Photooxidation mechanism of As(III) by straw-derived dissolved organic matter

Journal Pre-proof Photooxidation mechanism of As(III) by straw-derived dissolved organic matter

Shaochong Liu, Mengxi Tan, Liqiang Ge, Fengxiao Zhu, Song Wu, Ning Chen, Changyin Zhu, Dongmei Zhou PII:

S0048-9697(20)37580-X

DOI:

https://doi.org/10.1016/j.scitotenv.2020.144049

Reference:

STOTEN 144049

To appear in:

Science of the Total Environment

Received date:

15 September 2020

Revised date:

18 November 2020

Accepted date:

19 November 2020

Please cite this article as: S. Liu, M. Tan, L. Ge, et al., Photooxidation mechanism of As(III) by straw-derived dissolved organic matter, Science of the Total Environment (2020), https://doi.org/10.1016/j.scitotenv.2020.144049

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

© 2020 Published by Elsevier.

Journal Pre-proof

Photooxidation mechanism of As(Ⅲ) by straw-derived dissolved organic matter Shaochong Liu1, Mengxi Tan1, Liqiang Ge2, Fengxiao Zhu1，Song Wu1，Ning Chen1， Changyin Zhu1,*, Dongmei Zhou1,* 1

State Key Laboratory of Pollution Control and Resource Reuse, School of the

Geological Survey of Jiangsu Province, Nanjing 210018, P. R. China *

Corresponding author.

pr

2

oo

f

Environment, Nanjing University, Nanjing 210023, P. R. China

Pr

e-

Email address: [email protected] (C. Zhu); [email protected] (D. Zhou)

Abstract

al

Straw return-to-field is a common agronomic practice that would affect the

rn

physicochemical characteristics of the paddy soil and overlying water, but few studies

Jo u

have focused on the possible impacts of straw return on the conversion of pollutants. In this study, the photooxidation of As(III) in aqueous solution by straw-derived dissolved organic matter (S-DOM) was investigated. The results showed that dissolved organic matter derived from wheat straw (DOMws) and rape straw (DOMrs) exhibited good spectroscopic features and could efficiently oxidize As(III) under irradiation at pH 5.0, with the kobs values of As(III) oxidation being 0.15 h-1 and 0.17 h-1 for DOMws and DOMrs, respectively. Quenching studies indicated that hydroxyl radical (•OH) dominated the oxidation of As(III) for both types of dissolved organic matter (DOM), though singlet oxygen (1O2) also played a role in the DOMrs system.

Journal Pre-proof Since acidic conditions are favorable for the formation of •OH, As(III) oxidation decreased with an increase of pH value. Additionally, the oxidation efficiency of As(III) was inhibited in the presence of NO3− (0.2-2 mM) while enhanced in the presence of Fe(III) (5-50 μM). This study is of great significance for understanding the removal/transformation behavior of pollutants in paddy fields that receive straw return.

oo

f

Keywords: Straw-derived dissolved organic matter; As; •OH; Photooxidation

pr

1. Introduction

e-

Crop straw is an important component of biomass resources, which has been widely used as domestic heating fuel, fertilizer, livestock feeding, building and

Pr

industrial raw materials in rural areas for a long history in China (Zhao et al., 2014).

al

In order to reduce air pollution by straw burning and excessive use of chemical

rn

fertilizers, straw incorporation in soil has been encouraged in many countries (Pathak

Jo u

et al., 2006; Zhu et al., 2010). Previous studies have revealed that straw return can improve the physical, chemical and biological properties of soil (Li et al., 2018). For example, straw contains large amounts of organic matters, nitrogen, phosphorous, potassium and other trace elements, which renders it an excellent organic fertilizer. Straw return has been reported to increase the productivity of agriculture by 1.7-145.8% (Zeng et al., 2002). Meanwhile, straw return was found to insignificantly influence soil pH and electrical conductivity (Blanco-Canqui and Lal, 2009). Straw return can also provide nutrients needed by nitrogen-fixing anaerobic bacteria and lead to stronger reducing conditions in soils (Tanji et al., 2003; Gao et al., 2004). Moreover,

Journal Pre-proof the decomposition of straw can increase the organic matter content of the overlying water of paddy fields, which might enhance the photochemical reaction processes (Zhou et al., 2018). Dissolved organic matter (DOM) is recognized to affect various environmental processes in aquatic systems (Berg et al., 2019; Buffam et al., 2011; Mostafa et al., 2013), such as the sequestration, transportation, and transformation of various

oo

f

constituents in ecosystems (Canonica and Schonenberger, 2019). A particular area of

pr

interest involves the role of DOM as a naturally occurring photosensitizer, which could enhance the formation of reactive oxygen species (ROS), such as hydroxyl

e-

radicals (•OH), singlet oxygen (1O2) and triplet excited state DOM (3DOM*) (McKay

Pr

et al., 2015; Wan et al., 2019; De Laurentiis et al., 2013). DOM derives from different

al

sources will be diverse in composition and photochemical behavior (Boyle et al., 2009;

rn

Cavani et al., 2009), which affect its ability to form ROS (Maizel et al., 2017; Maizel

Jo u

and Remucal, 2017; McCabe and Arnold, 2017). For example, Niu found that the •OH formation and the apparent •OH quantum yield of algal organic matter under simulated sunlight were higher than those of Suwannee River hydrophobic acid (Niu et al., 2019). Study have investigated the formation of •OH and 1O2 from different fractions of effluent organic matter (EfOM) under simulated solar irradiation and found that the hydrophobic and transphilic fractions were the major sources of superoxide radical (O2•-), hydrogen peroxide (H2O2) and •OH while the hydrophilic fraction dominated the production of Rosario-Ortiz, 2013).

1

O2 (Zhang et al., 2014; Mostafa and

Journal Pre-proof ROS plays nonnegligible role in pollutants transformation. 1O2 was believed to be responsible for the oxidation of As(III) by fulvic acid under 282 nm UV irradiation (Ding et al., 2016) while the photodegradation of 2,4-dihydroxybenzophenone (BP-1) occurred mainly via the pathway involving 3DOM* for the DOM extracted from coastal seawaters and 3DOM*, 1O2 and •OH for DOM derived from freshwaters (Wang et al., 2019). The study of metoprolol photodegradation in the presence of fulvic acids

oo

f

(FA) extracted from Vouga River (Portugal) revealed that •OH was the main reactive

pr

species, but other reactive species were also involved, such as the triplet excited states

e-

of FA and 1O2 (Filipe et al., 2020).

