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Zhou R, Zhang X. Effects of Tryptophan and Tyrosine on the Transformation of Monophenols in Chromophoric Dissolved Organic Matter Solutions: Enhance the Forward Transformation and Reduce the Reverse Transformation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:10108-10115. [PMID: 38813774 DOI: 10.1021/acs.est.4c02518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2024]
Abstract
Tryptophan (Trp) and tyrosine (Tyr) are the primary precursors of protein-like components in dissolved organic matter. Phenolic compounds are ubiquitous in aquatic environments and are considered the main electron donor in chromophoric dissolved organic matter (CDOM). Our results showed that Trp and Tyr (50 μM) enhanced the transformation of six monophenols (20 μM) with varying numbers of -CH3 and -OCH3 substituent groups by a factor of 1.0-1.8. The enhancement factor increased with the ratio of Trp (Tyr) to monophenols. In four different CDOM solutions (5 mg C/L, pH 8.0), a maximum enhancement factor of 3.2-6.7 was observed at a Trp/monophenol concentration ratio of 50. Conversely, monophenols greatly inhibited the transformation of Trp or Tyr. The enhancement factor decreased as the initial pH increased from 3.0 to 10.0. Additionally, the enhancement factor was not directly proportional to the oxidation potential of monophenol. We propose that the promotion effects are generated through the direct oxidation of monophenols by Trp (Tyr) radicals as well as through the reaction between Trp (Tyr) radicals and the one-electron reductant of CDOM.
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Affiliation(s)
- Ruiya Zhou
- Department of Environmental Science, School of Resources and Environmental Science, Wuhan University, Wuhan 430079, P. R. China
| | - Xu Zhang
- Department of Environmental Science, School of Resources and Environmental Science, Wuhan University, Wuhan 430079, P. R. China
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2
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Kong Q, Yao L, Ye L, Pan Y, Deng Y, Tan Z, Zhou Y, Shi G, Yang X. Photochemical Transformation of Monochloramine Induced by Triplet State Dissolved Organic Matter. JOURNAL OF HAZARDOUS MATERIALS 2024; 471:134366. [PMID: 38678708 DOI: 10.1016/j.jhazmat.2024.134366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 03/31/2024] [Accepted: 04/18/2024] [Indexed: 05/01/2024]
Abstract
The photoexcited dissolved organic matter (DOM) could produce reactive intermediates, affecting chemical oxidant transformation in UV based advanced oxidation processes (AOPs). This study confirmed the critical role of triplet state DOM (3DOM*), generated from DOM photoexcitation, in the transformation of monochloramine (NH2Cl), a commonly used chemical oxidant and disinfectant in water treatment. NH2Cl (42.25 μM, as Cl2) was decayed by 17.4-73.4 % within 60 min, primarily due to 3DOM* , in DOM (2-30 mgC L-1) solutions irradiated by 365 nm, where NH2Cl has no absorption. The second-order quenching rate constants of triplet state model photosensitizers by NH2Cl were determined to be 0.95(± 0.04)-4.49(± 0.04)× 108 M-1 s-1 by using laser flash photolysis. As a reductant, 3DOM* reacted with NH2Cl through one-transfer mechanism, leading to amino radical (NH2•) generation, which then transferred to ammonia (NH4+, pKa 9.25) through H-abstraction by the phenolic moieties in DOM. Additionally, the intermediate product of 3DOM* oxidized by NH2Cl or those triplet state quinones can hydrolyze to form phenolic moieties, elevating NH4+ yield to higher than 99% upon 365 nm irradiation. These findings suggest that the widespread DOM can be applied to convert NH2Cl via 3DOM* with minimal toxic risks.
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Affiliation(s)
- Qingqing Kong
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
| | - Liaoliao Yao
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
| | - Lei Ye
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
| | - Yanheng Pan
- School of Civil and Environmental Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Yanchun Deng
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
| | - Zijie Tan
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
| | - Yangjian Zhou
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
| | - Guojing Shi
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China; School of Civil and Environmental Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Xin Yang
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China.
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Li F, Bai X, Ji Y, Kang M. Understanding microplastic aging driven by photosensitization of algal extracellular polymeric substances. JOURNAL OF HAZARDOUS MATERIALS 2024; 469:133949. [PMID: 38452677 DOI: 10.1016/j.jhazmat.2024.133949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 02/17/2024] [Accepted: 03/01/2024] [Indexed: 03/09/2024]
Abstract
The aging of microplastics (MPs) is extremely influenced by photochemically-produced reactive intermediates (PPRIs), which are mediated by natural photosensitive substances. Algal extracellular polymeric substances (EPS) can produce PPRIs when exposed to sunlight. Nonetheless, the specific role of EPS in the aging process of MPs remains unclear. This work systematically explored the aging process of polystyrene (PS) MPs in the EPS secreted by Chlorella vulgaris under simulated sunlight irradiation. The results revealed that the existence of EPS accelerated the degradation of PS MPs into particles with sizes less than 1 µm, while also facilitating the formation of hydroxy groups on the surface. The release rate of dissolved organic matter (DOM) from PS MPs was elevated from 0.120 mg·L-1·day-1 to 0.577 mg·L-1·day-1. The primary factor contributing to the elevated levels of DOM was humic acid-like compounds generated through the breakdown of PS. EPS accelerated the aging process of PS MPs by primarily mediating the formation of triplet excited states (3EPS*), singlet oxygen (1O2), and superoxide radicals (O2∙-), resulting in indirect degradation. 3EPS* was found to have the most substantial impact. This study makes a significant contribution to advance understanding of the environmental fate of MPs in aquatic environments impacted by algal blooms.
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Affiliation(s)
- Fengjie Li
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210098, China
| | - Xue Bai
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210098, China; Yangtze Institute for Conservation and Development, Hohai University, Nanjing 210098, China.
| | - Yetong Ji
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210098, China
| | - Mengen Kang
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210098, China
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Jiang H, Zhao M, Hong W, Song W, Yan S. Mechanistic and Kinetic Consideration of the Photochemically Generated Oxidative Organic Radicals in Dissolved Black Carbon Solutions under Simulated Solar Irradiation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024; 58:760-770. [PMID: 38149879 DOI: 10.1021/acs.est.3c07216] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
The photochemically generated oxidative organic radicals (POORs) in dissolved black carbon (DBC) was investigated and compared with that in dissolved organic matter (DOM). POORs generated in DBC solutions exhibited higher one-electron reduction potential values (1.38-1.56 V) than those in DOM solutions (1.22-1.38 V). We found that the photogeneration of POORs from DBC is enhanced with dissolved oxygen (DO) increasing, while the inhibition of POORs is observed in reference to DOM solution. The behavior of the one-electron reducing species (DBC•-/DOM•-) was employed to explain this phenomenon. The experimental results revealed that the DO concentration had a greater effect on DBC•- than on DOM•-. Low DO levels led to a substantial increase in the steady-state concentration of DBC•-, which quenched the POORs via back-electron reactions. Moreover, the contribution of POORs to the degradation of 19 emerging organic contaminants (EOCs) in sunlight-exposed DBC and DOM solutions was estimated. The findings indicate that POORs play an important role in the photodegradation of EOCs previously known to react with triplets, especially in DBC solutions. Compared to DOM solutions, POOR exhibits a lower but considerable contribution to EOC attenuation. This study enhances the understanding of pollutant fate in aquatic environments by highlighting the role of DBC in photochemical pollutant degradation and providing insights into pollutant transformation mechanisms involving POORs.
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Affiliation(s)
- Hongyu Jiang
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
| | - Mengzhe Zhao
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
| | - Wenjie Hong
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
| | - Weihua Song
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
| | - Shuwen Yan
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
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5
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Pan Y, Garg S, Fu QL, Peng J, Yang X, Waite TD. Copper Safeguards Dissolved Organic Matter from Sunlight-Driven Photooxidation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:21178-21189. [PMID: 38064756 DOI: 10.1021/acs.est.3c07549] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/20/2023]
Abstract
Sunlight plays a crucial role in the transformation of dissolved organic matter (DOM) and the associated carbon cycle in aquatic environments. This study demonstrates that the presence of nanomolar concentrations of copper (Cu) significantly decreases the rate of photobleaching and the rate of loss of electron-donating moieties of three selected types of DOM (including both terrestrial and microbially derived DOM) under simulated sunlight irradiation. Employing Fourier transform ion cyclotron resonance mass spectrometry, we further confirm that Cu selectively inhibits the photooxidation of lignin- and tannin-like phenolic moieties present within the DOM, in agreement with the reported inhibitory impact of Cu on the photooxidation of phenolic compounds. On the basis of the inhibitory impact of Cu on the DOM photobleaching rate, we calculate the contribution of phenolic moieties to DOM photobleaching to be at least 29-55% in the wavelength range of 220-460 nm. The inhibition of loss of electrons from DOM during irradiation in the presence of Cu is also explained quantitatively by developing a mathematical model describing hydrogen peroxide (a proxy measure of loss of electrons from DOM) formation on DOM irradiation in the absence and presence of Cu. Overall, this study advances our understanding of DOM transformation in natural sunlit waters.
