Legacy Mercury Re-emission and Subsurface Migration at Contaminated Sites Constrained by Hg Isotopes and Chemical Speciation

作者：Wei Zhu, Zhonggen Li, Ping Li, Jonas Sommar, Xuewu Fu, Xinbin Feng, Ben Yu, Wei Zhang, Ana Teresa Reis, Eduarda Pereira · 发表于：Environmental Science & Technology · 年份：2024 · DOI：10.1021/acs.est.3c07276 · 被引用次数：19 · 研究领域：Mercury impact and mitigation studies、Heavy Metal Exposure and Toxicity、Heavy metals in environment

The re-emission and subsurface migration of legacy mercury (Hg) are not well understood due to limited knowledge of the driving processes. To investigate these processes at a decommissioned chlor-alkali plant, we used mercury stable isotopes and chemical speciation analysis. The isotopic composition of volatilized Hg(0) was lighter compared to the bulk total Hg (THg) pool in salt-sludge and adjacent surface soil with mean ε 202 Hg Hg(0)-THg values of −3.29 and −2.35‰, respectively. Hg(0) exhibited dichotomous directions ( E 199 Hg Hg(0)-THg = 0.17 and −0.16‰) of mass-independent fractionation (MIF) depending on the substrate from which it was emitted. We suggest that the positive MIF enrichment during Hg(0) re-emission from salt-sludge was overall controlled by the photoreduction of Hg(II) primarily ligated by Cl – and/or the evaporation of liquid Hg(0). In contrast, O-bonded Hg(II) species were more important in the adjacent surface soils. The migration of Hg from salt-sludge to subsurface soil associated with selective Hg(II) partitioning and speciation transformation resulted in deep soils depleted in heavy isotopes (δ 202 Hg = −2.5‰) and slightly enriched in odd isotopes (Δ 199 Hg = 0.1‰). When tracing sources using Hg isotopes, it is important to exercise caution, particularly when dealing with mobilized Hg, as this fraction represents only a small portion of the sources.