Arsenic (As) is one of the most toxic pollutants in the environment and its

Pr

occurrence in waters and soils has long been a health concern (Muehe et al., 2019;

al

Qiao et al., 2018). According to the drinking water guideline value of 10 μg/L for As

rn

proposed by World Health Organization (WHO) (Gorny et al., 2015), many natural

Jo u

waters in Argentina, Chile, Mexico, West Bengal, Bangladesh, and Vietnam are contaminated (Burgess et al., 2010). The Food and Agricultural Organization (FAO) recommends that total As in irrigation water should be under 100 μg/L (Buschmann et al., 2007). The As concentration in geothermal water can be up to 50 µg/L and natural groundwaters in As-rich provinces have high As concentration of 1500 µg/L (Fitzmaurice et al., 2009). In recent years, much attention has been paid to As contamination in paddy fields because irrigation with polluted water may result in As pollution and rice is the stable food for billions of people (Kumarathilaka et al., 2018). Field surveys of Bangladeshi paddy soils show total As concentrations up to 80 mg/kg

Journal Pre-proof (Khan et al., 2010). As(III) has higher toxicity, mobility and bioavailability compared with As(V) and long-term exposure of As(III) may lead to cancer (Tareq et al., 2013). Thus, the transformation of As(III) in paddy fields attracts extensive attention (Seyfferth et al., 2014). Straw returning to the field is an important agronomic measure in the paddy field. The straw can release large amount of organic matter and mineral elements to the soil

oo

f

and the overlying water of paddy fields, which might affect the production of •OH.

pr

Our recent work has shown that straw returning to the field can enhance the formation

e-

of •OH in paddy soil (Liu et al., 2020). But DOM derived from straw has not yet been evaluated in terms of its optical properties, and the contribution of ROS produced

Pr

from the irradiation of straw-derived organic products to the oxidation of As(III) is

al

still unclear.

rn

In environmentally relevant conditions such as acid sulfate soil wetlands and

Jo u

acid mine drainage, As can co-occur with Fe and high DOM (Kim et al., 2019). Previous studies have indicated that As(III) could be oxidized by the •OH formed from the irradiation of Fe and organic matter under acidic conditions (Sarmiento et al., 2007; Kohfahl et al., 2016). It was supposed that ROS could form in overlying water of paddy and affect the transformation of As(III). Therefore, straw-derived dissolved organic matter was chosen to explore the formation of ROS and oxidation of As(III) under simulated sunlight conditions. The main objectives of this study were: 1) to investigate the spectroscopic properties of straw-derived dissolved organic matter, 2) to elucidate the oxidation mechanism of As(III) in the presence of straw-derived

Journal Pre-proof dissolved organic matter, and 3) to evaluate the effect of dissolved oxygen concentration, solution pH and common anions and cations (NO3- and Fe3+) on As(III) oxidation. The present study suggests that the photochemical of DOM derived from straw may be an important pathway for the transformation of As(III) in paddy fields that receive straw return. 2. Materials and methods

oo

f

2.1. Chemicals

pr

Sodium arsenite was purchased from Sigma-Aldrich. HPLC grade methanol

e-

(MeOH) was supplied from TEDIA Company (USA), while nitrotetrazolium blue (NBT) was purchased from the Sinopharm Chemical Reagent Co. Ltd. (Shanghai,

Pr

China). Potassium hydroxide, N,N-diethyl-p-phenylenediamine (DPD), peroxidase

al

(POD), perchloric acid, benzoic acid (BA), thiourea, potassium borohydride, ascorbic

rn

acid, citric acid, sodium citrate, furfuryl alcohol (FFA) and phosphoric acid were

Jo u

purchased from J&K Scientific Ltd, China. Other chemical reagents were of analytical grade or better. Solutions were prepared with deionized (DI) water having a resistivity of 18.2 MΩ cm-1 (25 ℃) obtained from a Milli-Q system (Millipore, Billerica, MA, USA). 2.2 Preparation of straw-derived dissolved organic matter (S-DOM) Wheat straw and rape straw (which are largely available in China) were used for preparation of S-DOM used in this study. The straw was obtained from a farm in Lianyungang, Jiangsu Province, China. The straw samples were oven-dried at 65 ℃ for 24 h and then transferred into serum bottles for anaerobic decomposition in

Journal Pre-proof ultrapure water (straw/water ratio of 1:40 (w/v)). Meanwhile, 5 mL of fresh soil extract solutions containing soil microorganisms (10 g of fresh soil was mixed with 450 mL distilled water and shaken for 2 h, and then the supernatant was filtered with sterile quantitative filter paper) was added as inoculating solution at the beginning of the experiment. The straw decomposition trials were kept in the dark at 25 ℃ for 30 days under airtight conditions. Then the decomposed samples were filtrated using

oo

f

0.45 μm glass-fiber filters and named as DOMws (wheat straw) and DOMrs (rape

pr

straw), respectively. The composition of elements C, H, O and N of the S-DOM are

2.3 Characterization of S-DOM

Pr

for DOMrs.

e-

0.69 %, 26.13 %, 3.60 %, 31.81 % for DOMws and 0.89 %, 33.24 %, 4.65 %, 36.90 %

al

The DOC content in each of the samples was measured using a TOC analyser

rn

(Vario Elementar, Germany). UV/Vis absorbance of the solutions was measured by a

Jo u

spectrophotometer (Cary 60, Agilent). Fluorescence emission-excitation matrix (EEM) spectra was collected using a Hitachi F-7000 spectrofluorometer (Tokyo, Japan) with a 1 cm quartz cuvette. EEM spectra was obtained at 5 nm intervals for excitation wavelengths from 200 to 500 nm and emission ones from 200 to 450 nm in 5 nm intervals. The S-DOM solutions were freeze-dried by a freeze-dryer (Christ, Germany). The Fourier Translation Infrared spectroscopy (FTIR) spectra of S-DOM were recorded on a Vector-22 FTIR spectrometer (Bruker, Germany) with the KBr pellet technique. Elemental analysis involved C, H, N and O was measured using an Elementar vario EL cube (Vario Elementar, Germany).

Journal Pre-proof 2.4 Photochemical experiments A photochemical reaction apparatus (Nanjing Xujiang, China) equipped with a 500 W xenon lamp was employed for all irradiation experiments. The xenon lamp was equipped with a cooling water jacket to maintain a constant temperature of 25 ± 2 ℃. All experiments were performed in triplicates. The kinetics of As(III) oxidation were evaluated by conducting batch

oo

f

experiments. In the first experiment, the concentration gradient of S-DOM (10, 20, 30,

pr

40, 60 and 80 mg/L) and 100 μg/L As(III) were prepared, while the pH of the reaction

e-

solutions were adjusted to the specific values (5.0±0.1) with HClO4 and NaOH. In the second experiment, the effect of solution pH (5.0, 6.0, 7.0, 8.0) on As oxidation

Pr

was examined under 40 mg/L S-DOM and 100 μg/L As(III) conditions. MeOH (500

al

mM), NBT (200 μM) or FFA (50 μM) was added respectively to the solutions to

rn

evaluate the contribution of •OH, O2•− and 1O2 to As(III) oxidation. In all experiments,

Jo u

the 50 mL quartz photoreactor containing the solutions were stirred in photochemical reaction apparatus at room temperature (25 ± 0.5 ℃) during the reaction. An aliquot of 0.5 mL of reaction solution was withdrawn from each reactor at specific time intervals during the irradiation (0, 0.5, 1, 2, 3, 4 h). 2.5 Analytical methods The concentrations of As(III) was determined by hydride generation atomic fluorescence spectrometry (HG-AFS, AFS-230E, Beijing Haiguang Instrumental Company, China), following the procedure as described in previous studies (Xu et al., 2011). Briefly, an aliquot of sample solution was prepared in sodium citrate buffer (0.4