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Affiliation(s)
- Yanheng Pan
- School of Civil and Environmental Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Shikha Garg
- School of Civil and Environmental Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Qing-Long Fu
- School of Environmental Studies, China University of Geosciences, Wuhan 430078, China
| | - Jianglin Peng
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Xin Yang
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - T David Waite
- School of Civil and Environmental Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia
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6
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Le Roux DM, Powers LC, Blough NV. Direct Evidence of a Light-Dependent Sink of Superoxide within Chromophoric Dissolved Organic Matter. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:20627-20635. [PMID: 38044674 DOI: 10.1021/acs.est.3c08254] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/05/2023]
Abstract
Superoxide (O2• -) is produced photochemically in natural waters by chromophoric dissolved organic matter (CDOM) via the reaction of molecular oxygen with photoproduced one-electron reductants (OERs) within CDOM. In the absence of other sinks (metals or organic radicals), O2• - is believed to undergo primarily dismutation to produce hydrogen peroxide (H2O2). However, past studies have implicated the presence of an additional light-dependent sink of O2• - that does not lead to H2O2 production. Here, we provide direct evidence of this sink through O2• - injection experiments. During irradiations, spikes of O2• - are consumed to a greater extent (∼85-30% loss) and are lost much faster (up to ∼0.09 s-1) than spikes introduced post-irradiation (∼50-0% loss and ∼0.03 s-1 rate constant). The magnitude of the loss during irradiation and the rate constant are wavelength-dependent. Analysis of the H2O2 concentration post-spike indicates that this light-dependent sink does not produce H2O2 at low spike concentrations. This work further demonstrates that simply assuming that the O2• - production is twice the H2O2 production is not accurate, as previously believed.
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Affiliation(s)
- Danielle M Le Roux
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
| | - Leanne C Powers
- Department of Chemistry, State University of New York (SUNY) College of Environmental Science and Forestry, Syracuse, New York 13210, United States
| | - Neil V Blough
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
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7
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Zhou R, Liu J, Zhou C, Zhang X. Phototransformation of Lignin-related Compounds in Chromophoric Dissolved Organic Matter Solutions. WATER RESEARCH 2023; 245:120586. [PMID: 37717330 DOI: 10.1016/j.watres.2023.120586] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/2023] [Revised: 08/25/2023] [Accepted: 09/04/2023] [Indexed: 09/19/2023]
Abstract
Lignin is a major terrestrial source of chromophoric dissolved organic matter (CDOM), and studying the phototransformation of lignin monomers and their related compounds can enhance our understanding of CDOM intramolecular interactions. Coniferyl aldehyde (Coni) and sinapaldehyde (Sina) form ground-state complexes with CDOM, with equilibrium constants of 7,800 (± 1,800) and 20,000 (± 2,000) M-1, respectively. In comparison, vanillin (Van) exhibits minimal affinity for CDOM complexation. The bimolecular reaction rate constants between singlet oxygen (1O2) and these phenolic carbonyl compounds ranged from 0.46 (± 0.02) to 1.8 (± 0.1) × 107 M-1s-1, which is approximately one order of magnitude lower than their reaction rate constants (0.51 (± 0.02)-1.25 (± 0.02) × 108 M-1s-1) with the triplet excited state of CDOM (3CDOM*). In acidic CDOM solutions (pH 5.0), 1O2, H2O2, and organic peroxyl radicals had negligible impact on the transformation. Comparing the initial transformation rate in the presence and in the absence of NaN3 or furfuryl alcohol led to an overestimation of the contribution of 1O2 to the transformation of Van, Coni, or Sina. 3CDOM* scavengers could not fully inhibit the transformation of Coni or Sina. The remaining transformation is considered to arise from either the unquenched intra-CDOM phase 3CDOM* or a fraction of Coni⊂CDOM or Sina⊂CDOM complex, which underwent intramolecular photoinduced chemical reactions.
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Affiliation(s)
- Ruiya Zhou
- School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, P.R. China
| | - Juan Liu
- School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, P.R. China
| | - Chi Zhou
- Hubei Water Resources Research Institute, Wuhan, 430070, P.R. China.
| | - Xu Zhang
- School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, P.R. China.
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8
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Zeng G, Shi M, Dai M, Zhou Q, Luo H, Lin L, Zang K, Meng Z, Pan X. Hydroxyl radicals in natural waters: Light/dark mechanisms, changes and scavenging effects. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 868:161533. [PMID: 36640880 DOI: 10.1016/j.scitotenv.2023.161533] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/17/2022] [Revised: 01/06/2023] [Accepted: 01/07/2023] [Indexed: 06/17/2023]
Abstract
Hydroxyl radicals (•OH) are the most active, aggressive and oxidative reactive oxygen species. In the natural aquatic environment, •OH plays an important role in the biogeochemistry cycle, biotransformation, and pollution removal. This paper reviewed the distribution and formation mechanism of •OH in aquatic environments, including natural waters, colloidal substances, sediments, and organisms. Furthermore, factors affecting the formation and consumption of •OH were thoroughly discussed, and the mechanisms of •OH generation and scavenging were summarized. In particular, the effects of climate change and artificial work on •OH in the largest natural aquatic environment, i.e., marine environment was analyzed with the help of bibliometrics. Moreover, Fenton reactions make the •OH variation more complicated and should not be neglected, especially in those areas with suspended particles and sediments. Regarding the •OH variation in the natural aquatic environment, more attention should be given to global change and human activities.
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Affiliation(s)
- Ganning Zeng
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China; Key Laboratory of Ocean Space Resource Management Technology, MNR, Hangzhou 310012, China
| | - Ming Shi
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
| | - Mengzheng Dai
- College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, China
| | - Qian Zhou
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
| | - Hongwei Luo
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
| | - Liangyu Lin
- Key Laboratory of Ocean Space Resource Management Technology, MNR, Hangzhou 310012, China; Zhejiang Academy of Marine Science, Hangzhou 310012, China
| | - Kunpeng Zang
- Zhejiang Carbon Neutral Innovation Institute, Zhejiang University of Technology, Hangzhou 310014, China
| | - Zhu Meng
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China
| | - Xiangliang Pan
- College of Environment, Zhejiang University of Technology, Hangzhou 310014, China.
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9
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Cui S, Qi Y, Zhu Q, Wang C, Sun H. A review of the influence of soil minerals and organic matter on the migration and transformation of sulfonamides. THE SCIENCE OF THE TOTAL ENVIRONMENT 2023; 861:160584. [PMID: 36455724 DOI: 10.1016/j.scitotenv.2022.160584] [Citation(s) in RCA: 20] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Revised: 11/25/2022] [Accepted: 11/26/2022] [Indexed: 06/17/2023]
Abstract
Sulfonamides (SAs) are common antibiotics that are widely present in the environment and can easily migrate in the environment, so they pose an environmental risk. Minerals and organic matter influence the antibiotic migration and transformation in sewage treatment plants, activated sludge, surface water, and soil environment. In the present paper, the influence of the process and mechanism of minerals and organic matter on the adsorption, degradation, and plant uptake of SAs in soil were summarized. In the impact process of mineral and organic matter on the SAs migration and transformation, the pH value is undoubtedly the most important factor because it determines the ionic state of SAs. In terms of influence mechanisms, the minerals absorb SAs well via cation exchange, complexation, H-bonding, and cation bridging. Mineral photodegradation is also one of the primary removal methods for SAs. Soil organic matter (SOM) can significantly increase the SAs adsorption. The adsorption forces of SAs and SOM or dissolved organic matter (DOM) were very similar, but SOM decreased SAs mobility in the environment, while DOM increased SAs availability. DOM generated active substances and aided in the photodegradation of SAs. This review describes the effects of minerals and organic matter on the fate of SAs in soil, which is useful in controlling the migration and transformation of SAs in the soil environment.
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Affiliation(s)
- Shengyan Cui
- Key Laboratory of Pollution Processes and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China
| | - Yuwen Qi
- Key Laboratory of Pollution Processes and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China
| | - Qing Zhu
- Key Laboratory of Pollution Processes and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China
| | - Cuiping Wang
- Key Laboratory of Pollution Processes and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China.
| | - Hongwen Sun
- Key Laboratory of Pollution Processes and Environmental Criteria, Ministry of Education, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of Environmental Science and Engineering, Nankai University, Tianjin 300071, China
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10
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Bacilieri F, Vähätalo AV, Carena L, Wang M, Gao P, Minella M, Vione D. Wavelength trends of photoproduction of reactive transient species by chromophoric dissolved organic matter (CDOM), under steady-state polychromatic irradiation. CHEMOSPHERE 2022; 306:135502. [PMID: 35803378 DOI: 10.1016/j.chemosphere.2022.135502] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2022] [Revised: 06/23/2022] [Accepted: 06/24/2022] [Indexed: 06/15/2023]
Abstract
The formation quantum yields of photochemically produced reactive intermediates (PPRIs) by irradiated CDOM (in this study, Suwannee River Natural Organic Matter and Upper Mississippi River Natural Organic Matter) decrease with increasing irradiation wavelength. In particular, the formation quantum yields of the excited triplet states of CDOM (3CDOM*) and of singlet oxygen (1O2) have an exponentially decreasing trend with wavelength. The •OH wavelength trend is different, because more effective •OH production occurs under UVB irradiation than foreseen by a purely exponential function. We show that the parameter-adjustable Weibull function (which adapts to both exponential and some non-exponential trends) is suitable to fit the mentioned quantum yield data, and it is very useful when CDOM irradiation is carried out under polychromatic lamps as done here. Model calculations suggest that, thanks to the ability of CDOM to also absorb visible radiation, and despite its decreasing quantum yield of •OH generation with increasing wavelength, CDOM would be able to trigger •OH photogeneration in deep waters, to a higher extent than UVB-absorbing nitrate or UVB + UVA-absorbing nitrite.
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Affiliation(s)
- Federico Bacilieri
- Department of Chemistry, University of Turin, Via Pietro Giuria 5, 10125, Torino, Italy
| | - Anssi V Vähätalo
- Department of Biological and Environmental Science, University of Jyväskylä, P.O.Box 35, FI-40014, Jyväskylä, Finland
| | - Luca Carena
- Department of Chemistry, University of Turin, Via Pietro Giuria 5, 10125, Torino, Italy
| | - Mingjie Wang
- Department of Chemistry, University of Turin, Via Pietro Giuria 5, 10125, Torino, Italy
| | - Pin Gao
- College of Environmental Science and Engineering, Donghua University, Shanghai, 201620, China
| | - Marco Minella
- Department of Chemistry, University of Turin, Via Pietro Giuria 5, 10125, Torino, Italy
| | - Davide Vione
- Department of Chemistry, University of Turin, Via Pietro Giuria 5, 10125, Torino, Italy.
