Photochemical Degradation of Short-Chain Chlorinated Paraffins in Aqueous Solution by Hydrated Electrons and Hydroxyl Radicals

10.26434/chemrxiv.13218809.v1 ◽

2020 ◽

Author(s):

Brian DiMento ◽

Cristina Tusei ◽

Christoph Aeppli

Keyword(s):

Organic Pollutants ◽

Hydroxyl Radicals ◽

Surface Waters ◽

Rate Constants ◽

Chlorine Content ◽

Short Chain ◽

Photochemical Degradation ◽

Chlorinated Paraffins ◽

Wide Range ◽

Hydrated Electrons

Short-chain chlorinated paraffins (SCCPs) are a complex mixture of polychlorinated alkanes (C10-C13, chlorine content 40-70%). While these compounds are categorized as persistent organic pollutants, there are knowledge gaps about their environmental degradation, particularly the effectiveness and mechanism of photochemical degradation in surface waters. Photochemically-produced hydrated electrons (e-(aq)) have been shown to degrade highly chlorinated compounds in environmentally-relevant conditions more effectively than hydroxyl radicals (·OH), which can degrade a wide range of organic pollutants. This study aimed to evaluate the potential for e-(aq) to degrade SCCPs, and compare this reaction to ·OH-mediated degradation. To this end, the degradation of SCCP model compounds was investigated under laboratory conditions that photochemically produced e-(aq) or ·OH. Resulting SCCP degradation rate constants for e-(aq) were on the same order of magnitude as well-known chlorinated pesticides. Experiments in the presence of ·OH yielded similar or higher second-order rate constants. By compiling literature data for a wide range of chlorinated compounds, it was found that higher chlorine content results in higher rate constants for e-(aq) and lower for ·OH. Above a composition of approximately 60 % Cl, the e-(aq) second-order rate constants were higher than rate constants for ·OH reactions. The results of this study imply that SCCPs are susceptible to photochemical degradation in the environment, facilitated by dissolved organic matter and other sources of reactive intermediates in sunlit surface waters.

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Photochemical Degradation of Short-Chain Chlorinated Paraffins in Aqueous Solution by Hydrated Electrons and Hydroxyl Radicals

10.26434/chemrxiv.13218809 ◽

2020 ◽

Author(s):

Brian DiMento ◽

Cristina Tusei ◽

Christoph Aeppli

Keyword(s):

Organic Pollutants ◽

Hydroxyl Radicals ◽

Surface Waters ◽

Rate Constants ◽

Chlorine Content ◽

Short Chain ◽

Photochemical Degradation ◽

Chlorinated Paraffins ◽

Wide Range ◽

Hydrated Electrons

Short-chain chlorinated paraffins (SCCPs) are a complex mixture of polychlorinated alkanes (C10-C13, chlorine content 40-70%). While these compounds are categorized as persistent organic pollutants, there are knowledge gaps about their environmental degradation, particularly the effectiveness and mechanism of photochemical degradation in surface waters. Photochemically-produced hydrated electrons (e-(aq)) have been shown to degrade highly chlorinated compounds in environmentally-relevant conditions more effectively than hydroxyl radicals (·OH), which can degrade a wide range of organic pollutants. This study aimed to evaluate the potential for e-(aq) to degrade SCCPs, and compare this reaction to ·OH-mediated degradation. To this end, the degradation of SCCP model compounds was investigated under laboratory conditions that photochemically produced e-(aq) or ·OH. Resulting SCCP degradation rate constants for e-(aq) were on the same order of magnitude as well-known chlorinated pesticides. Experiments in the presence of ·OH yielded similar or higher second-order rate constants. By compiling literature data for a wide range of chlorinated compounds, it was found that higher chlorine content results in higher rate constants for e-(aq) and lower for ·OH. Above a composition of approximately 60 % Cl, the e-(aq) second-order rate constants were higher than rate constants for ·OH reactions. The results of this study imply that SCCPs are susceptible to photochemical degradation in the environment, facilitated by dissolved organic matter and other sources of reactive intermediates in sunlit surface waters.

