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. 2020 Sep 16;5(38):24881–24889. doi: 10.1021/acsomega.0c03661

Degradation of a Novel Pesticide Antiviral Agent Vanisulfane in Aqueous Solution: Kinetics, Identification of Photolysis Products, and Pathway

Xingang Meng 1,*, Niao Wang 1, Xiaofang Long 1, Deyu Hu 1,*
PMCID: PMC7528319  PMID: 33015507

Abstract

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Hydrolysis degradation kinetics of vanisulfane in water was investigated in detail under exogenous substances conditions. The experimental results indicated that the degradation rate of vanisulfane in aqueous solution increases with the increase of concentration of Cu2+. The degradation of vanisulfane did not change significantly in Ni2+, Zn2+, Pb2+, and Fe3+ aqueous solutions. Surfactants have no significant effect on the degradation of vanisulfane, and the degradation rate of vanisulfane increases with increasing concentration of fulvic acid. In addition, the photolysis products were identified by ultra-high-performance liquid chromatography coupled with Orbitrap high-resolution mass spectrometry. Five photolysis products were identified, and the degradation reaction pathway and the mechanism of vanisulfane were proposed, which mainly involved cleavage of thioether, back into aldehyde, cleavage of ether bond, demethylation, and intramolecular dehydration processes. This research on vanisulfane can be helpful for its security evaluation and increased understanding of vanisulfane in water environments.

1. Introduction

Cucumber mosaic caused by cucumber mosaic virus (CMV) is the most important destructive plant pathogens in the cucumber-growing period. Vanisulfane, 2,2′-(((4-((4-chlorobenzyl)oxy)-3-methoxyphenyl)methylene))bis-(2-hydroxyethyl)dithioacetal (Figure 1), is a novel antiviral agent that exhibits pronounced curative and protection activities against CMV with half-maximal effective concentration (EC50) values of 206.3 and 186.2 μg/mL, respectively, which are superior to commercial agents, such as ribavirin (858.2 and 766.5 μg/mL, respectively), dufulin (471.2 and 465.4 μg/mL, respectively), and ningnanmycin (426.1 and 405.3 μg/mL, respectively).1 Vanisulfane was developed as a new dithioacetal class of antiviral agent by our research group, whose CAS registry number is 2088490-79-1. The patent of vanisulfane (CN106467478A) has been granted by the State Intellectual Property Office, the People’s Republic of China in March, 2017. Field trials have been performed, and the results show that vanisulfane has potent control efficiency against cucumber mosaic in China. Because of the potential and valuable development prospects of vanisulfane in China, a sensitive and accurate detection method and degradation study on vanisulfane are required.

Figure 1.

Figure 1

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Chemical structure of vanisulfane.

In the last decades, many studies have reported the detection and degradation of pesticides in the environment.2−6 Degradation of pesticides is generally affected by metal ions that are widely present in the water. In natural water, the hydrolysis process of these compounds is less likely to be significantly affected by metal ions, but in some special environments, with high concentrations of metal ions, such effects are not negligible. Studies have shown that metal ions such as the dissolved Cu2+, Pb2+, Ni2+, Zn2+, Fe3+, Hg2+, and Mn2+ in water may affect the hydrolysis of pesticides. The dissolved metal species may affect the hydrolysis of pesticides in various ways.7,8,11−14 In the experiment of the influence of metal ions such as Co2+, Ni2+, Cu2+, Zn2+, and Pb2+ on the hydrolysis of thiophosphoric acid ester and its corresponding phosphate pesticides,9 the result indicated that Cu2+ could effectively promote the hydrolysis of organophosphorus pesticides, such as chlorpyrifos-methyl, zinophos, diaznon, parathion-methyl, and ronnel, at the concentration of 1 mM. Compared with the catalytic ability of Cu2+, Pb2+ can also promote the hydrolysis of phosphate pesticides but with weak effect, and the three ions of Co2+, Ni2+, and Zn2+ have almost no catalytic effect. The studies reported the effect of Fe3+ on the hydrolysis of methyl parathion in the pH range of 2–7, and Fe3+ can effectively promote the acid hydrolysis of methyl parathion.10 Moreover, surfactants also have a certain effect on the degradation of pesticides. Surfactants are a common class of chemical products that are often accompanied by a large amount of surfactants as a blending agent during the application of pesticides.15,16 Soluble organic matter is commonly found in natural water, such as fulvic acid (FA), which sometimes changes the rate of hydrolysis and degradation of some organic pollutants in the environment.17,19−22 For example, photochemistry degradation of the herbicide bromoxynil was investigated using a narrow band of ultraviolet radiation at 313 nm with soil FAs. The results indicate that the photolysis rate of bromoxynil decreased as the amount of FAs increased at concentrations of 5, 10, 15, 20, 40, 45, 60, and 100 mg L–1 in aqueous solutions.18

