Mercury Isotopic Fractionation during Pedogenesis in a Tropical Forest Soil Catena (French Guiana): Deciphering the Impact of Historical Gold Mining

S. Guédron, D. Amouroux, E. Tessier, C. Grimaldi, J. Barre, S. Berail, V. Perrot, M. Grimaldi

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

We used natural mercury (Hg) stable isotopes to investigate the Hg cycle in a rainforest soil catena (French Guiana) partially gold-mined during the early 1950s. Litterfall showed homogeneous Δ 199Hg values [-0.18 ± 0.05‰, i.e., a modern gaseous elemental Hg (GEM) isotopic signature]. After litter decomposition, Hg bound to organic matter (OM) is mixed with Hg from pristine (-0.55 ± 0.22‰) or gold-mined (-0.09 ± 0.16‰) mineral materials. Negative Δ 199Hg values in deep pristine mineral horizons (-0.60 ± 0.16‰) suggest the transfer of Hg bound to dissolved OM depleted in odd isotopes due to mass-independent fractionation during Hg abiotic reduction. Perennial palm tree leaves collected above gold-mined and pristine soil recorded contrasting Δ 199Hg signatures likely resulting from GEM re-emission processes from soils and leaf surfaces. Upslope, soil δ 202Hg signatures showed a negative shift (ϵ ∼-1‰) with depth attributed to mass-dependent fractionation during Hg sorption and complexation onto iron oxides and dissolved OM. Downslope, higher δ 202Hg values in soils resulted from hydromorphy [lower humification, greater Hg(II) reduction, etc.]. The unique Hg isotopic signatures of Amazonian soils probably result in multistep fractionation processes during pedogenesis (millions of years) and in a potentially different Hg isotopic signature of preanthropogenic background GEM.

Original languageEnglish
Article number20
Pages (from-to)11573-11582
Number of pages10
JournalEnvironmental Science & Technology
Volume52
Issue number20
DOIs
Publication statusPublished - 16 Oct 2018

Fingerprint Dive into the research topics of 'Mercury Isotopic Fractionation during Pedogenesis in a Tropical Forest Soil Catena (French Guiana): Deciphering the Impact of Historical Gold Mining'. Together they form a unique fingerprint.

Cite this