Journal Pre-proof M, pH 4.5), with 0.1 M citric acid as carrier solution. To determine total As, the sample solution was pretreated with a reducing agent containing 5 % (w/v) thiourea and 5 % (w/v) ascorbic acid, which reduced all As to As(III) prior to hydride generation. The resultant As(III) was converted to AsH3 by 2 % KBH4 in 0.5 % NaOH solution (w/v). The concentration of total As remains stable and the S-DOM has little influence on As(III) detection with the HG-AFS method (Fig.S1). The observed pseudo-first-order

oo

f

oxidation rate coefficients of As(III), kobs, were calculated using the following equation: (1)

pr

ln(Ct /C0 )=-kobs ×t

e-

where t is the reaction time (h), C0 and Ct are the total concentrations of As(III) at time 0 and t, respectively.

Pr

BA was used as a probe to detect the •OH. Benzoic acid at a concentration of 10

al

mM is reported to be able to capture more than 99 % of the •OH produced in the

rn

solution (Joo et al., 2005). At a given time point, 0.5 mL soil suspensions were

Jo u

collected and quenched with 0.5 mL methanol solutions. The production of •OH (represented by hydroxy-benzoic acid) was detected using HPLC (Shimadzu, Japan) equipped with a C18 column. The mobile phase was a mixture of 65 % methanol and 35 % phosphoric acid aqueous solution, with a flow rate of 1 mL·min-1. The production of •OH was detected at a wavelength of 254 nm. The concentration of H2O2 in S-DOM was determined by using DPD photometric method at wavelength of 551 nm. Briefly, 27 mL of sample was pipetted into a beaker and 3 mL of buffer solution was added to maintain pH 6. Then 50 μL DPD (10 mg/mL) and 50 μL POD (1 mg/ mL) solutions were added immediately. The

Journal Pre-proof absorbance was detected after the addition of the POD for 45 ± 5 s (Wang et al., 2013). 3. Results and discussion 3.1 Spectroscopic properties of S-DOM The S-DOM from wheat straw and rape straw was characterized by FTIR, UV-vis

f

and EEM. The FTIR spectra of DOMws and DOMrs are illustrated in Fig. 1a. The

oo

major bands of the S-DOM can be assigned to the stretching vibrations of amino group

pr

(3412 cm–1), the stretching vibrations of C-H on benzene ring (2968 cm–1), the C-H

e-

stretching vibration of the CH2 in alkyl chain (2960 and 2855 cm-1), the C=O stretching

Pr

vibration in benzene rings (1565 cm-1), the deformation vibration of -COO (1426 cm-1), and the C-O stretching vibration of methoxyl in aromatic compounds (1054 cm-1)

al

(Abdulla et al., 2010). UV-vis spectroscopy showed that DOMws had a higher

rn

absorbance than DOMrs (Fig. 1b). Previous studies have shown that specific UV

Jo u

absorbance (SUVA254) positively correlates with DOM aromaticity (Bodhipaksha et al., 2015), whereas E2:E3 is inversely proportional to molecular weight (Helms et al., 2008). In this study, DOMrs had a lower SUVA254 and a higher E2/E3 value (Table 1), implying that DOMrs was less aromatic and smaller in molecular weight than DOMws. The differences in the spectroscopic characteristics of DOM derived from multifarious sources might influence the generation of ROS when subjected to light irradiation. To further understand the compositional changes of S-DOM, the EEM of DOMws and DOMrs were obtained and compared (Fig. 1c and d). DOMws and DOMrs exhibited the features of biologically-impacted aromatic substances, as peaks

Journal Pre-proof representing protein-like moieties (Ex 220 nm/Em 300 nm), soluble microbial metabolites (Ex 280 nm/Em 300 nm), and fulvic-like substances (Ex 240 nm/Em 400 nm) were detected (Niu et al., 2019; Xu et al., 2020). Previous studies have shown that microorganisms could transform the structure of organic matter decomposed from straw or other organic matter into a protein-like structure via the actions of enzymes and •OH could be formed during the irradiation of protein-like structure organic matter

oo

f

(Ma et al., 2015).

pr

3.2 As(III) photooxidation by S-DOM

e-

The oxidation of As(III) in the presence of S-DOM under the irradiation was investigated. As shown in Fig. 2, As(III) oxidation occurred at a higher rate with the

Pr

increase of S-DOM concentrations (0-40 mg/L). The oxidation efficiency of As(III)

al

reached 46.79±0.01 % and 49.56±0.01 % in the presence of 40 mg/L DOMws and

rn

DOMrs, respectively, while only 9.97±0.08 % As(III) was transformed to As(V) in

Jo u

the absence of S-DOM under irradiation within 4 h. The As(III) oxidation kinetic curves in the presence of 40 mg/L DOMws and DOMrs fitted well with the pseudo-first-order equations, the kobs values of As(III) oxidation were 0.15 h-1 and 0.17 h-1, respectively. But the oxidation efficiency of As(III) decreased with further increase of S-DOM concentration to 60-80 mg/L. This might be because the S-DOM competed with As(III) for the ROS which inhibit As(III) oxidation. The lower concentration of As(III) can be oxidized quickly (Fig.S2). These results indicated that DOMws and DOMrs could induce As(III) oxidation, which was possibly due to the formation of ROS under light irradiation.

Journal Pre-proof 3.3 Identification of reactive radical responsible for As(III) oxidation Previous studies have indicated that DOM can produce ROS (•OH and 1O2) under irradiation (McKay et al., 2017; Page et al., 2011; Qu et al., 2012; Xu et al., 2020). To investigate the contribution of •OH in the oxidation of As(III), MeOH, an efficient scavenger of •OH with a rate constant of 9.7×108 M-1 s-1 (Fang et al., 2013) was applied in this study. Significant inhibition of oxidation was found in both the

oo

f

DOMws and DOMrs solutions with the addition of MeOH. The oxidation efficiency

pr

of As(III) decreased from 46.79±0.01 % to 10.01±0.01 % for the DOMws treatment and from 49.56±0.01 % to 19.21±0.03 % for the DOMrs treatment (Fig. 3a and b).

e-

The results indicated that the •OH was the main oxidant responsible for As(III)

Pr

oxidation, which was consistent with previous studies (Chen et al., 2018; Dutta et al.,

al

2005). BA was used to quantify the formation of •OH from the photoreaction of

rn

S-DOM (Fig. 3c). The concentration of •OH reached 6.63±0.13 μM for DOMws and

Jo u

7.90±0.13 μM for DOMrs within 4 h, which further proved that •OH was generated in this system under irradiation. Interestingly, 19.21±0.03 % of As(III) was removed in the S-DOMrs/As(III)/MeOH system which was higher than that in the blank control (9.97± 0.08 %) or the S-DOMws/As(III)/MeOH system (10.01±0.01 %) (Fig 2a and b), suggesting that other reactive species might also participate in As(III) oxidation in the DOMrs/As(III) solution. Under light irradiation, 1O2 was another ROS which might be formed in the solution containing DOM. FFA (50 μM), an efficient scavenger of 1O2 was used to explore the contribution of 1O2 in this system. As(III) oxidation was not affected by

