Dechlorination-Hydroxylation of Atrazine to Hydroxyatrazine with

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Remediation and Control Technologies

Dechlorination-Hydroxylation of Atrazine to Hydroxyatrazine with Thiosulfate: A Detoxification Strategy in Seconds Yi Mu, Guangming Zhan, Cuimei Huang, Xiaobing Wang, Zhihui Ai, Jian-Ping Zou, Shenglian Luo, and Lizhi Zhang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b06351 • Publication Date (Web): 22 Feb 2019 Downloaded from http://pubs.acs.org on February 23, 2019

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Environmental Science & Technology

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Dechlorination-Hydroxylation of Atrazine to Hydroxyatrazine with

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Thiosulfate: A Detoxification Strategy in Seconds

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Yi Mua, b, Guangming Zhana, Cuimei Huanga, Xiaobing Wanga, Zhihui Aia,*, Jianping Zoub,*,

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Shenglian Luob, Lizhi Zhanga,*

5 a

6

Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Institute of

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Environmental Chemistry, Central China Normal University, Wuhan 430079, People’s Republic of

8

China

9 10 11 12

b

Key Laboratory of Jiangxi Province for Persistent Pollutants Control and Resources Recycle, Nanchang Hangkong University, Nanchang 330063, People’s Republic of China *Corresponding

author. Phone/fax: +86-27-6786 7535.

Email address: jennifer.ai@mail.ccnu.edu.cn; zjp_112@126.com; zhanglz@mail.ccnu.edu.cn

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Abstract: Hydroxylation of atrazine to nontoxic hydroxyatrazine is generally considered as an

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efficient detoxification method to remediate atrazine-contaminated soil and water. However,

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previous studies suggested that hydroxylation was not the dominant pathway for atrazine degradation

17

in the hydroxyl radical-generating systems such as Fenton reaction, ozonation and UV/H2O2. Herein

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we report that the addition of sodium thiosulfate can realize rapid hydroxylation of atrazine to

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hydroxyatrazine at pH ≤ 4 under room temperature. High resolution mass spectra and isotope

20

experiments results revealed that the hydroxylation of atrazine was involved with nucleophilic

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substitution and subsequent hydrolysis reaction as follows. HS2O3-, as a species of thiosulfate only at

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pH ≤ 4, first attacked C atom connecting to chlorine of atrazine to dechlorinate atrazine and produce

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C8H14N5S2O3-. Subsequently, the S−S bond of C8H14N5S2O3- was cleaved easily to form SO3 and

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C8H14N5S-. Next, C8H14N5S- was hydrolyzed to generate hydroxyatrazine and H2S. Finally, the

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comproportionation of SO3 and H2S in-situ produced S0 during hydroxylation of atrazine with

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thiosulfate. This study clarifies the importance of degradation pathway on the removal of pollutants,

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and also provides a non-oxidative strategy for atrazine detoxification in seconds.

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Keywords: Atrazine; Thiosulfate; Detoxification; Nucleophilic substitution; Hydroxylation;

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Hydroxyatrazine

31 32

Introduction

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Atrazine (2-chloro-4-(ethylamino)-6-isopropylamino-s-triazine) has been introduced to control the

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agricultural weeds since 1950s and it has become one of the most widely used herbicides with 70000

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- 90000 tons per year in the world. Because of its large scale application and resistance to microbial

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degradation,1 atrazine is frequently detected in the natural water.2 The pollution of atrazine has raised

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growing concerns because of its endocrine disrupting effect3,

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Recently, atrazine has been regarded as a class C carcinogen by World Health Organization (W. H.

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O).7 Thus, it has been forbidden in the EU. However, atrazine is still widely used in many countries.

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So it is imperative to advance a facile and effective strategy to remove atrazine.

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4

and the risk to human health.5,

6

Various strategies have been developed to remove atrazine from water, such as biological

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methods,8,

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photolytic destruction,10 advanced oxidation processes,11 advanced reduction

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processes,12 electrochemical oxidation,13 molecular oxygen activation,14 microwave induced

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degradation,15 and ozonation. Generally, the pathways of atrazine degradation with these strategies

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usually involved the dealkylation, alkylic-oxidation, dechlorination, and hydroxylation processes

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simultaneously.16 Thus, different intermediates could be detected during the degradation process

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such as desisopropylatrazine (CEAT), desethylatrazine (CIAT), desethyldesisopropylatrazine

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(CAAT),

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1-(4-chloro-6-(isopropylamino)-

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4-ethylamino-6-isopropylamino-s-triazine (EIT), and hydroxyatrazine. Although these intermediates

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are less toxic than atrazine,17-19 their further degradation was substantially slower than atrazine.

