Cyclohexanone oxime

Endpoint summary

Description of key information

The critical endpoint of the toxicity of cyclohexanone oxime (CHO) is haematotoxicity. A reliable rat study (RL2) reveals a LOAEL of 0.25 mg/kg bw/day after 90 days of oral exposure. Effects at this dose level were increased reticulocytes, appearance of Howell-Jones bodies, anisocytosis and poikilocytosis, haemosiderose and extramedullary erythropoiesis in the spleen. According to the authors, the effects were considered to be not severe and recovery could be expected, so that this LOAEL can be considered as marginal. A reliable rat study with shorter exposure duration and studies on mice confirm the relevant endpoint at higher doses.
No information is available for inhalation and dermal exposure

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

Study period:

1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Equivalent to guidellne with limited documentation

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

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

GLP compliance:

not specified

Limit test:

no

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles
River Breeding Laboratories (Kingston, NY, USA)
- Housing: individually

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 2
- Humidity (%): 50 +/- 5

Route of administration:

oral: gavage

Vehicle:

water

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: with distilled water

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

90 days (main study)
30, 60 days (satellite groups)

Frequency of treatment:

5 days/week

Remarks:

Doses / Concentrations:
0, 0.25, 2.5 or 25 mg/kg bw/day
Basis:
actual ingested

No. of animals per sex per dose:

20 (main study)
10 (satellite groups)

Control animals:

yes, concurrent vehicle

Details on study design:

- Post-exposure recovery period in satellite groups: no

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: daily

BODY WEIGHT: Yes
- Time schedule for examinations: days -14, 7, 0 (start of exposure), 1, 4, 7 and weekly thereafter

FOOD CONSUMPTION:
- Time schedule for examinations: weekly

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: days -7, 7 and monthly thereafter
- Dose groups that were examined: all

HAEMATOLOGY: Yes
- Time schedule for collection of blood: on morning of necropsy
- Anaesthetic used for blood collection: No data
- Animals fasted: Yes
- How many animals: all
- Parameters: white blood cells (WBC), red blood cells, hemoglobin, hematocrit, mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH) , mean corpuscular hemoglobin concentration, white cell differential count, platelet count, and reticulocyte count
Osmotic fragilities determined in 5 animals per sex and group

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: on morning of necropsy
- Animals fasted: Yes
- How many animals: all
- Parameters: calcium, chloride, blood urea nitrogen, glucose, total protein, albumin, total bilirubin, serum glutamicoxaloacetic transaminase, creatinine phosphokinase, lactate dehydrogenase, sodium, potassium, phosphorus

URINALYSIS: Yes
- Time schedule for collection of urine: 19 h sample prior to necropsy
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters: volume, sodium, potassium, chloride, pH, protein, glucose, specific gravity, phosphorus, and osmolality

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: daily
- Dose groups that were examined: all
- Battery of functions tested: observational screen

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
Complete necropsy


HISTOPATHOLOGY: Yes
Brain (three levels), eyes with optic nerves, pituitary, cervical spinal cord, major salivary glands, cervical lymph nodes, heart, thymus and mediastinal contents, larynx with thyroid and parathyroid, trachea, lungs, esophagus, stomach, duodenum, ileum, lymph nodes, adrenals, pancreas, liver, spleen, kidneys, bladder, testes with epididymis, prostate, ovaries, uterus, femur with marrow, sternebrae with marrow, and skeletal muscle from proximal hind limb

Other examinations:

Organ weights: brain, lung with trachea, heart, liver, spleen, each kidney, each testis with epididymis, and each ovary. Organ and terminal body weights were used to calculate organ/body weight ratios

Statistics:

Continuous variables: Bartlett's homogeneity of variance, analysis of variance, and Duncan's multiple range test.
If Bartlett's test indicated heterogeneous variance or where data were ranked or suspected to be nonparametric, Kruskall-Wallis nonparametric analysis of variance and Wilcoxan rank sum tests were used.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

see details on results below

Mortality:

mortality observed, treatment-related

Description (incidence):

see details on results below

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:

effects observed, treatment-related

Description (incidence and severity):

see details on results below

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

see details on results below

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

see details on results below

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

see details on results below

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY
Through the first 9 weeks of the study: Highest dose males: persistent red nasal discharge, chromodacryorrhea and swollen conjuntiva (also mid dose), the effects gradually subsided and had disappeared by the end of the study
Females after 2 weeks of exposure: chromodacryorrhea (high dose) and corneal opacity (high and mid dose), which both gradually subsided but persisted at study termination

Three females of the high dose died (additionally on female of low dose group due to dosing accident)

OPHTHALMOSCOPIC EXAMINATION
Corneal opacity (transiently in males of all treated groups, persistent in females at >= 2.5 mg/kg bw /day))

HAEMATOLOGY
Dose-related decreases in erythrocyte counts, haemoglobin, increase in MCV, nucleated erythrocytes, lymphocytes (significant at highest dose in both sexes), increased white blood cell counts (significant at >= 2.5 mg/kg bw/day in males, at highest dose in fermales)
Increase in reticulocyte counts and Howell-Jones bodies, anisocytosis and poikilocytosis (significant in all treated males, at highest dose in females)

