Mass-independent fractionation of mercury isotopes in the environment

Abstract

The toxicity of mercury's methylated species and its biomagnification in aquatic food chains and global dispersion by the atmosphere are the cause of worldwide health problems. Recent reports have observed natural mass-dependent fractionation in mercury isotopes, and recent theoretical work has demonstrated that isotopic separation in mercury is due primarily to nuclear field shifts (nuclear volume effect), and the magnetic spin effect gives rise to mass-independent fractionation (MIF) of odd neutron number isotopes. Now we present analytical evidence of mass-independent isotopic variations in mercury produced by both nuclear volume and magnetic isotope processes. Even mass number isotopes exhibit a pattern indistinguishable from that produced by mass-dependent fractionation, with both positive and negative 199Hg and 201Hg anomalies. MIF is easier to reliably determine in Hg isotopes than mass-dependent fractionation alone, and thus it provides a potentially important key in constraining models of mercury sources and pathways in the environment. Copyright 2008 by the American Geophysical Union.