Irvin M. Pritts

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.

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.

Effects of ethylene on micronucleus formation in the bone marrow of rats and mice following four weeks of inhalation exposure

Male Fischer 344 rats and male B6C3F1 mice (10/species/group) were exposed to ethylene 6 h/day, 5 days/week, for 4 weeks. The ethylene target concentrations were 0, 40, 1000, and 3000 ppm. An ethylene oxide (EO) control group for each species was exposed under the same conditions at a target concentration of 200 ppm. Bone marrow was collected approximately 24 h after the final exposure. Polychromatic erythrocyte (PCE) to normochromatic erythrocyte (NCE) ratios were determined and 2000 PCE/animal were scored for the presence of micronuclei. Ethylene did not produce statistically significant, exposure-related increases in the frequency of micronucleated PCE (MNPCE) in the bone marrow of either rats or mice when compared to air-exposed control animals. As expected, EO exposure resulted in significant increases in the frequencies of MNPCE in both species.

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.

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 (con trol) 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 fol lowing 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 mag nitude. 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 nephro sis with regard to human exposure is unknown.

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.

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)

Developmental toxicity evaluation of inhaled methyl isobutyl ketone in Fischer 344 rats and CD-1 mice.

Pregnant Fischer 344 rats and CD-1 mice were exposed to methyl isobutyl ketone vapor (CAS No. 108-10-1) by inhalation on Gestational Days 6 through 15 at concentrations of 0, 300, 1000, or 3000 ppm (mean analytical values of 0, 305, 1012, and 2997 ppm, respectively). The animals were sacrificed on Gestational Day 21 (rats) or 18 (mice), and live fetuses were examined for external, visceral, and skeletal alterations. In rats, exposure to 3000 ppm resulted in maternal toxicity expressed as clinical signs, decreased body weight and body weight gain, increased relative kidney weight, and decreased food consumption, and in fetotoxicity expressed as reduced fetal body weight per litter and reductions in skeletal ossification. In mice, exposure to 3000 ppm resulted in maternal toxicity expressed as exposure-related increases in deaths (12.0%, 3/25 dams), clinical signs, and increased absolute and relative liver weight, and in fetotoxicity expressed as increased incidence of dead fetuses, reduced fetal body weight per litter, and reductions in skeletal ossification. No treatment-related increases in embryotoxicity or fetal malformations were seen in either species at any exposure concentration tested. There was no evidence of treatment-related maternal, embryo, or fetal toxicity (including malformations) at 1000 or 300 ppm in either species.

Developmental toxicity study of inhaled acrylic acid in New Zealand white rabbits

In range-finding and definitive developmental toxicity studies, timed pregnant New Zealand White rabbits were exposed to acrylic acid (CAS No. 79-10-7) vapour for 13 consecutive days during pregnancy. In the range-finding study, eight pregnant does/group were exposed to 30, 60, 125 or 250 ppm acrylic acid vapour on gestation days (gd) 10-22 of pregnancy. Monitors of toxicity included body weight measurements, daily food consumption measurements and clinical observations. Three of the eight does/group were killed on the day following the last exposure (gd 23), and the remaining does were killed and autopsied on gd 29. At autopsy, special attention was given to gross observation of maternal nasal turbinates, and nasal turbinates from all does were evaluated histologically. No evaluation of foetuses was performed in the range-finding study. In the definitive study, 16 does/group were exposed to concentrations of 25, 75 or 225 ppm acrylic acid vapour from gd 6 to 18, the major period of organogenesis. Monitors of maternal toxicity included clinical observations and measurements of body weight and daily food consumption measurements. Does were killed and autopsied on gd 29. Maternal liver and kidney weights were measured and external, visceral and skeletal evaluations of foetuses were conducted. Maternal nasal turbinates were not evaluated histologically in the definitive study. Effects in does from both studies included consistent concentration-related reductions in food consumption and body weight gains throughout the exposure period at concentrations of acrylic acid vapour above 60 ppm. Characteristic clinical signs of sensory irritation, including perinasal and perioral wetness and severe nasal congestion, were noted in does from both studies at or above vapour concentrations of 75 ppm. Gross observation of nasal turbinates immediately following exposures in the range-finding study indicated colour changes in the nasal turbinates of does in the 60 and 250 ppm groups. Colour changes in the nasal turbinates were noted in one doe from the 250 ppm exposure group killed on gd 29. Pertinent autopsy findings in the does from the definitive study included ulceration of the nasal turbinates of a single doe in the 225 ppm group. Histological evaluation of turbinates from does killed the day following exposures in the range-finding study revealed lesions in the nasal epithelium in all acrylic acid-exposed groups. The severity of the lesions was concentration related. Microscopic evaluation of turbinates from does killed on gd 29 showed the presence of nasal lesions in the 60, 125 and 250 ppm groups. However, the nasal tissues had recovered considerably during the post-exposure interval. Despite the severe effects on the nasal mucosa of does in both studies, there was no evidence of developmental toxicity including teratogenicity at any exposure concentration used in the definitive study.