Cyclohexanone

Endpoint summary

Description of key information

Repeated dose toxicity: oral

In a subchronic drinking water study according to OECD guideline 408 (study duration: 3 months) rats were given 500, 2000 and 7000 ppm (about 40, 143 and 407 mg/kg) cyclohexanone. The NOAEL was found to be 2000 ppm, corresponding to 143 mg/kg. The main effects observed were decreases in water consumption in all three concentrations and decreases in food consumption in the mid and high dose groups. 10% reduction of body weights was observed in the animals treated with the high concentrations. Increases in total cholesterol, total protein, globulins and platelets were observed in the high dose group (BASF,1994).

In a subchronic drinking water study performed by the National Cancer Institute (Lijinsky and Kovatch, 1986), rats were given cyclohexanone doses of up to 6.5 g/L with the drinking water for 90 days. The only effects observed were limited to reductions in body weight gain of about 10 % in the highest dose group.

In a mouse study performed in parallel, groups of 20 B6C3F₁mice (10 per sex) received cyclohexanone with acidified drinking water at 0, 400, 2300, 6500, 13000, 25000, 34000 or 47000 ppm for 13 weeks (Lijinsky and Kovatch 1986). Mice were observed for the following endpoints: survival, body weight, gross pathology and histopathology. In the high-dose group, 3/10 females and 6/10 males died. In the mid-does group, one male animal died. Animals exposed to 47000 ppm developed liver damage and hyperplasia of the thymus. In the 34000 ppm dose group, body weight gains were reduced relative to the control values by 15% for the females and 24% for the males. Even at 25000 ppm, body weight gains were reduced by 19% for male animals.

In a 2-year drinking water study by the National Cancer Institute (Lijinsky and Kovatch, 1986), F344 rats and B6C3F₁mice were exposed for two years to the following cyclohexanone concentrations in drinking water: 3.3 and 6.0 g/L for male and female rats; 6.5 and 13 g/L for male mice and 6.5, 13 and 25 g/L for female mice. The survival of the rats in the high dose groups was slightly reduced, body weight gains decreased with increasing dose. At concentrations of 3.3 g/L, 13% of the male rats developed adenomas of the adrenal cortex. This type of tumors was not found in the females and in only 1/51 male animal of the high dose group. In the male rats of the high dose group there was an increase in follicular tumors of the thyroid.

Only 50% of the female mice from the high dose group survived the first year of treatment. After 75 weeks only 25% were alive. At concentrations of 13000 ppm survival of the males was slightly reduced and of the females greatly reduced. For both sexes body weight gains were reduced in the highest dose groups. An increase in lymphomas was observed in the females from the 6500 ppm group. There was a slight increase in the incidence of adenomas and carcinomas in the liver in the male mice given 6500 ppm cyclohexanone in drinking water.

 

Repeated dose toxicity: inhalation

There are two inhalation studies available:

In a 28-day inhalation study performed according to OECD guideline 412 (Lee et al., 2018), B6C3F1 mice were exposed to 0, 50, 150, and 250 ppm of cyclohexanone for 6 hours/day, 5 days/week via whole-body exposure. Mortality, clinical signs, body weights, food consumption, hematology, serum biochemistry, organ weights, as well as gross and histopathological findings were evaluated between the control and exposure groups. No mortality or remarkable clinical signs were observed during the study. No adverse effects on body weight, food consumption, hematology, serum biochemistry, and organ weights, gross or histopathological lesions were observed in any male or female mice in any of the exposure groups. The authors concluded the NOAEL of the study to be > 250 ppm.

In a 90 day study performed by the same lab (Lim et al., 2018), 10 male and 10 female F344 rats and B6C3F1 mice per test group were exposed to cyclohexanone vapors via whole body exposure at 0, 100, 250, and 625 ppm for 6 h per day, 5 d per week, for 13 weeks.

