R.R. Miller

Toxicity of Methoxyacetic Acid in Rats

Male Fischer 344 rats were given eight daily doses of 0, 30, 100 or 300 mg/kg methoxyacetic acid by gavage. The high dose resulted in decreased body weight, severe degeneration of testicular germinal epithelium, decreased size of the thymus with depletion of thymic cortical lymphoid elements, and reductions in bone marrow cellularity resulting in depressions of red blood cell counts, hemoglobin concentration, packed cell volume, and white blood cell counts. Some of these observations were apparent to a lesser degree in rats given 100 mg/kg. The low dose produced no apparent effects during the course of the study. These toxicological properties of methoxyacetic acid are remarkably similar to ethylene glycol monomethyl ether (EGME), and the adverse effects of EGME in rats are probably the result of in vivo bioactivation of EGME to methoxyacetic acid.

Chronic Toxicity and Oncogenicity Bioassay of Inhaled Ethyl Acrylate in Fischer 344 Rats and B6c3f1 Mice

Male and female Fischer 344 rats and B6C3F1 mice were exposed to 0, 25 or 75 ppm (0, 0.10 or 0.31 mg/l) ethyl acrylate vapors, 6 hours per day, 5 days per week, for a total of 27 months. Additional rats and mice were exposed to 225 ppm (0.92 mg/l) for 6 months and then held for 21 additional months post-exposure. Histopathologic changes in olfactory portions of the nasal mucosa were present in animals in all of these three exposure groups. These microscopic exposure-related changes were concentration-dependent, primarily in terms of distribution of the lesions within the nasal cavity. Generally those areas of the nasal mucosa normally lined by olfactory epithelium were altered, while the regions lined by respiratory epithelium were relatively unaffected. There was no indication of an oncogenic response in any organ or tissue in either rats or mice. A follow-up study in which Fischer 344 rats and B6C3F1 mice were exposed to 5 ppm (0.02 mg/l) for 24-months revealed no treatment-related changes in the nasal mucosa.

Inhalation Toxicity of Acrylic Acid

Male and female Fischer 344 rats and B6C3F1 mice were exposed to 0, 5, 25 or 75 ppm acrylic acid vapors 6 hours per day, 5 days per week, for 13 weeks. These exposure levels were selected after conducting a 2-week probe study in which 225 ppm caused pronounced growth retardation and nasal lesions in both rats and mice. The 13-week exposures had no adverse effect on the growth of male and female rats and male mice. However, mean body weight gains of female mice in the 25 and 75 ppm exposure groups were statistically significantly lower than for controls after 12 weeks of exposure. There were no pronounced treatment related effects on organ weights, hematologic parameters, clinical chemistry parameters or urinary parameters. Histopathologic examinations revealed lesions of the nasal mucosa in rats in the 75 ppm exposure group, and in some or all mice at each treatment level. The nasal lesions were primarily localized to the olfactory epithelium; the respiratory epithelium was relatively unaffected. The histopathologic observations in both rats and mice included degeneration, and inflammatory cell infiltration in the olfactory mucosa. In mice there were also instances of hyperplasia of the submucosal glands and, replacement of olfactory epithelium by respiratory epithelium. These effects were attributed to the irritant properties of acrylic acid vapors.

Metabolism of acrylate esters in rat tissue homogenates

Methyl, ethyl and butyl acrylate were hydrolyzed to acrylic acid in rat liver, kidney and lung homogenates. The rates of hydrolysis of the various esters in these in vitro studies were comparable; hydrolysis rates were approximately 20 times higher in liver homogenates than in kidney or lung homogenates. The esters also disappeared rapidly when added to blood in vitro. However, the disappearance in blood was not associated with the appearance of acrylic acid. Ethyl acrylate was found to react spontaneously with GSH in vitro and this reaction was catalyzed greatly by enzymes in 100 000 x g liver supernatant. Acrylic acid did not react with GSH in vitro. Ethyl acrylate, but not acrylic acid, depletes non-protein sulfhydryls when added to blood in vitro. Thus, the disappearance of acrylate esters in blood in vitro could be due at least in part to binding with non-protein sulfhydryls in red blood cells rather than to hydrolysis.

Ethylene Glycol Monomethyl Ether II. Reproductive and Dominant Lethal Studies in Rats

Groups of male and female Sprague-Dawley (CD) rats were exposed to 0, 30, 100, or 300 ppm ethylene glycol monomethyl ether (EGME) vapor 6 hours/day, 5 days/week for 13 weeks. The 0 and 30 ppm groups each contained 30 rats/sex and the 100 and 300 ppm groups each had 20 rats/sex. Following the exposure period, males were bred to unexposed females to evaluate reproductive capability and dominant lethality. Additional matings of control and 300 ppm exposed males were performed during the post-exposure period in order to evaluate the recovery of fertility. Exposed females were bred with unexposed males to assess reproductive parameters. Results of the present study indicate a potential for inhaled EGME to completely suppress fertility in male rats at the 300 ppm level. Fertility of these rats was partially restored at 13 weeks post-exposure. Body weights of animals in the 300 ppm group were reduced as a result of the exposures. No dominant lethal effect or impaired fertility was observed in male rats exposed to 30 or 100 ppm EGME. Treatment-related pathologic alterations were observed only in male rats at the 300 ppm level and induced decreased testicular size and atrophic seminiferous tubules. Female rats tolerated up to 300 ppm EGME without any adverse reproductive effects. Based on these results, it was concluded that the no-adverse effect level of EGME for fertility and reproduction was 100 ppm in rats.

