Hydrogen peroxide (H2O2) is ubiquitously present in natural waters and has numerous direct impacts on aquatic biogeochemical processes. While the formation of H2O2 is theoretically likely to occur upon oxidation of the hydroquinone (H2Q) moieties in dissolved organic matter (DOM), the assessment of this abiotic H2O2 formation pathway in natural waters has not been conducted. This study is a systematic investigation of the H2O2 formation upon O2-oxidation of three electrochemically reduced DOM samples. In addition, the H2O2 formation was examined in three model H2Q compounds with different reduction potentials (Eh) upon air-exposure. The results show significant H2O2 formation upon O2-oxidation of both model H2Q and DOM samples, in which the H2O2 formations were highly pH-dependent. In H2Q solutions, H2O2 rapidly formed within few seconds and the yield was high for low-Eh H2Q (close to 100%) and low for high-Eh H2Q. In comparison, the productions of H2O2 in DOM samples were slower (~hours) and highly dependent on the DOM redox activities. Terrestrial DOM that contained higher H2Q content produced more H2O2 than aquatic DOM. The amount of electron transfer from DOM to O2 was counted by monitoring the electron accepting capacity change of DOM before and after O2-oxidation. Around 0.13 unit H2O2 was formed per unit electron transfer from DOM to O2 at circumneutral pH. We attribute the low H2O2 yield (26%) in DOM to the decay of H2O2 by reaction with reduced DOM.

Dark formation of hydrogen peroxide upon oxidation of dissolved organic matter

253rd National Meeting (2017)

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