Volatile anaesthetics and the atmosphere: atmospheric lifetimes and atmospheric effects of halothane, enflurane, isoflurane, desflurane and sevoflurane.

The atmospheric lifetimes of the halogenated anaesthetics halothane, enflurane, isoflurane, desflurane and sevoflurane with respect to reaction with the hydroxyl radical (OH.) and UV photolysis have been determined from observations of OH. reaction kinetics and UV absorption spectra. Rate coefficients for the reaction with OH radicals for all halogenated anaesthetics investigated ranged from 0.44 to 2.7 x 10(-14) cm3 molec-1 s-1. Halothane, enflurane and isoflurane showed distinct UV absorption in the range 200-350 nm. In contrast, no absorption in this wavelength range was detected for desflurane or sevoflurane. The total atmospheric lifetimes, as derived from both OH. reactivity and photolysis, were 4.0-21.4 yr. It has been calculated that up to 20% of anaesthetics enter the stratosphere. As a result of chlorine and bromine content, the ozone depletion potential (ODP) relative to chlorofluorocarbon CFC-11 varies between 0 and 1.56, leading to a contribution to the total ozone depletion in the stratosphere of approximately 1% for halothane and 0.02% for enflurane and isoflurane. Estimates of the greenhouse warming potential (GWP) relative to CFC-12 yield values of 0.02-0.14, resulting in a relative contribution to global warming of all volatile anaesthetics of approximately 0.03%. The stratospheric impact of halothane, isoflurane and enflurane and their influence on ozone depletion is of increasing importance because of decreasing chlorofluorocarbons globally. However, the influence of volatile anaesthetics on greenhouse warming is small.