Degradation of methylmercury into Hg(0) by the oxidation of iron(II) minerals

• Published in: Water research (Oxford) Vol. 256; p. 121645
• Main Authors: Xie, Fuyu, Yuan, Qingke, Meng, Ying, Luan, Fubo
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.06.2024
• Subjects: Abiotic demethylation; Light-independent; Mercury cycling; Redox fluctuations; Light-independent; Mercury cycling; Redox fluctuations; Abiotic demethylation
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2024.121645

•Abiotic demethylation of methylmercury occurs during oxidation of iron(II) minerals.•Oxidation of iron(II) minerals produces hydroxyl and superoxide radicals.•Hydroxyl and superoxide radicals induce oxidative demethylation of methylmercury.•The generated Hg(II) was rapidly reduced into Hg(0) by iron(II) minerals. Mercury contamination is a global concern, and the degradation and detoxification of methylmercury have gained significant attention due to its neurotoxicity and biomagnification within the food chain. However, the currently known pathways of abiotic demethylation are limited to light-induced photodegradation process and little is known about light-independent abiotic demethylation of methylmercury. In this study, we reported a novel abiotic pathway for the degradation of methylmercury through the oxidation of both mineral structural iron(II) and surface-adsorbed iron(II) in the absence of light. Our findings reveal that methylmercury can be oxidatively degraded by reactive oxygen species, specifically hydroxyl and superoxide radicals, which are generated from the oxidation of iron(II) minerals under dark conditions. Surprisingly, Hg(0) trapping experiments demonstrated that inorganic Hg(II) resulting from the oxidative degradation of methylmercury was rapidly reduced to gaseous Hg(0) by iron(II) minerals. The demethylation of methylmercury, coupled with the generation of Hg(0), suggests a potential natural attenuation process for methylmercury. Our results highlight the underappreciated roles of iron(II) minerals in the abiotic degradation of methylmercury and the release of gaseous Hg(0) into the atmosphere. [Display omitted]