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11
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Kong Q, Pan Y, Lei X, Zhou Y, Lei Y, Peng J, Zhang X, Yin R, Shang C, Yang X. Reducing properties of triplet state organic matter ( 3DOM*) probed via the transformation from chlorine dioxide to chlorite. WATER RESEARCH 2022; 225:119120. [PMID: 36126426 DOI: 10.1016/j.watres.2022.119120] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2022] [Revised: 08/08/2022] [Accepted: 09/13/2022] [Indexed: 06/15/2023]
Abstract
The triplet states of dissolved organic matter (3DOM*) have been well known to oxidize various organic contaminants, but evidence of their reducing properties are largely scarce. In this work, chlorine dioxide (ClO2) as a single-electron oxidant was used as a probe to evaluate the reduction property of 3DOM*. The reduction of ClO2 to chlorite was observed in the solutions of model photosensitizers (i.e., 4-carboxybenzophenone, benzophenone, acetophenone, 3-methoxyacetophenone, naphthalene, and xanthone) during UV irradiation with the presence of ClO2, though they are resistant to ClO2 oxidation in the dark. The reducing property of the triplet states of photosensitizers was verified and their second-order reaction rate constants with ClO2 were determined to be in the range of 1.45(± 0.03)× 109 - 2.18(± 0.06) × 109 M-1 s-1 at pH 7.0. The quenching tests excluded the role of other reactive species (e.g., HO•, O(3P), Cl•, ClO• and HOCl/OCl-, O2•- and eaq-) in ClO2 reduction to chlorite when using model photosensitizers and DOM isolates. Chlorite formation was 48.1-90.4% and 4812.8-7721.8% higher during UV irradiation with the presence of ClO2 and DOM than those without UV irradiation or without DOM present, respectively. The enhancement was attributed to the enhanced electron donating capacity (chlorite precursors) of DOM upon UV irradiation and also to 3DOM* acting as an electron donor reducing ClO2 to chlorite. This study highlighted the important role of 3DOM* as a reductant.
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Affiliation(s)
- Qingqing Kong
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Yanheng Pan
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Xin Lei
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Yangjian Zhou
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Yu Lei
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Jianglin Peng
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Xinran Zhang
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
| | - Ran Yin
- Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR 999066, China
| | - Chii Shang
- Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong SAR 999066, China
| | - Xin Yang
- School of Environmental Science and Engineering, Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China.
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12
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Sha H, Yan S, Deng Y, Song W. Photosensitized Transformation of Hydrogen Peroxide in Dissolved Organic Matter Solutions under Simulated Solar Irradiation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:14080-14090. [PMID: 36121751 DOI: 10.1021/acs.est.2c04819] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Hydrogen peroxide plays an important role in photochemical processes in aquatic environments. However, whether it can be transformed by photoexcited chromophoric dissolved organic matter (CDOM) remains unclear. Therefore, this study examined the photosensitized degradation of H2O2 in CDOM-enriched solutions under simulated solar irradiation. Our results suggest that the presence of CDOM enhances the photodegradation rate of H2O2 via the photosensitization process and ·OH is generated stoichiometrically with H2O2 attenuation. Experimental results with model photosensitizers indicate that one-electron reducing species of CDOM (CDOM·-), not triplet CDOM, is the primary reactive species that reduces H2O2 to yield ·OH. By monitoring the variation of CDOM·-, the reaction rate constant of CDOM·- with H2O2 was estimated to be 1.5-fold greater than that with O2. Furthermore, a wastewater effluent was exposed to simulated solar irradiation with the addition of H2O2, and the results demonstrated that the photodegradation of trace organic contaminants (TrOCs) was significantly enhanced by the increased ·OH level. Overall, the current study provided new insights into the photochemical formation of ·OH via the one-electron reduction of H2O2 by CDOM·-. The solar irradiation of wastewater with H2O2 enhancement could be a useful and economically beneficial advanced oxidation process for TrOC abatement.
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Affiliation(s)
- Haitao Sha
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
| | - Shuwen Yan
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
| | - Yang Deng
- Department of Earth and Environmental Studies, Montclair State University, Montclair, New Jersey 07043, United States
| | - Weihua Song
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
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13
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Gao Z, Liu J, Skurie C, Zhu Y, Jun YS. Photochemical reactions of dissolved organic matter and bromide ions facilitate abiotic formation of manganese oxide solids. WATER RESEARCH 2022; 222:118831. [PMID: 35872522 DOI: 10.1016/j.watres.2022.118831] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2022] [Revised: 07/04/2022] [Accepted: 07/05/2022] [Indexed: 06/15/2023]
Abstract
Manganese (Mn) oxide solids are ubiquitous in nature, acting as both electron donors and acceptors in diverse redox reactions in the environment. Reactions of Mn(III/IV) oxides with dissolved natural organic matter (DOM) are commonly described as reductive dissolutions that generate Mn2+(aq). In this study, we investigated the role of photochemical reactions of DOM in Mn2+(aq) oxidation and the resulting formation of Mn oxide solids. During the photolysis of DOM, reactive intermediates can be generated, including excited triplet state DOM (3DOM*), hydroxyl radicals (•OH), superoxide radicals (O2•-), hydrogen peroxide, and singlet oxygen. Among these, we found that O2•- radicals were mainly responsible for Mn oxidation. The solution pH controlled the formation of Mn oxide solids by affecting both Mn2+ oxidation by O2•- during photolysis of DOM and reductive dissolutions of Mn oxide solids by DOM. Further, with the addition of bromide ions (Br-), reactions between 3DOM* and Br-, together with reactions between •OH and Br-, can form reactive bromide radicals. The formed Br radicals also promoted Mn oxide formation. In DOM with more aromatic functional groups, more Mn2+ was oxidized to Mn oxide solids. This enhanced oxidation could be the result of promoted pathways from charge-transfer state DOM (DOM•+/•-) to O2•-. These new observations advance our understanding of natural Mn2+ oxidation and Mn(III/IV) oxide formation and highlight the underappreciated oxidative roles of DOM in the oxidation of metal ions in surface water illuminated by sunlight.
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Affiliation(s)
- Zhenwei Gao
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, One Brookings Drive, Campus Box 1180, St. Louis, MO 63130, United States
| | - Jing Liu
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, One Brookings Drive, Campus Box 1180, St. Louis, MO 63130, United States
| | - Charlie Skurie
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, One Brookings Drive, Campus Box 1180, St. Louis, MO 63130, United States
| | - Yaguang Zhu
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, One Brookings Drive, Campus Box 1180, St. Louis, MO 63130, United States
| | - Young-Shin Jun
- Department of Energy, Environmental and Chemical Engineering, Washington University in St. Louis, One Brookings Drive, Campus Box 1180, St. Louis, MO 63130, United States.
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14
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Zhou H, Xiao D. Role of NOM in the Photolysis of Chlorine and the Formation of Reactive Species in the Solar/Chlorine System. ACS OMEGA 2022; 7:7769-7776. [PMID: 35284752 PMCID: PMC8908494 DOI: 10.1021/acsomega.1c06616] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/23/2021] [Accepted: 02/14/2022] [Indexed: 06/14/2023]
Abstract
The solar/chlorine system has been proposed as a novel advanced oxidation process (AOP) for efficient pollutant degradation and water disinfection by producing a series of reactive species including hydroxyl radicals (HO•), chlorine radicals (Cl•), and so forth. In this study, the role of natural organic matter (NOM) in the photolysis of free available chlorine (FAC) and the formation of HO• and Cl• in the solar/chlorine system was investigated employing nitrobenzene and benzoic acid as selective chemical probes. The decay rate of FAC was significantly accelerated in the presence of NOM at pH 5.5 under simulated solar irradiation, likely due to the photoreaction between FAC and the photoexcited NOM. The decay rate of FAC increased upon increasing the electron-donating capacity of NOM, which indicated that phenolic components play a significant role in the photodegradation of FAC. This acceleration mechanism was further verified using 4-nitrophenol as a model phenolic compound. NOM promoted Cl• formation and quenched HO• in the solar/chlorine system. The proposed reaction mechanism included the reaction of excited singlet phenolic compounds in NOM with FAC, which yielded Cl•. This study provides a useful insight into future applications for using the solar/chlorine system as a novel AOP for wastewater treatment or disinfection.
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15
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Nie J, Zou J, Yan S, Song W. Photosensitized Transformation of Peroxymonosulfate in Dissolved Organic Matter Solutions under Simulated Solar Irradiation. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:1963-1972. [PMID: 35050612 DOI: 10.1021/acs.est.1c07411] [Citation(s) in RCA: 20] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Sulfate radical (SO4•-)-mediated advanced oxidation processes via peroxymonosulfate (PMS) activation have been extensively investigated. However, the phototransformation of PMS in sunlit dissolved organic matter (DOM) solution has not been previously examined. For the first time, the photosensitized transformation of PMS in DOM-enriched solutions under simulated solar irradiation was observed. The generation of reactive species, including 1O2, SO4•-, and •OH, was confirmed by electron paramagnetic resonance and quantified by chemical probes. SO4•- was the primary reactive species generated via the reaction of excited triplet DOM (3DOM*) with PMS. 3DOM* acted as a reactive reductant and was quickly oxidized by PMS, with an estimated reaction rate constant of (4.09 ± 0.21) × 108 M-1 s-1. Compared to 3DOM*, one-electron-reducing DOM (DOM•-) was a minor contributor to the photosensitized transformation of PMS, and the contribution of DOM•- relied on the phenolic constituents. In addition, a series of different types of DOM, including terrestrial DOM, autochthonous DOM, and effluent organic matter and its fractions, were employed to examine the photosensitized transformation kinetics of PMS. Overall, the photosensitized transformation of PMS by irradiated DOM could be a useful and economical approach to generate SO4•- under environmentally relevant conditions.