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Therefore, the cumulative toxicity of these intermediates to aquatic creatures might be greater than

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that of atrazine.20 Among these intermediates, hydroxyatrazine was regarded as a totally nontoxic

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compound.21 Thus, direct transformation of atrazine to hydroxyatrazine is considered as one of most

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efficient methods to remove atrazine contamination.

2-acetamido-4-chloro-6-(isopropylamino)-s-triazine 1,3,5-triazin-2-ylamino)

-ethanol

(CDIT), (CNIT),

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Hydroxyl radical (•OH) was a strong oxidant (E0(•OH/OH-) = 2.8 V vs SHE) and highly reactive

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with most organic compounds. The reaction constant of •OH and atrazine was as high as 2.4 -

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3.0×109 M-1•s-1.22,

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atrazine might be proceeded via •OH attack of the s-triazine ring at the position of the chlorine group

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(Eq. 1). In recent years, scientists intensively investigated the mechanism of atrazine degradation in

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•OH generating systems including Fenton reaction,24,

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H2O2/UV,26,

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chlorine on s-triazine ring by •OH was rather difficult, because the dechlorination-hydroxylation of

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atraznie is not the dominant degradation pathway in these •OH generating systems (Figure S1).29 For

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example, in the Fenton reaction system, atrazine was proposed to form chlorinated products (e.g.

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CIAT, CEAT, CAAT, CDAT, and CAAT).23 Although trace amount of hydroxylated by-products

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could also be found, the dealkylation pathway is usually predominant. This was because attacking

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side chains of atrazine by •OH has priority, generating these chlorinated products.30 Further

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dechlorination-hydroxylation of these chlorinated products under attack of •OH was more difficult to

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take place owing to the low reactivity of •OH toward these chlorinated products. Thus, it still

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challenges us to propose a facile and efficient dechlorination-hydroxylation strategy to complete

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transformation of atrazine to nontoxic hydroxyatrazine.

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23

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It was thus thought that the dechlorination and subsequent hydroxylation of

25

ozone oxidation,23 TiO2 photocatalysis,17

and electrochemical oxidation.28 Unfortunately, they found that displacement of

(1)

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Rather than the oxidation by hydroxyl radical, SN2 nucleophilic substitution was found to be an

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effective dechlorination strategy.31-33 Among various nucleophiles, thiosulfate is the most widely

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used one for its low cost, nontoxic, and high reactivity.34 For example, Gan et al. reported that

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thiosulfate could facilitate the removal of halogen content from the halogenated aliphatic

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hydrocarbons, such as 1,3-dichloropropene, chloropicrin, methyl bromide, propargyl bromide, and

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methyl iodide, via nucleophilic substitution.35, 36 They further discovered that the chloroacetanilide

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herbicides, including propachlor, alachlor, metolachlor, and acetochlor, could be dechlorinated by

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thiosulfate.37 Given that atrazine has a special structure of Cl substitution on s-triazine ring, it is still

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unknown whether atrazine could be dechlorinated by thiosulfate via nucleophilic substitution, which

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might largely eliminate the acute toxicity of atrazine.

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In this study, we systematically investigate the reaction of atrazine and thiosulfate at different pH

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values, and check the degradation products with high performance liquid chromatography (HPLC),

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ion chromatograph (IC), liquid chromatography mass spectrometry (LC-MS), and liquid

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chromatography-high resolution mass spectrometry (LC-HRMS). According to the results of

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LC-HRMS and isotope experiments, the possible reaction mechanism is proposed. Meanwhile, the

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reactions of thiosulfate and other typical s-triazine pollutants are also checked, aiming to elucidate

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the intrinsic reactivity of thiosulfate to remove chlorinated s-triazine compounds.