Journal Pre-proof FFA in the DOMws solution but was inhibited in the DOMrs solution. As shown in Fig. 3b, the oxidation efficiency of As(III) was decreased from 49.56±0.01 % to 40.44±0.06 % in DOMrs/As(III) solution with the addition of FFA, confirming that 1

O2 was formed in the DOMrs/As(III) system and accounted for about 9% of the

oxidation of As(III). The results show that under light conditions, the ROS produced by the decomposition of different straw types may also be different.

oo

f

It is well known that dissolved oxygen can readily accept electrons to form O2•-.

pr

Therefore, in order to explore the generation pathway of •OH, NBT, an O2•- scavenger,

e-

was added to the solutions to test if O2•- was the precursor of •OH. As illustrated in Fig. 3a and b, the presence of NBT significantly retarded the oxidation of As(III) in

Pr

DOMrs and DOMws solutions. The removal of As(III) was only 9.93±0.01 % and

al

19.43±0.08 % in the DOMws/As(III) and DOMrs/As(III) systems with the addition

rn

of 200 μM NBT within 4 h, respectively. The results indicated that O2•- was the

Jo u

precursor of •OH. H2O2 was also an important intermediate of •OH (Page et al., 2011), thus the concentration of H2O2 formed during the illumination of S-DOM was also analyzed. As shown in Fig. 3d, the concentration of H2O2 was relatively low (0.23-1.68 μmol/L) and decreased as the reaction proceeded; this was mainly because the formed H2O2 would be further transformed to •OH under illumination. Studies have shown that H2O2 can also oxidize As(III) (Qin et al., 2016), which formed through superoxide anion (Wang et al., 2013). However, the reaction rate between H2O2 and As(III) (k = 5.5×10-3 M-1 s-1) is low (Woods et al., 1963), indicating that the direct contribution of H2O2 to As oxidation is limited. Therefore, it was concluded that

Journal Pre-proof H2O2 mainly acted in the form of •OH precursor, rather than directly oxidized As(III). Above results indicate O2•- and H2O2 was the intermediate of

•

OH. The

photo-oxidation of As(III) was possibly following the route: DOM produced electron under light irradiation (2), which could react with dissolved oxygen to generate O2•via reaction (3); then, H2O2 was generated via reaction (4), which was further activated to produce •OH via reaction (5).

oo

f

DOM→DOM+• +eaq -

H2 O2 +hv→2• OH

e-

2O2 •- +2H+ →H2 O2 +O2

pr

eaq -+O2 →O2 •-

(2) (3) (4) (5)

Pr

3.4 Effect of solution chemistry on the oxidation of As(III)

al

pH: The variation in pH values of the system can have an influence on DOM

rn

properties, such as particle size, functional group and molecular weight (Gu et al.,

Jo u

2017). It is expected that the pH value of the system would affect the photooxidation of As(III). As shown in Fig. 4, the oxidation efficiency of As(III) decreased with an increase in pH value for both DOMws and DOMrs. For example, the efficiency of photochemical oxidation of As(III) at pH 5.0 was 49.56±0.01 % in DOMrs solution and decreased to 36.42±0.03 %, 35.85±0.04 % and 30.08±0.04 % when pH increased to 6, 7 and 8, respectively. The kobs values of As(III) oxidation decreased from 1.50×10-1 h-1 (pH=5) to 0.92×10-1 h-1 (pH=8) for DOMws and from 1.74×10-1 h-1 (pH=5) to 0.87×10-1 h-1 (pH=8) for DOMrs. The results showed that solution pH had significant effect on the photooxidation of As(III) and high pH inhibited As(III)

Journal Pre-proof oxidation. Two reasons might be responsible for the results. Firstly, the formation of H2O2 needs H+ and acidic conditions favor the activation of H2O2 (Wang et al., 2013). Secondly, the charge of DOM and As(III) were neutral under acid condition and gradually becomes negative with the pH rose from 5 to 8 (the speciation of As is converted from H3AsO3 to H2AsO3-) (Guan et al., 2012). Increasing solution pH enhanced the repulsion of DOM and As, and therefore decreased the oxidation of

oo

f

As(III) by ROS formed from DOM. Thus, acidic conditions favored the formation of OH and promoted the oxidation of As(III) NO3−: Nitrate is a common anion existing

pr

•

e-

in paddy fields, and the concentration of nitrate increases significantly after fertilization (Said-Pullicino et al., 2014). As a ubiquitous ingredient in natural waters

Pr

(Zuo et al., 2006), nitrate can absorb sunlight in the UV range (λ＜350 nm) with a

al

maximum at 302 nm (ε= 7.2 M−1 cm−1) (Chen et al., 2013), and it is the primary

rn

source of •OH in natural waters ( Lam et al.,2003). (6)

NO3 -* →NO2 • +O•-

(7)

O•- +H2 O→ •OH+OH-

(8)

Jo u

NO3 - +hv→NO3 -*

The photooxidation experiments of As(III) were conducted in aqueous solutions containing S-DOM with different nitrate concentrations ranging from 0.2 to 2 mM under irradiation for 4 h (Fig.5). Theoretically, NO3- could favor As(III) oxidation since the light irradiation of NO3- can produce •OH (Brezonik et al., 1998). However, the addition of nitrate significantly inhibited the oxidation of As(III). In the presence of 2 mM NO3-, As(III) oxidation decreased from 46.79±0.01 % and 49.56 ±0.01 %

Journal Pre-proof to 37.44 ±0.34 % and 36.77±1.01 % for DOMws and DOMrs, respectively. Two likely reasons might have contributed to the observed results. Firstly, colored dissolved organic matter (CDOM), the main chromophore under these conditions, decreased the sunlight absorption and •OH formation by NO3- (Carena and Vione, 2017). Secondly, NO3- could efficiently react with •OH with the reaction rate of 8.8×107 M-1s-1 and therefore quenched As(III) oxidation by •OH. In order to further

oo

f

investigate the effect of the coexistence of DOM and NO3- on •OH formation,

pr

experiment containing 0.8 mM NO3- with the concentration of DOC in the range of

e-

0-80 mg/L was also conducted. As(III) was completely oxidized in sole medium of NO3-, while the oxidation efficiency of As(III) decreased to 57.87±0.90 % and 51.67

