The administration of bis(2-chloroethoxy)methane for 2 years resulted in increased incidences of nonneoplastic lesions in the nose of male and female rats, the forestomach of male rats, the heart of male and female mice, and the forestomach and skin of male mice.
Bis(2-chloroethoxy)methane is used as a solvent and the starting agent in the production of fungicides and polysulfide polymers. Bis(2-chloroethoxy)methane was nominated for study by the National Institute of Environmental Health Sciences because of its widespread use as a starting material to produce polysulfide elastomers, and because there were no 2-year carcinogenicity studies reported in the literature. Male and female F344/N rats and B6C3F1 mice received dermal applications of bis(2-chloroethoxy)-methane in ethanol (greater than 98% pure) for 2 weeks, 3 months, or 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium and Escherichia coli, rat bone marrow cells, and mouse peripheral blood erythrocytes.
Two-week study in rats
Groups of five male and five female rats were dermally administered 0, 12.5, 25, 50, 100, or 200 mg bis(2-chloroethoxy)methane/kg body weight in ethanol, 5 days per week for 16 days. All rats survived to the end of the study. Mean body weights of dosed rats were similar to those of the vehicle control groups. There were no histopathologic lesions related to bis(2-chloroethoxy)methane administration.
Two-week study in mice
Groups of five male and five female mice were dermally administered 0, 12.5, 25, 50, 100, or 200 mg bis(2-chloroethoxy)methane/kg body weight in ethanol, 5 days per week for 17 days. All mice survived to the end of the study. Mean body weights of dosed mice were similar to those of the vehicle control groups. There were no histopathologic lesions related to bis(2-chloroethoxy)methane administration.
Three-month study in rats
Groups of 10 male and 10 female rats were dermally administered 0, 50, 100, 200, 400, or 600 mg bis(2-chloroethoxy)methane/kg body weight in ethanol, 5 days per week for 14 weeks. Additional clinical pathology groups of 10 male and 10 female rats were administered the same doses for 23 days. All core study 600 mg/kg males and females and two 400 mg/kg females died before the end of the study. The cause of death was considered to be related to the cardiotoxic effect of bis(2-chloroethoxy)methane. There were no significant differences between final mean body weights of dosed rats and those of the vehicle control groups; the mean body weight gain of 400 mg/kg males was significantly less than that of the vehicle controls. Clinical findings included prostration and ataxia in 600 mg/kg rats during the first week of the study and nasal/eye discharge, lethargy, ataxia, and abnormal breathing in 400 and 600 mg/kg females beginning week 5. An enlarged heart was noted in one 100 mg/kg female rat. Relative kidney weights of 100, 200, and 400 mg/kg males were significantly greater than that of the vehicle control group. Increased incidences and severities of myofiber cytoplasmic vacuolization and interstitial mononuclear cell infiltration in the heart occurred in 400 and 600 mg/kg male and female rats and in 200 mg/kg females. Increased incidences and severities of myofiber necrosis occurred in 600 mg/kg males and females; one female each in the 200 and 400 mg/kg groups also had this lesion. Three 600 mg/kg males had atrial thrombosis.
Three-month study in mice
Groups of 10 male and 10 female mice were dermally administered 0, 50, 100, 200, 400, or 600 mg bis(2-chloroethoxy)methane/kg body weight in ethanol, 5 days per week for 14 weeks. Except for three 600 mg/kg females, all mice survived to the end of the study. Mean body weights of dosed and vehicle control mice were similar. One 600 mg/kg female that died early exhibited lethargy, abnormal breathing, and tremors, and one animal had clonic seizures. One 600 mg/kg female that died early had focal erosion of the glandular stomach and a focus in the duodenum found to consist of acute suppurative inflammation and thrombosis. Absolute and relative kidney weights of 400 and 600 mg/kg males and 600 mg/kg females were significantly greater than those of the vehicle control groups. Absolute liver weights of 400 and 600 mg/kg females were also significantly increased. Significantly increased incidences of myofiber cytoplasmic vacuolization occurred in 400 and 600 mg/kg females.