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Experiment Section

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Chemicals. Atrazine (C8H14N5Cl), simazine (C7H12N5Cl), desethylatrazine (CIAT; C6H10N5Cl),

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desisopropylatrazine (CEAT; C5H8N5Cl), hydroxyatrazine (OIET; C5H9N5O) and sodium thiosulfate

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(Na2S2O3) were bought from Alfa Aesar. Sodium bisulfite (NaHSO3), sodium sulfide (Na2S),

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isopropanol (CH3CH2(OH)CH3), ethanol (CH3CH2OH), H2SO4 and NaOH were purchased from

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National Medicines Corporation Ltd., China. Superoxide dismutase (SOD) and catalase (CAT) were

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bought from Sigma-Aldrich.

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Atrazine Degradation Experiments. Atrazine degradation experiments (10 mg•L-1, 100 mL) were

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conducted in conical flasks at 25 oC. The initial pH was adjusted to predetermined pH values (2, 3, 4,

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5, and 6) with 1 mol•L-1 NaOH and 1 mol•L-1 HCl solutions. 0.066 g of Na2S2O3 was adding into the

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flask, followed by transferred the flask into a shaker (100 r•min-1) to initiate the atrazine degradation

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immediately. 500 μL of solution was withdrawn at regular intervals (5 s, 15 s, 25 s, 40 s, and 60 s).

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Subsequently, 500 μL of NaOH (pH = 12) was added instantly to stop the reaction as atrazine

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degradation was completely inhibited at alkaline condition (Figure S2). After that, the mixture was

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filtered through 0.22 μm filter membranes for the subsequent measurement. During a typical

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anaerobic atrazine degradation with thiosulfate process, a 100 mL three-neck flask containing 0.066

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g of Na2S2O3 was vacuumed and filled with nitrogen gas. Then 100 mL of anoxic atrazine solution

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(10 mg•L-1) was added into the three-neck flask. The subsequent experimental procedures were the

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same as those of aerobic atrazine degradation. After the reaction, some precipitate was generated in

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the solution. The reaction solution was then centrifuged to separate the precipitate from solution. The

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obtained precipitate was dried under anaerobic condition and then characterized with X-ray

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diffraction (XRD, D8 Advance, Cu Kα radiation, λ = 0.15418 nm, Bruker, Germany).

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Analysis Methods. The atrazine concentrations were measured by high pressure liquid

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chromatograph (HPLC, Ultimate 3000, Thermo) with a TC-C18 reverse phase column (150 mm ×

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4.6 mm, 5 µm, Agilent) and a ultraviolet detector (wavelength: 220 nm). The concentrations of Cl-

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were determined by ion chromatograph (IC, Dionex ICS-900, Thermo). Atrazine degradation

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products were detected by liquid chromatography–mass spectrometry (LC-MS, TSQ Quantum

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Access MAX, Thermo). The detailed analysis methods were provided in the Supporting Information

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(SI). To detect the shortly lived and highly reactive intermediates during atrazine degradation with

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sodium thiosulfate, a Dionex Ultimate 3000 series liquid chromatography combined with Q Exactive

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hybrid Quadrupole-Orbitrap mass spectrometer (Thermo Scientific, Bremen, Germany) was

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introduced to acquire accurate masses, possible elemental compositions and structure of degradation

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intermediates.38, 39 Thanks to the exceptional selectivity of high resolution MS, sample pretreatment

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was not needed and the solution could be fed into the MS directly. The system was worked with a

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heated electrospray ionization (HESI) source in negative mode with a spray voltage of -3.2 kV. The

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capillary temperature was set as 300 °C, the S-lens rf level was set as 50% and a mass resolution of

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70 000 was used. Other parameters were set as default values.40 The mass and charge ratio (m/z)

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value of target ions was restricted between 100.00 and 500.00. The mass spectra were analyzed by

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Xcalibur 2.1 software (Thermo Scientific). The possible molecular formulas of the selected peaks in

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the full mass scan were calculated within 5 ppm mass tolerance allowing the elements of C, H, N, O

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and S.