Pr

± 2.07 % with 5 mg/L S-DOM and further decreased with higher S-DOM

al

concentration (Fig.6). The result indicated that the presence of S-DOM also inhibited

rn

As(III) oxidation in the NO3-/irradiation system, which was mainly due to the

•

Jo u

screening and radical quenching effect of the DOM (the reaction rate of DOM with OH was 1.4×104 L mg C-1s-1) (Yi et al., 2016; Zeng et al., 2012). It was concluded

that the simultaneous existence of DOM and NO3- might not favor As(III) oxidation, although the oxidation of As(III) occurred with sole DOM or NO3-. The results provide a new perspective when investigating the oxidation ability of photocatalytic reaction in complex environments containing both DOM and NO3-. Fe3+: Iron is an important mineral element in soil and iron cations could be easily released into water bodies (Faust and Hoigne, 1990; Wu and Deng, 2000). Fe has strong complexing ability and mostly exists in the form of complex Fe(III)-DOM in

Journal Pre-proof water environment (Wang et al., 2012). Previous studies have found that certain organic Fe(III) complexes can be photolyzed to generate ROS through a ligand-to-metal charge transfer (LMCT) path, such as O2•-, H2O2, •OH (Feng et al., 2014; Garg et al., 2013), which can greatly influence the fate of many organic contaminants and heavy metals in the environment. To study the effects of Fe(Ⅲ) on the photochemical activity of dissolved organic matter (DOM) in aquatic

oo

f

environments, experiment was carried out with Fe(Ⅲ) concentration of 0-50 μM. The

pr

oxidation of As(III) was promoted when Fe(III) was added, with As(III) oxidation

e-

efficiency increasing from 46.79±0.01 % to 62.83±0.91 % for DOMws and from 49.56±0.01 % to 64.14±0.95 % for DOMrs in the presence of 50 μM Fe(III) (Fig. 7).

Pr

The results were possibly due to the fact that more •OH was generated through Fenton

al

reaction, which could promote the oxidation of As(III) (Kong and He, 2016; Pang et

rn

al., 2019). Firstly, the illumination of Fe(III)-DOM complex produced organic radicals

Jo u

which could react with O2 to form O2•-. Then O2•- further reacted with H+ or Fe(II) to form H2O2 (Batista et al., 2014; Wu and Deng, 2000). The consumption of H2O2 by the Fenton reaction led to an overall enrichment in •OH ( Faust and Hoigne, 1990; Hug et al., 2001). Fe(III)-organiccomplex+hv→Fe(II)+Org•

(9)

Org• +O2 →Oxidizedorg +O2 •

(10)

2O2 •- +2H+ →H2 O2 +O2

(11)

O2 •- +Fe(II)+2H+ →Fe(III)+H2 O2

(12)

Fe(II)+H2 O2 →Fe(III)+• OH+OH-

(13)

Journal Pre-proof 4. Conclusions Straw returning to the field is an important agronomic measure and would provide large amount of S-DOM to the paddy fields. This study found that the irradiation of S-DOM could induce the formation of ROS which was responsible for As(III) oxidation. •OH, as the main ROS, played a key role in the oxidation of As(III) in both DOMws and DOMrs systems while 1O2 also participated in As(III) in the

oo

f

DOMrs solution, which might due to the different composition and spectroscopic

pr

properties of S-DOM. Moreover, the photooxidation efficiency of As(III) under light

e-

irradiation of S-DOM was affected by solution chemistry such as pH, NO3- and Fe3+ concentration.

Pr

In summary, the S-DOM has a significant effect on the transformation behavior

al

of As in paddy fields or water bodies via producing ROS under illumination

rn

conditions. S-DOM from other straws such as rice, soybeans and corn straw might

Jo u

possess different spectroscopic properties which affect ROS formation. The transformation of As and other organic pollutants in overlying water during the decomposition of straw in the real paddy field environment also need further research. Credit Author Statement Shaochong Liu: Methodology, Writing - original draft. Mengxi Tan: Writing - original draft. Liqiang Ge: Writing - review & editing. Fengxiao Zhu: Writing - review & editing. Song Wu: Writing - review & editing. Ning Chen: Writing - review & editing. Changyin Zhu: Writing - review & editing, Funding acquisition. Dongmei Zhou: Methodology, Resources, Funding acquisition.

Journal Pre-proof Acknowledgements This work was supported by grants from National Key R&D Program of China (2019YFC1805103), the Key Research and Development Program of Jiangsu Province (BE2019624) and the 333 Project of Jiangsu Province (BRA2019106).

Jo u

rn

al

Pr

e-

pr

oo

f

References Abdulla HA, Minor EC, Dias RF, Hatcher PG. Changes in the compound classes of dissolved organic matter along an estuarine transect: A study using FTIR and 13C NMR. Geochimica et Cosmochimica Acta 2010; 74(13): 3815-3838. doi:10.1016/j.gca.2010.04.006 Batista AP, Cottrell BA, Nogueira RF. Photochemical transformation of antibiotics by excitation of Fe(III)-complexes in aqueous medium. Journal of Photochemistry and Photobiology A: Chemistry 2014; 274: 50-56. doi:10.1016/j.jphotochem.2013.09.017 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(20): 11725-11734. doi:10.1021/acs.est.9b03007 Blanco-Canqui H, Lal R. Crop Residue Removal Impacts on Soil Productivity and Environmental Quality. Critical Reviews in Plant Sciences 2009; 28(3): 139-163. doi:10.1080/07352680902776507 Bodhipaksha LC, Sharpless CM, Chin YP, Sander M, Langston WK, MacKay AA. Triplet photochemistry of effluent and natural organic matter in whole water and isolates from effluent-receiving rivers. Environmental Science & Technology 2015; 49(6): 3453-3463. doi:10.1021/es505081w Boyle ES, Guerriero N, Thiallet A, Vecchio RD, Blough NV. Optical Properties of Humic Substances and CDOM- Relation to Structure. Environmental Science & Technology 2009; 43: 2262-2268. doi: 10.1021/es803264g Brezonik PL, Fulkerson-Brekken J. Nitrate-Induced Photolysis in Natural Waters: Controls on Concentrations of Hydroxyl Radical Photo-Intermediates by Natural Scavenging Agents. Environmental Science & Technology 1998; 32: 3004-3010. doi:10.1021/es9802908 Buffam I, Turner MG, Desai AR, Hanson PC, Rusak JA, Lottig NR, Carpenter SR. Integrating aquatic and terrestrial components to construct a complete carbon budget for a north temperate lake district. Global Change Biology 2011; 17(2): 1193-1211. doi:10.1111/j.1365-2486.2010.02313.x Burgess WG, Hoque MA, Michael HA, Voss CI, Breit GN, Ahmed KM. Vulnerability of deep groundwater in the Bengal Aquifer System to contamination by arsenic. Nature Geoscience 2010; 3(2): 83-87. doi:10.1038/ngeo750 Buschmann J, Berg M, Stengel C, Sampson ML. Arsenic and manganese contamination of drinking water resources in Cambodia: coincidence of risk