Two-year study in rats
Groups of 50 male and 50 female rats were dermally administered 0, 75, 150, or 300 mg bis(2-chloroethoxy)methane/kg body weight in ethanol, 5 days per week for 105 weeks. Survival of all dosed groups of rats was generally similar to that of the vehicle controls. Mean body weights of dosed rats were similar to those of the vehicle controls throughout the study. Clinical findings in 300 mg/kg females that died during the first year of the study included abnormal breathing, lethargy, thinness, nasal discharge, and ataxia.
Significantly increased incidences of degeneration of the olfactory epithelium in the nose occurred in all dosed groups of males and in 150 and 300 mg/kg females. The incidences of inflammation of the forestomach were significantly increased in 150 and 300 mg/kg males, and the incidence of ulcers was significantly increased in 300 mg/kg males. Increased incidences of cystic degeneration of the liver occurred in 150 and 300 mg/kg male rats; the incidence was significantly increased in the 300 mg/kg group.
Two-year study in mice
Groups of 50 male mice were dermally administered 0, 150, 300, or 600 mg bis(2-chloroethoxy)methane/kg body weight in ethanol, 5 days per week for 105 weeks. Groups of 50 female mice were dermally administered 0, 100, 200, or 400 mg/kg in ethanol, 5 days per week for 104 weeks. Survival of 600 mg/kg male mice was significantly less than that of the vehicle control group. Mean body weights of dosed mice were generally similar to those of the vehicle controls throughout the study. Clinical findings observed in 600 mg/kg male mice that died during the first year of the study included lethargy and thinness.
Myocardial heart changes were recorded according to the characteristic lesions of cardiomyopathy syndrome (necrosis, mononuclear cell infiltration, myocardial cell vacuolization, and interstitial fibrosis) separately, and in addition, where appropriate, they were also categorized as cardiomyopathy. Increased incidences of cardiomyopathy and mononuclear cell infiltration occurred in 600 mg/kg males and 400 mg/kg females; the incidences were significantly increased in 600 mg/kg males compared to the vehicle controls. Significantly increased incidences of cardiomyocyte vacuolization and interstitial fibrosis occurred in 600 mg/kg males. A few early deaths in the 600 mg/kg males were considered to be due, at least in part and probably exclusively, to bis(2-chloroethoxy)methane-induced cardiotoxicity.
The incidence of ulceration of the forestomach was significantly increased in 600 mg/kg males.
Significantly increased incidences of dermal inflammation and fibrosis and epidermal hyperplasia at the site of application occurred in 600 mg/kg male mice.
Genetic toxicology
Bis(2-chloroethoxy)methane was mutagenic in S. typhimurium strains TA100 and TA1535 in the presence of exogenous metabolic activation enzymes (S9) in one study; results from a second bacterial mutagenicity test were judged to be equivocal based on responses observed in TA100 and in E. coli strain WP2 uvrA/pKM101 in the presence of S9. No mutagenicity was observed in other tester strains or in the absence of S9. Bis(2-chloroethoxy)methane did not increase the frequency of micronucleated reticulocytes in bone marrow of male F344/N rats following three daily treatments by gavage or micronucleated erythrocytes in peripheral blood of male or female mice after 3 months of dermal exposure.
Conclusions
Under the conditions of these 2-year dermal studies, there was no evidence of carcinogenic activity of bis(2-chloroethoxy)methane in male or female F344/N rats administered 75, 150, or 300 mg/kg. There was no evidence of carcinogenic activity of bis(2-chloroethoxy)methane in male B6C3F1 mice administered 150, 300, or 600 mg/kg or in female B6C3F1 mice administered 100, 200, or 400 mg/kg.
