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Mercury Biogeochemical Cycling: a Synthesis of Recent Scientific Advances

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Mercury Biogeochemical Cycling: a Synthesis of Recent Scientific Advances Science of the Total Environment 737 (2020) 139619 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv Mercury biogeochemical cycling: A synthesis of recent scientific advances Mae Sexauer Gustin a,⁎, Michael S. Bank b,c, Kevin Bishop d, Katlin Bowman e,f, Brian Branfireun g, John Chételat h, Chris S. Eckley i, Chad R. Hammerschmidt j, Carl Lamborg f, Seth Lyman k, Antonio Martínez-Cortizas l, Jonas Sommar m, Martin Tsz-Ki Tsui n, Tong Zhang o a Department of Natural Resources and Environmental Science, University of Nevada, Reno, NV 89439, USA b Department of Contaminants and Biohazards, Institute of Marine Research, Bergen, Norway c Department of Environmental Conservation, University of Massachusetts, Amherst, MA 01255, USA d Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Box 7050, 75007 Uppsala, Sweden e Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA f University of California Santa Cruz, Ocean Sciences Department, 1156 High Street, Santa Cruz, CA 95064, USA g Department of Biology and Centre for Environment and Sustainability, Western University, London, Canada h Environment and Climate Change Canada, National Wildlife Research Centre, 1125 Colonel By Drive, Ottawa, ON K1A 0H3, Canada i U.S. Environmental Protection Agency, Region-10, 1200 6th Ave, Seattle, WA 98101, USA j Wright State University, Department of Earth and Environmental Sciences, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA k Bingham Research Center, Utah State University, 320 N Aggie Blvd., Vernal, UT, USA l EcoPast (GI-1553), Facultade de Bioloxía, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Spain m State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China n Department of Biology, University of North Carolina at Greensboro, Greensboro, NC 27402, USA o College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Tianjin 300350, China HIGHLIGHTS GRAPHICAL ABSTRACT • This paper provides a brief summary of recent advances in Hg science. • Details are presented in 10 papers in a Virtual Special Issue of STOTEN. • Presented are updates in scientific knowledge regarding the fate and trans- port of Hg. • Advances in measurement methods are synthesized. • Discussion is provided as to how these fit within the Minamata Convention. article info abstract Article history: The focus of this paper is to briefly discuss the major advances in scientific thinking regarding: a) processes Received 19 May 2020 governing the fate and transport of mercury in the environment; b) advances in measurement methods; and Accepted 20 May 2020 c) how these advances in knowledge fit in within the context of the Minamata Convention on Mercury. Details Available online 23 May 2020 regarding the information summarized here can be found in the papers associated with this Virtual Special Issue of STOTEN. Keywords: Crown Copyright © 2020 Published by Elsevier B.V. All rights reserved. Minamata Convention Mercury isotopes Methylmercury Fluxes Archives Wildlife ⁎ Corresponding author. E-mail address: [email protected] (M.S. Gustin). https://doi.org/10.1016/j.scitotenv.2020.139619 0048-9697/Crown Copyright © 2020 Published by Elsevier B.V. All rights reserved. 2 M.S. Gustin et al. / Science of the Total Environment 737 (2020) 139619 1. Introduction The biogeochemical cycle of an atom of Hg starts with the emission from natural and anthropogenic sources. Once emitted an atom enters Mercury (Hg) is a unique element, being one of two that exist as a the global atmospheric pool. This atom may be deposited to surfaces liquid at ambient conditions, the other being bromine. Because of the and then re-emitted. It also may be actively taken up by plants that se- presence of Hg as a liquid, it is volatilized to the atmosphere from terres- quester an estimated 1/3rd of the Hg emitted each year (Arnold et al., trial and aquatic surfaces. Elemental Hg is generally considered to be 2018). Hg also may be oxidized in the air promoting deposition. This somewhat inert and is globally transported via the atmosphere. How- Hg may be sequestered, converted to methyl- or di-methylmercury, or ever, elemental Hg can be deposited to the surfaces relatively quickly reduced and re-emitted back to the atmosphere. once emitted (Miller and Gustin, 2013; Gustin et al., 2013). Elemental Mercury pollution is an important environmental and public health Hg is oxidized by a variety of compounds and Hg (II) compounds have issue. In August 2017, the United Nation's Minamata Convention on Mer- a higher