1,1-difluoroethane

Carcinogenicity

Description of key information

Chronic inhalation, rat, Equivalent to OECD 453, NOAEC = 67485 mg/m3 (25000 ppm) , Reliability = 1

Key value for chemical safety assessment

Carcinogenicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: This study was selected as the key study because the information provided for the hazard endpoint is sufficient for the purpose of classification and labelling and/or risk assessment.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

Deviations:

yes

Remarks:

Only 30 animals/sex/concentration tested; body weights collected 2 times/month during the first 13 weeks; no food consumption data collected; deviations in haematology, clinical chemistry, urinalysis, and pathology in Tables 1-4 in Materials and methods

GLP compliance:

yes

Species:

rat

Strain:

other: Crl:CD®Br

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 54 days
- Weight at study initiation: Mean male body weight week 0 was 217.6-245.6 g; mean female body weight week 0 was 159.3-166.2 g
- Fasting period before study: No
- Housing: Males and females of each concentration group were housed together and each of the four groups was housed in a separate animal room
- Diet (e.g. ad libitum): ad libitum, except during exposures
- Water (e.g. ad libitum): ad libitum, except during exposures
- Acclimation period: Approximately 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 24±3°C
- Humidity (%): 50±10%
- Air changes (per hr): Not reported
- Photoperiod (hrs dark / hrs light): 12 hours light/12 hours dark

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

other: Air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Four 4.6 m3 stainless steel and glass chambers, quadrangular in shape with pyramidal tops and bottoms
- Method of holding animals in test chamber: Not reported
- Source and rate of air: Not reported
- Method of conditioning air: Not reported
- System of generating particulates/aerosols: The chambers were operated in a one-pass, flow-through mode. Atmospheres were generated by metering the test substance vapours from cylinders of liquid test substance, maintained at room temperature, through rotometers into the chamber air flow. The control chamber received dilution air only.
- Temperature, humidity, pressure in air chamber: 24±5°C, 50±10%, pressure not reported
- Air flow rate: approximately 1200 L/min.
- Air change rate: Not reported
- Treatment of exhaust air: Not reported

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatograph equipped with a programmable recording terminal. Atmospheres were measured at approximately 30-minute intervals during each 6-hour exposure with daily average concentrations for each chamber calculated from these data.
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Over the 106-week exposure period, the overall means of the weekly averages for the low, intermediate, and high concentrations were all 100% of design. While 93.4, 96.3, and 100% of the individual weekly average concentrations for the low, intermediate, and high exposures, respectively, were within 10% of design, all of the weekly averages for each exposure were within 15% of design. The overall means and standard deviations of the weekly average exposure concentrations were 0.2±0.001, 1.0±0.05, and 2.5±0.06%.

Duration of treatment / exposure:

Approximately 104 weeks

Frequency of treatment:

6 hours/day, 5 days/week, excluding holidays

Remarks:

Doses / Concentrations:
0.2, 1.0, 2.5% (v/v)
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0.2±0.001%; 1.0±0.05%; 2.5±0.06%
Basis:
other: mean and standard deviation of the weekly average exposure concentration

No. of animals per sex per dose:

30 per sex per concentration

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Male rats were exposed to 0 or 100000 ppm of the test substance in air for 6 hours per day, 5 days per week for 2 weeks, with half of the animals given a 14-day recovery period. During exposures, the rats appeared lethargic and were poorly responsive to sound. No other abnormalities attributable to the test substance were observed.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Twice monthly for the first 14 months, then once monthly for the remainder of the study
BODY WEIGHT: Yes
- Time schedule for examinations: Twice monthly for the first 14 months, then once monthly for the remainder of the study, and at sacrifice. One unscheduled weighing was added during the 12th month to monitor unusual weight loss observed in the preceding scheduled weighing interval.
FOOD CONSUMPTION: No
FOOD EFFICIENCY: No
WATER CONSUMPTION: No
OPHTHALMOSCOPIC EXAMINATION: No
HAEMATOLOGY: Yes
- Time schedule for collection of blood: Approximately 1, 3, 6, 12, 18, and 24 months after start of the study
- Anaesthetic used for blood collection: No
- Animals fasted: No data
- How many animals: 10 rats/sex/concentration
- Parameters checked in table No. 1 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: Approximately 1, 3, 6, 12, 18, and 24 months after start of the study
- Animals fasted: No data
- How many animals: 10 rats/sex/concentration
- Parameters checked in table No. 2 were examined.

URINALYSIS: Yes
- Time schedule for collection of urine: Approximately 1, 3, 6, 12, 18, and 24 months after start of the study
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters checked in table No. 3 were examined.

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table No. 4)

HISTOPATHOLOGY: Yes (see table No. 4)

All high-exposure and control animals sacrificed at the 3- and 12-month interim and 24-month terminal examinations, and all animals from all groups which died or were sacrificed in extremis during the study, received histopathologic evaluation of the organs and tissues. Kidney and nasal tissues at the 3-month interim and 24-month final sacrifices, respectively, from all intermediate- and low-exposure rats received histopathological evaluation. All other organs and tissues collected at the 3- and 24-month sacrifices, and all organs and tissues collected at the 12-month sacrifice from intermediate- and low-exposure rats, were processed to the block stage and held without histopathologic evaluation.

