Degradation of methyl and ethyl mercury by singlet oxygen generated from sea water exposed to sunlight or ultraviolet light

Abstract

Photodegradation of methyl mercury (MeHg) and ethyl Hg (EtHg) in sea water was studied by sunlight or ultraviolet (UV) light exposure, and by determining inorganic Hg produced by degradation. Sea water containing 1 microM MeHg or EtHg was exposed to sunlight or UV light. N-Acetyl-L-cysteine was added to the solution for preventing Hg loss during the light exposure. MeHg and EtHg in sea water were degraded by sunlight (> 280 nm), UV light A (320-400 nm) and UV light B (280-320 nm), though the amounts of inorganic Hg produced from MeHg were 1/6th to 1/12th those from EtHg. Inorganic Hg production was greater with increasing concentration of sea water. Degradation of MeHg and EtHg by the UV light A exposure was inhibited by singlet oxygen (1O2) trappers such as NaN3, 1,4-diazabicyclo[2,2,2]octane, histidine, methionine and 2,5-dimethylfuran. On the other hand, inhibitors or scavengers of superoxide anion, hydrogen peroxide or hydroxyl radical did not inhibit the photodegradation of alkyl Hg. These results suggested that 1O2 generated from sea water exposed to sunlight, UV light A or UV light B was the reactive oxygen species mainly responsible for the degradation of MeHg and EtHg.

Photo-induced chemical vapour generation with formic acid: novel interface for high performance liquid chromatography-atomic fluorescence spectrometry hyphenated system and application in speciation of mercury

“…This perhaps can be ascribed to the degradation and reduction of mercury species by singlet oxygen and hydrogen radicals generated under UV irradiation. 25,26 The fluorescence intensities of mercury species sharply increased when formic acid was present in the reaction solution and the fluorescence intensities of mercury compounds were found to depend greatly on the concentration of formic acid, as is shown in Fig. 2.…”

“…UV irradiation can induce radical reactions in water to produce H, OH or singlet oxygen, which result in the decomposition of organo-mercurials 25 and reduction of Hg 2+ . 26 Therefore, four mercury species can still be detected even without formic acid in the post-column reaction solution.…”

Possible alkylation of inorganic Hg(II) by photochemical processes in the environment

“…Inorganic Hg 2+ was found to be the photo-degradation product of MeHg and EtHg. Due to the instability of EtHg (Suda et al, 1993), the photo-degradation of EtHg was relatively faster than that of MeHg (as shown in Fig. S4).…”

Um novo método para quantificar mercúrio orgânico (Hg orgânico) empregando a espectrometria de fluorescência atômica do vapor frio

“…Nestes, o emprego da Análise por Injeção em Fluxo (FIA) tem sido uma boa associação para quantificação destas espécies. Entretanto, o emprego do CVAAS resulta em limites de detecção na ordem de μg L -1 , o que é importante para a quantificação de Hg orgânico em solos e sedimentos, mas para amostras de água este limite está bastante distante das concentrações comumente encontradas (sub ng L -1 ) 8,[12][13][14][15][16] . Desta maneira, o desenvolvimento de um método empregando CVAFS tornaria possível a quantificação de Hg orgânico em águas naturais.…”