The following findings were noted in cyclohexanone-exposed F344 rats: increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, increased liver weight, and bile duct hyperplasia in the males exposed to 250 and 625 ppm cyclohexanone, increased ALT levels and bile duct hyperplasia in the females exposed to 625 ppm cyclohexanone, and increased blood urea nitrogen (BUN) and tubular basophilia in the renal cortex in the males exposed to 625 ppm cyclohexanone. B6C3F1 mice exposed to cyclohexanone showed no obvious exposure related effects. Based on the findings, the no-observed-adverse-effect level (NOAEL) was determined to be 100 ppm in F344 rats and > 625 ppm in B6C3F1 mice.

The setting of the NOAEL for rats based on the 90-day inhalation study is considered conservative for the following reasons:

- AST and ALT levels are statistically significantly elevated. However, as the elevation is lower than twofold, the biological relevance and adversity can be questioned as small increases in transaminase levels of less than twofold are regarded as indicators of minimal and reversible hepatic injury (for further information please refer to Hall et al., 2012).

- In addition to that, there is no histopathological correlate in liver cells (like liver cell hypertrophy).

- Hyaline droplets and corticular tubular basophilia in the kidneys of male rats of the 250 ppm dose group have been recognized by the authors as an age-related common finding. According to Thoolen et al., 2010, dilatation of intrahepatic bile ducts is a spontaneous, age-associated lesion that is more common in rats than in mice. Given the fact, that no historical control data are given, this finding is hard to classify as adverse, also in light of the missing histopathological findings in female rats up to the highest dose level. In addition to that, bile duct hyperplasia is often a nonspecific response to hepatic injury and, in general, has no evidence of functional alteration or progression (Wallig et al., 2018)

 

 

References:

Hall, A.P. et al. (2012): Liver hypertrophy: A review of adaptive (adverse and non-adverse) changes - conclusions from the 3rd international ESTP workshop. Toxicologic Pathology, 00: 1 -24.

Thoolen, B. et al. (2010): Proliferative and non-proliferative lesions in the rat and mouse hepatobiliary system. Toxicologic Pathology, 38: 5S-81S.

Wallig, M.A. et al. (2018): Fundamentals of toxicologic pathology. 3rd Edition

 

Repeated dose toxicity: intravenous

Greener et al. (1982) reported an assessment of the toxicity to cyclohexanone administered intravenously to Wistar and Gunn rats. Male animals were given intravenously doses of 50 or 100 mg/kg over a study period of 28 days. The authors concluded, that the Gunn rat, despite its inability to form glucuronide conjugates of bilirubin, is capable of forming glucuronide conjugates of cyclohexanol after administration of cyclohexanone. With the dose schedule employed in this study, there was neither accumulation nor evidence of potential toxicity in Wistar and Gunn rats when cyclohexanone was administered i.v. for 28 consecutive days. The NOAEL was found to be 100 mg/kg (for both strains).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

GLP compliance:

yes (incl. QA statement)

Remarks:

testing lab.

Limit test:

no

Specific details on test material used for the study:

purity: 99.9%

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

Only animals were used which were clinically free from any signs of disease. The rats were identified unambiguously by tattooing of the respective animal number into the ears.
During the study period the rats were housed singly. The animal cages were placed on the racks in such a way that uniform conditions (air inflow/air outflow/light) were guaranteed. The animals were housed in a fully air-conditioned room. The day/night rhythm was 12 hours. The food used was ground Kliba maintenance diet rat/mouse/hamster, 343 meal, which was available to the animals ad libitum as was drinking water.

Route of administration:

oral: drinking water

Vehicle:

water

Details on oral exposure:

The stability of the test substance in drinking water over a period of 4 days was checked analytically at the beginning of the study. To check the correctness of the concentrations of the drinking water solutions samples of each concentration were sent for analysis at the beginning and at the end of the study.
The preparations of the drinking water solutions was carried out twice a week. Weighed amounts of the test substance for the specific test group were diluted with the appropriate weighed amounts of drinking water. The mixtures were subsequently stirred with at magnetic stirrer for a least 30 minutes to reach complete solubility of the test substance in the drinking water.
The food used in the study was assayed for chemical as well as for microbiological contaminants. The drinking water is regularly assayed for chemical contaminants by the municipal authorities of Frankenthal and the Technical Services of BASF Aktiengesellschaft, as well as for the presence of microbes by a contract laboratory.

