New JACC Report on Difluoromethane (HFC-32) CAS No. 75-10-5

'JACC 054' updates an earlier ECETOC review and presents a critical evaluation of the available data on the ecotoxicity, toxicity, environmental fate and impact of difluoromethane (HFC-32).
JACC 054 - Difluoromethane (HFC-32) CAS No. 75-10-5 (Second Edition)
This report has been produced as part of the ECETOC Joint Assessment of Commodity Chemicals (JACC) programme. It updates an earlier ECETOC review[1] and presents a critical evaluation of the available data on the ecotoxicity, toxicity, environmental fate and impact of difluoromethane (HFC-32). The report includes results of recent and unpublished studies conducted by the Programme for Alternative Fluorocarbon Toxicity Testing (PAFT)[2].

Difluoromethane (HFC-32) is a colourless, flammable gas that is used in refrigerant blends with other hydrofluorocarbons. Any HFC-32 released to the environment will volatilise to the atmosphere where it has been detected. In air, HFC-32 will degrade slowly to carbon dioxide and hydrogen fluoride. HFC-32 does not accumulate in living organisms and there is low risk to the aquatic environment. HFC-32 does not deplete stratospheric ozone because it does not contain chlorine or bromine. The contribution of HFC-32 to global warming is insignificant, due to its low global warming potential and low atmospheric concentration.

HFC-32 is poorly absorbed in the body of mammalian species. Any absorbed HFC-32 is either exhaled unchanged, or rapidly metabolised and excreted, principally as exhaled carbon dioxide.

HFC-32 is essentially non-toxic to laboratory animals. There were minor effects, such as reduced breathing rate and salivation, during brief exposure to high concentrations (86,000 ppm for 4hours). Once the exposure stopped, animals behaved normally. HFC-32 (up to 350,000 ppm) did not cause cardiac sensitisation to adrenaline, but there were head and limb tremors (pre-narcosis) at 250,000 ppm and above.

Repeated exposure studies in rats (up to 50,000 ppm for 4 or 13 weeks) showed no effects that could be attributed to HFC-32. HFC-32 is not genotoxic in vitro or in vivo. HFC-32 is poorly absorbed and does not form any toxicologically significant metabolites. As a consequence, HFC-32 is unlikely to be carcinogenic.

In developmental toxicity studies in rats and rabbits, HFC-32 (up to 50,000 ppm) did not interfere with embryo-foetal development or fertility, but foetotoxicity (in the rat) could not be ruled out completely.

There are no known adverse health effects of HFC-32 on humans. In the USA, an occupational exposure limit (8-hour time-weighted-average concentration) of 1,000 ppm is recommended by the American Industrial Hygiene Association.

[1] ECETOC (1995). JACC 032
[2] A cooperative research effort (1987-2000) sponsored by 16 of the leading CFC producers [www.afeas.org/paft/]

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