In addition, the wide application of pesticides may lead to environmental contamination. Thus, to further possible degradation pathways of pesticide in the environment, it is important to evaluate their transport and fate23,24 and to identify the degradation products.25,27,28,30 The degradation mode and mechanism of pesticide are closely related to the molecular structure of pesticides. Generally, pesticides with functional groups such as haloalkyl, amide, amine, carbamate, epoxy, cyano, phosphate, and sulfate are easily hydrolyzed.31−36 Photolysis products and photolysis mechanisms of thiram were identified by high-performance liquid chromatography– mass spectrometry (MS)/MS. The experimental results showed that the degradation mechanism includes hydrolysis, oxidation, N-dealkylation, and S-hydroxylation processes. The electron-transfer reaction of hydroxyl radicals causes the C=S bond to break to form −OH and −SH. All of the photolysis products lost the methyl group by N-dealkylation.26 The degradation pathway and degradation mechanism of sulfonate (TBT) and sulcotrione (SCT) in water were identified by high-resolution mass spectrum (ultraperformance liquid chromatography in tandem with high-resolution mass spectrometry, UPLC–HRMS). The main mechanism of its degradation is that chlorination initially occurs on the α-carbon atoms of the three carbonyl functional groups. The reaction is a well-known haloform reaction, which ultimately produces chloroform. At the same time, the ring opening of cyclohexanedione forms the degradation products T1 and S1. The same chlorine substitution reaction in the second and third steps occurs by releasing glutaric acid on the same carbon atom to form degradation products T2 and S2. Finally, the degradation products T3 and S3 were formed by hydrolyzing chloroform. The degradation products T4 and S4 were produced by oxidative decarboxylation of T3 and S3, while the degradation products T5 and S5 were formed by internal cyclization of the intermediate because of the high electrophilicity of carbon dichloride.29

To the best of our knowledge, no research on the degradation kinetics, identification of degradation products, and the degradation mechanism of vanisulfane in aqueous solution has been published. In addition, the degradation and mechanism of vanisulfane in the aquatic environment are unclear. Describing degradation kinetics, possible degradation products, and degradation mechanism of vanisulfane in aqueous solutions is necessary. Given these considerations, vanisulfane was selected as a degradation of the research object in the present work to evaluate the efficiency of the hydrolysis and photolysis process. The objectives of the present study are as follows: (I) to demonstrate the degradation kinetics of vanisulfane in water under exogenous substances conditions, (II) to identify the potential photolysis degradation intermediates of vanisulfane in water, and (III) to elucidate the reaction mechanism and pathways of vanisulfane in water.

2. Results and Discussion

2.1. Effects of Metallic Ions

Six types of metallic ions (Cu2+, Ni2+, Zn2+, Pb2+, and Fe3+) were evaluated for the effects on vanisulfane degradation. An aqueous solution containing metal ions was set to 10 mg/L level of vanisulfane in the dark, 25 ± 2 °C, at pH 5 (Figure 2A). For the degradation effect of the Cu2+ aqueous solution experiment, the residues of vanisulfane were detected up to the 28th d in the initial concentration of 0.01 and 0.1 g/L Cu2+ aqueous solution. On the 28th d of sampling, 42.70 and 91.37% residues of vanisulfane remained in 0.01 and 0.1 g/L Cu2+ aqueous solution, respectively. Dissipation constants of vanisulfane in Cu2+ aqueous solution were calculated using the first-order rate equation. The degradation kinetic parameters clearly showed (Table S1) that the degradation half-time (t1/2) of vanisulfane in 0.01 and 0.1 g/L Cu2+ aqueous solution was 34.66 and 7.88 d, and the degradation rate constant (K) of vanisulfane was 0.020 and 0.088, respectively. The degradation rate of vanisulfane in 1 g/L Cu2+ aqueous solution was faster than the above conditions. The degradation half-time (t1/2) of vanisulfane in 1 g/L Cu2+ aqueous solution was 7.88 h, and the degradation rate constant (K) of vanisulfane was 0.088. This experimental result indicated that the degradation rate of vanisulfane in aqueous solution increases with the increase of Cu2+ concentration.

