Occurrence of Mercurous [Hg(I)] Species in Environmental Solid Matrices as Probed by Mild 2-Mercaptoethanol Extraction and HPLC-ICP-MS Analysis

Abstract

Mercurous Hg [Hg(I)] is, from the perspective of chemistry, an inevitable intermediate in Hg(II)/Hg(0) redox, presumably playing a critical role in the environmental transformation of common toxic Hg species, such as Hg(II), Hg(0), and methylmercury. The occurrence of Hg(I) in the environment, however, has been scarcely documented, due to its instability, which greatly limits its isolation and identification. We probed the occurrence of Hg(I) in various environmental solid matrices by developing and employing a method based on mild 2mercaptoethanol extraction and HPLC-ICP-MS analysis. Various complexation agents and assisted extraction methods were investigated for their effects on Hg(I) stability. A variety of solid matrices were used to demonstrate extraction, separation, and detection of Hg(I) under optimized conditions. The occurrence of Hg(I) was widely evident in various solid matrices, including desulfurized gypsum, fly ash, phosphorus powder in used fluorescent lamps, PM 2.5 , soil, and plants, despite Hg(I) reduction possibly being catalyzed by a solid matrix during extraction that could underestimate Hg(I) in the samples. More importantly, Hg(I) was detected in Hg(II)-exposed microalgae, exemplifying the environmental relevance of Hg(II) to Hg(I) transformation. These findings highlight the environmental significance of Hg(I), which should be further studied to examine the role of Hg(I) in the transformation, bioavailability, and toxicity of Hg.

Gaseous Elemental Mercury [Hg(0)] Oxidation in Poplar Leaves through a Two-Step Single-Electron Transfer Process

“…The loss of Hg(I) was likely caused by its transformation to Hg(0) or Hg(II) during sample pretreatment. 29 Hg(II) concentrations in poplar leaves collected at different times were close to THg concentrations (Table 1), suggesting that Hg(II) is the predominant Hg form in foliage after Hg(0) exposure. Hg(I) was also detected in poplar leaves after Hg(0) exposure with its concentration being 3 orders of magnitude lower than Hg(II) in leaves after 3, 6, and 12 h exposure (Figure S4).…”

“…Recoveries for the spiked Hg­(I) and Hg­(II) in freeze-dried poplar leaves were 51 ± 1% and 99 ± 8%, respectively. The loss of Hg­(I) was likely caused by its transformation to Hg(0) or Hg­(II) during sample pretreatment …”

“…Hg­(I) was proposed as an intermediate during biological Hg(0) oxidation, but this hypothesis could not be verified due to the deficiencies in the analytical method for Hg­(I) . A method employing extraction with 2-mercaptoethanol and followed by HPLC-ICP-MS analysis for simultaneous determination of Hg­(I) and Hg­(II) in environmental samples was recently developed in our group . Using this method, the occurrence of Hg­(I) in plant leaves exposed to Hg(0) could be demonstrated.…”

“…19 A method employing extraction with 2-mercaptoethanol and followed by HPLC-ICP-MS analysis for simultaneous determination of Hg(I) and Hg(II) in environmental samples was recently developed in our group. 29 Using this method, the occurrence of Hg(I) in plant leaves exposed to Hg(0) could be demonstrated.…”

Matrix effects on the performance and mechanism of Hg removal from groundwater by MoS2 nanosheets

“…46 Consequently, ˙HgCl radicals could either dimerize into the Hg 2 Cl 2 precipitate ( K sp = 5 × 10 −20 ) 64 or accept another electron from MoS 2 and reduce to Hg 0 . 65 Owing to the stability of Hg( i ) associated with Cl, the stepwise reduction of Hg( ii ) by MoS 2 was favored leading to the enhanced total Hg removal. Meanwhile the resulting ˙OH radicals caused nearly complete oxidation of MoS 2 to soluble Mo and S species.…”