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Theory Calculations. Density functional theory (DFT) calculations were conducted with Gaussian

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09 software package (Gaussian 09, Revision D.01, Gaussian, Inc., Wallingford CT, 2013). Structures

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of reactants (HS2O3-, Atrazine), transition states, intermediates (C8H14N5S2O3H) and products were

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optimized at the B3LYP/6-311G (d, p) level. Solvent effects were included by using self-consistent

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reaction field (SCRF) technique. The obtained structures of the transition states were confirmed by

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vibrational analysis and the transition states have one imaginary frequency. Intrinsic reaction

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coordinate (IRC) calculations were carried out to verify the connectivity between the calculated

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transition states to the corresponding reactants and products. The Gibbs free energies of activation

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(∆G⧺) and the reaction (∆Gr) for the nucleophilic substitution (reaction between HS2O3- and atrazine)

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and hydrolysis reaction (reaction between C8H14N5S- and H2O) were calculated.41

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Results and discussion

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Figure 1a displays the time profiles of atrazine reacting with sodium thiosulfate under different initial

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pH values. It was found that pH 2 favored the reaction of atrazine and sodium thiosulfate, achieving

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nearly 100% of atrazine degradation within 120 s. However, the atrazine degradation efficiency

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gradually decreased with increasing the pH value from 2.0 to 4.0, and the atrazine degradation was

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completely inhibited at pH ˃ 4. As shown in Figure 1b, S2O32- was the major thiosulfate species at

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pH ≥ 2, while 30%, 6% and 1.2% of thiosulfate existed as HS2O3- at pH = 2, 3, and 4, respectively.

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We did not observe the degradation of atrazine at pH ˃ 4 without HS2O3-. So the pH dependent

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reactivity of thiosulfate to atrazine might be related to the speciation of thiosulfate generated at

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different pH values, and the gradual decrease of atrazine degradation efficiency along with the

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increase of pH values might be arisen from the thiosulfate species change from HS2O3- to S2O32-.

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Meanwhile, we also monitored the temporal pH change of the systems versus reaction time, and

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observed that pH values did not change obviously throughout the entire degradation process (SI

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Figure S3), ruling out the contribution of pH change to the atrazine degradation with thiosulfate. It is

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worth noting that some precipitate was generated during the atrazine degradation, and the precipitate

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mainly consisted of S0, as revealed by XRD patterns (SI Figure S4). To check the effect of in-situ

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generated S0 on degradation of atrazine, the precipitate was collected and then used to degrade

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atrazine. However, atrazine could not be removed by the precipitate (SI Figure S5), ruling out the

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contribution of in situ generated S0 to the atrazine degradation. For comparison, thiosulfate was

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replaced with other sulfate species (such as S2- and SO32-) for the atrazine degradation reaction at pH

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2.0. As shown in Figure S5, neither S2- nor SO32- could remove atrazine even prolonging the reaction

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time to 30 min. We therefore concluded that thiosulfate offered an efficient and environmentally

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benign strategy to remediate atrazine contamination in acid condition.

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The amount of thiosulfate on the degradation of atrazine was then investigated at pH = 2 and the

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initial atrazine concentrations of 10 mg•L-1 (Figure 1c). All the atrazine degradation curves obeyed

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pseudo first-order reaction kinetic equations, and the rate constants (k) were 0.035, 0.034, 0.024,

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0.020, 0.014 and 0.008 s-1 at the thiosulfate to atrazine molar ratios of 180, 90, 45, 20, 10, 2.5,

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respectively (Figure 1d). Although the atrazine degradation rate gradually decreased with the

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decrease of thiosulfate amount, more than 35% of atrazine could still be degraded within 120 s at the

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thiosulfate to atrazine molar ratio of 2.5. As the atrazine degradation rate did not increase when

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increasing the thiosulfate to atrazine molar ratio from 90 to 180, we chose 90 as the optimal initial

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thiosulfate to atrazine molar ratio in this study.

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Subsequently, we identified the intermediates and products of atrazine degradation at pH = 2. As

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shown in Figure 2a, the Cl- concentration rapidly increased along with the decrease of atrazine

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concentration and then approached the theoretical value (0.046 mmol•L-1) within 120 s, indicating

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that the dechlorination process took place along with the atrazine degradation. We thus checked the

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degradation products with HPLC and LC-MS. During the atrazine degradation, only one product

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peak (retention time 6.48 min) appeared after 15 s. The peak intensity of this product quickly

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increased along with the decrease of atrazine concentration (Figure 2b). This product was identified

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as hydroxyatrazine by LC-MS analysis (SI Figure S6). The concentration of hydroxyatrazine was

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0.046 mmol·L-1 after 5 min of treatment and the corresponding selectivity reached 99.2% (SI Figure

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S7). Subsequently, we also investigated the reaction hydroxyatrazine and thiosulfate with the same

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experimental procedure as that of atrazine degradation, and found that hydroxyatrazine could not be

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removed by HS2O3- even extending the reaction time to 30 min (SI Figure S8). This result suggested

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that the cleavage of the C−Cl bond of atrazine and subsequent formation of hydroxyatrazine was the

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sole pathway for the atrazine degradation with HS2O3-, which could avoid the generation of toxic

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dealkylation and alkylic-oxidation intermediates.