Figure 2.

Figure 2

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Effect of different initial concentrations of Cu2+ (A), Ni2+, (B), Zn2+ (C), Pb2+ (D), and Fe3+ (E) on the degradation of vanisulfane in aqueous solution.

For the degradation effect of other metallic ion aqueous solution experiment, the result showed that these metallic ions, such as Ni2+, Zn2+, Pb2+, and Fe3+, had no significant effect on the degradation of vanisulfane in aqueous solution. The residues of vanisulfane were detected up to the 21st d in the initial concentration of 0.01, 0.1, and 1 g/L Ni2+ aqueous solution. On the 21st d of sampling, 9.72, 9.79, and 9.94 mg/L residues of vanisulfane remained in 0.01, 0.1, and 1 g/L Ni2+ aqueous solution, respectively. The degradation of vanisulfane did not change significantly with the detection time in Ni2+ aqueous solution (Figure 2B). The residues of vanisulfane were detected up to the 21st d in the initial concentration of 0.01, 0.1, and 1 g/L Zn2+ aqueous solution. On the 21st d of sampling, 9.72, 9.78, and 9.98 mg/L residues of vanisulfane remained in 0.01, 0.1, and 1 g/L Zn2+ aqueous solution, respectively. The degradation of vanisulfane did not change significantly with the detection time in the Zn2+ aqueous solution (Figure 2C). The residues of vanisulfane were detected up to the 21st d in the initial concentration of 0.01, 0.1, and 1 g/L Pb2+ aqueous solution. On the 21st d of sampling, 9.82, 9.88, and 9.85 mg/L residues of vanisulfane remained in 0.01, 0.1, and 1 g/L Pb2+ aqueous solution, respectively. The degradation of vanisulfane did not change significantly with the detection time in the Pb2+ aqueous solution (Figure 2D). The residues of vanisulfane were detected up to the 21st d in the initial concentration of 0.01, 0.1, and 1 g/L Fe3+ aqueous solution. On the 21st d of sampling, 9.92, 9.96, and 9.92 mg/L residues of vanisulfane remained in 0.01, 0.1, and 1 g/L Fe3+ aqueous solution, respectively. The degradation of vanisulfane did not change significantly with the detection time in Fe3+ aqueous solution (Figure 2E). Generally, the interaction between the metal center and the organic substrate plays a key role, and these effects also accelerate the hydrolysis of organic pollutants through surface catalysis. Cu2+ has a complexation reaction with the functional groups that may be hydrolyzed by vanisulfane, making the attack of the affinity reagent (such as H2O, OH–) more convenient. However, Ni2+, Zn2+, Pb2+, and Fe3+ did not undergo the complexation reaction with vanisulfane, so they did not affect the degradation of vanisulfane.

2.2. Effects of Surfactants and FA

Different initial concentrations of FA were evaluated for the effects on vanisulfane degradation. The aqueous solution containing FA was set to 10 mg/L level of vanisulfane in the dark, 25 ± 2 °C (Figure 3A). For the degradation effect of the FA aqueous solution experiment, the residues of vanisulfane were detected up to the 28th d in the initial concentration of 0.01 and 0.1 g/L FA aqueous solution. On the 28th d of sampling, 37.46 and 51.88% residues of vanisulfane remained in 0.01 and 0.1 g/L FA aqueous solution, respectively. Dissipation constants of vanisulfane in FA aqueous solutions were calculated using the first-order rate equation. The degradation kinetic parameters clearly showed (Table S2) that the degradation half-times (t1/2) of vanisulfane in 0.01 and 0.1 g/L FA aqueous solution were 46.21 and 23.90 d, and the degradation rate constants (K) of vanisulfane were 0.015 and 0.029, respectively. The degradation rate of vanisulfane in 1 g/L FA aqueous solution was faster than those of the above two conditions. On the 10th d of sampling, the residues of vanisulfane have already reached 88.91% in 1 g/L FA aqueous solution. The degradation half-time (t1/2) of vanisulfane in 1 g/L FA aqueous solution was 3.18 d, and the degradation rate constant (K) of vanisulfane was 0.218. This experimental result indicated that the degradation rate of vanisulfane in aqueous solution increases with the increase of FA concentration.

