Metabolism and disposition of difluoromethane (HFC32) in the mouse

1. Difluoromethane (HFC32) is under development as a replacement for chlorofluorocarbons (CFCs) in some refrigeration applications. 2. The metabolism and disposition of [14C]-difluoromethane ([14C]-HFC32) was determined in male Swiss mice as a consequence of a single 6 h inhalation exposure to atmospheres of 10 000 p.p.m. 3. Of the inhaled dose, about 1-2% was recovered in expired air, urine, faeces and carcass suggesting that systemic absorption of this hydrofluorocarbon from the alveolar air space of the lung into blood is poor. Upon cessation of exposure the majority of the systemically absorbed HFC32 was exhaled within 1 h. 4. Carbon dioxide was a major metabolite of HFC32. Carbon dioxide measured post-exposure accounted for about 0.3% of the inhaled dose. Urinary and faecal excretion of non-volatile metabolites accounted for about 0.34% and 0.07% of the inhaled dose, respectively. 5. Carbon monoxide could not be detected. 6. Total metabolism, measured as the sum of the radioactivity recovered in urine, faeces, as carbon dioxide and that retained in the carcass, amounted to about 0.8% of the inhaled dose, equivalent to 64% of the total radioactivity recovered. 7. Analysis of a range of tissues at 4 days post-exposure showed a relatively uniform distribution of radioactivity with the highest concentration in the lung, liver and kidney. There was no evidence of a specific retention in any organ or tissue.