Summary

"Groups 10 mated Alderley Park female rats were exposed to 15000 and 50000 ppm HFC-32 in the day 7-16 of pregnancy for 6 hrs/day up to day 5 post partum. Each virgin female was paired overnight with an unrelated male of the same strain. On the following morning, vaginal smears were examined and the day when spermatozoa were detected was considered as the day 1 of gestation. Animals were housed individually in metal cages and exposed whole body in chambers. HFC-32 concentrations were monitored during the exposure periods. All females were subjected to daily examination for clinical signs of toxicity. Body weight gain and food consumption were measured regularly during exposure. Days 1 and 5 after the delivery, the foetotoxicty and teratogenicity potential of the substance was assessed by evaluating the litter size, pup survival and body weight."

"The study was conducted in two phases because of the constraints of the exposure chambers in relation to the number of animals used. Both phases consisted of 48 animaIs supplied in three consecutive batches: the first batch of animals from the second phase of the study was delivered 4 days after termination of the first phase. Statistical analyses of bodyweight and litter data showed that there were no interaction between exposure and phase allowing presentation of the combined data from the two phases."

Test Organisms

Source: ICI Pharmaceuticals (Alderley Park, Macclesfield, Cheshire, UK)
Age: approximately 11 weeks
Weight at study initiation: 231-276
Housing: individually
Diet: ad libitum
Water: ad libitum

Environmental Conditions

Temperature (°C): 19-22
Humidity (%): 34-86
Air changes (per hr): 20-30
Photoperiod (hrs dark / hrs light): 12 / 12

Administration/Exposure:

Name of test material: difluoromethane
Source: ICI Chemicals and Polymers
Batch number: RB21048/74
CTL reference number: Y2105/005
Purity: 99.95% v/v
Route of administration: inhalation
Type of inhalation exposure (if applicable): whole body
Vehicle: unchanged (no vehicle)
Atmosphere generation: The test atmospheres were generated by passing liquid HFC 32 into a copper co il placed in a Techne TE-7 water bath maintained at 45°C. The resultant vapour was then passed through a copper equilibrium coil to flowmeters via a copper distribution plenum. From these flowmeters, the HFC 32 vapour was metered to individual exposure chambers via copper transfer lines and then diluted by addition of clean dried air (dried and filtered using equipment supplied by Atlas-Copco, Sweden) into the top of each chamber at a flow rate of 25 l/min.
Exposure chamber: ICI-designed PERSPEX chambers, 100 l
Temperature, humidity: 18-22 °C, 17-44%
Test Atmosphere: Test atmospheres of HFC 32 were sampled using an automatic air sampling system and analysed automatically using a gas chromatograph equipped with a gas sampling valve and flame ionisation detector. The resultant peak area attributable to HFC 32 was used to calculate the atmospheric concentration in parts-per-million (ppm v/v). Control atmospheres and room air were also sampled and analysed. Daily concentrations were found within 10% of the target value."

Examinations:

Maternal examinations:

Clinical observations: at least once daily
Maternal body weight: on gestation days 1, 7 to 16 and 21
Ovaries and uterine content: not examined

Fetal examinations:

Litter data (number of litters, litter size, mortality and litter weight): on post-partum days 1 and 5

Statistics:

Two-tailed Student's test

Principles of method if other than guideline: modified Chernoff-Kavlock assay (complying with TSCA Health Effects Testing Guidelines part 798.4420).

GLP compliance: yes

Limit test: no

P0 Female Alderley Park Rats