Figure 3.

Figure 3

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Effect of different initial concentrations of FA (A), SDBS (B), CTAB (C), and Tween 80 (D) on the degradation of vanisulfane in aqueous solution.

Different types of surfactants, such as cationic surfactant (cetyltrimethyl ammonium bromide, CTAB), anionic surfactant (sodium dodecyl benzene sulfonate, SDBS), and nonionic surfactant (Tween 80) were evaluated for the effects on the vanisulfane degradation. The aqueous solution containing surfactants was set to 10 mg/L level of vanisulfane in the dark, 25 ± 2 °C, at pH 7 (Figure 3B–D). The result indicated that these surfactants had no significant effect on the degradation of vanisulfane in aqueous solution. The residues of vanisulfane were detected up to the 28th d in the initial concentrations of 0.01, 0.1, and 1 g/L SDBS aqueous solution. On the 28th d of sampling, 9.96, 9.92, and 9.92 mg/L residues of vanisulfane remained in 0.01, 0.1, and 1 g/L SDBS aqueous solution, respectively. The degradation of vanisulfane did not change significantly with the detection time in SDBS aqueous solution. The residues of vanisulfane were detected up to the 28th d in the initial concentrations of 0.01, 0.1, and 1 g/L CTAB aqueous solution. On the 28th d of sampling, 9.62, 9.85, and 9.95 mg/L residues of vanisulfane remained in 0.01, 0.1, and 1 g/L CTAB aqueous solutions, respectively. Figure 3C showed that the degradation of vanisulfane was not changed significantly with the increase of detection time in the CTAB aqueous solution. The residues of vanisulfane were detected up to the 28th d in the initial concentrations of 0.01, 0.1, and 1 g/L Tween 80 aqueous solution. On the 28th d of sampling, 9.96, 9.95, and 9.98 mg/L residues of vanisulfane remained in 0.01, 0.1, and 1 g/L Tween 80 aqueous solutions, respectively. The degradation of vanisulfane was not changed significantly with the increase of detection time in CTAB aqueous solution (Figure 3D).

2.3. Identification of Photolysis Products and Degradation Pathways by UPLC–HRMS

2.3.1. Identification of Photolysis Products

The identification of photolysis products of vanisulfane was conducted in aqueous solution. The structures of potential degradation products were analyzed further by the UPLC–HRMS system via the comparison of the retention time (RT), MS spectra, MS2 spectra, and observed mass data from those of the vanisulfane photolysis sample. The total ion chromatogram of photolysis samples is depicted in Figure 4. The total ion chromatogram shows that six peaks were labeled with the probable degradation products via the detection of photolysis samples. The peaks were identified by their RTs and protonated molecular ions, as follows: RT 12.16 min, m/z 459.07083, labeled P0; RT 16.82 min, m/z 275.04805, labeled P1; RT 16.82 min, m/z 275.04805, labeled P1; RT 3.88 min, m/z 77.00611, labeled P2; RT 8.78 min, m/z 381.03914, labeled P3; RT 5.37 min, m/z 141.01863, labeled P4; RT 18.28 min, m/z 151.04735, labeled P5. For the P0 peaks, the RT, MS, and MS2 of P0 were the same as those of the vanisulfane standard sample. Therefore, P0 was confirmed as vanisulfane.

Figure 4.

Figure 4

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Total ion current chromatogram of vanisulfane degradation in aqueous solution [(a), TIC MS, (b) FTMS-pESI FullMS].