Statistics:

Clinical measurements were subjected to partially-nested and crossed analysis of variance. Organ weight and final body weight data were subjected to one-way analysis of variance and Dunnett’s test. The least significant differences from control values were calculated whenever the ratio of variances (F-ratio) indicated that differences existed among the study groups. Body weight data were subjected to one-way analysis of variance. Significance was judged at p≤0.05 level of significance. The results of histopathologic examination were analyzed by the Fisher’s Exact test for differences between control and exposed groups and by the Mantel-Haenszel test for a dose-related trend.

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

effects observed, treatment-related

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS AND MORTALITY: Refer to DI.K1.2YR.InhVap.RD/CARC.R.HL-8-82.KD in section 7.5.3 (Repeated dose toxicity: inhalation) for additional information on repeated dose toxicity

HAEMATOLOGY: Refer to DI.K1.2YR.InhVap.RD/CARC.R.HL-8-82.KD in section 7.5.3 (Repeated dose toxicity: inhalation) for additional information on repeated dose toxicity

CLINICAL CHEMISTRY: Refer to DI.K1.2YR.InhVap.RD/CARC.R.HL-8-82.KD in section 7.5.3 (Repeated dose toxicity: inhalation) for additional information on repeated dose toxicity

URINALYSIS: Refer to DI.K1.2YR.InhVap.RD/CARC.R.HL-8-82.KD in section 7.5.3 (Repeated dose toxicity: inhalation) for additional information on repeated dose toxicity

ORGAN WEIGHTS: Refer to DI.K1.2YR.InhVap.RD/CARC.R.HL-8-82.KD in section 7.5.3 (Repeated dose toxicity: inhalation) for additional information on repeated dose toxicity

HISTOPATHOLOGY: Refer to DI.K1.2YR.InhVap.RD/CARC.R.HL-8-82.KD in section 7.5.3 (Repeated dose toxicity: inhalation) for additional information on repeated dose toxicity

24-Month Sacrifice: One male and 1 female rat at 2.5% each revealed an adenoma which was located in the respiratory epithelial lining of the nasoturbinate. The incidence of the tumour was not statistically significant in either group when compared with controls. Three males at 2.5% revealed osteomas that appeared to originate from the skull and replaced the olfactory and frontal regions of the brain in each rat. The incidence of osteoma in this group was not statistically significant when compared to the male controls. Generally, histopathologic changes documented by the peer review were in close agreement with the original interpretations. There was no distinct evidence of test substance-induced toxicity or carcinogenicity in any tissue examined as part of the review.

Relevance of carcinogenic effects / potential:

The test substance was not carcinogenic.

Dose descriptor:

NOAEC

Effect level:

2.5 other: % (v/v)

Sex:

male/female

Basis for effect level:

other: No carcinogenicity was observed at the highest concentration tested.

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

Conclusions:

The study and the conclusions which are drawn from it fulfil the quality criteria (validity, reliability, repeatability). The test substance was not carcinogenic and produced no life-shortening toxic effects.

Executive summary:

Male and female rats were exposed, whole body, via inhalation for 6 hours a day, 5 days a week to 0, 0.2, 1.0, or 2.5% (v/v) of the test substance for 2 years. Ten rats per sex per concentration were subjected to clinical pathological evaluation after 1, 3, 6, 12, 18, and 24 months on test. An additional 10 rats per sex per concentration at 3 and 12 months on study and all surviving rats at 24 months on study were sacrificed and, together with animals found dead or sacrificed in extremis, were subjected to gross pathological examination.  All high-concentration and control animals plus all animals found dead or sacrificed in extremis were subjected to complete histopathological evaluation while only the kidneys and nasal tissues at the 3-month interim and 24-month final sacrifices, respectively, from the low- and intermediate-concentration animals were examined histopathologically. 

 

 In conclusion, the test substance administered by inhalation intermittently over a 2-year period was not carcinogenic.  Generally, histopathologic changes documented by the peer review were in close agreement with the original interpretations. There was no distinct evidence of test substance-induced toxicity or carcinogenicity in any tissue examined as part of the review.  The peer review indicated that the original pathology methods and interpretations were adequate in scope and accuracy, and that the test substance is not toxic or carcinogenic to CD rats under the conditions of the study.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

67 485 mg/m³

Study duration:

chronic

Species:

rat

Justification for classification or non-classification

Based on results of repeated inhalation studies, the substance does not need to be classified for carcinogenicity according the EU Directive 67/548/EEC and EU Classification, Labelling and Packaging of Substances and Mixtures (CLP) Regulation (EC) No. 1272/2008.

Additional information

Male and female rats were exposed to 0, 0.2, 1 or 2.5% v/v via inhalation for 24 months. No survival or life-shortening effects were observed at any exposure concentration. Carcinogenic effects were not observed at any concentration tested. Based on this information, the NOAEC was 2.5% (67485 mg/m³).

Justification for selection of carcinogenicity via inhalation route endpoint:
Equivalent to OECD 453, Reliability = 1