deposition velocity than elemental Hg (Ariya et al., 2015). Mer- cury entered into force. The Minamata Convention on Mercury is legally cury is ubiquitous in the atmosphere and atmospheric concentrations binding and is the main international policy instrument for managing have increased substantially since the onset of civilization (Amos anthropogenic Hg emissions (air) and releases (water) to the environ- et al., 2013). ment, and to also protect human health (Minamataconvention.org). Given the volatility of elemental Hg and the lack of long-term sinks, The foundation for successful implementation of the Minamata Conven- once an atom of Hg is released to the atmosphere it can remain in circu- tion on Mercury is the use of recent policy relevant scientific advances lation for N1000 years (Fig. 1). The only true sink is burial in ocean sed- that have furthered our understanding of Hg biogeochemical cycling iment and soil (Amos et al., 2013). Prior to development of human and its impacts on humans and terrestrial and marine ecosystems populations, major sources of Hg to the air included volcanic eruptions, (Bank, 2020). Here we synthesize the recent scientific advances emissions from rocks and soil enriched in Hg, and re-emission of that (discussed in detail in this issue) in understanding Hg biogeochemical deposited to surfaces, coal burning events (Burger et al., 2019), and for- cycling and outline critical topics and research avenues to guide future est fires (Webster et al., 2016). Prior to humans, the major sink would investigations and efforts. have been uptake by plants. With the appearance of humans, Hg mining activities began, creating a novel and important source of Hg to the bio- 2. Results and discussion geochemical cycle. Values in archives before 2000 BCE, as proposed by Amos et al. 2.1. Utility of stable mercury isotopes for understanding sources and processes (2013), are considered to reflect pre-anthropogenic emissions. After this time, civilizations utilizing Hg and biomass burning, potentially Due to the pioneering work of Professor Joel Blum and others in caused by humans, would have released Hg to the air. Hg has been the early 2000s, Hg stable isotopes have become an important tool used by societies for ≥2500 years and is found in Egyptian tombs & used to understand source apportionment dynamics of Hg contami- amalgams dating back to ca. 500 BCE. Greeks & Romans used it for med- nating any component of an ecosystem and processes affecting the icine and cosmetics, and China's first emperor (Qin Shi Huang 221–210 fate and transport of Hg in the environment. Several review papers BCE) was buried within a moat of Hg. Prior to the Industrial Revolution have recently been published on this topic (e.g., Bergquist and major sources were silver, gold, and cinnabar mining (Outridge et al., Blum, 2009; Yin et al., 2010; Blum, 2011; Kritee et al., 2013; Blum 2018). Primary anthropogenic emissions of Hg to the atmosphere are et al., 2014; Yin et al., 2014; Sun et al., 2016; Blum and Johnson, currently considered to be artisanal gold mining N fossil fuel 2017; Buchachenko, 2018). See Tsui et al. (2020) for basic systemat- combustion N nonferrous metal and cement production (UNEP Global ics for Hg isotopes and discussion of fractionation processes as well Mercury Assessment, 2013). as advancements in measurements. Fig. 1. Temporal movement dynamics of Hg through different environmental reservoirs. The y-axis represents a unit pulse of Hg released to the atmosphere and the x-axis depicts how it partitions over time. This conceptual model represents a unit pulse of Hg as the perturbation, thus is independent of historical emission estimates and is meant to illustrate the relevant temporal scales involved in Hg movement through different environmental reservoirs. Re-drawn and modified from Amos et al. (2013). M.S. Gustin et al. / Science of the Total Environment 737 (2020) 139619 3 The utility of stable Hg isotopes is greater than many other common method has yielded unexpected results, such as emissions as being the isotope tracers such as stable isotopes of carbon and nitrogen, primarily current dominant flux from bogs (Osterwalder et al., 2017). Hg0 dry de- because mass-dependent fractionation (MDF) and mass independent position is now recognized as the major component of the total Hg de- fractionation (MIF) can change the natural abundance of isotope ratios position in remote areas. Dry deposition of Hg0 via plant uptake displays that can be used to understand complex biogeochemical processes af- profound dominance in terrestrial vegetated ecosystems with divalent fecting Hg cycling. MDF occurs during many biogeochemical
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