The compound P1 (at 3.88 min) was identified as the degradation of vanisulfane. The characteristic fragment ion peak was m/z 275.04840 (Table 1 and Figure 5a). Compared with the theory of molecular formula m/z C15H13ClO3 = 275.04805, the error of molecular ion was 1.29293 ppm. MS2 spectra data of the vanisulfane photolysis product were obtained by fragmenting protonated molecular ions and were used to elucidate the structure of the degradation product (Figure 5b). The characteristic ion at m/z 260.02478, error, 0.80801 ppm, which appeared in the MS2 spectra of P1 was produced by the loss of one −CH3. The characteristic ion at m/z 232.02919, error, −2.00542, appeared in the MS2 spectra of P1, was formed by the loss of one −CO. According to the basis of fragmentation analysis, the structure of the compound P1 was identified as 4-((4-chlorobenzyl)oxy)-3-methoxybenzaldehyde. P2, with m/z of 77.00523 (Table 1), was considered a product of vanisulfane photolysis, which has been previously regarded as 2-mercaptoethan-1-ol. Compared with the theory of molecular formula m/z C2H6OS = 77.00611, error, −3.12756 ppm, the structure of the P2 compound is easily identified because of the simpler molecular ion. The characteristic ion appeared in the MS2 spectra of P3 at m/z 77.00666, error, −2.47054 ppm; m/z 217.04221, error, −1.65954 ppm; m/z 245.03740, error, −0.33182 ppm; and m/z 261.03262, error, 0.87380 ppm. According to the m/z 77.00666, error, −2.47054 ppm, the structure of the P3 compound contained the structure of 2-mercaptoethan-1-ol. It represented such a cleavage by one protonated molecular cleavage of a C–S bond. At m/z 245.03740, error, −0.33182 ppm, the molecular ion contained twice cleavage of the C–S bond. On this basis of this identification, the fragment ion of m/z 217.04221 was produced by the cleavage of C–C bond and C–O bond. The fragment ion of m/z 261.03262 may be formed by the cleavage of C–S bond and the replacement of sulfur atom by an oxygen atom. According to the theoretical molecular ion of P3 compound with m/z C18H19ClO3S2 = 381.03914, experimental molecular ion m/z 381.03931, error, 0.44562 ppm and the MS2 spectra of P3, the structure of the P3 compound was identified as 2-((4-chlorobenzyl)oxy)-5-(((2-hydroxyethyl)thio)(vinylthio)methyl)cyclohexa-2,5-dien-1-one. P4, with m/z of 141.01843 (Table 1), was considered a product of P0 photolysis and produced by the cleavage of a side chain of benzene ring C–O bond, which has been previously regarded as (4-chlorophenyl)methanol. Compared with the theory of molecular formula m/z C7H7ClO = 141.01863, error, −2.13241 ppm, the structure of the P4 compound was identified. P5, with m/z of 151.04733, was considered a product of P0 photolysis that was produced by the cleavage of a C–O bond and the process of disulfide-acetal back into aldehyde, which has been previously regarded as 4-hydroxy-3-methoxybenzaldehyde (Table 1). Compared with the theory of molecular formula m/z C8H8O3 = 151.04735, error, −0.12324 ppm, the structure of the P4 compound was easily identified because of the simpler molecular ion.

Table 1. Degradation Products Identified during Photolysis Processes.

2.3.1.

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Figure 5.

Figure 5

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Mass spectrum of photolysis product P1: MS, (a); MS2, (b).

Additionally, Figure 6 shows the change with the time for these photolysis products of vanisulfane, described as relative abundance with photolysis reaction time. It is assumed that the responsivity of the different photolysis products is no obvious difference. Relative abundance from mass spectra was used for exact quantitation of each product because of the lack of standards. According to the detection of these photolysis products, as the time curves are shown in Figure 6, the compound vanisulfane decreased gradually with the increase of photolysis reaction time. The content of product P1 was more than other photolysis products, which increased with the photolysis reaction time, while followed by a gradual decrease after approximately 5 min of photolysis reaction. In the same way, the P3 compound showed a continuous increase with the photolysis reaction time, followed by a gradual decrease after approximately 15 min of photolysis reaction. The photolysis product of P2, P4, and P5 showed a continuous decrease after around 10, 20, and 25 min, respectively.

Figure 6.

Figure 6

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Evolution of the time profiles for these degradation products of vanisulfane during the photolysis process.

