1) School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, United States, 2) Department of Earth and Space Sciences, University of California, Los Angeles, California, United States, 3) Department of Geology, University of Illinois, Urbana, Illinois, United States, 4) Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, United States Environmental Science and Technology (2013), V47(6), pp2542–2547, doi: 10.1021/es303940p Unique Hg Stable Isotope Signatures of Compact Fluorescent Lamp-Sourced Hg Chris Mead (1), James R. Lyons (2), Thomas M. Johnson (3) and Ariel D. Anbar (1,4) The recent widespread adoption of compact fluorescent lamps (CFL) has increased their importance as a source of environmental Hg. Stable isotope analysis can identify the sources of environmental Hg, but the isotopic composition of Hg from CFL is not yet known. Results from analyses of CFL with a range of hours of use show that the Hg they contain is isotopically fractionated in a unique pattern during normal CFL operation. This fractionation is large by comparison to other known fractionating processes for Hg and has a distinctive, mass-independent signature, such that CFL Hg could be uniquely identified from other sources. The fractionation process described here may also explain anomalous fractionation of Hg isotopes in precipitation.