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Affiliation(s)
- Jianxin Nie
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
| | - Jianmin Zou
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
| | - Shuwen Yan
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
| | - Weihua Song
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200438, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
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16
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Le Roux DM, Powers LC, Blough NV. Photoproduction Rates of One-Electron Reductants by Chromophoric Dissolved Organic Matter via Fluorescence Spectroscopy: Comparison with Superoxide and Hydrogen Peroxide Rates. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:12095-12105. [PMID: 34383497 DOI: 10.1021/acs.est.1c04043] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
One-electron reductants (OER) photoproduced by chromophoric dissolved organic matter (CDOM) have been shown to be likely precursors for the formation of superoxide and subsequently hydrogen peroxide. An improved method that employs a nitroxide radical probe (3AP) has been developed and utilized to determine the photoproduction rates of OER from a diverse set of CDOM samples. 3AP reacts with OER to produce the hydroxylamine, which is then derivatized with fluorescamine and quantified spectrofluorometrically. Although less sensitive than traditional methods for measuring RO2•-, measuring RH provides a simpler and faster method of estimating RO2•- and is amenable to continuous measurement via flow injection analysis. Production rates of OER (RH), superoxide (RO2•-), and hydrogen peroxide (RH2O2) have a similar wavelength dependence, indicating a common origin. If all the OER react with molecular oxygen to produce superoxide, then the simplest mechanism predicts that RH/RH2O2 and RO2•-/RH2O2 should be equal to 2. However, our measurements reveal RH/RH2O2 values as high as 16 (5.7-16), consistent with prior results, and RO2•-/RH2O2 values as high as 8 (5.4-8.2). These results indicate that a substantial fraction of superoxide (65-88%) is not undergoing dismutation. A reasonable oxidative sink for superoxide is reaction with photoproduced phenoxy radicals within CDOM.
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Affiliation(s)
- Danielle M Le Roux
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
| | - Leanne C Powers
- University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, Solomons, Maryland 20688, United States
| | - Neil V Blough
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
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17
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Li H, McKay G. Relationships between the Physicochemical Properties of Dissolved Organic Matter and Its Reaction with Sodium Borohydride. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:10843-10851. [PMID: 34291922 DOI: 10.1021/acs.est.1c01973] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The reaction of dissolved organic matter (DOM) with sodium borohydride has been used to understand the geographic origin of DOM and investigate the photophysical model underlying DOM's optical properties. However, the physicochemical properties of DOM (e.g., molecular size and charge) that influence the kinetics and ultimate reducibility of DOM by borohydride remain poorly characterized. Herein, we studied the kinetics of DOM-borohydride reactions by recording absorbance and fluorescence spectra at a high temporal frequency (every ∼10 min for 24 h) for a diverse set of DOM isolates of aquatic and soil origin. The reducibility of DOM by sodium borohydride (as judged by relative removal of initial absorbance) varied appreciably among the DOM samples studied, with soil humic substances being less reducible than aquatic humic substances and natural organic matter. While statistically significant correlations were found between the reducibility of DOM and descriptors of molecular size, these descriptors were not able to differentiate the reducibility of soil versus aquatic DOM isolates that had similar bulk properties. Thus, it appears that the extent of absorbance removal by borohydride is largely driven by the origin of the humic substance isolate (aquatic vs soil) instead of molecular size or charge. Borohydride reduction resulted in increased fluorescence emission across UV and visible excitation wavelengths. However, the enhanced emission at visible excitation decreased over a time period of hours to days, suggesting that reduction of an important subset of DOM chromophores is reversible. This reversibility in fluorescence emission is consistent with the small role of quinones in the absorbance of DOM but suggests a more important role for quinone-containing charge-transfer contacts in the fluorescence of DOM, particularly at visible excitation wavelengths.
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Affiliation(s)
- Hang Li
- Zachry Department of Civil & Environmental Engineering, Texas A&M University, College Station, Texas 77845, United States
| | - Garrett McKay
- Zachry Department of Civil & Environmental Engineering, Texas A&M University, College Station, Texas 77845, United States
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18
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Wang Z, Lv J, Zhang S, Christie P, Zhang S. Interfacial Molecular Fractionation on Ferrihydrite Reduces the Photochemical Reactivity of Dissolved Organic Matter. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:1769-1778. [PMID: 33494598 DOI: 10.1021/acs.est.0c07132] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The selective sorption of dissolved organic matter (DOM) on minerals is a widespread geochemical process in the natural environment. Recent studies have explored the influence of this process on the molecular fractionation of DOM at water-mineral interfaces. However, it remains unclear how molecular fractionation affects the photochemistry of DOM. Here, we demonstrate that the adsorptive fractionation of DOM on ferrihydrite greatly reduces its photoproduction of reactive oxygen species (ROS) including 1O2, O2•-, and •OH normalized to organic carbon (ROSOC). The ROSOC for 1O2, O2•-, and •OH were positively correlated with the abundances of polyphenols and oxygenated polycyclic aromatics, which were also observed using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis to be preferentially sequestered by ferrihydrite. The molecules that preferentially remained in the solution after adsorption displayed low levels of ROSOC. The molecular fractionation of DOM induced by adsorption on ferrihydrite therefore influenced the molecular components and also significantly reduced the photoreactive fractions of DOM in waters. These results are very important in promoting our understanding of the effects of molecular fractionation on the biogeochemical features, behaviors, and implications of DOM in the environment.
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Affiliation(s)
- Zhe Wang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of the Chinese the Academy of Sciences, Beijing 100049, China
| | - Jitao Lv
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Suhuan Zhang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of the Chinese the Academy of Sciences, Beijing 100049, China
| | - Peter Christie
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Shuzhen Zhang
- State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
- University of the Chinese the Academy of Sciences, Beijing 100049, China
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19
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Xi N, Li Y, Chen J, Yang Y, Duan J, Xia X. Elevated Temperatures Decrease the Photodegradation Rate of Pyrethroid Insecticides on Spinach Leaves: Implications for the Effect of Climate Warming. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:1167-1177. [PMID: 33356194 DOI: 10.1021/acs.est.0c06959] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Climate warming is seldom considered in the transformation of pesticides on a plant leaf. This study investigated the effects of photodegradation temperature and spinach growth temperature from 15 to 21 °C on the photodegradation of bifenthrin, cypermethrin, fenvalerate, and deltamethrin on spinach leaves under xenon lamp irradiation in climate incubators. The photodegradation temperature had minor effects on pyrethroid photodegradation. Interestingly, the photodegradation rates decreased with increasing spinach growth temperature. For example, the photodegradation rate constant of bifenthrin on a spinach cultivated at 15 °C (3.73 (±0.59, 95% confidence level) × 10-2 h-1) was 1.9 times higher than that at 21 °C (1.96 (±0.17) × 10-2 h-1). Hydroxyl radicals (·OH) played a dominant role in the photodegradation. We speculate that ·OH originated from the degradation of hydroperoxide that was formed by oxidation of phenolic CH═CH, aliphatic CH3 and aromatic C-O-C, and subsequent hydrogen abstraction. The contents of these functional groups decreased with increasing growth temperature, which resulted in lower photodegradation rates at higher growth temperatures. A possible photodegradation pathway including ester bond cleavage, decyanation, and phenyl group removal was proposed. This work provides new insight into the effects of climate warming on the generation of reactive oxygen species and the transformation of pesticides on a plant leaf.
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Affiliation(s)
- Nannan Xi
- State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Yang Li
- State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Jian Chen
- State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Yixiao Yang
- The International Department, The Experimental High School Attached to Beijing Normal University, Beijing 100875, People's Republic of China
| | - Jiajun Duan
- State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, People's Republic of China
| | - Xinghui Xia
- State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, People's Republic of China
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20
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Sun J, Ma J, Lian L, Yan S, Song W. Photochemical Formation of Methylhydroperoxide in Dissolved Organic Matter Solutions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:1076-1087. [PMID: 33373203 DOI: 10.1021/acs.est.0c07717] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Although it is known that the solar irradiation of chromophoric dissolved organic matter (CDOM) solutions generates H2O2, whether or not organic hydroperoxides (ROOHs) are photochemically formed remains unclear. This study employs high-performance liquid chromatography with the postcolumn enzymatic derivatization method to examine whether ROOHs can be formed in CDOM solutions under simulated solar irradiation. Methylhydroperoxide (MHP) is the only identified ROOH under our experimental conditions, and the quantum yields of MHP (ΦMHP) vary from (1.09 ± 0.09) × 10-6 to (4.95 ± 0.11) × 10-6 in the tested CDOM solutions, including four reference natural organic matters and two effluent organic matters. The quantum yields of H2O2 (ΦH2O2) are simultaneously measured, and the ratios of ΦH2O2 to ΦMHP range from 147 to 676. The formation of MHP is highly related to the presence of superoxide radical ions (O2•-) and methyl radicals (CH3•); therefore, a photoformation mechanism of MHP has been proposed. The photochemically generated CH3• reacts with O2 to yield CH3OO•. Subsequently, CH3OO• is reduced to MHP by O2•-. Our results also suggest that the yield of CH3• to MHP under air-saturated conditions is 52% and increases to 98% under oxygen-saturated conditions. The decays of MHP and H2O2 are very similar in terms of photodegradation, hydrolysis, Fenton, and photo-Fenton reactions. This study can be useful to understand the photochemical formation of organic peroxides in surface waters.
