Environ. Sci. Technol. 2001, 35, 3616-3619
Carbon Isotope Ratios for Chloromethane of Biological Origin: Potential Tool in Determining Biological Emissions D A V I D B . H A R P E R , * ,† R O B E R T M . K A L I N , ‡ J O H N T . G . H A M I L T O N , †,§ A N D C L A R E L A M B †,‡ Microbial Biochemistry Section, School of Agriculture and Food Science, The Queen’s University of Belfast, Newforge Lane, Belfast BT9 5PX, U.K., Environmental Engineering Research Centre, School of Civil Engineering, The Queen’s University of Belfast, Belfast BT9 5AG, U.K., and Department of Agriculture and Rural Development for Northern Ireland, Newforge Lane, Belfast, BT9 5PX, U.K.
Chloromethane (CH3Cl) with a global atmospheric burden of 5.3 million t is the most abundant halocarbon in the atmosphere. However, the origin of ca. 50% of the estimated annual global input of 4 million t of the gas to the atmosphere has yet to be determined. As the oceanic contribution to the global CH3Cl flux is now tightly constrained, an important terrestrial source is either underestimated or unrecognized. It has recently been proposed that higher plants may represent a CH3Cl source of sufficient magnitude to resolve the global budget imbalance. A potentially useful tool in validating CH3Cl emission flux estimates is comparison of the carbon isotope ratio of atmospheric CH3Cl with those of CH3Cl originating from various sources. Here we report the first measurements of δ13C for CH3Cl produced biologically. The CH3Cl released by the higher plant species Batis maritima and Solanum tuberosum was dramatically depleted in 13C with respect to plant tissue (∆13C ) -36.8‰ and -34.5‰, respectively); CH3Cl released by the fungus Phellinus pomaceus also showed significant 13C depletion with respect to the wood growth substrate (∆13C ) -17.9‰). When reliable δ13C values for the other major sources of atmospheric CH3Cl become available, the distinctive isotopic signature of plantderived CH3Cl should help constrain the contribution to the atmospheric burden from this source.
Introduction CH3Cl is responsible for around 17% of chlorine-catalyzed ozone destruction in the stratosphere; only man-made CFCl3 (CFC 11) and CF2Cl2 (CFC 12) display greater individual ozone-depleting effects than CH3Cl at current atmospheric * Corresponding author phone: 44-28-90255343; fax: 44-2890255006; e-mail:
[email protected]. † Microbial Biochemistry Section, School of Agriculture and Food Science, The Queen’s University of Belfast. ‡ Environmental Engineering Research Centre, School of Civil Engineering, The Queen’s University of Belfast. § Department of Agriculture and Rural Development for Northern Ireland. 3616
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mixing ratios (1). However, in contrast to the CFCs, only a small proportion (
