Mercury reduction and complexation by natural organic matter in anoxic environments

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 108; no. 4; pp. 1479 - 1483
• Main Authors: Gu, Baohua, Bian, Yongrong, Miller, Carrie L, Dong, Wenming, Jiang, Xin, Liang, Liyuan
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 25.01.2011; National Acad Sciences
• Subjects: Acid soils; Anaerobiosis; Aquatic environment; binding capacity; Binding sites; Biodegradation, Environmental; Biological Sciences; Chemical reduction; Dissolved organic matter; DNA methylation; Humic acids; Humic Substances; Hypoxia; Mercury; Mercury - chemistry; Mercury - metabolism; Methylation; Methylmercury; methylmercury compounds; Methylmercury Compounds - chemistry; Methylmercury Compounds - metabolism; Models, Chemical; Molecules; Organic Chemicals - chemistry; Organic Chemicals - metabolism; Oxidation; Oxidation-Reduction; Sedimentary soils; Sediments; Shewanella putrefaciens - metabolism; Soil organic matter; Soil pollution; Sulfur; Thiols; toxicity; Water Pollutants, Chemical - chemistry; Water Pollutants, Chemical - metabolism; Water pollution
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1008747108

Mercuric Hg(II) species form complexes with natural dissolved organic matter (DOM) such as humic acid (HA), and this binding is known to affect the chemical and biological transformation and cycling of mercury in aquatic environments. Dissolved elemental mercury, Hg(0), is also widely observed in sediments and water. However, reactions between Hg(0) and DOM have rarely been studied in anoxic environments. Here, under anoxic dark conditions we show strong interactions between reduced HA and Hg(0) through thiolate ligand-induced oxidative complexation with an estimated binding capacity of approximately 3.5 μmol Hg/g HA and a partitioning coefficient >10⁶ mL/g. We further demonstrate that Hg(II) can be effectively reduced to Hg(0) in the presence of as little as 0.2 mg/L reduced HA, whereas production of Hg(0) is inhibited by complexation as HA concentration increases. This dual role played by DOM in the reduction and complexation of mercury is likely widespread in anoxic sediments and water and can be expected to significantly influence the mercury species transformations and biological uptake that leads to the formation of toxic methylmercury.