Article pubs.acs.org/est
Photoreducible Mercury Loss from Arctic Snow Is Influenced by Temperature and Snow Age Erin A. Mann,†,‡ Mark L. Mallory,§ Susan E. Ziegler,‡ Trevor S. Avery,§ Rob Tordon,∥ and Nelson J. O’Driscoll*,† †
Department of Earth and Environmental Science, and §Department of Biology, Acadia University, Wolfville, NS Canada Department of Earth Science, Memorial University of Newfoundland, St. John’s, NL Canada ∥ Air Quality Science Division, Environment Canada, Dartmouth, NS Canada ‡
S Supporting Information *
ABSTRACT: Mercury (Hg) is an important environmental contaminant, due to its neurotoxicity and ability to bioaccumulate. The Arctic is a mercury-sensitive region, where organisms can accumulate high Hg concentrations. Snowpack mercury photoredox reactions may control how much Hg is transported with melting Arctic snow. This work aimed to (1) determine the significance of temperature combined with UV irradiation intensity and snow age on Hg(0) flux from Arctic snow and (2) elucidate the effect of temperature on snowpack Hg photoreduction kinetics. Using a Teflon flux chamber, snow temperature, UV irradiation, and snow age were found to significantly influence Hg(0) flux from Arctic snow. Cross-correlation analysis results suggest that UV radiation has a direct effect on Hg(0)flux, while temperature may indirectly influence flux. Laboratory experiments determined that temperature influenced Hg photoreduction kinetics when snow approached the melting point (>−2 °C), where the pseudo-first-order reduction rate constant, k, decreased twofold, and the photoreduced Hg amount, Hg(II)red, increased 10-fold. This suggests that temperature influences Hg photoreduction kinetics indirectly, likely by altering the solid:liquid water ratio. These results imply that large mass transfers of Hg from snow to air may take place during the Arctic snowmelt period, altering photoreducible Hg retention and transport with snow meltwater.
1. INTRODUCTION 1.1. Mercury Speciation and Arctic Implications. Mercury (Hg) exists in three main environmentally relevant forms: elemental (Hg(0)), divalent (Hg(II)), and organic methylmercury (MeHg). Elemental Hg is volatile and has very low solubility,1 existing primarily in the gas phase, with a typical atmospheric lifetime of ∼0.5−2 years.2,3 Hg(II) is found in condensed phases in the atmosphere and is deposited to the earth’s surface. Reactive gaseous mercury (RGM) is an operationally defined form of atmospheric Hg thought to be primarily gas phase Hg(II), with an atmospheric lifetime of a few hours4 to a few days.5 Newly deposited Hg is very bioavailable to bacteria and might be more easily methylated than Hg(II) that has been resident in the ecosystem for long periods.6 In addition, Hg deposited with snow tends to be more bioavailable than Hg deposited with rain,7 making snowpack Hg dynamics very important from an ecosystem health perspective. The majority of Hg in a snowpack exists in condensed phases, with