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Affiliation(s)
- Jiaqian Sun
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Jianzhong Ma
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Lushi Lian
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Shuwen Yan
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
| | - Weihua Song
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
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21
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Tang X, Cui Z, Bai Y, Su R. Indirect photodegradation of sulfathiazole and sulfamerazine: Influence of the CDOM components and seawater factors (salinity, pH, nitrate and bicarbonate). THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 750:141762. [PMID: 32877789 DOI: 10.1016/j.scitotenv.2020.141762] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 08/02/2020] [Accepted: 08/15/2020] [Indexed: 06/11/2023]
Abstract
Sulfonamides (SAs) are ubiquitous antibiotics that are increasingly detected in the aquatic environment, and may cause potential harm to the environment and humans. Indirect photodegradation has been considered to be a promising natural degradation process for antibiotics in the environment. Chromophoric dissolved organic matter (CDOM) is an important participant in the indirect photodegradation of antibiotics. Indirect photodegradation of sulfathiazole (ST) and sulfamerazine (SM) were studied in the presence of CDOM and marine factors (salinity, pH, nitrate (NO3-) and bicarbonate (HCO3-)) to simulate photodegradation of these compounds in the coastal seawater environment. The main findings are as follows. First, the indirect photodegradation rates of ST and SM in the presence of CDOM were significantly increased and followed the pseudofirst order kinetics. Second, 1O2 played a critical role in the indirect photodegradation of ST and its contribution rate was 54.2%; 3CDOM⁎ performed similarly in the case of SM with a 58.0% contribution rate. Third, CDOM was divided into four fluorescent components by excitation-emission matrix spectroscopy and parallel factor analysis (EEMs-PARAFAC), including three exogenous components and an autochthonous component. The exogenous components with high molecular weight and higher number of aromatic groups played a decisive role in the indirect photodegradation of ST and SM due to their ability to generate higher levels of reactive intermediates (RIs). Finally, seawater factors (salinity, pH, NO3- and HCO3-) influenced the indirect photodegradation of ST and SM by influencing the steady-state concentrations of RIs. This report is the first study of indirect photodegradation of ST and SM from the perspective of the CDOM components and simulated coastal waters.
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Affiliation(s)
- Xinyu Tang
- Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China
| | - Zhengguo Cui
- Key Laboratory of Sustainable Development of Marine Fisheries, Ministry of Agriculture and Rural Affairs, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China; Laboratory for Marine Fisheries Science and Food Production Processes, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266071, China
| | - Ying Bai
- Key Laboratory of Sustainable Development of Marine Fisheries, Ministry of Agriculture and Rural Affairs, Yellow Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences, Qingdao 266071, China; Laboratory for Marine Fisheries Science and Food Production Processes, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266071, China.
| | - Rongguo Su
- Laboratory of Marine Chemistry Theory and Technology, Ministry of Education, Ocean University of China, Qingdao 266100, China.
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22
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Wang Y, Ma J. Quantitative determination of redox-active carbonyls of natural dissolved organic matter. WATER RESEARCH 2020; 185:116142. [PMID: 32823193 DOI: 10.1016/j.watres.2020.116142] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 07/01/2020] [Accepted: 07/02/2020] [Indexed: 06/11/2023]
Abstract
Natural dissolved organic matter (DOM) is ubiquitous in environment and plays an important role in numerous environmental processes. Although the molecular basis of the reactivity of DOM remains poorly understood due to its extreme complexity, redox-active carbonyls (aromatic ketones/aldehydes and quinones) within DOM are believed vitally important. Except the rough determination of total carbonyls (including non-redox active -COOR) based on inflexible 13C chemical shift range by expensive and time-consuming solid-state nuclear magnetic resonance (NMR), there is no ready method to quantify redox-active carbonyls in DOM. Here we show that after treatment with sodium borohydride (NaBH4) by selectively eliminating redox-active carbonyls, quenched fluorescence of carbon quantum dots (CD) by DOM recovered dramatically, and displayed a good linear relationship between redox-active carbonyls detected and DOM concentration (R2 ≥ 0.977), thus allowing first quantitative determination of the redox-active carbonyls of DOM. Eight DOM isolates present 0.59%-0.90% redox-active carbonyls by the current method. And this method is robust from coexisting proteins and salts. This method could provide better or equal instructive results compared with solid-state NMR for total carbonyls or electrochemical method for electron-accepting capacities (EAC). Our results provide the underlying structural basis of many important geochemical processes that mediated by DOM. We posit that this method could apply to other complex molecular systems such as the atmospheric aerosols and extracellular polymeric substances (EPS), too.
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Affiliation(s)
- Ya Wang
- School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jiahai Ma
- School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing, 100049, China.
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23
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Chen Y, Liu J, Zhang X, Blough NV. Time-Resolved Fluorescence Spectra of Untreated and Sodium Borohydride-Reduced Chromophoric Dissolved Organic Matter. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:12109-12118. [PMID: 32845124 DOI: 10.1021/acs.est.0c03135] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Time-resolved fluorescence spectra of chromophoric dissolved organic matter (CDOM) from different sources were acquired using UV (280 and 375 nm) and visible light (440 and 640 nm) excitation to probe the structural basis of the emission properties of CDOM. Emission decays were faster at the blue and red edges, particularly at the red edge, relative to those acquired from 480 to 550 nm. Based on the lifetime distribution and multiexponential analysis of the emission decays recorded at different time resolution, current findings demonstrate that the components recovered based on a superposition model have no defined physical meaning. A substantial increase in steady-state fluorescence intensity and only small changes (<30%) of amplitude-weighted average lifetime caused by sodium borohydride reduction suggest that intramolecular fluorescence quenching occurs mainly through formation of ground state charge-transfer interactions. Short-lived species (lifetime < 100 ps) dominate the emission decays over wavelengths from 400 to 800 nm, particularly under excitation at long wavelengths (440 and 640 nm). Compared to locally excited (LE) states, the contribution of charge-transfer excited (ECT) states and other short-lived species to the steady-state emission is small because of their very rapid nonradiative relaxation. This study suggests that a careful choice of observation wavelength is needed to distinguish LE states from ECT states.
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Affiliation(s)
- Yuan Chen
- Department of Environmental Science, School of Resources and Environmental Science, Wuhan University, Wuhan 430079, P. R. China
| | - Juan Liu
- Department of Environmental Science, School of Resources and Environmental Science, Wuhan University, Wuhan 430079, P. R. China
| | - Xu Zhang
- Department of Environmental Science, School of Resources and Environmental Science, Wuhan University, Wuhan 430079, P. R. China
| | - Neil V Blough
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, United States
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Xiao Y, Carena L, Näsi MT, Vähätalo AV. Superoxide-driven autocatalytic dark production of hydroxyl radicals in the presence of complexes of natural dissolved organic matter and iron. WATER RESEARCH 2020; 177:115782. [PMID: 32294593 DOI: 10.1016/j.watres.2020.115782] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2019] [Revised: 03/31/2020] [Accepted: 04/01/2020] [Indexed: 06/11/2023]
Abstract
We introduced superoxide as potassium superoxide (KO2) to artificial lake water containing dissolved organic matter (DOM) without or with introduced ferric iron complexes (DOM-Fe(III)), and monitored the production rate of hydroxyl radicals as well as changes in the absorption and fluorescence properties of DOM. The introduction of KO2 decreased the absorption by DOM but increased the spectral slope coefficient of DOM more with complexed ferric Fe than without it. The introduction of KO2 increased the fluorescence of humic-like components in DOM without introduced ferric Fe but resulted in the loss of fluorescence in DOM with introduced ferric Fe. A single introduction of 13 μmol L-1 KO2 produced 10 μmol L-1 and 104 μmol L-1 hydroxyl radicals during a week-long experiment without and with the introduced DOM-Fe(III) complexes, respectively. The production rate of hydroxyl radicals decreased exponentially with time but levelled off and continued several days in DOM with introduced ferric Fe. These findings suggest that in the presence of DOM-Fe complexes, superoxide can trigger an autocatalytic Fenton reaction that produces hydroxyl radicals and breaks down DOM.
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Affiliation(s)
- Yihua Xiao
- Department of Biological and Environmental Science, University of Jyväskylä, 40014, Jyväskylä, Finland; School of Environmental & Municipal Engineering, Qingdao University of Technology, 266033, Qingdao, China.
| | - Luca Carena
- Dipartimento di Chimica, Università di Torino, Via Pietro Giuria 5, 10125, Torino, Italy
| | - Marja-Terttu Näsi
- Department of Biological and Environmental Science, University of Jyväskylä, 40014, Jyväskylä, Finland
| | - Anssi V Vähätalo
- Department of Biological and Environmental Science, University of Jyväskylä, 40014, Jyväskylä, Finland
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25
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Wang H, Zhou H, Ma J, Nie J, Yan S, Song W. Triplet Photochemistry of Dissolved Black Carbon and Its Effects on the Photochemical Formation of Reactive Oxygen Species. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:4903-4911. [PMID: 32227921 DOI: 10.1021/acs.est.0c00061] [Citation(s) in RCA: 58] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Dissolved black carbon (DBC) is an important component of dissolved organic matter pool; however, its photochemical properties are not fully understood. In this study, we determined the excited triplet-state quantum yields of DBC (3DBC*) and 1O2 quantum yields (Φ1O2) of six diverse DBCs using sorbic alcohol, 2,4,6-trimethylphenol (TMP), and furfuryl alcohol and compared the results with quantum yields of reference natural organic matters (NOMs). The average Φ1O2 of six DBCs (4.2 ± 1.5%) was greater than that of terrestrial NOM (2.4 ± 0.3%) and comparable to autochthonous NOM (5.3 ± 0.2%). Using TMP as a probe for oxidizing triplets, DBC presented significantly higher apparent quantum yield coefficients for degrading TMP (fTMP) than the reference NOM, reflecting that the fTMP values of low-energy 3DBC* were approximately 12-fold greater than those of low-energy 3NOM*. The differences in the fTMP and Φ1O2 trends among the DBCs indicated that the 3DBC* responsible for these reactions may be from different sources. In addition, DBC was much more effective than NOM, on a carbon-normalized basis, during photodegradation of pharmaceutically active compounds. This result confirms that the presence of DBC can accelerate the photodegradation of contaminants that are susceptible to one-electron oxidation by triplets.
