1-chloro-1,1-difluoroethane

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

repeated dose toxicity: inhalation

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP-compliant near-guideline study, available as confidential study report and published in peer-reviewed literature, no restrictions, fully adequate for assessment (SIDS score: 1b)

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1983

Report date:

1983

Reference 2

Reference Type:

publication

Title:

Toxicological evaluation of hydrochlorofluorocarbon 142b

Author:

Seckar JA, Trochimowicz HJ, Hogan GK.

Year:

1986

Bibliographic source:

Fd Chem. Toxic., 24, 237-240

Materials and methods

Principles of method if other than guideline:

Combined 2-year whole body inhalation chronic toxicity and carcinogenicity study with rats

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

1-chloro-1,1-difluoroethane

EC Number:

200-891-8

EC Name:

1-chloro-1,1-difluoroethane

Cas Number:

75-68-3

Molecular formula:

C2H3ClF2

IUPAC Name:

1-chloro-1,1-difluoroethane

Details on test material:

Name of test material: 1-chloro-1,1-difluoroethane .
Provided by the Pennwalt Corporation, Calvert City, KY. The test-material was presented as compressed form in several 750 kg gas cylinders provided periodically by the supplier over the 2 year exposure periode, with a purity level ranging from 99.85 to 99.99%.

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeging Laboratories, Wilmington, MA
- Age at study initiation: 7 weeks
- Housing: individually in suspended, stainless-steel, mesh cages
- Diet: Purina Lab Chow 5001, Ralston Purina co. Inc., St. Louis, MO, ad libitum
- Water: ad libitum
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 +/- 2 C
- Humidity (%): 50 +/- 10%
- Photoperiod (hrs dark / hrs light): 12 / 12

Administration / exposure

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 10 m3 Rochester-design chamber
- Exposure generation: Test material passed through 0.5 inch diameter copper tubing immersed in an ethylene glycol chilled bath and through a liquid volume flowmeter prior to division into three delivery lines, volatilisation at 38 oC.
- Source of air: filtered, temperature- and humidity-controlled, non-recirculated air
- Air flow rate: 2.06-3.4 m3/min
- Air change rate: 12.4-20.4 air changes/hour

TEST ATMOSPHERE
- Brief description of analytical method used: gas liquid chromatography with flame-ionization detector

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

On-line gas-liquid chromatography (Tracor model 550 equipped with a flame-ionization detector, 5% OV-101 on 80-100 mesh Supercoport column, 50 oC column temperature and 200 oC detector temperature).

Duration of treatment / exposure:

104 weeks

Frequency of treatment:

6 hours per day, 5 days per week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
1000, 10000 and 20000 ppm (0.1, 1.0 and 2.0%, v/v)
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0.099 +/- 0.02, 1.01 +/- 0.11 and 1.95 +/- 0.20% (v/v)
Basis:
analytical conc.

No. of animals per sex per dose:

110/sex/dose

Control animals:

yes, concurrent vehicle

Details on study design:

Post-exposure period: none

Examinations

Observations and examinations performed and frequency:

- Mortality/gross signs: twice daily
- Bodyweight: weekly during weeks 1-14 and 81-104 and biweekly during weeks 16-80
- Clinical observations and pulpations: weekly; 
- Ophtalmoscopic exams: yearly; 
- Hematology, clinical chemistry and urinalysis: 10 animals/sex/group at 12, 18 and 24 months of treatment. 

Sacrifice and pathology:

- Sacrifices were conducted on 10 animalss/sex/group at 12 months and on all survivors at 24 months.
- Organs weighted: brain, pituitary, lungs, liver, kidneys, speen, adrenals, gonads and thymus
- Morphological exams: adipose tissue, abdominal aorta, adrenals, bone marrow, femur, brain (3 sections), Zymbal gland, oesophagus, eyes, optic nerve, lacrimal gland, ovaries, testes with epididymis, heart, whole intestin, kidneys, liver, lungs, lymph nodes, mammary gland, nasal turbinates, pancreas, pituitary, prostate, salivary glands, sciatic nerve, skeletal muscle, skin, spinal cord, spleen, thymus, trachea , thyroid, parathyroid, urinary bladder, uterus, all gross lesions and tissue masses (all these tissues were preserved from all animals; all rats from control and high dose groups were examined microscopically).

Statistics:

Parametric data: F distribution and Dunett's test; 
Non-parametric data: Kruskal-Wallis and Dunn summed rank tests; 
Equality of variance: Bartlet's test;
Neoplastic lesions and survival: NCI statistical programs.

