METABOLISM AND DISPOSITION OF DIFLUOROMETHANE (HFC32) IN THE MOUSE

1 Difluoromethane (HFC32) is under development as a replacement for ch lorofluorocarbons (CFCs) in some refrigeration applications. 2 The met abolism and disposition of [C-14]-difluoromethane ([C-14]-HFC32) was d etermined in male Swiss mice as a consequence of a single 6 h inhalati on exposure to atmospheres of 10 000 p.p.m. 3 Of the inhaled dose, abo ut 1-2% was recovered in expired air, urine, faeces and carcass sugges ting that systemic absorption of this hydrofluorocarbon from the alveo lar air space of the lung into blood is poor, Upon cessation of exposu re 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. U rinary and faecal excretion of non-volatile metabolites accounted for about 0.34% and 0.07% of the inhaled dose, respectively. 5 Carbon mono xide could not be detected, 6 Total metabolism, measured as the sum of the radioactivity recovered in urine, faeces, as carbon dioxide and t hat retained in the carcass, amounted to about 0.8% of the inhaled dos e, equivalent to 64% of the total radioactivity recovered. 7 Analysis of a range of tissues at 4 days post-exposure showed a relatively unif orm distribution of radioactivity with the highest concentration in th e lung, liver and kidney. There was no evidence of a specific retentio n in any organ or tissue.