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To understand how HS2O3- could induce the hydroxylation of atrazine, we first check the possible

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generation of reactive oxygen species (ROS, i.e., •O2-, H2O2, and •OH) and their contribution to

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hydroxylation of atrazine with thiosulfate by adding excess scavengers (SOD for •O2-, iso-propanol

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for •OH and catalase for H2O2) (Figure 3a).42-43 We found that the atrazine degradation rates did not

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change after addition of the scavengers, suggesting that •O2-, H2O2 or •OH were not involved in the

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atrazine degradation in this study. We also explored the effect of molecular oxygen on atrazine

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degradation with HS2O3- by comparing the aerobic atrazine degradation rate with anaerobic one at an

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initial pH of 2 (SI Figure S9a). Both aerobic and anaerobic atrazine degradation curves followed a

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pseudo first-order kinetics model (SI Figure S9b). The anaerobic atrazine degradation rate constant

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(0.032 s-1) was almost the same as the aerobic one (0.033 s-1), ruling out the participation of

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molecular oxygen in atrazine degradation with thiosulfate at pH = 2.

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Previous study suggested that the peripheral S atom of thiosulfate was more nucleophilic than its

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ligand O,44 and could attack an electron deficient site. Chlorine substituent on the s-triazine ring of

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atrazine would decrease the electron density of neighboring C atom because chlorine was an electron

205

withdrawing group. Therefore, HS2O3- could facilitate dechlorination-hydroxylation of atrazine into

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hydroxyatrazine in the manner of nucleophilic substitution reaction. To gain mechanic insight into

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the nucleophilic substitution of atrazine with HS2O3-, density functional theory (DFT) calculations

208

were first introduced to simulate the possible pathway. Figure 4a presents the geometrical

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information of transition state corresponding to the nucleophilic substitution of atrazine with HS2O3-.

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The transition state was obtained using the B3LYP method with the 6-311G (d, p) basis set.

211

Frequency calculation was conducted to confirm that the transition state possessed only one

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imaginary frequency corresponding to vibration of peripheral S atom moving between HS2O3- anion

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and atrazine. IRC analysis was used to further validate that obtained transition state corresponded to

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the mechanism of nucleophilic substitution reaction between HS2O3- and atrazine (SI Figure S10).

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We found that two bonds were undergoing substantial changes during the nucleophilic substitution,

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which were the breaking C-Cl bond of atrazine and forming S−C bond (dash line in Figure 4a),

217

resulting in formation of product C8H14N5S2O3H (SI Figure S11). B3LYP/6-311G (d, p) energy

218

profiles for the nucleophilic substitution in Figure 4b revealed that the Gibbs free energy of this

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reaction was -20 kJ•mol-1, suggesting that nucleophilic substitution of atrazine with HS2O3- was

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energetically favorable.

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The rapid transformation of atrazine to hydroxyatrazine with HS2O3- suggested that this

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nucleophilic substitution intermediate (C8H14N5S2O3H) might be shortly lived and easily dissociated

223

in the reaction solution. We thus employed nanospray liquid chromatography-high resolution mass

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spectrometry (LC-HRMS) to check the generation of C8H14N5S2O3H during hydroxylation of

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atrazine with HS2O3-. In the negative ion mode mass spectra of reaction solution, the deprotonated

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nucleophilic substitution product C8H14N5S2O3- (m/z 292.05569) was detected and its mass tolerance

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was -1.574 ppm (Figure 4c and S12). Besides C8H14N5S2O3-, another organic sulfide peak of m/z

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212.09787 was also found, corresponding to C8H14N5S- with the mass tolerance of -4.217 ppm

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(Figure 4d and S13). The appearance of C8H14N5S- suggested that the S−S bond of C8H14N5S2O3-

230

was cleaved easily to form C8H14N5S- and SO3 (Eq 3). Therefore, hydroxyatrazine might be derived

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from C8H14N5S-. As stated above, neither molecular oxygen nor reactive oxygen species (i.e., •O2-,

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•OH, H2O2) were involved in the transformation of atrazine into hydroxyatrazine in the presence of