Results and discussion

Results of examinations

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 specified

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

no effects observed

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

MORTALITY
Mortality was higher than expected for treated and control groups during the first year, reaching 11-16 and 2-10% in treated male and female groups, respectively, and 12 and 8% in ale and female controls, by week 52. Clinical signs and macroscopic pathology suggested a respiratory infection in some animals. Microscopic pathology confirmed the presence of bronchopneumonia in some treated and control animals. Diagnostic microbiology failed to identify either a consistent pathogen or the cause/origin. Neither the health status nor the mortality compromised the studies or the conclusions.
The survivorship figures at termination of exposure did not show dose-related effect on mortality in the treated males or females throughout the study.

CLINICAL SIGNS
Most significant signs were respiratory distress which were considered factors in several increases of mortality: control group males betweeen weeks 48 and 72 and low dose female group between weeks 40 and 48 and between weeks 72 and 80. However adequate number of animals in these groups survived the 2-year period and the effect of this respiratory distress was considered to be insignificant as far as toxicological and oncogenic assessment of the test material is concerned.

BODY WEIGHT AND WEIGHT GAIN
Inter-group differences in body weight that occured during the study did not indicate any exposure-related responses to 1-chloro 1,1-difluoroethane.

OPHTHALMOSCOPIC EXAMINATION
Exams at weeks 52 and 104 did not indicate any responses to exposure.

HAEMATOLOGY
The mean hematology values for the treated males and females were comparable to the control animals at 12, 18 and 24 month intervals and were within normal biological limits.

CLINICAL CHEMISTRY
In the low dose female group  a statistically significant increase of the mean creatinine phosphokinase value (P < 0./05 by Dunnett's test) was observed at 12 months but not therafter at 18 and 24 months. In addition there was no such increase in mid and high dose groups, at any time  and the the effect was considered not related to exposure.  This finding was attributed to abnormally low control values. All other clinical chemistry values in both treated males and females were comparable to control animals and all parameters were considered within normal biological limits.

URINALYSIS
There were no differences from control values in any of the urine parameters evaluated which were considered related to the administration of the test material. Fluoride levels were comparable between treated and control animals.

ORGAN WEIGHTS
The values were considered within the range of normal expectation and there were no treatment related changes of absolute and relative organ weights.

GROSS PATHOLOGY
Findings at necropsy of decedents or those rats sacrificed after 12 or 24 months of treatment, as well as those dying spontaneously or sacrificed in a moribund condition throughout the study, were considered typical for rats of similar age and strain and no treatment-related effects were apparent.

HISTOPATHOLOGY: NON-NEOPLASTIC
Non-neoplastic microscopic pathology findings at the interim and final sacrifices were similar in treated and control groups and were confined to degenerative lesions typical of rats of this strain and age.  

HISTOPATHOLOGY: NEOPLASTIC
Neoplastic findings in animals that died during the study or in survivors to termination were similar in all groups and comprised predominently tumours of the mammary and subcutaneous tissues in females, and pituitary and adrenal adenomas in both sexes. No treatment-related increases in tumours of the respiratory tract were noted.

Effect levels

Dose descriptor:

NOAEL

Effect level:

> 20 000 ppm

Sex:

male/female

Basis for effect level:

other: No adverse effects at the highest level tested.

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Rats receiving exposures to atmosphere of 1-chloro -1,1-difluoroethane at concentrations up to 20000 ppm for 6h/d, 5d/w during 104 weeks, showed no treatment-related effects upon mortality, body weight, hematology, clinical chemistry, urinalysis and ophtalmological examinations, histopathological evaluation of selected tissues, or statistical analysis of neoplasms incidences. The NOAEL was established to exceed 20000 ppm (the highest dose tested).

Executive summary:

1-chloro-1,1-difluoroethane was administered to three groups of Sprague-Dawley rats (110/sex/group) at exposure levels of 1000, 10000 and 20000 ppm (0.1, 1.0 and 2.0%, v/v) for 6 h/d, 5 d/week, for 104 weeks. Approximately 40% of the animals survived the duration of the study and the mortality was considered to be unaffected by the treatment. Statistically significant changes in body weight, hematological, clinical chemistry and organ weight values occurred sporradically and were considered to be no attributable to the treatment. Ophthalmology and urinalysis were not remarkable. Also no treatment-related effects were found upon histopathological evaluation of selected tissues or statistical analysis of neoplasm incidence data. The NOAEL was established to exceed 20000 ppm.