Mercury photochemistry in snow and implications for Arctic ecosystems

Abstract

Mercury is a toxic and bioaccumulative environmental contaminant, which may be transported to remote regions around the world, such as the Arctic. Snowmelt is a major source of mercury to many surface water environments, but the amount of mercury in snow varies considerably. This variation is due to the balance of mercury retention and losses from snow, which is largely controlled by photochemical mechanisms controlling speciation. As such, quantifying these photochemical reaction rates and the factors affecting them will allow for the prediction of mercury speciation and movement into receiving water bodies. This will consequently improve our ability to predict exposure of aquatic organisms to mercury. This review highlights knowledge gaps in the quantification of mercury photochemical kinetics and the specific research required to advance the science of mercury photochemistry in snow, while examining the physical and chemical snowpack variables that influence snowpack mercury reactions. At present, our lack of mechanistic and kinetic knowledge of mercury reactions in snow is one of the greatest gaps preventing accurate predictions of mercury fate in regions containing seasonal snowpacks.Résumé : Le mercure constitue un contaminant environnemental toxique et biocumulatif, pouvant être transporté dans des régions éloignées partout au monde, comme dans l'Arctique. La fonte des neiges représente une source majeure de mercure pour plusieurs plans d'eau de surface, mais la quantité de mercure dans la neige varie considérablement. Cette variation est due à la balance entre la rétention du mercure et les pertes à partir de la neige, celles-ci étant fortement contrôlées par des mécanismes photochimiques déterminant la spéciation. Comme telle, la quantification des taux de ces réactions photochimiques et des facteurs les affectant permettront de prédire la spéciation du mercure et le mouvement vers les milieux aquatiques réceptifs. Conséquemment, ceci améliorera notre capacité à prédire l'exposition des organismes aquatiques au mercure. Cette revue insiste sur les manques de connaissances concernant la quantification de la cinétique photochimique du mercure ainsi que les recherches spécifiques nécessaires à l'avancement de la science sur la photochimie du mercure dans la neige, tout en examinant les variables physiques et chimiques influençant les réactions du mercure dans les bancs de neige. Présentement, l'absence de connaissances mécanistiques et cinétiques des réactions du mercure dans la neige constitue une des plus grandes lacunes empêchant les prédictions sur le devenir du mercure dans les régions connaissant des enneigements saisonniers. [Traduit par la Rédaction]

Mercury Stable Isotopes in Ornithogenic Deposits As Tracers of Historical Cycling of Mercury in Ross Sea, Antarctica

“…Third, except for snow and atmospheric deposition, most other Hg inputs are primarily associated with particles (e.g., in soils) or biological tissues (e.g., in feces and vegetation), which have a relatively short residence time in pond water and are unlikely susceptible to aqueous photoreduction. 68 The MIF extent and signature of the oldest sediment section matches well with the modern seal excrement samples (Δ 199 Hg = 1.16 and 1.18‰, Δ 199 Hg/Δ 201 Hg = 1.16), further supporting seal excrement as the major source of Hg. The comparison of modern seal feces to the sediments is complicated because the modern feces was collected from different locations and it belongs to a different seal species than the seals that likely contributed to the sediment.…”

Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

“…Photochemical transformation of contaminants may become more important in regions where the total area of non-turbid thermokarst ponds is increasing, as these shallow ecosystems are irradiated constantly during the polar summer (e.g. Mann et al, 2014).…”

Historical variations of mercury stable isotope ratios in Arctic glacier firn and ice cores

“…The Hg deposited in Arctic snow during these events undergoes rapid postdepositional photochemical reduction and evasion from the snowpack [Steffen et al, 2008;Durnford and Dastoor, 2011]. These processes can modify the concentration and speciation of Hg in the uppermost layers (typically, a few centimeters) of the snowpack [Durnford and Dastoor, 2011;Mann et al, 2014]. Sherman et al [2010] have shown that photoreduction of Hg II and subsequent evasion of Hg 0 (g) from Arctic snow is accompanied by both MDF and MIF.…”