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Affiliation(s)
- Hui Wang
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Huaxi Zhou
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Jianzhong Ma
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Jianxin Nie
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Shuwen Yan
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
| | - Weihua Song
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
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26
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Zhou Q, Zhang X, Zhou C. Transformation of amino acid tyrosine in chromophoric organic matter solutions: Generation of peroxide and change of bioavailability. CHEMOSPHERE 2020; 245:125662. [PMID: 31864059 DOI: 10.1016/j.chemosphere.2019.125662] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/07/2019] [Revised: 11/07/2019] [Accepted: 12/12/2019] [Indexed: 06/10/2023]
Abstract
Studying the photochemical transformation mechanism of dissolved free amino acids (DFAA) in chromophoric dissolved organic matter (CDOM) solution facilitates the understanding of DFAA's environmental fate and bioavailability change upon solar irradiation in natural surface waters. Tyrosine oxidation product (Tyr-OH) was synthesized to quantify the primary transformation product (tyrosine peroxide, Tyr-OOH) in CDOM solution. Both reactions between superoxide radical anion (O2-) and tyrosine radical (Tyr) and between singlet oxygen (1O2) and tyrosine (Tyr) yield Tyr-OOH, which is subsequently transformed into Tyr-OH. The reaction between O2- and Tyr not only generated Tyr-OOH but also caused the regeneration of Tyr. O2- and 1O2 contributed 30-44% to Tyr's transformation in CDOM solutions at pH 8.0, in which 1O2 oxidation accounted for 6-11%. The contribution of O2- to Tyr's phototransformation process was the difference between the total contribution of O2- and 1O2 and the individual contribution of 1O2. Compared with the fast assimilation of Tyr, Tyr-OH was stable in natural water under dark incubation, indicating that phototransformation decreased the bioavailability of Tyr.
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Affiliation(s)
- Qing Zhou
- Department of Environmental Science, School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, PR China.
| | - Xu Zhang
- Department of Environmental Science, School of Resources and Environmental Science, Wuhan University, Wuhan, 430079, PR China.
| | - Chi Zhou
- Hubei Water Resources Research Institute, Hubei Water Resources and Hydropower Science and Technology Promotion Center Wuhan, 430070, PR China.
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27
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Ma J, Nie J, Zhou H, Wang H, Lian L, Yan S, Song W. Kinetic Consideration of Photochemical Formation and Decay of Superoxide Radical in Dissolved Organic Matter Solutions. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2020; 54:3199-3208. [PMID: 32073838 DOI: 10.1021/acs.est.9b06018] [Citation(s) in RCA: 61] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The photochemical formation and decay rates of superoxide radical ions (O2•-) in irradiated dissolved organic matter (DOM) solutions were directly determined by the chemiluminescent method. Under irradiation, uncatalyzed and catalyzed O2•- dismutation account for ∼25% of the total O2•- degradation in air-saturated DOM solutions. Light-induced O2•- loss, which does not produce H2O2, was observed. Both the O2•- photochemical formation and light-induced loss rates are positively correlated with the electron-donating capacities of the DOM, suggesting that phenolic moieties play a dual role in the photochemical behavior of O2•-. In air-saturated conditions, the O2•- quantum yields of 12 DOM solutions varied in a narrow range, from 1.8 to 3.3‰, and the average was (2.4 ± 0.5)‰. The quantum yield of O2•- nonlinearly increased with increasing dissolved oxygen concentration. Therefore, the quantum yield of one-electron reducing intermediates, the precursor of O2•-, was calculated as (5.0 ± 0.4)‰. High-energy triplets (3DOM*, ET > 200 kJ mol-1) and 1O2 quenching experiments indicate that 3DOM* and 1O2 play minor roles in O2•- production. These results are useful for predicting the photochemical formation and decay of O2•- in sunlit surface waters.
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Affiliation(s)
- Jianzhong Ma
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - JianXin Nie
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Huaxi Zhou
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Hui Wang
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Lushi Lian
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
| | - Shuwen Yan
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
| | - Weihua Song
- Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, P. R. China
- Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P. R. China
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28
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Dark biological superoxide production as a significant flux and sink of marine dissolved oxygen. Proc Natl Acad Sci U S A 2020; 117:3433-3439. [PMID: 32015131 PMCID: PMC7035516 DOI: 10.1073/pnas.1912313117] [Citation(s) in RCA: 28] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Extracellular production of the reactive oxygen species (ROS) superoxide results from the one-electron reduction of O2. Nearly all major groups of marine microbes produce extracellular superoxide. In this global estimate of marine microbial superoxide production we determine that dark extracellular superoxide production is ultimately a net sink of dissolved oxygen comparable in magnitude to other major terms in the marine oxygen cycle. This abundant source of superoxide to the marine water column provides evidence that extracellular ROS play a significant role in carbon oxidation and the redox cycling of metals in marine environments. Consideration of this significant reductive flux of dissolved oxygen is essential for field, laboratory, and modeling techniques for determining productivity and oxygen utilization in marine systems. The balance between sources and sinks of molecular oxygen in the oceans has greatly impacted the composition of Earth’s atmosphere since the evolution of oxygenic photosynthesis, thereby exerting key influence on Earth’s climate and the redox state of (sub)surface Earth. The canonical source and sink terms of the marine oxygen budget include photosynthesis, respiration, photorespiration, the Mehler reaction, and other smaller terms. However, recent advances in understanding cryptic oxygen cycling, namely the ubiquitous one-electron reduction of O2 to superoxide by microorganisms outside the cell, remains unexplored as a potential player in global oxygen dynamics. Here we show that dark extracellular superoxide production by marine microbes represents a previously unconsidered global oxygen flux and sink comparable in magnitude to other key terms. We estimate that extracellular superoxide production represents a gross oxygen sink comprising about a third of marine gross oxygen production, and a net oxygen sink amounting to 15 to 50% of that. We further demonstrate that this total marine dark extracellular superoxide flux is consistent with concentrations of superoxide in marine environments. These findings underscore prolific marine sources of reactive oxygen species and a complex and dynamic oxygen cycle in which oxygen consumption and corresponding carbon oxidation are not necessarily confined to cell membranes or exclusively related to respiration. This revised model of the marine oxygen cycle will ultimately allow for greater reconciliation among estimates of primary production and respiration and a greater mechanistic understanding of redox cycling in the ocean.
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29
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Berg SM, Whiting QT, Herrli JA, Winkels R, Wammer KH, Remucal CK. The Role of Dissolved Organic Matter Composition in Determining Photochemical Reactivity at the Molecular Level. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:11725-11734. [PMID: 31509695 DOI: 10.1021/acs.est.9b03007] [Citation(s) in RCA: 102] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Dissolved organic matter (DOM) composition influences its ability to form photochemically produced reactive intermediates (PPRI). While relationships have been established between bulk DOM properties and triplet DOM (3DOM) and singlet oxygen (1O2) quantum yields, contradictory evidence exists for hydroxyl radical (•OH) and hydroxylating species. Furthermore, little is known about these relationships at the molecular level. We evaluated DOM composition and photochemical reactivity of water samples from a wastewater treatment plant and the St. Louis River in Minnesota and Wisconsin, U.S.A. Bulk characterization using ultraviolet-visible spectroscopy demonstrates that color and apparent size of DOM decrease downstream, while molecular composition analysis using Fourier-transform ion cyclotron resonance mass spectrometry reveals that saturation and chemodiversity is highest near Lake Superior. 3DOM quantum yield coefficients and 1O2 quantum yields increase downstream and correlate strongly with saturated formulas. Similar results are observed for carbon-normalized photodegradation rate constants of atorvastatin, carbamazepine, and venlafaxine, which react primarily with 3DOM and 1O2. In contrast, •OH quantum yields are lowest downstream and correlate with less saturated, more oxygenated DOM, suggesting that 3DOM is not its major precursor. Mixed relationships are observed for DEET, which reacts with multiple PPRI. Molecular-level compositional data reveal insights into the differing formation pathways of individual PPRI, but information about specific contaminants is needed to predict their photochemical fate.
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Affiliation(s)
- Stephanie M Berg
- Environmental Chemistry and Technology Program University of Wisconsin - Madison , Madison , Wisconsin 53706 , United States
| | - Quinn T Whiting
- Department of Chemistry University of St. Thomas , St. Paul , Minnesota 55105 , United States
| | - Joseph A Herrli
- Department of Chemistry University of St. Thomas , St. Paul , Minnesota 55105 , United States
| | - Ronan Winkels
- Department of Chemistry University of St. Thomas , St. Paul , Minnesota 55105 , United States
| | - Kristine H Wammer
- Department of Chemistry University of St. Thomas , St. Paul , Minnesota 55105 , United States
| | - Christina K Remucal
- Environmental Chemistry and Technology Program University of Wisconsin - Madison , Madison , Wisconsin 53706 , United States
- Department of Civil and Environmental Engineering University of Wisconsin - Madison , Madison , Wisconsin 53706 , United States
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30
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Ossola R, Schmitt M, Erickson PR, McNeill K. Furan Carboxamides as Model Compounds To Study the Competition between Two Modes of Indirect Photochemistry. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:9594-9603. [PMID: 31335132 DOI: 10.1021/acs.est.9b02895] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Singlet oxygen (1O2) and triplet chromophoric dissolved organic matter (3CDOM*) are photochemically produced reactive intermediates responsible for the photodegradation of several micropollutants in the sunlit surface waters. However, elucidating the mechanism of reactions involving both 1O2 and 3CDOM* can be complicated by the deeply interconnected nature of these two reactive species. In this work, we synthesized a series of model compounds inspired by the chemical structure of fenfuram, a fungicide used in the 1980s, and used them to investigate structure-reactivity relationships in photodegradation reactions involving 1O2 and 3CDOM*. A combination of steady-state and time-resolved approaches was employed to successfully predict the extent of 1O2-induced degradation. Conversely, the prediction of triplet-induced reactivity was complicated by the presence of repair mechanisms whose extent and relative importance were difficult to predict. The results of our work indicate that bimolecular rate constants measured via time-resolved techniques alone are not sufficient to accurately predict environmental half-lives, as intrinsic differences in the reaction mechanism can amplify the importance of secondary degradation pathways.
