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

Abstract

AbstractSoil 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 (ε202HgHg(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 E199HgHg(0)­‐soil = 0.67‰ to 0.76‰, n = 2) than the temperature‐controlled experiments (mean E199HgHg(0)‐­soil = 0.18 ± 0.04‰, 1 SD), whereas the E199HgHg(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.