ORGAN WEIGHTS
Increased spleen weights in males and kidney weights in females (significant at highest dose)

GROSS PATHOLOGY
Splenomegaly in high dose males

HISTOPATHOLOGY: NON-NEOPLASTIC
Spleen: increased haemosiderin pigmentation, extramedullary haematopoesis; increased erythropoesis also in bone marow, all treated males

Dose descriptor:

LOAEL

Remarks:

90-days study

Effect level:

0.25 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Haematotoxicity, extramedullary erythropesis in spleen, increased erythropoesis in bone marrow

Dose descriptor:

LOAEL

Remarks:

60-days study

Effect level:

25 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Haematotoxicity, increased spleen weight

Dose descriptor:

NOAEL

Remarks:

60-days study

Effect level:

2.5 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Dose descriptor:

LOAEL

Remarks:

30-days study

Effect level:

25 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Haematotoxicity, increased spleen weight

Dose descriptor:

NOAEL

Remarks:

30-days study

Effect level:

2.5 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Critical effects observed:

not specified

Similar effects were oberved in the satellite groups with 30 or 60 days of exposure, but to a lesser extent. However, the increase in spleen weight was also significant in the male animals of the highest dose group; significant haematological alterations were restricted to the highest dose group. Therefore the LOAEL and NOAEL of the 30- and 60 -days studies are 25 and 2.5 mg/kg bw/day, respectively.

Conclusions:

Under the conditions of this study the test substance was haematotoxic at all dose levels, especially in males (LOAEL 0.25 mg/kg bw/day).

Executive summary:

Groups of F-344 rats (20 per sex per dose) were treated by oral gavage with the test substance for 5 days/w for 90 days at doses of 0, 0.25, 2.5 or 25 mg/kg body weight. Satellite groups with 10 animals per sex and dose were exposed for 30 and 60 days. The 30-days study revealed increased spleen weights and haematotoxicity at the highest dose, with a NOAEL of 2.5 mg/kg bw/day. In the main study, there were no significant effects on either body weight or food consumption; mortality occurred at the highest dose (3 female rats). In males, treatment-related clinical effects were observed (red nasal discharge, highest dose only; chromodacryorrhea and swollen conjunctiva (2.5 mg/kg bw/day and above), and corneal opacity (all doses)). These effects gradually subsided and disappeared by the end of the study. In females, clinical signs included chromodacryorrhea (high dose) and corneal opacity (high and mid dose), both of which gradually subsided but persisted at study termination. There was a dose-related decrease in erythrocytes, hemoglobin and hematocrit, accompanied by an increase in circulating reticulocytes and nucleated erythrocytes, the appearance of Howell-Jones bodies, anisocytosis and poikilocytosis. This was confirmed by the observation of haemosiderose, extramedullary erythropoesis in all exposed males and splenomegaly at the highest dose. According to the authors, all observed effects are a compensatory increase in erythropoesis following erythrocyte destruction, were considered "to be not severe and recovery could be expected". No other organs or tissues were adversely affected, including reproductive organs.

Based on dose-related haematotoxic effects, observable at all dose levels, the LOAEL of this 90-days study is 0.25 mg/kg bw/day and a NOAEL could not be determined.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LOAEL

250 µg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

Based on reliable studies

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

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

Additional information

Oral exposure

 

- Rat studies:

Gad et al.(1985), RL2: Groups of F-344 rats were treated by oral gavage with the test substance for 5 days/w for 90 days at doses of 0, 0.25, 2.5 or 25 mg/kg body weight. Satellite groups were exposed for 30 and 60 days. The 30-days and 60 days-studies revealed increased spleen weights and haematotoxicity at the highest dose, with a NOAEL of 2.5 mg/kg bw/day. In the main study, mortality occurred at the highest dose (3 female rats). Treatment-related clinical effects were observed in males (red nasal discharge, highest dose only; chromodacryorrhea and swollen conjunctiva at 2.5 mg/kg bw/day and above, and corneal opacity (all doses)). These effects gradually subsided and disappeared by the end of the study. In females, clinical signs included chromodacryorrhea (high dose) and corneal opacity (high and mid dose), both of which gradually subsided but persisted at study termination. There was a dose-related decrease in erythrocytes, hemoglobin and hematocrit, accompanied by an increase in circulating reticulocytes and nucleated erythrocytes, the appearance of Howell-Jones bodies, anisocytosis and poikilocytosis. This was confirmed by the observation of haemosiderose, extramedullary erythropoesis in the spleen in all exposed males and splenomegaly at the highest dose. According to the authors, all effects are a compensatory increase in erythropoesis following erythrocyte destruction, were

considered to be not severe and recovery could be expected. No other organs or tissues were adversely affected, including reproductive organs.Based on dose-related haematotoxic effects, observable at all dose levels in males, the LOAEL of this 90-days study is 0.25 mg/kg bw/day and a NOAEL could not be determined.