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Critical Review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (⋅OH/⋅O− in Aqueous Solution

Journal of Physical and Chemical Reference Data ◽

10.1063/1.555805 ◽

1988 ◽

Vol 17 (2) ◽

pp. 513-886 ◽

Cited By ~ 6496

Author(s):

George V. Buxton ◽

Clive L. Greenstock ◽

W. Phillips Helman ◽

Alberta B. Ross

Keyword(s):

Aqueous Solution ◽

Hydroxyl Radicals ◽

Rate Constants ◽

Critical Review ◽

Hydrogen Atoms ◽

Hydrated Electrons

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Mechanism of photodegradation of aqueous organic pollutants. 2. Measurement of the primary rate constants for reaction of hydroxyl radicals with benzene and some halobenzenes using an EPR spin-trapping method following the photolysis of hydrogen peroxide

Environmental Science & Technology ◽

10.1021/es00026a004 ◽

1992 ◽

Vol 26 (2) ◽

pp. 262-265 ◽

Cited By ~ 98

Author(s):

Jan Kochany ◽

James R. Bolton

Keyword(s):

Hydrogen Peroxide ◽

Organic Pollutants ◽

Hydroxyl Radicals ◽

Rate Constants ◽

Spin Trapping ◽

Trapping Method ◽

Epr Spin Trapping

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Photodegradation of EDTA and NTA in the UV / H2O2 Process

Zeitschrift für Naturforschung B ◽

10.1515/znb-1995-1211 ◽

1995 ◽

Vol 50 (12) ◽

pp. 1845-1853 ◽

Cited By ~ 24

Author(s):

Martin Sörensen ◽

Fritz H. Frimmel

Keyword(s):

Hydroxyl Radicals ◽

Degradation Rate ◽

Catalytic Effect ◽

Advanced Oxidation Process ◽

Strong Increase ◽

Radical Scavenger ◽

Photochemical Degradation ◽

Uv Degradation ◽

Degradation Rates ◽

Grade Steel

The influence of H2O2 on the UV degradation of the broadly used aminopolycarboxylates EDTA and NTA in aqueous solution was investigated. The photochemical degradation in the UV /H2O2 process was compared with classical oxidative treatment of potable water. The German drinking water regulation (Trinkwasserverordnung) was the orientation for all experiments. The Advanced Oxidation Process (AOP) turned out to be superior to the classical oxidation processes. The photochemical degradation of EDTA and NTA by UV irradiation could be significantly stimulated in the presence of H2O2. There was a strong increase in the degradation rate and a decrease in the quantum yield of the aminopolycarboxylates. Experiments with butyl chloride as radical scavenger proved the photolytically generated hydroxyl radicals to be responsible for the increase in the degradation rates.The effect of increasing the degradation rate at higher concentrations of H2O2 was limited, because the steady-state concentrations of the hydroxyl radicals as reactive species, did not increase at the same rate as the initial concentration of H2O2.Low amounts of iron dissolved from the high-grade steel photoreactor walls had a significant catalytic effect on the degradation.

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Influence of the vapor wall loss on the degradation rate constants in chamber experiments of levoglucosan and other biomass burning markers

Atmospheric Chemistry and Physics ◽

10.5194/acp-18-10915-2018 ◽

2018 ◽

Vol 18 (15) ◽

pp. 10915-10930 ◽

Cited By ~ 7

Author(s):

Amelie Bertrand ◽

Giulia Stefenelli ◽

Simone M. Pieber ◽

Emily A. Bruns ◽

Brice Temime-Roussel ◽

...

Keyword(s):

Hydroxyl Radicals ◽

Biomass Burning ◽

Rate Constants ◽

Degradation Rate ◽

Phase Reaction ◽

Particle Phase ◽

Phase Concentration ◽

Wall Loss ◽

Atmospheric Chamber

Abstract. Vapor wall loss has only recently been shown a potentially significant bias in atmospheric chamber studies. Yet, previous works aiming at the determination of the degradation rate of semi-volatile organic compounds (SVOCs) often did not account for this process. Here, we evaluate the influence of vapor wall loss on the determination of the gas-phase reaction rate kOH of several biomass burning markers (levoglucosan, mannosan, coniferyl aldehyde, 3-guaiacyl propanol, and acetosyringone) with hydroxyl radicals (OH). Emissions from the combustion of beech wood were injected into a 5.5 m3 Teflon atmospheric chamber, and aged for 4 h (equivalent to 5–8 h in the atmosphere). The particle-phase compound concentrations were monitored using a thermal desorption aerosol gas chromatograph coupled to a high-resolution time-of-flight aerosol mass spectrometer (TAG-AMS). The observed depletion of the concentration was later modeled using two different approaches: the previously published approach which does not take into consideration partitioning and vapor wall loss, and an approach with a more complex theoretical framework which integrates all the processes likely influencing the particle-phase concentration. We find that with the first approach one fails to predict the measured markers' concentration time evolution. With the second approach, we determine that partitioning and vapor wall loss play a predominant role in the particle-phase concentration depletion of all the compounds, while the reactivity with OH has a non-significative effect. Furthermore, we show that kOH cannot be determined precisely without a strong constraint of the whole set of physical parameters necessary to formally describe the various processes involved. It was found that the knowledge of the saturation mass concentration C* is especially crucial. Therefore, previously published rate constants of levoglucosan and more generally SVOCs with hydroxyl radicals inferred from atmospheric chamber experiments must be, at least, considered with caution.

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