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

3 months

Frequency of treatment:

continuously

Dose / conc.:

500 ppm

Remarks:

about 40 mg/kg bw

Dose / conc.:

2 000 ppm

Remarks:

about 143 mg/kg bw

Dose / conc.:

7 000 ppm

Remarks:

about 407 mg/kg bw

No. of animals per sex per dose:

10

Control animals:

yes, concurrent no treatment

Details on study design:

Data used for dose selection: 1. Subchronic studies of cyclohexanone, Final report from Frederick Cancer Research Center to NCI, January 10, 1979 partly published in 2 . W . Lijinsky and R.M. Kovatch (1986) Chronic Toxicity Study of Cyclohexanone in Rats and Mice. JNCI 77, pp. 941 - 949. 3. Preliminary results of a palatability test study (Project No. 12S0332/92069).

Observations and examinations performed and frequency:

General observation of the animals was performed twice on working days and once on weekends or holidays. A comprehensive clinical examination was performed once weekly. Body weight of the animals as well as food and drinking water consumption was determined weekly. Daily weight change, foodeficiency and test substance intake were calculated from these data.

Sacrifice and pathology:

A complete necropsy including weighing of selected organs and gross pathological evaluation was performed in all animals. Histopathology of numerous organs was performed as required by the corresponding test guidelines.

Other examinations:

Ophthalmoscopy was performed in all animals prior to the begining of the treatment and in the high dose group and control group at the end of treatment period. Hematological and clinico-chemical examinations of numerous parameters as well as urinalysis were performed at the end of the treatment period.

Statistics:

The statistical evaluation and calculation of the data were carried out on the computer systems of the Department of Toxicology of BASF Aktiengesellschaft.

Clinical signs:

no effects observed

Description (incidence and severity):

No signs of toxicity were observed during clinical examination.
A yellowish-orange discoloration of urine in the bedding in the mid and high dosage groups is judged to be due to excretion of some metabolites of the test substance.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

A statistically significant reduction of body weights was observed in the animals of the high dosage group, which occurred earlier during the study period in male animals than in females. At the end an about 10% reduction of body weight resulted in this test group. This reduced body weight development was also demonstrated by decreased body weight change in test group 3 animals. In the female animals of test group 2 a reduction of weight change values occurred without leading to a statistically significant reduction of the absolute body weight.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Food consumption was not influenced in test group 1 and male test group 2 animals. It was sporadically significantly reduced in female animals of group 2 and 3, but nearly over the whole administration period in males of test group 3.
These findings were attributed to the strong odor and taste the test substance, preventing full acceptance of the treated water and the food by the animals.

Food efficiency:

no effects observed

Description (incidence and severity):

There was no clearcut influence of treatment on food efficiency.

Water consumption and compound intake (if drinking water study):

effects observed, treatment-related

Description (incidence and severity):

Statistically significant decreases in water consumption occurred sporadically in test group 1, more often in test group 2 and over the whole study period in test group 3. In test group 3 the overall water consumption of males was reduced about 31% and that of females about 37%.
These findings were attributed to the strong odor and taste the test substance, preventing full acceptance of the treated water and the food by the animals.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No signs of toxicity were observed during examination of ophthalmoscopy.

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

In the hematology, the following test substance related changes were observed:
- Test group 3 (7000 ppm): Increase in platelets in the females.
- Test group 1 and 2 (500 ppm and 2000 ppm): No test substance related changes.
However, the increase in platelets in the females is considered of minor toxicological importance, because the significance of this isolated finding is not obvious.
In conclusion, the results of the hematology examinations revealed some treatment-related effects in the highest dose group only which are probably a result of slight changes in lipid metabolism or of reduced water consumption.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

In the clinical chemistry, the following test substance related changes were observed:
- Test group 3 (7000 ppm): Increase in total cholesterol, total protein and globulins in both sexes.
- Test group 1 and 2 (500 ppm and 2000 ppm): No test substance related changes.
The major treatment-related effect noted in the clinical pathology testing was the increase in total cholesterol in the serum of both sexes, which is probably due to a slight impairment of lipid metabolism at that high concentration of 7,000 ppm.
The increase in serum proteins seen in the high-dose animals might be related to the reduced water consumption.
In conclusion, the results of the clinical chemistry examinations revealed some treatment-related effects in the highest dose group only which are probably a result of slight changes in lipid metabolism or of reduced water consumption.