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thiosulfate, we thus proposed that the formation of hydroxyatrazine was proceed via hydrolysis of

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C8H14N5S- and oxygen atoms in hydroxyatrazine might be originated from the solvent H2O.45 To

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validate this point, we employed DFT calculations to investigate the reaction between C8H14N5SH

236

and H2O (Figure 4e), and found the Gibbs free energies of activation (ΔG⧺) and reaction (ΔGr) were

237

35.4 kJ•mol-1 and -19.6 kJ•mol-1 respectively, suggesting that hydrolysis of C8H14N5SH is virtually

238

irreversible (Figure 4f). To further check the origin of O atom in hydroxyatrazine, we performed the

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atrazine degradation with thiosulfate in solvent H2O18 under aerobic condition. As shown in the

240

Figure 4g, only the deprotonated hydroxyatrazine C8H14N518O- of m/z 198.10301 was detected,

241

confirming that solvent H2O supplied O atom for hydroxyatrazine via hydrolysis reaction.

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According to the above results, we proposed a possible pathway for the rapid hydroxylation of

243

atrazine to hydroxyatrazine with HS2O3- (Scheme 1). First, HS2O3-, as a species of thiosulfate only at

244

pH ≤ 4, was functioned as a nucleophile to attack C atom connecting to chlorine substituent of

245

atrazine, resulting in the dechlorination of atrazine and the formation of C8H14N5S2O3- (Eq. 2).

246

Subsequently, the S−S bond of C8H14N5S2O3- was cleaved easily to form SO3 and C8H14N5S- (Eq. 3).

247

Next, C8H14N5S- was hydrolyzed to generate hydroxyatrazine and H2S (Eq. 4), as confirmed by the

248

results of isotope experiments. Finally, the comproportionation of SO3 and H2S in-situ produced S0

249

during the hydroxylation of atrazine with HS2O3- (Eq. 5).

250

C8H14N5Cl + HS2O3- → C8H14N5S2O3- + HCl

(2)

251

C8H14N5S2O3- + H2O → C8H14N5SH + SO3 + OH-

(3)

252

C8H14N5SH + H2O → C8H14N5OH +H2S

(4)

253

3H2S + SO3 → 4S0↓ + 3H2O

(5)

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The generality of thiosulfate in the hydroxylation of s-triazine compounds was also investigated

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via degradation experiments of other three typical s-triazine pollutants such as simazine (SIM),

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desethylatrazine (CIAT), and desisopropylatrazine (CEAT). As shown in Figure 5a, thiosulfate

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exhibited extremely high reactivity for the degradation of simazine, CIAT, and CEAT, and only one

258

hydroxylated product was generated during the reaction procedure (Figure 5b - 5d), suggesting that

259

thiosulfate can be used to remove different s-triazine pollutants generally. Moreover, we found that

260

SO42-, NO3-, PO43-, Cl-, and NH4+, the typical coexisted ions in the pesticide wastewater,46 did not

261

affect the atrazine degradation with thiosulfate (SI Figure S14 - S15). Therefore, this thiosulfate

262

induced detoxification method was applicable to the pesticide wastewater treatment.

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Environmental implications. Hydroxylation of atrazine to nontoxic hydroxyatrazine is considered

264

as one of the most efficient methods to remediate atrazine contamination. Scientists mainly focus on

265

the hydroxylation of atrazine with •OH, although the hydroxylation of atrazine with •OH is not the

266

dominate degradation pathway, and thus the dealkylation and alkylic-oxidation intermediates are

267

often generated during the traditional •OH-based advanced oxidation processes, while the cumulative

268

toxicity of dealkylation and alkylic-oxidation intermediates might be greater than that of atrazine. In

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this study, we have proposed a non-oxidative strategy to hydroxylate atrazine into nontoxic

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hydroxyatrazine with thiosulfate. Different from the •OH-based oxidative strategy, thiosulfate could

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induce complete transformation of atrazine to nontoxic hydroxyatrazine at pH ≤ 4, and thus avoid the

272

toxic dealkylation and alkylic-oxidation intermediates generation. Although thiosulfate could not

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mineralize atrazine into CO2 and NH3+, its hydroxylation of atrazine into nontoxic hydroxyatrazine

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could greatly alleviate the biological toxicity and improve the biodegradability of atrazine. This

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study clarifies the importance of degradation pathway on the removal of pollutants, and also provides

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a non-oxidative strategy for atrazine detoxification in seconds.