2.3.2. Photolysis Reaction Pathway

Based on the degradation product, the probable photolysis pathway is shown in Figure 7. The degradation of vanisulfane in aqueous solution involves cleavage of thioether, back into aldehyde, cleavage of ether bond, demethylation, and intramolecular dehydration process, which prompted the formation of five photolysis products. After photolysis of vanisulfane by ultraviolet light, the product P1 is produced by reduction to an aldehyde (step 2). Vanisulfane (P0) and photolysis product P1 undergo cleavage of the C–O bond on the molecular of 9 and 10 position benzene rings side chain to form a photolysis product P4 (steps 5, 6, 8). P0 was subjected to the break of the C–S bond in the 16 position between the 17 position and the 18 position to form the photolysis product P2 (step 1). The formation of the photolysis product P5 is mainly due to the simultaneous cleavage of the C–O bond at the 9 and 10 position benzene ring side chains and the cleavage of the C–S bond at the 16 position between the 17 position and the 18 position (steps 2, 7). Photolysis product P5 can also be formed by cleaving a C–O bond of compound P1 (step 7). Photolysis product P3 is formed by intramolecular hydrolysis and dealkylation (step 3). The photolysis product P2 can also be formed by breaking the C–S bond of compound P3 (step 4).

Figure 7.

Figure 7

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Proposed degradation pathways of vanisulfane in aqueous solution.

3. Conclusions

The hydrolysis degradation kinetics of vanisulfane in water was investigated in this paper. The experimental results showed that the degradation rate of vanisulfane in aqueous solution increased with the increase in the concentration of Cu2+ and FA. Cu2+ and FA played critical roles in the degradation rate of vanisulfane in water. The degradation rate of vanisulfane in aqueous solution increased with the increase of concentrations of Cu2+ and FA. In other words, Cu2+ and FA substantially accelerated the degradation of vanisulfane in aqueous solution. The degradation of vanisulfane did not change significantly with the detection time in Ni2+, Zn2+, Pb2+, and Fe3+ aqueous solutions. Surfactants have no significant effect on the degradation of vanisulfane in aqueous solution. In addition, five photolysis products of vanisulfane were identified by high-resolution mass spectrometry and the reaction pathway, and the mechanism of vanisulfane in aqueous solution was proposed, which involved cleavage of thioether, back into aldehyde, cleavage of ether bond, demethylation, and intramolecular dehydration processes. This research on vanisulfane can be helpful for its security evaluation and increasing the understanding of vanisulfane in water environments.

4. Materials and Methods

4.1. Materials and Chemicals

Vanisulfane (99.6% purity) was provided by the Key Laboratory of Green Pesticide and Agricultural Bioengineering, Ministry of Education, Guizhou University (Guiyang, China). Mass spectrometric-grade acetonitrile, methanol, and formic acid were purchased from Merck (Darmstadt, Germany). Analytical-grade methylene chloride, ethyl acetate, petroleum ether, methanol, potassium biphthalate (KHP), KH2PO4, Na2B4O7·10H2O, KCl, and NaOH were purchased from Jinshan Chemical Reagent Co. (Chengdu, China). A syringe filter (nylon, 0.22 μm) was purchased from Peaksharp Technologies (Yibin, China). Distilled water was obtained from Watsons Co. Ltd. (Dongguan, China).

The stock standard solution of vanisulfane was prepared by methanol at a concentration of 100 mg/L. Series standard solutions of vanisulfane at 0.1, 0.5, 1, 5, 10, and 20 mg/L were also prepared by methanol dilution. The standard solutions were stable when stored at −18 °C in the dark.

4.2. UPLC Quantitative Analysis

Vanisulfane was quantitatively detected by a Waters ACQUITY UPLC system equipped with, a PDA detector, a quaternary solvent manager, and a sample manager. The column, an ACQUITY UPLC BEH Shield RP18 column (50.0 mm × 2.1 mm i.d., 1.7 μm film thickness), was put into the thermostat at 40 °C during quantitative analysis. The mobile phase was acetonitrile/water with 0.1% formic acid (35/65, v/v) at a flow rate of 0.3 mL/min, and 3 μL of sample volume was injected in UPLC system. Vanisulfane was analyzed by absorbance measurement at 230 nm.

