PAFT Programme for Alternative Fluorocarbon Toxicity Testing

HFC-32 is one of a series of fluorocarbon alternatives being studied as part of the Programme for Alternative Fluorocarbon Toxicity Testing (PAFT). HFC-32 is being considered primarily as an alternative, in blends, for refrigeration systems.

Summary of Testing Results HFC-32 has very low acute and subchronic inhalation toxicity. HFC-32 is not a developmental toxicant. HFC-32 is not mutagenic.

HFC-32 has very low toxicity by inhalation. The lowest concentration that causes mortality in experimental animals -- the approximate lethal concentration (ALC) -- for a 4-hour exposure is greater than 760,000 ppm (76%). Anaesthetic-like effects, such as lethargy and incoordination, are observed in rats at very high inhalation concentrations (greater than 110,000 ppm).

As with many other halocarbons and hydrocarbons, inhalation of HFC-32 followed by intravenous injection of epinephrine, which simulates human stress reactions, results in a cardiac sensitization response in experimental screening studies with dogs. This cardiac sensitization response is observed at approximately 350,000 ppm of HFC-32, a level well above expected exposures. By comparison, a cardiac sensitization response is observed with CFC-11 at approximately 5,000 ppm, and with CFC-12 at approximately 50,000 ppm.

In repeated inhalation exposure studies, the low toxicity of HFC-32 continues to be evident. No adverse effects were observed in rats exposed by inhalation at concentrations of up to 50,000 ppm for up to 90 days.

Inhalation developmental toxicity studies with rats and rabbits have been completed. The results indicate that HFC-32 is not teratogenic, and does not cause fetal effects at inhalation concentrations of up to 50,000 ppm.

In genetic toxicity testing, HFC-32 was not mutagenic in an Ames assay, a Chinese Hamster Lung (CHL) assay, or a chromosomal aberration study with human lymphocytes. These studies were in vitro assays. Also, HFC-32 was not active in an in vivo mouse micronucleus study.

Metabolism studies with HFC-32 have indicated only very low levels of metabolism (less than 0.5%).

The testing of HFC-32 under PAFT V has been completed. The results are summarized in the sidebar above.

An exposure limit of 1,000 ppm (8-hour time-weighted average) for HFC-32 has been recommended by the American Industrial Hygiene Association's Workplace Environmental Exposure Limit (WEEL) Committee.

As for all chemicals, PAFT recommends that exposures be kept to a practicable minimum.

September 1995

Last updated October 11, 1996