Urinalysis findings:

no effects observed

Description (incidence and severity):

The only substance related pathomorphological effect was the decreased terminal body weight in the high dosage group. All other findings were judged to be of spontaneous or incidental nature.

Dose descriptor:

NOAEL

Effect level:

143 mg/kg bw/day (nominal)

Sex:

male/female

Basis for effect level:

other: overall effects

Critical effects observed:

not specified

Conclusions:

At the concentration of 7000 ppm signs of toxicity were observed. The reduction of water and food consumption at the lower concentrations is not considered to be an adverse health effect, but caused by the strong odor and taste of the test substance. Therefore, the NOAEL for this drinking water study is 2 000 ppm, corresponding to a dose of 143 mg/kg body weight.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

143 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

Deviations:

not specified

Remarks:

no historical control data; whole body exposure without justification

GLP compliance:

yes

Limit test:

no

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source: ACROS, Netherlands
- Lot no.: SNGYB and B2XGG
- Purity: 99.7% (SNGYB) and 99.6% (B2XGG)

Species:

other: mouse and rat

Strain:

other: B6C3F1 and F344

Details on species / strain selection:

Species were selected for the study because these animals are generally used in subchronic toxicity studies and the availability of considerable
background information for these species.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Japan SLC, Inc. (Shizuoka, Japan)
- Age at study initiation: 6 weeks
- Housing: single
- Diet: provided rodent diet
- Water: filtered tap water
- Acclimation period: 1 week

DETAILS OF FOOD AND WATER QUALITY:

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 3
- Humidity (%): 50 +/- 20
- Air changes (per hr): 10-20
- Photoperiod (hrs dark / hrs light): not specified

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

clean air

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: LVG-04-A, HCT Co., Seoul, Korea
- Method of concentration analysis: valve control system (VCS-06, HCTm, Seoul, Korea) and GC (Trace 1300, Thermo Fischer Scientific Co., Waltham, MA)
- System of generating particulates/aerosols: saturated vapor was evaporated by bubbling clean air and using a hot water bath.

TEST ATMOSPHERE
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Cyclohexanone concentrations in the chambers were automatically recorded through the valve control system (VCS-06, HCTm, Seoul, Korea) by using a pump and analyzed by gas chromatography (Trace 1300, Thermo Fisher Scientific Co., Waltham, MA) at 30-min intervals during the exposure period.

Duration of treatment / exposure:

13 weeks

Frequency of treatment:

6 h/day, 5 days/week

Dose / conc.:

100 ppm

Remarks:

equivalent to ca. 408 mg/m³

Dose / conc.:

250 ppm

Remarks:

equivalent to ca. 1020 mg/m³

Dose / conc.:

625 ppm

Remarks:

equivalent to ca. 2550 mg/m³

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale:
The highest exposure concentration of 650 ppm was selected based on the results of an acute inhalation toxicity study (Smyth et al., 1969;mOECD, 1996) which reported 1/6 rats exposed to 2000 ppm for 4 h died and a 4-week repeated inhalation toxicity study (Lee et al., 2018) which reported no effects at exposure concentrations up to 250 ppm in B6C6F1 mice. In addition, conditions of generation of cyclohexanone before starting the study were checked, and it was confirmed that the highest concentration that can be stably and continuously generated at the facility was 650 ppm.