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

areas with low relief topography. Environmental Science & Technology 2007; 41(7): 2146-2152. doi: 10.1021/es062056k Canonica S, Schonenberger U. Inhibitory Effect of Dissolved Organic Matter on the Transformation of Selected Anilines and Sulfonamide Antibiotics Induced by the Sulfate Radical. Environmental Science & Technology 2019; 53(20): 11783-11791. doi:10.1021/acs.est.9b04105 Carena L, Vione D. A Model Study of the Photochemical Fate of As(III) in Paddy-Water. Molecules 2017; 22(3):445-456. doi:10.3390/molecules22030445 Cavani L, Halladja S, Terhalle A, Guyot G, Corrado G, Ciavatta C, Boulkamh A, Richard C. Relationship between photosensitizing and emission properties of peat humic acid fractions obtained by tangential ultrafiltration. Environmental Science & Technology 2009; 43: 4348-4354. Chen Y, Zhang K, Zuo Y. Direct and indirect photodegradation of estriol in the presence of humic acid, nitrate and iron complexes in water solutions. Science of the Total Environment 2013; 463-464: 802-809. doi:10.1016/j.scitotenv.2013.06.026 Chen Z, Jin J, Song X, Zhang G, Zhang S. Redox Conversion of Arsenite and Nitrate in the UV/Quinone Systems. Environmental Science & Technology 2018; 52(17): 10011-10018. doi:10.1021/acs.est.8b03538 De Laurentiis E, Buoso S, Maurino V, Minero C, Vione D. Optical and photochemical characterization of chromophoric dissolved organic matter from lakes in Terra Nova Bay, Antarctica. Evidence of considerable photoreactivity in an extreme environment. Environmental Science & Technology 2013; 47(24): 14089-14098. doi:10.1021/es403364z Ding W, Romanova TE, Pozdnyakov IP, Salomatova VA, Parkhats MV, Dzhagarov B M, Shuvaeva OV. Photooxidation of arsenic(III) in the presence of fulvic acid. Mendeleev Communications 2016; 26(3): 266-268. doi:10.1016/j.mencom.2016.05.016 Dutta PK, Pehkonen SO ， Sharma VK, Ray AK. Photocatalytic oxidation of arsenic(III): evidence of hydroxyl radicals. Environmental Science & Technology 2005; 39: 1827-1834. doi: 10.1021/es0489238 Fang G, Gao J, Dionysiou DD, Liu C, Zhou DM. Activation of persulfate by quinones: free radical reactions and implication for the degradation of PCBs. Environmental Science & Technology 2013; 47(9): 4605-4611. doi:10.1021/es400262n Faust BC, Hoigne J. Photolysis of Fe (III)-hydroxy complexes as sources of OH radicals in clouds, fog and rain. Atmospheric Environment 1990; 24: 79-89. doi: 10.1016/0960-1686(90)90443-Q Feng XN, Chen Y, Fang Y, Wang XY, WangZP, Tao T, Zuo YG. Photodegradation of parabens by Fe(III)-citrate complexes at circumneutral pH: Matrix effect and reaction mechanism. Science of the Total Environment 2014; 472: 130-136. doi: 10.1016/j.scitotenv.2013.11.005

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Filipe OM, Santos EB, Otero M, Goncalves EA, Neves M. Photodegradation of metoprolol in the presence of aquatic fulvic acids. Kinetic studies, degradation pathways and role of singlet oxygen, OH radicals and fulvic acids triplet states. Journal of Hazardous Materials 2020; 385: 121523. doi:10.1016/j.jhazmat.2019.121523 Fitzmaurice AG, Bilgin AA, O’Day PA, Illera V, Burris DR, Reisinger HJ, Hering JG. Geochemical and hydrologic controls on the mobilization of arsenic derived from herbicide application. Applied Geochemistry 2009; 24 (11): 2152-2162. doi: 10.1016/j.apgeochem.2009.09.019 Gao ST, Tanji KK, Scardaci SC. Impact of Rice Straw Incorporation on Soil Redox Status and Sulfide Toxicity. Agronomy Journal 2004; 96: 70-76. doi: 10.2134/agronj2004.0070 Garg S, Jiang C, Miller CJ, Rose AL, and Waite TD. Iron Redox Transformations in Continuously Photolyzed Acidic Solutions Containing Natural Organic Matter: Kinetic and Mechanistic Insights. Environmental Science & Technology 2013; 47: 9190-9197. doi: 10.1021/es401087q Gorny J, Billon G, Lesven L, Dumoulin D, Made B, Noiriel C. Arsenic behavior in river sediments under redox gradient: a review. Science of the Total Environment 2015; 505: 423-434. doi:10.1016/j.scitotenv.2014.10.011 Gu Y, Lensu A, Peramaki S, Ojala A, Vahatalo AV. Iron and pH Regulating the Photochemical Mineralization of Dissolved Organic Carbon. ACS Omega 2017; 2(5): 1905-1914. doi:10.1021/acsomega.7b00453 Guan XH, Du JS, Meng XG, Sun YK, Sun Bo, Hu QH. Application of titanium dioxide in arsenic removal from water: A review. Journal of Hazardous Materials 2012; 215-216: 1-16. doi:10.1016/j.jhazmat.2012.02.069 Helms JR, Stubbins A, Ritchie JD, Minor EC, Kieber DJ, Mopper K. Absorption spectral slopes and slope ratios as indicators of molecular weight, source, and photobleaching of chromophoric dissolved organic matter. Limnology and oceanography 2008; 53: 955-969. doi: 10.4319/lo.2008.53.3.0955 Hug SJ, Canonica L, Wegelin M, Gechter D. Solar oxidation and removal of arsenic at circumneutral pH in iron containing waters. Environmental Science & Technology 2001; 35: 2114-2121. doi: 10.1021/es001551s Joo SH, Feitz AJ, Sedlak DL, Waite TD. Quantification of the oxidizing capacity of nanoparticulate. Environmental Science & Technology 2005; 39: 1263-1268. doi: 10.1007/0-387-28826-0_6 Khan MA, Stroud J, Zhu YG, McGrath SP, Zhao FJ. Arsenic Bioavailability to Rice Is Elevated in Bangladeshi Paddy Soils. Environmental Science & Technology 2010; 44: 8515-8521. doi: 10.1021/es101952f Kim HB, Kima JG, Choi JH, Kwon EE, Baek K. Photo-induced redox coupling of dissolved organic matter and iron in biochars and soil system: Enhanced mobility of arsenic. Science of the Total Environment 2019; 689: 1037-1043. doi: 10.1016/j.scitotenv.2019.06.478 Kohfahl C, Sanchez-Rodas Navarro D, Mendoza JA, Vadillo I, Giménez-Forcada E. Algae metabolism and organic carbon in sediments determining arsenic