According to the authors, the observed effects are a compensatory increase in erythropoesis following erythrocyte destruction and were considered "to be not severe and recovery could be expected". Therefore the effects at the LOAEL can be considered as marginal.

Derelanko et al. (1985), RL2: Groups of rats were exposed to the test substance via gavage to doses of 0, 10, 25, 75, 150 and 300 mg/kg body weight on 5 days/week for 2 weeks. No compound-related mortality was observed, no clinical signs of toxicity noted. Body weight gain was unaffected. Relative liver weights were increased at 300 mg/kg bw/day in both sexes. Haematological effects were evident at 25 mg/kg bw/day and above (dose-related decrease in erythrocyte number, haemoglobin and haematocrit in animals of both sexes, significant in males at >= 25 mg/kg bw/day and females of the highest dose group; reticulocytes and nucleated erythrocytes increased significantly in both sexes >= 25 mg/kg bw/day), as well as an increase in spleen weight (significantly at >= 25 mg/kg bw/day), accompanied by congestion with foci of nucleated erythroblasts and macrophages. Erythroblastic hyperplasia was evident in sternal marrow. No additional effects were seen in the recovery groups (0 or 300 mg/kg bw/day). Spleen (males only) and liver weights (both sexes) were still significantly increased.The haematological effects were still evident (and partially still significantly altered in males), but the magnitude of alterations were smaller after recovery. Under the conditions of the study the LOAEL and NOAEL in rats were 25 and 10 mg/kg bw/day, respectively.

 

Komsta et al. (1989), RL3: Sprague-Dawley rats were treated orally via gavage with doses of 0, 1, 10 or 100 mg/kg bw/day in corn oil for 14 consecutive days. The body weights were unaffected at any dose. Effects in the 100 mg/kg bw/day group (data at lower doses are not stated) include significantly increased relative spleen weights in both sexes at highest dose, splenic sinusoidal hyperplasia (more severe in females), increased serum potassium in males, increased microsomal aniline hydroxylase activity (both sexes), decreased erythrocyte counts, haemoglobin, haematocrit, increased MCV (both sexes), increased platelet counts (males), altered bone marrow cellularity with decreased number of myeloid cells, increased number of erythroids and decreased number of lymphocytes and monocytes (more severe in females). As the study did not report the results of exposure to the lower doses tested, no definite conclusions can be drawn.

 

- Mouse studies:

 

Burka (1996), RL2: In a range-finding study, B6C3F1 mice were exposed to the test item in drinking water in concentrations of 0, 106, 312, 625, 1250 or 2500 mg/L for 14 days. Body weight gain, liver and spleen weights as well as gross lesions were examined. Increased liver weights were evident in males at 312 mg/L and above, spleen weights were increased at the highest concentrations. Based on the restricted range of examination, the LOAEL of this study was 312 mg/L in males for an increase in liver weight (69 mg/kg bw/day), the NOAEL 106 mg/L (27 mg/kg bw/day).

Burka (1996), RL2: B6C3F1 mice were exposed to the test item in drinking water in concentrations of 0, 625, 1250, 2500, 5000 or 10000 mg/L for 90 days. Increased mortality was observed at 10000 mg/L, body weights were reduced at 5000 mg/L (females) and 10000 mg/L (both sexes). Absolute and relative spleen weights were increased at 5000 mg/L and above, and relative liver weights at 10000 mg/L. Haematopoetic cell proliferation occurred in the spleens of males and females at 5000 mg/L and above. Centrilobular cell hypertrophy was observed in males at >= 2500 mg/L and in females at >= 5000 mg/L. All treated females showed degeneration of the olfactory epithelium, this effect was evident in males at 1250 mg/L and above. There were no treatment-related differences in sperm motility or vaginal cytology parameters. Therefore the LOAEL of this study was 625 mg/L in females for olfactory epithelial degeneration (132 mg/kg bw/day), a NOAEL could not be determined.

Inhalation and dermal exposure:

No reliable information is avaliable. A secondary source information (SIDS, 2008) reports haematological disorders in humans exposed to the test substance, but no details are presented. However, this (per se not reliable) data can be considered as corroborative for the relevance of the haematotoxic action of CHO for humans.

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
most sensitive endpoint (haematotoxicity)

Repeated dose toxicity: via oral route - systemic effects (target organ) cardiovascular / hematological: hematopoiesis

Justification for classification or non-classification

Based on the results of reliable rat studies, the critical endpoint of CHO is haematotoxicity. An unreliable report from experience of occupational exposure corroborates the relevance for humans. Therefore, a classification for specific target organ toxicity at repeated exposure is necessary: STOT-RE 2, H373, according to Regulation (EC) No 1272/2008). Despite a LOAEL of 0.25 mg/kg bw/day in a reliable rat study, the classification STOT-RE 1 in not recommended, because the effects below 10 mg/kg bw/day were not severe and expected to be reversible.