A Laboratory Study on the Isotopic Composition of Hg(0) Emitted From Hg‐Enriched Soils in Wanshan Hg Mining Area

Abstract

Soil Hg(0) emissions are an important source of atmospheric mercury (Hg), but the Hg isotopic signatures of this source remain poorly characterized. In this study, the fractionation of Hg isotopes during Hg (0) emissions from Hg-enriched agricultural and forest soils in Wanshan Hg mining area were investigated through laboratory experiments. Significant mass-dependent fractionation (MDF) of Hg isotopes and mass independent fractionation of odd Hg isotopes (odd-MIF) were observed. Mean MDF enrichment factors (ε 202 Hg Hg(0)-soil) of agricultural soil were in the range of −2.03‰ to −1.34‰ for agricultural soil in light-, light moisture-, and temperature-controlled experiments, which were higher than those of forest soil in similar controls (means = −3.38‰ to −1.98‰). Temperature-controlled experiments exhibited a larger MDF compared to light-and light moisture-controlled experiments. Photoreduction of Hg in agricultural soil in the presence and absence of soil water generated a larger positive odd-MIF (mean E 199 Hg Hg(0)-soil = 0.67‰ to 0.76‰, n = 2) than the temperature-controlled experiments (mean E 199 Hg Hg(0)-soil = 0.18 ± 0.04‰, 1 SD), whereas the E 199 Hg Hg(0)-soil of forest soil in temperature controls (mean = 0.23 ± 0.03‰, 1 SD) were higher than that in light (mean = 0.18 ± 0.06‰, 1 SD) and light moisture-controlled experiments (mean = −0.03 ± 0.06‰, 1 SD). It is speculated that photoreducible Hg (II) likely dominantly bound to S-containing ligands in agricultural soil but to both S-containing and sulfurless ligands in forest soil, resulting in significant positive odd-MIF in Hg(0) product during photoreduction in the former case and a small magnitude of positive to some negative odd-MIF in the latter case.

Mercury Isotope Variations in Lake Sediment Cores in Response to Direct Mercury Emissions from Non-Ferrous Metal Smelters and Legacy Mercury Remobilization

“…We suggest that Hg in recent sediments of near-field lakes was primarily derived from tailing fugitive dust, which is expected to have comparable Hg isotope compositions as fed ores (i.e., no significant Hg isotope fractionation during mechanical separation). , We attribute the negative shifts in δ 202 Hg values in recent sediments from the middle- and far-field lakes to increasing contributions from the re-emission of legacy Hg from tailing deposits and contaminated soils. Re-emission of Hg involves reduction and volatilization processes, which are expected to enrich light Hg isotopes in the emitted gaseous elemental Hg(0). − , …”

“…Based on the above studies, we suggest that Hg isotope signatures of the Flin Flon smelter emissions could be recorded in sediments of distant lakes (e.g., hundreds of kilometers away) located at the downwind direction during the peak Hg emission period of the smelter (the late 1970s–1990s), and the negative shift of δ 202 Hg in recent sediments might be indicative of the increasing contribution of legacy Hg previously deposited near Flin Flon. Hg emissions from tailing deposits or contaminated terrestrial surfaces are expected to have very negative δ 202 Hg values. − …”

Katabatic Wind and Sea–Ice Dynamics Drive Isotopic Variations of Total Gaseous Mercury on the Antarctic Coast

“…The slope can diagnose typical environmental processes. For instance, a slope of ∼1.0 has been observed in natural media attributed to the photo-reduction of aquatic Hg­(II), in surface snow and ambient air during the re-emissions, and in re-emitted Hg(0) from airborne particles , and surface soil . These three processes may also contribute to TGM at the GWS located in the coastal area.…”

“…For instance, a slope of ∼1.0 has been observed in natural media attributed to the photoreduction of aquatic Hg(II), 34 in surface snow and ambient air during the re-emissions, 6 and in re-emitted Hg(0) from airborne particles 47,55 and surface soil. 76 These three processes may also contribute to TGM at the GWS located in the coastal area. On the other hand, lower slopes were observed in TGM in the Arctic regions and at other remote sites.…”

Demystifying mercury geochemistry in contaminated soil–groundwater systems with complementary mercury stable isotope, concentration, and speciation analyses

“…71 This journal is © The Royal Society of Chemistry 2022 The surface sample (À0.25 m) could be enriched in heavier isotopes due to (photo)reduction and evaporative losses. 84 We relate the difference in d 202 Hg between the high concentration articial lling layers (more negative) and its underlying layers (more positive) to kinetic and/or equilibrium fractionation resulting in a preferential retention of lighter isotopes in the solid-phase of the lower articial lling layers and enrichment of the liquid-phase Hg leaching into the underlying layers in heavier isotopes. While THg concentrations are signicantly lower in both the loess and Rhine sediment layers of SCB1 (p < 0.001), they are >2 mg kg À1 in all samples except the uppermost sample of the Rhine sediments (À4.75 m; see footnote §).…”