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

mobilisation in ground- and surface water. A field study in Doñana National Park, Spain. The Science of the Total Environment 2016; 544: 874-882. doi:10.1016/j.scitotenv.2015.11.138 Kong LH, He MC. Mechanisms of Sb(III) Photooxidation by the Excitation of Organic Fe(III) Complexes. Environmental Science & Technology 2016; 50: 6974-6982. doi: 10.1021/acs.est.6b00857 Kumarathilaka P, Seneweera S, Meharg A, Bundschuh J. Arsenic speciation dynamics in paddy rice soil-water environment: sources, physico-chemical, and biological factors - A review. Water Research 2018; 140: 403-414. doi:10.1016/j.watres.2018.04.034 Lam MW, Tantuco K, Mabury SA. PhotoFate: A New Approach in Accounting for the Contribution of Indirect Photolysis of Pesticides and Pharmaceuticals in Surface Waters. Environmental Science & Technology 2003; 37: 899-907. doi.org/10.1021/es025902+ Li H, Dai M, Dai S, Dong X. Current status and environment impact of direct straw return in China's cropland - A review. Ecotoxicology and Environmental Safety 2018; 159: 293-300. doi:10.1016/j.ecoenv.2018.05.014 Liu SC, Wang DX, Zhu CY, Zhou DM. Effect of Straw Return on Hydroxyl Radical Formation in Paddy Soil. Bulletin of Environmental Contamination and Toxicology 2020. Doi: 10.1007/s00128-020-02974-y Ma H, Zhang J, Tong L, Yang J. Photochemical production of hydrogen peroxide from natural algicides: decomposition organic matter from straw. Environmental Science-Processes & Impacts 2015; 17(8): 1455-1461. doi:10.1039/c5em00224a Maizel AC, Li J, Remucal CK. Relationships Between Dissolved Organic Matter Composition and Photochemistry in Lakes of Diverse Trophic Status. Environmental Science & Technology 2017; 51(17): 9624-9632. doi:10.1021/acs.est.7b01270 Maizel AC, Remucal CK. Molecular Composition and Photochemical Reactivity of Size-Fractionated Dissolved Organic Matter. Environmental Science & Technology 2017; 51(4): 2113-2123. doi:10.1021/acs.est.6b05140 McCabe AJ, Arnold WA. Reactivity of Triplet Excited States of Dissolved Natural Organic Matter in Stormflow from Mixed-Use Watersheds. Environmental Science & Technology 2017; 51(17): 9718-9728. doi:10.1021/acs.est.7b01914 McKay G, Huang W, Romera-Castillo C, Crouch JE, Rosario-Ortiz FL, Jaffe R. Predicting Reactive Intermediate Quantum Yields from Dissolved Organic Matter Photolysis Using Optical Properties and Antioxidant Capacity. Environmental Science & Technology 2017; 51(10): 5404-5413. doi:10.1021/acs.est.6b06372 McKay G, Rosario-Ortiz FL. Temperature dependence of the photochemical formation of hydroxyl radical from dissolved organic matter. Environmental Science & Technology 2015; 49(7): 4147-4154. doi:10.1021/acs.est.5b00102

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Mostafa S, Rosario-Ortiz FL. Singlet oxygen formation from wastewater organic matter. Environmental Science & Technology 2013; 47(15): 8179-8186. doi:10.1021/es401814s Muehe EM, Wang T, Kerl CF, Planer-Friedrich B, Fendorf S. Rice production threatened by coupled stresses of climate and soil arsenic. Nature Communications 2019; 10(1): 4985. doi:10.1038/s41467-019-12946-4 Niu XZ, Croue JP. Photochemical production of hydroxyl radical from algal organic matter. Water Research 2019; 161: 11-16. doi:10.1016/j.watres.2019.05.089 Page SE, Arnold WA, McNeill K. Assessing the contribution of free hydroxyl radical in organic matter-sensitized photohydroxylation reactions. Environmental Science & Technology 2011; 45(7): 2818-2825. doi:10.1021/es2000694 Pang HW, Zhang Q, Wang HL, Cai DM, Ma YG, Li Li, Li KN, Lu XH, Chen H, Yang X, Chen JM. Photochemical Aging of Guaiacol by Fe(III)−Oxalate Complexes in Atmospheric Aqueous Phase. Environmental Science & Technology 2019; 53: 127-136. doi: 10.1021/acs.est.8b04507 Pathak H, Singh R, Bhatia A, Jain N. Recycling of rice straw to improve wheat yield and soil fertility and reduce atmospheric pollution. Paddy and Water Environment 2006; 4(2): 111-117. doi:10.1007/s10333-006-0038-6 Qiao JT, Li XM, Hu M, Li FB, Young LY, Sun WM, Cui JH. Transcriptional Activity of Arsenic-Reducing Bacteria and Genes Regulated by Lactate and Biochar during Arsenic Transformation in Flooded Paddy Soil. Environmental Science & Technology 2018; 52(1): 61-70. doi:10.1021/acs.est.7b03771 Qin W, Wang Y, Fang G, Liu C, Sui Y, Zhou D. Oxidation mechanism of As(III) in the presence of polyphenols: New insights into the reactive oxygen species. Chemical Engineering Journal 2016; 285: 69-76. doi:10.1016/j.cej.2015.09.095 Qu S, Kolodziej EP, Cwiertny DM. Phototransformation rates and mechanisms for synthetic hormone growth promoters used in animal agriculture. Environmental Science & Technology 2012; 46(24): 13202-13211. doi:10.1021/es303091c Said-Pullicino D, Cucu MA, Sodano M, Birk JJ, Glaser B, Celi L. Nitrogen immobilization in paddy soils as affected by redox conditions and rice straw incorporation. Geoderma 2014; 228-229: 44-53. doi:10.1016/j.geoderma.2013.06.020 Sarmiento AM, Oliveira V, Gómez-Ariza JL, Nieto JM, Sánchez-Rodas D. Diel cycles of arsenic speciation due to photooxidation in acid mine drainage from the Iberian Pyrite Belt (SW Spain). Chemosphere 2007; 66(4): 677-683. doi: 10.1016/j.chemosphere.2006.07.084 Seyfferth AL, McCurdy S, Schaefer MV, Fendorf S. Arsenic concentrations in paddy soil and rice and health implications for major rice-growing regions of Cambodia. Environmental Science & Technology 2014; 48(9): 4699-4706. doi:10.1021/es405016t