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ASSOCIATED CONTENT

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Supporting Information

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Additional descriptions, Figures, and tables as mentioned in the text. This material is available free

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of charge via the Internet at http://pubs.acs.org.

282 283

AUTHOR INFORMATION

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Corresponding Author

285

*Phone/Fax: +86-27-6786 7535; e-mail: jennifer.ai@mail.ccnu.edu.cn; zjp_112@126.com;

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zhanglz@mail.ccnu.edu.cn.

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Notes

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The authors declare no competing financial interest.

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Acknowledgements. This work was supported by Natural Science Funds for Distinguished Young

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Scholars (Grant 21425728), National Key Research and Development Program of China (Grant

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2016YFA0203002), the 111 Project (Grant B17019), Self-Determined Research Funds of CCNU

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from the Colleges’ Basic Research and Operation of MOE (Grant CCNU14Z01001 and

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CCNU16A02029), Excellent Doctorial Dissertation Cultivation Grant from Central China Normal

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University (2015YBZD024 and 2016YBZZ031), and the CAS Interdisciplinary Innovation Team of

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the Chinese Academy of Sciences. Specially, we gratefully acknowledge the help of Yue’e Peng

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and Menglan Zhang in China University of Geosciences, Wuhan for their mass spectrometer

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analysis.

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Figure Captions

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Figure 1. (a) Time profiles of atrazine reacting with NaS2O3 under different initial pH values. The

429

initial concentration of atrazine and NaS2O3 were 10 mg·L-1 (0.0464 mmol·L-1) and 0.66 g·L-1 (4.18

430

mmol·L-1), respectively. (b) Thiosulfate speciation as a function of pH values. The thiosulfate

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species distribution was calculated by the speciation program Visual MINTEQ 3.0. (c) Degradation

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of atrazine and (d) plot of ln(C0/C) versus time in different thiosulfate/atrazine molar ratio systems.

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The initial pH values were 2. The initial concentration of atrazine was 10 mg·L-1 (0.0464 mmol·L-1).

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Figure 2. (a) Time profiles of atrazine (black line) and dechlorination efficiency (green line) in

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NaS2O3 system. (b) The HPLC chromatogram of the samples at different reaction time. The peaks at

438

retention time 6.48 min and 10.78 min were belonged to hydroxyatrazine and atrazine, respectively.

439

The initial concentration of atrazine and NaS2O3 were 10 mg·L-1 (0.0464 mmol·L-1) and 0.66 g·L-1

440

(4.18 mmol·L-1). The initial pH of the system was 2.0.

441 442

Figure 3. (a) Time profiles of atrazine in NaS2O3 system with addition of different scavengers (SOD

443

for •O2-, CAT for H2O2, iso-propanol for •OH). (b) The corresponding atrazine degradation rate

444

constant.

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Figure 4. (a) Basic geometrical parameters of the transition state structures for nucleophilic

448

substitution between atrzaine and thiosulfate (HS2O3-). (b) Profile of the potential energy surface for

449

the nucleophilic substitution process. Mass spectra of atrazine degradation intermediates ((c)

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C8H14N5S2O3-, m/z 292.05569; (d) C8H14N5S-, m/z 212.09760) detected by nanospray liquid

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chromatography-high resolution mass spectrometry. (e) Basic geometrical parameters of the

452

transition state structures for hydrolysis reaction. (f) Profile of the potential energy surface for the

453

nucleophilic hydrolysis reaction. (g) The mass spectra of hydroxyatrazine (C8H14N518O-, m/z

454

198.10301) detected in isotope experiments.

455

456 457

Scheme 1. The possible pathway for the transformation of atrazine to hydroxyatrazine with HS2O3-.

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Figure 5. (a) Time profiles of the atrazine, simazine, 2-chloro-4-amino-6- isopropylamino-1, 3,

460

5-triazine (CAIT), and 2-chloro-4-ethylamino-6-amino-1, 3, 5-triazine (CEAT) degradation in

461

thiosulfate systems. The initial pH values were 2. The initial concentration of target pollutants was

462

10 mg·L-1. The initial concentration of thiosulfate was 0.66 g·L-1. The HPLC chromatograms of (b)

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SIM, (c) CIAT, and (d) CEAT degradation product sampled at different reaction time.

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TOC Art Figure

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