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

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 2-mercaptoethanol 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, PM2.5, 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.