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Affiliation(s)
- Rachele Ossola
- Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science , ETH Zurich , 8092 Zurich , Switzerland
| | - Markus Schmitt
- Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science , ETH Zurich , 8092 Zurich , Switzerland
| | - Paul R Erickson
- Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science , ETH Zurich , 8092 Zurich , Switzerland
| | - Kristopher McNeill
- Institute of Biogeochemistry and Pollutant Dynamics (IBP), Department of Environmental Systems Science , ETH Zurich , 8092 Zurich , Switzerland
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31
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Schendorf TM, Del Vecchio R, Bianca M, Blough NV. Combined Effects of pH and Borohydride Reduction on Optical Properties of Humic Substances (HS): A Comparison of Optical Models. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:6310-6319. [PMID: 31063364 DOI: 10.1021/acs.est.9b01516] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The combined effects of pH and borohydride reduction on the optical properties of a series of humic substances and a lignin model were examined to probe the molecular moieties and interactions that give rise to the observed optical properties of these materials. Increasing the pH from 2 to 12 produced significantly enhanced absorption across the spectra of all samples, with distinct spectral responses observed over pH ranges attributable to the deprotonation of carboxylic acids and phenols. Borohydride reduction substantially attenuated the broadband absorption enhancements with pH, clearly indicating that the loss of absorption due to ketone/aldehyde reduction is coupled with the pH-dependent increase in absorption due to deprotonation of carboxylic acids and phenols. These results cannot be easily explained by a superposition of the spectra of independently absorbing chromophores (superposition model) but are readily interpretable within a charge transfer (CT) model. Changes of fluorescence emission with pH for both untreated and borohydride reduced samples suggest that a pH-dependent structural reorganization of the HS may also be influencing the fluorescence emission. Independent of optical model, these results demonstrate that chemical tests targeted to specific moieties can identify distinct structural differences among HS sources as well as provide insight into the molecular moieties and interactions that produce the observed optical and photochemical properties.
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32
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Wan D, Sharma VK, Liu L, Zuo Y, Chen Y. Mechanistic Insight into the Effect of Metal Ions on Photogeneration of Reactive Species from Dissolved Organic Matter. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2019; 53:5778-5786. [PMID: 31021612 DOI: 10.1021/acs.est.9b00538] [Citation(s) in RCA: 76] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The photogeneration of reactive species (RS) from dissolved organic matter (DOM) exhibits a great impact on the attenuation of pollutants in natural waters. However, the effect of metal ions on the photogeneration of excited triplet-state DOM (3DOM*), singlet oxygen (1O2), and hydroxyl radical (•OH) by effluent organic matter (EfOM), fulvic acid (FA), and humic acid (HA) is poorly understood. Here, we provided the first evidence that the quenching of 3DOM* was positively correlated with the complexation capacity of metal ions with DOM. Generally, the paramagnetic metal ions (Cr3+, Mn2+, Fe3+, and Cu2+) exhibited higher conditional stability constants (log KML) with DOM and stronger inhibition for RS than the others (Mg2+, Ca2+, Al3+, and Zn2+). For DOM of different sources, the metal binding capacity increased in the order of EfOM < HA < FA and the humic substances were more susceptible to metal ions. The inhibition was attributed to both static and dynamic quenching of 3DOM* by metal ions. The dynamic quenching rate constants of metal ions for 3DOM* were estimated as ∼109 M-1 s-1, which was positively related to the corresponding log KML. These findings highlight crucial links between metal-DOM complexation and 3DOM* quenching and, consequently, the inhibition of RS.
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Affiliation(s)
- Dong Wan
- School of Environmental Science and Engineering , Huazhong University of Science and Technology , Wuhan , Hubei 430074 , People's Republic of China
| | - Virender K Sharma
- Program for the Environment and Sustainability, Department of Environmental and Occupational Health, School of Public Health , Texas A&M University , College Station , Texas 77843 , United States
| | - Lu Liu
- School of Environmental Science and Engineering , Huazhong University of Science and Technology , Wuhan , Hubei 430074 , People's Republic of China
| | - Yuegang Zuo
- University of Massachusetts Dartmouth , 285 Old Westport Road , North Dartmouth , Massachusetts 02747-2300 , United States
| | - Yong Chen
- School of Environmental Science and Engineering , Huazhong University of Science and Technology , Wuhan , Hubei 430074 , People's Republic of China
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33
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Chen Y, Zhang X, Feng S. Contribution of the Excited Triplet State of Humic Acid and Superoxide Radical Anion to Generation and Elimination of Phenoxyl Radical. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2018; 52:8283-8291. [PMID: 29916697 DOI: 10.1021/acs.est.8b00890] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Contributions of excited triplet state of humic acid (3HA*) and superoxide radical anion (O2•-), which is mainly generated via the reaction of O2 with HA-derived reducing intermediates (HA•-), to phenol transformation were revealed using acetaminophen, 2,4,6-trimethylphenol and tyrosine as probe molecules. Phenol transformation was initiated by 3HA*, leading to the formation of the phenoxyl radical (PhO•), but the distribution of transformation intermediates was codetermined by 3HA* and HA•-. The influence of HA•- essentially resulted from the production of O2•-, which affected the fate of PhO•. PhO• could undergo dimerization, or react with O2•-, leading to either phenol peroxide formation (radical addition) or phenol regeneration (electron transfer). In addition, PhO• could bind to HA or react with HA radicals, particularly in the absence of O2 and O2•-. These PhO• reactions were dependent on the reduction potential and structure of PhO•. This study also proved that the reaction of phenol with 1O2 and the reaction of PhO• with O2•- lead to the same oxidation product. The contributions of 3HA* and its generated 1O2, HA•- and its generated O2•- to phenol transformation were pH-dependent.
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Affiliation(s)
- Yuan Chen
- Department of Environmental Science , School of Resources and Environmental Science, Wuhan University , Wuhan 430079 , P.R. China
| | - Xu Zhang
- Department of Environmental Science , School of Resources and Environmental Science, Wuhan University , Wuhan 430079 , P.R. China
| | - Shixiang Feng
- Department of Environmental Science , School of Resources and Environmental Science, Wuhan University , Wuhan 430079 , P.R. China
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34
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Del Vecchio R, Schendorf TM, Blough NV. Contribution of Quinones and Ketones/Aldehydes to the Optical Properties of Humic Substances (HS) and Chromophoric Dissolved Organic Matter (CDOM). ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:13624-13632. [PMID: 29125750 DOI: 10.1021/acs.est.7b04172] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The molecular basis of the optical properties of chromophoric dissolved organic matter (CDOM) and humic substances (HS) remains poorly understood and yet to be investigated adequately. This study evaluates the relative contributions of two broad classes of carbonyl-containing compounds, ketones/aldehydes versus quinones, to the absorption and emission properties of a representative suite of HS as well as a lignin sample. Selective reduction of quinones to hydroquinones by addition of small molar excesses of dithionite to these samples under anoxic conditions produced small or negligible changes in their optical properties; however, when measurable, these changes were largely reversible upon exposure to air, consistent with the reoxidation of hydroquinones to quinones. With one exception, estimates of quinone content based on dithionite consumption by the HS under anoxic conditions were in good agreement with past electrochemical measurements. In contrast, reduction of ketones/aldehydes to alcohols employing excess sodium borohydride produced pronounced and largely, but not completely, irreversible changes in the optical properties. The results demonstrate that (aromatic) ketones/aldehydes, as opposed to quinones, play a far more prominent role in the optical absorption and emission properties of these HS, consistent with these moieties acting as the primary acceptors in charge-transfer transitions within these samples. As a method, anoxic dithionite titrations may further allow additional insight into the content and impact of quinones/hydroquinones on the optical properties of HS and CDOM.
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Affiliation(s)
- Rossana Del Vecchio
- Earth System Science Interdisciplinary Center, University of Maryland , College Park, Maryland 20742, United States
| | - Tara Marie Schendorf
- Department of Chemistry and Biochemistry, University of Maryland , College Park, Maryland 20742, United States
| | - Neil V Blough
- Department of Chemistry and Biochemistry, University of Maryland , College Park, Maryland 20742, United States
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35
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Ma J, Zhu C, Lu J, Ouyang B, Xie Q, Liu H, Peng S, Chen T. Kinetics analysis of interfacial electron-transfer processes in goethite suspensions systems. CHEMOSPHERE 2017; 188:667-676. [PMID: 28923730 DOI: 10.1016/j.chemosphere.2017.09.029] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2017] [Revised: 09/04/2017] [Accepted: 09/07/2017] [Indexed: 06/07/2023]
Abstract
The photochemical behavior of goethite has been one of the most important topics in the field of environmental science due to it plays a significant role in the removal and transformation process of numerous pollutants. However, the interfacial electron transfer process of goethite is not clear. Using a nanosecond laser flash photolysis spectrometer, we report the transient spectroscopic observations of interfacial electron-transfer reactions in goethite dispersion under UV irradiation. Excitation of goethite generated conduction-band electron (ecb-) and hole (h+). The conduction band electron (ecb-) reacted with an electron acceptor, methylviologen dichloride hydrate (MV2+), forming reduced methylviologen (MV+) with a second-order rate constant of (2.6 ± 0.3) × 109 L mol-1 s-1. The concentration of MV+ was strongly influenced by MV2+ initial concentration and pH values. The flat band potential of goethite was calculated to be Efb (goethite, pH = 7) = 0.24 V (vs NHE). Oxygen did not react with conduction band electron of goethite. The present study provides a reliable method to investigate the photo-induced interfacial charge transfer of goethite.
