Hg isotopic composition of one-year-old spruce shoots: Application to long-term Hg atmospheric monitoring in Germany

Akane Yamakawa,David Amouroux,Emmanuel Tessier,Sylvain Bérail,Ina Fettig,Julien P.G Barre,Jan Koschorreck,Heinz Rüdel,Olivier F.X Donard

doi:10.1016/j.chemosphere.2021.130631

Abstract

The Hg isotopic composition of 1-year-old Norway spruce (Picea abies) shoots collected from Saarland cornurbation Warndt, Germany, since 1985 by the German Environmental Specimen Bank, were measured for a better understanding of the temporal trends of Hg sources. The isotopic data showed that Hg was mainly taken up as gaseous element mercury (GEM) and underwent oxidation in the spruce needles; this led to a significant decrease in the δ202Hg compared with the atmospheric Hg isotopic composition observed for deciduous leaves and epiphytic lichens. Observation of the odd mass-independent isotopic fractionation (MIF) indicated that Δ199Hg and Δ201Hg were close to but slightly lower than the actual values recorded from the atmospheric measurement of the GEM isotopic composition in non-contaminated sites in U.S. and Europe, whereas observation of the even-MIF indicated almost no differences for Δ200Hg. This confirmed that GEM is a major source of Hg accumulation in spruce shoots. Interestingly, the Hg isotopic composition in the spruce shoots did not change very significantly during the study period of >30 years, even as the Hg concentration decreased significantly. Even-MIF (Δ200Hg) and mass-dependent fractionation (MDF) (δ202Hg) of the Hg isotopes exhibited slight decrease with time, whereas odd-MIF did not show any clear trend. These results suggest a close link between the long-term evolution of GEM isotopic composition in the air and the isotopic composition of bioaccumulated Hg altered by mass-dependent fraction in the spruce shoots.

Highlights

Hg is a globally distributed toxic metal that is capable of long-Table of abbreviationsgaseous element mercury (GEM) gaseous oxidized mercury (GOM) mass-dependent fractionation (MDF) massindependent isotopic fractionation (MIF) particulate-bound mercury (PBM) TGMGaseous element mercury Gaseous oxidized mercury Mass-dependent fractionation Mass-independent fractionation Particulate-bound mercury Total gaseous mercury sources (Gonzalez-Raymat et al, 2017)
Even-MIF (D200Hg) and mass-dependent fractionation (MDF) (d202Hg) of the Hg isotopes exhibited slight decrease with time, whereas odd-MIF did not show any clear trend. These results suggest a close link between the long-term evolution of GEM isotopic composition in the air and the isotopic composition of bioaccumulated Hg altered by mass-dependent fraction in the spruce shoots
The Hg isotopic composition of the spruce samples did not exhibit a large variation within the study period, even as the Hg concentration greatly decreased

Summary

Introduction

Gaseous element mercury Gaseous oxidized mercury Mass-dependent fractionation Mass-independent fractionation Particulate-bound mercury Total gaseous mercury sources (Gonzalez-Raymat et al, 2017). The other two chemical species are gaseous oxidized mercury (GOM) or Hg2þ(g) and particulate-bound mercury (PBM) or Hg(p); they are relatively reactive and are efficiently removed from the atmosphere through wet and dry deposition (Lindberg et al, 2002; Liu et al, 2010). Forest ecosystems are the largest sink for atmospheric Hg. Previous studies showed that leaves and tree rings can be used as biomonitors for total gaseous mercury (TGM, GEM þ GOM) concentrations over space (Arnold et al, 2018; Peckham et al, 2019a, 2019b). GOM and PBM are adsorbed to leaf surfaces, and re-emitted to the atmosphere or leached by precipitation and deposited to the floor (Demers et al, 2007)

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