Methyl isobutyl ketone is used as a denaturant for rubbing alcohol; as a solvent for paints, varnishes, nitrocellulose, lacquers, and protective coatings; in industrial extraction processes; in dry-cleaning preparations; and in the synthesis of methyl isobutyl carbinol. Methyl isobutyl ketone was nominated for study by the National Cancer Institute and the United States Environmental Protection Agency because of its widespread use, the high potential for worker exposure due to its many industrial applications, and its high production volume. Male and female F344/N rats and B6C3F1 mice were exposed to methyl isobutyl ketone (greater than 99% pure) by inhalation for 2 years. Genetic toxicology studies were conducted in Salmonella typhimurium.
Two-year study in rats
Groups of 50 males and 50 females were exposed to methyl isobutyl ketone at concentrations of 0, 450, 900, or 1,800 ppm by inhalation, 6 hours plus T90 (12 minutes) per day, 5 days per week for 104 weeks. Survival of males exposed to 1,800 ppm was significantly less than that of the chamber controls. The mean body weights of the 900 and 1,800 ppm males were less than those of the chamber controls after weeks 97 and 89, respectively.
In the standard evaluation of the kidney, there were slightly increased incidences of renal tubule adenoma and renal tubule adenoma or carcinoma (combined) in males exposed to 900 or 1,800 ppm, and renal tubule carcinoma in males exposed to 1,800 ppm. The incidences of renal tubule hyperplasia were also significantly increased in the 450 and 1,800 ppm males, and the severities were greater than in the chamber controls. Chronic nephropathy occurred in all males exposed to 1,800 ppm and in 70% to 88% of exposed females, and the severity was increased in 1,800 ppm males. The incidences of transitional epithelial hyperplasia of the renal pelvis in males exposed to 900 or 1,800 ppm and mineralization of the renal papilla in all groups of exposed males were significantly increased. In addition, two female rats exposed to 1,800 ppm had renal mesenchymal tumors. In the extended evaluation of the kidney, renal tubule adenomas and renal tubule hyperplasia occurred in all groups of exposed male rats. In the combined single and step section analysis, the incidences of renal tubule adenoma and renal tubule adenoma or carcinoma (combined) were significantly increased in males exposed to 1,800 ppm. The incidences of renal tubule hyperplasia were also significantly increased in all exposed groups of males.
There was a positive trend in the incidences of mononuclear cell leukemia in males, and the incidence in the 1,800 ppm group was significantly increased. The incidence of adrenal medulla hyperplasia in the 1,800 ppm males was significantly increased.
Two-year study in mice
Groups of 50 males and 50 females were exposed to methyl isobutyl ketone at concentrations of 0, 450, 900, or 1,800 ppm by inhalation, 6 hours plus T90 (12 minutes) per day, 5 days per week for 105 weeks. Survival of males and females was similar to that of the chamber controls. The mean body weights of females exposed to 1,800 ppm were less than those of the chamber controls after week 17.
The incidences of hepatocellular adenoma and hepatocellular adenoma or carcinoma (combined) were significantly increased in males and females exposed to 1,800 ppm. The incidences of eosinophilic foci were significantly increased in 450 and 1,800 ppm females.
Genetic toxicology
Methyl isobutyl ketone was not mutagenic in Salmonella typhimurium strains TA97, TA98, TA100, or TA1535 when tested with and without hamster or rat liver metabolic activation enzymes.
Conclusions
Under the conditions of these 2-year studies, there was some evidence of carcinogenic activity of methyl isobutyl ketone in male F344/N rats based on increased incidences of renal tubule neoplasms. Increased incidences of mononuclear cell leukemia in 1,800 ppm male F344/N rats may have been related to methyl isobutyl ketone exposure. There was equivocal evidence of carcinogenic activity of methyl isobutyl ketone in female F344/N rats based on the occurrence of renal mesenchymal tumors in the 1,800 ppm group. There was some evidence of carcinogenic activity of methyl isobutyl ketone in male and female B6C3F1 mice based on increased incidences of liver neoplasms.
Exposure to methyl isobutyl ketone resulted in nonneoplastic lesions of the kidney characteristic of α2u-globulin accumulation in male rats and nephropathy in female rats.