Positive control:

no positive control included

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily

DETAILED CLINICAL OBSERVATIONS: Yes / No / Not specified
- Time schedule:

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION AND COMPOUND INTAKE: Yes
- Time schedule for examinations: weekly

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: Yes / No / Not specified

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: start of treatment and in the last week of exposure period
- Dose groups that were examined: all animals (start) and control and high dose (last week)

HAEMATOLOGY: Yes
- Time schedule for collection of blood: At necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: No
- How many animals: All surviving animals
- Checked parameters: leucocyte, platelet (PLT) count,
erythrocyte count, hemoglobin, hematocrit, mean corpuscular
volume, mean corpuscular hemoglobin, mean corpuscular
hemoglobin (MCH) concentration, prothrombin time
(PT, mice only), and activated partial thromboplastin time
(mice only).

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: At necropsy
- Parameters checked: glucose, total
bilirubin, blood urea nitrogen (BUN), potassium, total protein,
calcium, albumin (ALB), chloride, creatinine, inorganic
phosphorus, total cholesterol (TCHO), sodium, triglyceride,
aspartate aminotransferase (AST), alanine aminotransferase
(ALT), alkaline phosphatase (ALP), and c-glutamyl transpeptidase

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

IMMUNOLOGY: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes.
- Organs that were weighed: adrenal glands, ovaries (female only), brain, spleen, epididymides (male only), testes (male only), heart, thymus, kidneys, uterus (female only), liver, and lung

HISTOPATHOLOGY: Yes
- Organs checked: ovaries (female only), adrenal glands, pancreas, parathyroid glands, aorta (thoracic), pituitary gland, brain, prostate (male only), bone marrow, rectum, cecum, salivary glands, colon, sciatic nerve, duodenum, seminal vesicle (male only), epididymides (male only), skeletal muscle, esophagus, skin, eyes (with optic nerve), spinal cord (cervical, thoracic, lumbar), femur (F-T joint), spleen, gall bladder (mice only), Harderian glands, sternum, heart, stomach, ileum, teeth, jejunum, testes (male only), kidneys, thymus, larynx, thyroids, liver, trachea, lung, urinary bladder, lymph node, uterus with cervix (female only), mammary gland (female only), vagina (female only), and nasopharyngeal tissue.
- In addition to histopathological examination of the high exposure group of animals,
histopathological examination of the skin (mice only), liver (rats only) and kidney (rats only) was performed for all animals of the low- and medium-concentration groups.

Statistics:

Homogeneity of the variances: Levene test
When variances were homogeneous: one-way ANOVA
Differences between control and treated groups: Dunnett's test
Heterogeneity of the variances: Kruskal-Wallis test
Differences between control and treated groups: Dunn's rank sum test

Clinical signs:

no effects observed

Description (incidence and severity):

RATS
no effects observed

MICE
In all test groups, loss of hair was noted

Mortality:

mortality observed, non-treatment-related

Description (incidence):

RATS
no mortality observed

MICE
625 ppm: two males died
control: one female died

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

RATS
625 ppm: MCH in males decreased, PLT count increased, PT decreased in females

MICE
625 ppm: increased reticulocyte counts in males
250 ppm: increased leukocyte (WBC) counts in males
100 ppm: PLT count decreased in males

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

RATS
625 ppm: AST and ALT increased in males, and increased ALT in females. BUN levels increased in males. ALP levels decreased in females
250 ppm: AST and ALT increased in males, ALP levels increased in males

MICE (effects observed, non-treatment-related)
625 ppm: decreased total bilirubin levels in males, BUN levels increased in males, TCHO increased in females
250 ppm: decreased ALP levels in males

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

RATS
625 ppm: absolute and relative weights of the liver in males increased, relative weight of spleen in males increased, absolute weight of kidney increased in males
250 ppm: relative weight of the liver in males increased, relative weight of spleen in females increased
Females did not show a statistical significance increase in liver weights but showed a dose-dependent increase

MICE (effects observed, non-treatment-related)
650 ppm: absolute and relative liver weights increased in males, absolute liver weight increased in females, absolute kidney weight increased in males
250 ppm: relative kidney weight increased in females

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

RATS
625 ppm: white focal lesions in lungs of males
250 ppm: adhesions in the accessory lobe of the liver and right kidney in females

MICE
625 ppm: In two dead males, a black spot lesion of the stomach, small of spleen, and thymus were observed. A nodule was noted in thoracic muscle of one male
Control: small of the thymus in a dead female

