Photodegradation of methylmercury in the water body of the Three Gorges Reservoir

Role of Free Radicals/Reactive Oxygen Species in MeHg Photodegradation: Importance of Utilizing Appropriate Scavengers

“…Several pathways have been previously proposed for MeHg photodegradation in natural water, including ·OH, ,, 1 O 2 , 3 DOM*, and direct photodegradation of MeHg-DOM complexes . These findings mainly depended on the results of FR/ROS scavenger addition experiments without sufficient evaluation of the scavengers used (e.g., using NaN 3 and β-carotene as the scavengers of 1 O 2 , using DMSO, formic acid, and BA as the scavengers of ·OH). ,, Based on the results of this study, some of these previously used scavengers may affect the water chemical properties, thereby influencing MeHg photodegradation. For example, NaN 3 and β-carotene can significantly affect MeHg-DOM complexation and radiation absorbance, respectively.…”

“…Indirect pathways are primarily mediated by photomediated produced free radicals (FR) or reactive oxygen species (ROS) and they have been reported to play crucial roles in MeHg photodegradation. 2,10,17 Singlet oxygen ( 1 O 2 ) and hydroxyl radical (•OH) are the two species mostly reported to induce the photodegradation of MeHg, 13,16,19−21 whereas the involvement of triplet excited state of dissolved organic matters ( 3 DOM*) was also observed. 12,22 Direct photodegradation of MeHg-inorganic ligand complexes such as MeHgCl or MeHgOH under sunlight is theoretically difficult because of the low energy of sunlight that reaches to the earth.…”

“…Methylmercury (MeHg), a neurotoxin and the most toxic form of mercury (Hg) in the environment, has drawn extensive public attention because of its bioaccumulation through food chains and high risk to human health. Photodegradation is a major sink of MeHg in aquatic environments, − and great efforts have been made to elucidate the mechanisms governing this process. − The chemical reactions underlying this process have been reported to be system-specific. ,,− Both indirect ,,, and direct pathways have been proposed in previous studies. Indirect pathways are primarily mediated by photomediated produced free radicals (FR) or reactive oxygen species (ROS) and they have been reported to play crucial roles in MeHg photodegradation. ,, Singlet oxygen ( 1 O 2 ) and hydroxyl radical (·OH) are the two species mostly reported to induce the photodegradation of MeHg, ,,− whereas the involvement of triplet excited state of dissolved organic matters ( 3 DOM*) was also observed. , Direct photodegradation of MeHg-inorganic ligand complexes such as MeHgCl or MeHgOH under sunlight is theoretically difficult because of the low energy of sunlight that reaches to the earth .…”

“…Photodegradation is a major sink of MeHg in aquatic environments, − and great efforts have been made to elucidate the mechanisms governing this process. − The chemical reactions underlying this process have been reported to be system-specific. ,,− Both indirect ,,, and direct pathways have been proposed in previous studies. Indirect pathways are primarily mediated by photomediated produced free radicals (FR) or reactive oxygen species (ROS) and they have been reported to play crucial roles in MeHg photodegradation. ,, Singlet oxygen ( 1 O 2 ) and hydroxyl radical (·OH) are the two species mostly reported to induce the photodegradation of MeHg, ,,− whereas the involvement of triplet excited state of dissolved organic matters ( 3 DOM*) was also observed. , Direct photodegradation of MeHg-inorganic ligand complexes such as MeHgCl or MeHgOH under sunlight is theoretically difficult because of the low energy of sunlight that reaches to the earth . This premise is supported by experimental data. , In contrast, direct photodegradation of MeHg-DOM complexes has been proposed to dominate MeHg photodegradation in some aquatic systems. , Because of the difficulty of establishing experimental conditions that would allow for the examination of the direct photodegradation of MeHg-DOM complexes, the approaches taken in current studies were mainly depending on validating or excluding the involvement of FR/ROS. , Therefore, accurately identifying the role of FR/ROS in MeHg photodegradation is important not only in systems in which FR/ROS dominate this process but also in systems where FR/ROS are not involved.…”

Adsorption and Desorption Behaviors of Hg²⁺ by <i>Microcystis aeruginosa</i>

“…The toxicological effects of mercury are strongly dependent on its chemical species [2]. Once inorganic mercury species transformed into methylmercury, it will pose a detrimental threat to fish-eating animals and humans because methylmercury is a potent neurotoxin and can be accumulated by aquatic biota [3]. "Minamata disease" is the notorious incidents caused by mercury contamination in the 1950s and 1960s in Japan [2].…”