per week for two weeks. Then exposures to two mixtures of isobutane and propane for 1, 2 or 8 h per day for two days were studied. During the investigation all subjects were kept under comprehensive medical surveillance. No untoward subjective responses or abnormal physiological responses occurred during or following these exposures. Special emphasis was placed on evaluating the cardiac and pulmonary response to these exposures through the use of continuous ECG telemetry and serial computerized spirometric measurements. The following serial laboratory studies were unaltered by the exposures: complete blood count, urinalysis, serum alkaline phosphatase, SGOT, LDH, serum bilirubin, blood sugar, serum calcium, serum phosphorus, BUN, spontaneous electroencephalogram, visual evoked response, a battery of cognitive tests, and an ACTH stimulation test.