Subchronic Inhalation Toxicity of Ethylbenzene in Mice, Rats, and Rabbits

Mice, rats, and rabbits (five/sex/group) were exposed by inhalation to ethylbenzene (EB) vapors for 6 hr/day, 5 days/week for 4 weeks (20 exposures). Rats and mice received 0, 99, 382, or 782 ppm EB while rabbits received 0, 382, 782, or 1610 ppm. No changes were evident in mortality patterns, clinical chemistries, urinalyses, or treatment-related gross/microscopic (including ophthalmologic) lesions. Rats exhibited sporadic lacrimation and salivation, as well as significantly increased liver weights at 382 and 782 ppm, and small increases in leukocyte counts at 782 ppm. Males at this exposure level also showed marginal elevations in platelet counts. In mice, females showed statistically increased absolute and relative liver weights at 382 and 782 ppm, while males had statistically increased relative liver-to-brain weight ratios only at 782 ppm. Female rabbits at the high exposure level of 1610 ppm gained weight more slowly than controls (not statistically significant); males showed a similar transient downward trend after 1 week, but showed no differences from controls at studys end. A no observed adverse effect level (NOAEL) of 382 ppm appears appropriate for rats and mice with a lowest observed adverse effect level (LOAEL) of 782 ppm. A NOAEL of 782 ppm and LOAEL of 1610 ppm are appropriate for rabbits.

Hemolytic activity of ethylene glycol phenyl ether (EGPE) in rabbits.

Studies were conducted to characterize the hemolytic effects of EGPE in rabbits following oral and dermal exposure, and to evaluate the in vitro hemolytic potential of EGPE and its major metabolite using rabbit red blood cells (RBC). Gavage administration of EGPE to female New Zealand White rabbits at 100, 300, 600, or 1000 mg/kg/day for up to 10 consecutive days (one dose/day) resulted in a dose-related intravascular hemolytic anemia. The hemolytic anemia was characterized by decreased RBC count, hemoglobin concentration, packed cell volume, hemoglobinuria, splenic congestion, renal tubule damage, and a regenerative erythroid response in the bone marrow. The hemolytic anemia was observed without alterations in RBC glutathione or methemoglobin. Phenoxyacetic acid (PAA) was identified as a major blood metabolite of EGPE. In vitro exposure of female rabbit erythrocytes indicated EGPE to be considerably more hemolytic than PAA. In a 90-day dermal study in which EGPE was applied to the skin of male and female New Zealand White rabbits 6 hr/day, 5 days/week, at doses up to 500 mg/kg/day, there was no indication of a hemolytic response. The only treatment-related effects were sporadic occurrences of slight erythema and scaling of skin at the site of test material application in high dose group male and female rabbits. However, erythema and scaling were not associated with gross or histopathologic changes and were not considered toxicologically significant.

Incapacitation and Treatment of Rats Exposed to a Lethal Dose of Sulfuryl Fluoride

Rats exposed to 4000 ppm sulfuryl fluoride (VIKANE gas fumigant, SO2F2) were incapacitated within 45 min and died within several hours after exposure. Exposure to higher concentrations resulted in a shorter time to incapacitation and death occurred within minutes. Treatment with calcium gluconate before exposure to 4000 ppm SO2F2 for 45 min resulted in 80% survival. However, calcium gluconate did not alleviate SO2F2-induced convulsions. Administration of phenobarbital before or after exposure to 4000 ppm SO2F2 for 45 min effectively reduced the frequency and severity of convulsions and resulted in survival of all animals. Exposure of rats to 10,000 ppm SO2F2 for 15 min followed by treatment with phenobarbital reduced the frequency of convulsions and delayed death, but did not prevent death. Diazepam was less effective than phenobarbital while diphenylhydantoin had no beneficial effect and, in fact, made the convulsions more severe and longer in duration. The results of this study indicate that phenobarbital was effective in ameliorating the acute toxic effects of an overexposure to SO2F2 in rats.

Metabolism and Disposition of Dipropylene Glycol Monomethyl Ether (DPGME) in Male Rats

Male Fischer 344 rats were given a single oral dose of approximately 1289 mg/kg (8.7 mmol/kg) of [14C]DPGME. After dosing, expired air, excreta, and tissues were analyzed for 14C activity, and metabolites in urine were isolated and identified. Approximately 60% of the administered 14C activity was excreted in urine, while 27% was eliminated as 14CO2 within 48 hr after dosing. DPGME, PGME, dipropylene glycol, propylene glycol, as well as sulfate and glucuronide conjugates of DPGME were identified in urine of animals given [14C]DPGME. Results of the study indicate that DPGME is metabolized via the same routes to the same general types of metabolites as previously identified for propylene glycol monomethyl ether (PGME).

Diethylene Glycol Monomethyl Ether 13-Week Vapor Inhalation Toxicity Study in Rats

Male and female Fischer 344 rats were exposed to 0, 30, 100, or 216 ppm diethylene glycol monomethyl ether (DEGME) vapors (0, 0.15, 0.49, or 1.06 mg/liter) 6 hr/day, 5 days/week, for 13 weeks. The 216-ppm exposure level was the maximum practically attainable concentration, and it was more than 60% of the theoretical maximum vapor concentration for DEGME at 25 degrees C and 1 atm pressure. Body weights, organ weights, hematological analyses, clinical chemistry analyses, urinalyses, and gross and histopathological examinations revealed no indication of a treatment effect in either male or female rats. Based on the absence of treatment-related effects in this study and the low vapor pressure of the material, DEGME should not present the same degree of inhalation hazard as its structural homolog, ethylene glycol monomethyl ether.