No abnormal findings related to the test chemical were observed in the animals that survived until the scheduled terminal necropsy.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

RATS
625 ppm: indicative of alveolar macrophage aggregation in males, four cases of bile duct hyperplasia in the liver of male animals
250 ppm: adhesion of hepatocytes to the renal capsule and atrophy of the glomeruli and tubules in the renal cortex in females. Two cases of bile duct hyperplasia in the liver of male animals

Males showed hyaline droplet accumulation in the distal convoluted tubule and cortical tubular basophilia in the kidney. Hyaline droplet accumulation was observed in all test groups including the control groups. However, the extent increased in a concentrationdependent manner.
Tubular basophilia in the renal cortex had known a spontaneous lesion due to aging in the rats and was exacerbated by the test substance. The severity of tubular basophilia increased upon exposure to cyclohexanone in a dosedependent manner. Therefore, it was considered that tubular basophilia in the renal cortex may be aggravated by the progression of chronic progressive nephropathy due to cyclohexanone exposure

MICE (effects observed, non-treatment-related)
625 ppm: atrophy of the liver, spleen, and thymus and single-cell necrosis of the liver and erosion of the glandular stomach in the dead males
Control: atrophy of the liver, spleen, and thymus and single-cell necrosis of the liver in the dead female

No abnormal findings related to the test chemical were observed in the animals that survived until the scheduled terminal necropsy.

Dose descriptor:

NOAEL

Remarks:

rats

Effect level:

100 ppm

Based on:

test mat.

Sex:

male

Basis for effect level:

clinical biochemistry

histopathology: non-neoplastic

Dose descriptor:

NOAEL

Remarks:

mice

Effect level:

> 625 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no adverse effects observed

Critical effects observed:

yes

Lowest effective dose / conc.:

250 ppm

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Dose response relationship:

yes

Critical effects observed:

yes

Lowest effective dose / conc.:

250 ppm

System:

urinary

Organ:

kidney

Treatment related:

yes

Dose response relationship:

yes

Mean ± standard deviation values for the cyclohexanone concentrations in the inhalation chambers were 99.51 ± 4.63 ppm, 252.87 ± 8.38 ppm, and 625.32 ± 35.48 ppm for rats, and 103.63 ± 26.97 ppm, 251.36 ± 38.49 ppm, and

617.83 ± 86.41 ppm for mice throughout the 13-week exposure period. Deviations in the mean observed concentrations from the target concentrations were less than 11.5%.

Conclusions:

In conclusion, inhalation exposure to cyclohexanone vapors for 13 weeks induced hepatoxicity and renal toxicity in rats of both sexes. The authors concluded on a NOAEL of 100 ppm for the hepatic endpoint in F344 rats and >625 ppm in B6C3F1 mice.

Executive summary:

In this study, ten male and ten female rats (F344) and mice (B6C3F1) per group were exposed to cyclohexanone vapors at 100, 250, and 625 ppm concentrations for 6 h per day, 5 d per week, and for 13 weeks. Clean air was used as negative control. All rats and mice were killed after the exposure period. Clinical signs, body weight, feed intake, and ophthalmoscopy findings were recorded during the exposure period, and hematology, blood biochemistry, organ weights, gross findings, and histopathology were evaluated thereafter.

The following effects were recorded in cyclohexanone-exposed F344 rats: increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels, increased liver weight, and bile duct hyperplasia in the males exposed to 250 and 625ppm cyclohexanone, increased ALT levels and bile duct hyperplasia in the females exposed to 625ppm cyclohexanone, and increased blood urea nitrogen (BUN) and tubular basophilia in the renal cortex in the males exposed to 625 ppm cyclohexanone.

B6C3F1 mice exposed to cyclohexanone showed no obvious exposure-related effects.

Based on the findings in male rats, the NOAEL (rats) was set at 100 ppm and the NOAEL (mice) greater than 625 ppm.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

408 mg/m³

Study duration:

subchronic

Species:

rat

System:

hepatobiliary

Organ:

liver

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Based on the information available, no classification according to Regulation (EC) 1272/2008 is warranted.