RESEARCH FRONT CSIRO PUBLISHING Foreword www.publish.csiro.au/journals/env R. Ebinghaus, Environ. Chem. 2008, 5, 87–88. doi:10.1071/EN08024 Mercury cycling in theArctic – does enhanced deposition flux mean net-input? Ralf Ebinghaus GKSS Research Centre Geesthacht, Institute for Coastal Research, Max-Planck-Str. 1, D-21502 Geesthacht, Germany. Email: ralf.ebinghaus@gkss.de Environmental context. Mercury has unique physico-chemical characteristics that include long-range atmo- spheric transport, transformation into highly toxic methylmercury species, and the bioaccumulation of these compounds, especially in the marine environment.This has motivated intense international research on mer- cury as a pollutant of global concern. With respect to Polar regions, scientific interest and research activities were even accelerated after the discovery of the so-called atmospheric mercury depletion events (AMDEs), which are supposed to lead to enhanced mercury deposition flux into these pristine environments in the ecologically very sensitive period in polar spring. The polar ecosystems are generally considered to be the last pristine environments of the earth. The Arctic, for example is populated by few people, has minimal commercial fishing, little industrial activity (except for some areas in the RussianArctic [1] ) and is, therefore, perceived to be relatively unaffected by human activity. In comparison, Antarctica is considered to be even less affected by any kind of anthropogenic influences. Once contaminants reach the Polar regions, their lifetime in the troposphere depends on local removal processes. A totally unexpected finding on mercury in the Polar atmosphere was made in 1995. It was discovered that, during springtime, unexpectedly low concentrations of gaseous elemental mercury occurred in the Arctic air. This was surprising for a pollutant supposed to have a fairly long atmospheric residence time of six months to two years. This finding, the so-called atmospheric mercury depletion events (AMDEs), had significant influence on global mercury research and monitoring activities related to mercury cycling in Polar regions. Only five years after the first scientific publication of AMDEs in Nature by Schroeder et al., [2] more than 200 papers dedicated to the occurrence and environmental significance of this phenomenon have been pub- lished in the peer-reviewed literature. It is now well established that AMDEs are an annually recurring polar spring-time phe- nomenon that result in a deposition flux. However, whether the result in total is a net -deposition is still not clear. Mercury and many of its compounds exhibit unique behaviour in the environment because of their volatility, capability for methylation, and subsequent bioaccumulation, in contrast with most of the other heavy metals. Hg is emitted into Ralf Ebinghaus is an analytical and environmental chemist and heads the Department for Environmental Chemistry of the Institute for Coastal Research at GKSS Research Centre. He is a Professor at the University of Lüneburg and teachesAtmospheric and Marine Chemistry. Since 2003, Dr Ebinghaus has been an invited lecturer at the annual European Research Course on Atmospheres (ERCA). He has published more than 60 scientific papers and has co-edited two books and a special journal issue on mercury and related fields. Presently, Dr Ebinghaus is a member of the Steering Committee of the 9th International Conference on Mercury as a Global Pollutant, to be held in Guiyang, China, June 7–12 2009. the atmosphere from several natural as well as anthropogenic sources. Experimental field data and model estimates indicate that anthropogenic mercury emissions are at least as great as those from natural sources. [3–6] It is assumed that anthropogenic emissions lead to a general increase in Hg on local, regional, and global scales and that the increase in the overall global deposition since pre-industrial times is about a factor of 3 ± 1. [7] Long-range atmospheric transport, the transformation into more toxic methylmercuric compounds, and their biomagnifica- tion in the aquatic foodchain have motivated intensive research on Hg as a pollutant of global concern. Hg is on the priority list of a large (and increasing) number of international agreements, conventions, and national advisories aimed at the protection of the environment including all compartments, human health, and wildlife (e.g.AMAP, UN-ECE, HELCOM, OSPAR, and many others). In the atmospheric environment the most important species are gaseous elemental Hg, divalent reactive gaseous mercury (RGM), which consists of various oxidised Hg II compounds, and particle-bound Hg, which consists of various Hg compounds. It should be noted that information on the speciation/fractionation of these different chemical and physical forms is largely opera- tionally defined. Conversions between these different forms provide the basis of Hg’s complex distribution pattern on local, regional, and global scales. AMDEs were initially considered to result in an important net input of atmospheric mercury into the polar ecosystems during the spring period. But more recent studies, including the work © CSIRO 2008 87 1448-2517/08/020087