Darol E. Dodd

Ethylene glycol monobutyl ether: Acute, 9-day, and 90-day vapor inhalation studies in Fischer 344 rats

The acute 4-hr LC50 (with 95% confidence limits) for Fischer 344 rats was determined to be 486 (339 to 696) ppm of ethylene glycol monobutyl ether (EGBE) for males and 450 (315 to 645) ppm for females. Notable observations included loss of coordination, red stained urine, and enlarged discolored kidneys at 867 and 523 ppm. In a subsequent study, rats were exposed for 9 days (6 hr/day) to EGBE concentrations of 245, 86, 20, or 0 (control) ppm. There were significant depressions of red blood cell (RBC) count (approximately 20% below control values), hemoglobin (Hgb), and mean corpuscular hemoglobin (MCH) concentration and increases in nucleated erythrocytes, reticulocytes, and lymphocytes in males and females of the 245 ppm group. Decreased body weight gains and increased liver weights were also found. A 14-day postexposure recovery showed substantial reversal of the affected blood parameters. Similar, but less marked, hematologic effects were observed in rats exposed to 86 ppm of EGBE, while rats of the 20 ppm group were indistinguishable from controls. In a 90-day study, rats were exposed to EGBE concentrations of 77, 25, 5, or 0 ppm for 13 weeks (6 hr/day, 5 days/week). Slight, but statistically significant, decreases in RBC (13% below control) and Hgb, accompanied by an increase in MCH (11% above control) were observed in the 77 ppm-exposed females after 6 weeks. At the conclusion of the 90-day exposure regimen, the hematologic effects seen in the females had lessened (RBC was 7% below control) or returned to control value ranges. Furthermore, no treatment-related differences were found in body weight, organ weights, urine or serum chemistries, gross lesions, or microscopic lesions in males or females. There were no significant biological effects in rats exposed subchronically to 25 or 5 ppm. The subtle hematologic findings of these studies confirm the known RBC perturbations of EGBE.

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.

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.

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)

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.

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)

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 statically 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 occular 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.

Developmental 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).

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, 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)