4.3. UPLC–HRMS Qualitative Analysis

The degradation products of vanisulfane were qualitatively detected by Transcend Dionex UltiMate 3000 UPLC (Thermo Fisher Scientific, San Jose, CA, USA) assembled with an RS autosampler, an RS pump, and an RS column compartment, and a single-stage Orbitrap high-resolution mass (Q-Exactive). The experiment samples were detected with a heated electrospray interface (ESI, Thermo Fisher Scientific, San Jose, CA, USA) in negative ionization mode (ESI−). The version 3.0.63 of Xcalibur program from Thermo Fisher Scientific (Les Ulis, France) with Qual and Quanbrowser was used during the data processing. Mass range detection was applied. Thermo Scientific Dionex Chromeleon 6.8 was employed to screen the target compounds. Optimized mass spectra parameters were as follows: aux gas heater temperature at 300 °C; the capillary temperature at 300 °C; spray voltage at 3.0 kV, sheath gas, sweep gas, and auxiliary gas flow rates at 30, 3, and 10 a.u., respectively. UPLC separations were obtained using a Thermo scientific Hypersil GOLD C8 1.9 μm (2.1 × 100 mm) operating at 40 °C in the isocratic elution mode. The mobile phase was component A, 60% (water with 0.1% formic acid): component D, 40% (acetonitrile). The flow rate was 0.3 mL/min and the sample injection volume was 2 μL. Data were collected in negative mode within the range of 70 m/z to 800 m/z using full scan and t-sim ddMS2 analysis with a resolution of 140,000 during the entire process.

4.4. Degradation Kinetic Experiments

4.4.1. Effects of Metallic Ions

Hydrolysis kinetic experiments of vanisulfane were conducted in a 500 mL wide-mouth bottle in the dark. The effect of Cu2+, Ni2+, Zn2+, Pb2+, and Fe3+ and their different initial concentrations(0.01, 0.1, 1 g/L) on the hydrolysis of vanisulfane was investigated. All laboratory glassware was sterilized, and 0.2 g NaN3 was added to the aqueous solution to prevent the growth of bacteria. Under this experimental condition, the initial concentration of vanisulfane in aqueous solution was set to 10 mg/L. The residual amount of vanisulfane in aqueous solution is periodically sampled and detected. The samples were filtered with 0.22 μm syringe filters for UPLC analysis. All experiment results were based on the average of triplicate experiments.

4.4.2. Effects of Surfactants and FA

Effects of surfactants (SDBS; CTAB; Tween 80) and FA and their different initial concentrations (0.01, 0.1, 1 g/L) on hydrolysis kinetic experiments of vanisulfane were conducted in a 500 mL wide-mouth bottle in the dark. All laboratory glassware was sterilized, and 0.2 g of NaN3 was added to the aqueous solution to prevent the growth of bacteria. Under this experimental condition, the initial concentration of vanisulfane in aqueous solution was set to 10 mg/L. The residual amount of vanisulfane in aqueous solution is periodically sampled and detected. The samples were filtered with 0.22 μm syringe filters for UPLC analysis. All experiment results were based on the average of triplicate experiments.

4.5. Identification of Photolysis Products by UPLC–HRMS

Photolysis experiments of vanisulfane were conducted in a climate chamber with a 30 W UV lamp. The photon fluxes of 30 W UV lamps were 41.03 μmol m–2 s–1. Then, these photolysis experiments were performed in 250 mL quartz flasks. The standard of vanisulfane was directly dissolved in the water until a concentration of 100 mg L–1 was reached to obtain the detectable signals of potential degradation products on the UPLC–HRMS system. When most vanisulfane has been degraded, the samples were filtered with 0.22 μm syringe filters and then detected on the UPLC–HRMS system. These potential products were further analyzed to elucidate their structures using the UPLC–HRMS via RTs, MS, MS2, and observed mass differences compared with those of UPLC–HRMS.

Acknowledgments

The authors thank the National Key Research Development Program of China (2018YFD0200100) and the National Natural Science Foundation of China (no. 21867002) for financial support.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.0c03661.

  • Degradation kinetic parameters of vanisulfane in Cu2+ aqueous solution and degradation kinetic parameters of vanisulfane in FA aqueous solution (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao0c03661_si_001.pdf (72.7KB, pdf)

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