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Affiliation(s)
- Jianzhong Ma
- School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, PR China; Institute of Atmospheric Environment & Pollution Control, Hefei University of Technology, Hefei 230009, PR China
| | - Chengzhu Zhu
- School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, PR China; Institute of Atmospheric Environment & Pollution Control, Hefei University of Technology, Hefei 230009, PR China.
| | - Jun Lu
- Center of Analysis & Measurement, Hefei University of Technology, Hefei 230009, PR China
| | - Bin Ouyang
- Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, Cambs, England
| | - Qiaoqin Xie
- School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, PR China
| | - Haibo Liu
- School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, PR China
| | - Shuchuan Peng
- School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, PR China
| | - Tianhu Chen
- School of Resource and Environmental Engineering, Hefei University of Technology, Hefei 230009, PR China
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36
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Fujii M, Otani E. Photochemical generation and decay kinetics of superoxide and hydrogen peroxide in the presence of standard humic and fulvic acids. WATER RESEARCH 2017; 123:642-654. [PMID: 28710981 DOI: 10.1016/j.watres.2017.07.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2017] [Revised: 07/07/2017] [Accepted: 07/07/2017] [Indexed: 06/07/2023]
Abstract
Reactive oxygen species (ROS) such as superoxide (O2-) and hydrogen peroxide (H2O2) can be photochemically generated in aerobic waters containing natural organic matters (NOM) such as humic substances (HS). To investigate the effect of NOM molecular composition on the kinetics and mechanism of ROS transformation, photochemical O2- generation and subsequent H2O2 production via catalyzed and uncatalyzed (bimolecular dismutation) O2- decay were examined in the presence of 14 types of HS (pH 8.0). By using chemiluminescence and colorimetric techniques, the photochemical O2- generation rate, quasi-steady-state O2- concentration, catalyzed and uncatalyzed O2- decay rates, and H2O2 production rate were found to vary significantly by factors of 72, 18, 14, 320, and 7.7, respectively, depending on the type of HS and degree of photolysis. For more than half of the HS samples, both uncatalyzed and catalyzed reductive decay of photogenerated O2- were significantly involved in H2O2 generation, and their rates were comparable to those for O2- oxidative decay in which H2O2 is not generated. These results suggest that the chemical quality of HS influenced the H2O2 generation pathway. Correlation analyses indicated that rate constants associated with HS-mediated photochemical O2- and H2O2 generation are significantly correlated with HS molecular composition including total and aromatic C contents. In particular, practical indices representing NOM aromaticity including specific ultraviolet absorbance (SUVA) can be useful for predicting NOM-mediated ROS generation and decay kinetics. Overall, the present work suggests that NOM concentration and its quality influence NOM-mediated ROS dynamics in aqueous systems.
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Affiliation(s)
- Manabu Fujii
- Department of Civil and Environmental Engineering, Tokyo Institute of Technology, 2-12-1-M1-22 Ookayama, Tokyo 152-8552, Japan.
| | - Erika Otani
- Department of Civil and Environmental Engineering, Tokyo Institute of Technology, 2-12-1-M1-22 Ookayama, Tokyo 152-8552, Japan
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Zhou H, Yan S, Ma J, Lian L, Song W. Development of Novel Chemical Probes for Examining Triplet Natural Organic Matter under Solar Illumination. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:11066-11074. [PMID: 28858500 DOI: 10.1021/acs.est.7b02828] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Excited triplet states of chromophoric dissolved organic matter (3CDOM*) are critical transient species in environmental photochemistry. In the present study, sorbic amine (2,4-hexadien-1-amine) and sorbic alcohol were employed as new probe molecules for triplet measurements and compared to the results measured from sorbic acid under identical conditions. Unlike sorbic acid, sorbic amine and sorbic alcohol were not directly photolyzed under solar irradiation. Photosensitized isomerization of the probes with the conjugated diene structure could yield four geometrical isomers. The separation and quantitative determination of the geometrical isomers were accomplished using HPLC and high-resolution NMR analyses. When photoirradiated Suwannee River natural organic matter (SRNOM) was employed as a source of 3CDOM*, significantly different photosensitized isomerization rates were observed for the diverse charged probes. The bimolecular reaction rate constants between 3SRNOM* and the probes were calculated as (0.42 ± 0.1) × 109 M-1 s-1 for sorbic acid, (1.1 ± 0.1) × 109 M-1 s-1 for sorbic alcohol, and (5.2 ± 0.4) × 109 M-1 s-1 for sorbic amine, respectively. The average apparent Φtriplet was (0.96 ± 0.03)% based on an irradiation range of 290 to 400 nm. We developed highly selective and efficient probes for triplet determination and elucidated the different reaction behaviors of these conjugated dienes containing different charged substituents within the photochemical energy transfer process.
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Affiliation(s)
- Huaxi Zhou
- Department of Environmental Science & Engineering, Fudan University , Shanghai 200433, P. R. China
| | - Shuwen Yan
- Department of Environmental Science & Engineering, Fudan University , Shanghai 200433, P. R. China
| | - Jianzhong Ma
- Department of Environmental Science & Engineering, Fudan University , Shanghai 200433, P. R. China
| | - Lushi Lian
- Department of Environmental Science & Engineering, Fudan University , Shanghai 200433, P. R. China
| | - Weihua Song
- Department of Environmental Science & Engineering, Fudan University , Shanghai 200433, P. R. China
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Mckay G, Huang W, Romera-Castillo C, Crouch JE, Rosario-Ortiz FL, Jaffé R. Predicting Reactive Intermediate Quantum Yields from Dissolved Organic Matter Photolysis Using Optical Properties and Antioxidant Capacity. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2017; 51:5404-5413. [PMID: 28391701 DOI: 10.1021/acs.est.6b06372] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The antioxidant capacity and formation of photochemically produced reactive intermediates (RI) was studied for water samples collected from the Florida Everglades with different spatial (marsh versus estuarine) and temporal (wet versus dry season) characteristics. Measured RI included triplet excited states of dissolved organic matter (3DOM*), singlet oxygen (1O2), and the hydroxyl radical (•OH). Single and multiple linear regression modeling were performed using a broad range of extrinsic (to predict RI formation rates, RRI) and intrinsic (to predict RI quantum yields, ΦRI) parameters. Multiple linear regression models consistently led to better predictions of RRI and ΦRI for our data set but poor prediction of ΦRI for a previously published data set,1 probably because the predictors are intercorrelated (Pearson's r > 0.5). Single linear regression models were built with data compiled from previously published studies (n ≈ 120) in which E2:E3, S, and ΦRI values were measured, which revealed a high degree of similarity between RI-optical property relationships across DOM samples of diverse sources. This study reveals that •OH formation is, in general, decoupled from 3DOM* and 1O2 formation, providing supporting evidence that 3DOM* is not a •OH precursor. Finally, ΦRI for 1O2 and 3DOM* correlated negatively with antioxidant activity (a surrogate for electron donating capacity) for the collected samples, which is consistent with intramolecular oxidation of DOM moieties by 3DOM*.
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Affiliation(s)
- Garrett Mckay
- Department of Environmental Engineering, University of Colorado , Boulder, Colorado 80309, United States
| | | | | | - Jenna E Crouch
- Department of Environmental Engineering, University of Colorado , Boulder, Colorado 80309, United States
| | - Fernando L Rosario-Ortiz
- Department of Environmental Engineering, University of Colorado , Boulder, Colorado 80309, United States
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McNeill K, Canonica S. Triplet state dissolved organic matter in aquatic photochemistry: reaction mechanisms, substrate scope, and photophysical properties. ENVIRONMENTAL SCIENCE. PROCESSES & IMPACTS 2016; 18:1381-1399. [PMID: 27722628 DOI: 10.1039/c6em00408c] [Citation(s) in RCA: 237] [Impact Index Per Article: 29.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Excited triplet states of chromophoric dissolved organic matter (3CDOM*) play a major role among the reactive intermediates produced upon absorption of sunlight by surface waters. After more than two decades of research on the aquatic photochemistry of 3CDOM*, the need for improving the knowledge about the photophysical and photochemical properties of these elusive reactive species remains considerable. This critical review examines the efforts to date to characterize 3CDOM*. Information on 3CDOM* relies mainly on the use of probe compounds because of the difficulties associated with directly observing 3CDOM* using transient spectroscopic methods. Singlet molecular oxygen (1O2), which is a product of the reaction between 3CDOM* and dissolved oxygen, is probably the simplest indicator that can be used to estimate steady-state concentrations of 3CDOM*. There are two major modes of reaction of 3CDOM* with substrates, namely triplet energy transfer or oxidation (via electron transfer, proton-coupled electron transfer or related mechanisms). Organic molecules, including several environmental contaminants, that are susceptible to degradation by these two different reaction modes are reviewed. It is proposed that through the use of appropriate sets of probe compounds and model photosensitizers an improved estimation of the distribution of triplet energies and one-electron reduction potentials of 3CDOM* can be achieved.
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Affiliation(s)
- Kristopher McNeill
- Institute for Biogeochemistry and Pollutant Dynamics, ETH Zurich, Universitaetstrasse 16, 8092 Zurich, Switzerland.
| | - Silvio Canonica
- Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, 8600 Dübendorf, Switzerland
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