STABILITY OF TRIFLUOROMETHANE IN FOREST SOILS AND METHANOTROPHIC CULTURES

Trifluoromethane (TFM) has been reported as an endproduct of trinuoroa cetate degradation under oxic conditions. Although other halomethanes, such as chloroform, methyl bromide, and methyl fluoride, inhibit meth ane oxidation or are degraded by methanotrophs, the fate of TFM is unk nown. TFM had no affect on atmospheric methane consumption when added to forest soils at either 10 ppm or 10,000 ppm. No degradation of TFM was observed at either concentration for incubations of 6 days. Cultur es of Methylobacter albus BG8 and Methylosinus trichosporium OB3b grow n with and without added copper were also used to assay TFM degradatio n at 10-10000 ppm levels. TFM did not inhibit methane oxidation under any growth conditions, including those inducing expression of soluble methane monooxygenase, nor was it degraded at measurable rates. In con trast, parallel assays showed that both methyl fluoride and chloroform inhibited methane oxidation in M. trichosporium OB3b. Our results sug gest that TFM may be relatively inert with respect to methanotrophic d egradation. Although TFM has a negligible ozone depletion potential, i t absorbs infrared radiation and has a relatively long atmospheric res idence time. Thus, accumulation of TFM in the atmosphere as a conseque nce of the decomposition of hydrochlorofluorocarbons may have signific ant unpredicted climate impacts.