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Tanji KK, Gao S, Scardaci SC, Chow AT. Characterizing redox status of paddy soils with incorporated rice straw. Geoderma 2003; 114(3-4): 333-353. doi:10.1016/s0016-7061(03)00048-x Tareq SM, Maruo M, Ohta K. Characteristics and role of groundwater dissolved organic matter on arsenic mobilization and poisoning in Bangladesh. Physics and Chemistry of the Earth 2013; 58-60: 77-84. doi:10.1016/j.pce.2013.04.014 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(10): 5778-5786. doi:10.1021/acs.est.9b00538 Wang J, Chen J, Qiao X, Zhang YN, Uddin M, Guo Z. Disparate effects of DOM extracted from coastal seawaters and freshwaters on photodegradation of 2,4-Dihydroxybenzophenone. Water Research 2019; 151: 280-287. doi:10.1016/j.watres.2018.12.045 Wang Y, Xu J, Li J, Wu F. Natural montmorillonite induced photooxidation of As(III) in aqueous suspensions: roles and sources of hydroxyl and hydroperoxyl/superoxide radicals. Journal of Hazardous Materials 2013; 260: 255-262. doi:10.1016/j.jhazmat.2013.05.028 Wang Y, Xu J, Zhao Y, Zhang L, Xiao M, Wu F. Photooxidation of arsenite by natural goethite in suspended solution. Environmental Science and Pollution Research 2013; 20(1): 31-38. doi:10.1007/s11356-012-1079-6 Wang ZH, Chen CC, Ma WH, Zhao JC. Photochemical Coupling of Iron Redox Reactions and Transformation of Low-Molecular-Weight Organic MatterTransformation of Low-Molecular-Weight Organic Matter. The Journal of Physical Chemistry Letters 2012; 3: 2044-2051. doi:10.1021/jz3005333 Woods R, Kolthoff IM, Meehan EJ. Arsenic(IV) as an Intermediate in the Induced Oxidation of Arsenic(III) by the Iron(II)-Persulfate Reaction and the Photoreduction of Iron(III). I. Absence of Oxygen. Journal of the American Chemical Society 1963; 85: 2385-2390. doi: 10.1021/ja00899a010 Wu F, Deng N. Photochemistry of hydrolytic iron (III) species and photoinduced degradation. Chemosphere 2000; 41: 1137-1147. doi: 10.1016/S0045-6535(00)00024-2 Xu H, Li Y, Liu J, Du H, Du Y, Su Y, Jiang H. Photogeneration and steady-state concentration of hydroxyl radical in river and lake waters along middle-lower Yangtze region, China. Water Research 2020; 176: 115774. doi:10.1016/j.watres.2020.115774 Xu H, Li Y, Zhao L, Du H, Jiang H. Molecular weight-dependent heterogeneities in photochemical formation of hydroxyl radical from dissolved organic matters with different sources. Science of the Total Environment 2020; 725: 138402. doi:10.1016/j.scitotenv.2020.138402 Xu L, Zhao Z, Wang S, Pan R, Jia Y. Transformation of arsenic in offshore sediment under the impact of anaerobic microbial activities. Water Research 2011; 45(20): 6781-6788. doi:10.1016/j.watres.2011.10.041

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Yi Q, Bu L, Shi Z, Zhou S. Epigallocatechin-3-gallate-coated Fe3O4 as a novel heterogeneous catalyst of peroxymonosulfate for diuron degradation: Performance and mechanism. Chemical Engineering Journal 2016; 302: 417-425. doi:10.1016/j.cej.2016.05.025 Zeng C, Ji Y, Zhou L, Zhang Y, Yang X. The role of dissolved organic matters in the aquatic photodegradation of atenolol. Journal of Hazardous Materials 2012; 239-240: 340-347. doi:10.1016/j.jhazmat.2012.09.005 Zeng MX, Wang RF, Peng SQ,Zhang YJ, Cui Y, Shan XZ,Liao CZ,Tian YG. Summary of Returning Straw into Field of Main Agricultural Areas in China. Soil Science 2002;33: 336-339. doi:10.19336/j.cnki Zhang D, Yan S, Song W. Photochemically induced formation of reactive oxygen species (ROS) from effluent organic matter. Environmental Science & Technology 2014; 48(21): 12645-12653. doi:10.1021/es5028663 Zhao H, Sun B, Jiang L, Lu F, Wang X, Ouyang Z. Erratum to: How can straw incorporation management impact on soil carbon storage? A meta-analysis. Mitigation and Adaptation Strategies for Global Change 2014; 20(8): 1569-1569. doi:10.1007/s11027-014-9586-z Zhu H, Wu J, Huang D, Zhu Q, Liu S, Su Y, Li Y. Improving fertility and productivity of a highly-weathered upland soil in subtropical China by incorporating rice straw. Plant and Soil 2010; 331(1-2): 427-437. doi:10.1007/s11104-009-0263-z Zhou Y, Yao YL, Shi LZ, Chen JX, Zhang MK. Effects of Returning Zizania caduciflora Straw to Waterlogged Field on Migration and Transformation of Phosphorus in Soil-Water Interface. Acta Agriculturae Jiangxi 2018; 30(1): 22-26. doi:10.19386 /j.cnki.jxnyxb.2018.01.05 Zuo Y, Wang C, Van T. Simultaneous determination of nitrite and nitrate in dew, rain, snow and lake water samples by ion-pair high-performance liquid chromatography. Talanta 2006; 70(2): 281-285. doi:10.1016/j.talanta.2006.02.034 Table 1 Qualities of samples collected from straw derived dissolved organic matter (20 mg/L). DOMws DOMrs SUVA254 (L mg C-1 m-1)

1.05±0.03

0.6±0.01

E2/E3

2.45±0.31

2.75±0.42

SUVA280(L mg C-1 m-1)

0.98±0.01

0.56±0.03

NO3- (μM)

4.05±0.19

3.25±0.26

Fe3+ (μM)

0.3±0.05

0.29±0.02

Journal Pre-proof Figure Captions Fig.1. (a) The FTIR spectra of DOMws and DOMrs. (b) UV-Vis absorption of DOMws and DOMrs (20 mg C/L, 200-800 nm). (c) The fluorescence EEM of the DOMws. (d) The fluorescence EEM of the DOMrs Fig.2. Effect of DOMws (a) and DOMrs (b) concentration on the oxidation of As(III). Reaction condition: [As] = 100 μg/L, 25 ℃, pH=5.0.

oo

f

Fig.3. Free radical quenching studies, oxidation of As(III) in the DOMws (a) and DOMrs (b) solutions. Reaction condition: [S-DOM] = 40 mg/L, [MeOH] = 500 mM,

pr

[NBT] = 200 μM, [FFA] = 50 μM, [As] = 100 μg/L, 25 ℃, pH=5.0. (c) The

e-

concentrations of •OH accumulated in S-DOM solutions. Reaction condition:

Pr

[S-DOM] = 40 mg/L, [BA]=10 mM, 25 ℃, pH=5.0.(d) The concentrations of H2O2

pH=5.0.

al

formed in S-DOM solutions. Reaction condition: [S-DOM] = 40 mg/L, 25 ℃,

rn

Fig.4. Effect of pH on the oxidation of As(III) induced by the irradiation of DOMws

Jo u

(a) and DOMrs (b). Reaction condition: [S-DOM] = 40 mg/L, [As] = 100 μg/L, 25 ℃. Fig.5. Effect of NO3- on the oxidation of As(III) by S-DOM. Reaction condition: [S-DOM] = 40 mg/L, [As] = 100 μg/L, 25 ℃, pH=5.0. Fig.6. Effect of DOM on the oxidation of As(III) by the irradiation of NO3-. Reaction condition: [As] = 100 μg/L, [NO3-] = 0.8 mM, 25 ℃, pH=5.0. Fig.7. Effect of Fe(III) on the oxidation of As(III) by the irradiation of S-DOM. Reaction condition: [S-DOM] = 40 mg/L, [As] = 100 μg/L, 25 ℃, pH=5.0.

Journal Pre-proof Fig.1

rape straw

c

400

Ex/nm

Adsorbance/a.u

450

a

wheat straw

0 500 1000 1500 2000

350 300 250 200 200

4000 3600 3200 2800 2400 2000 1600 1200 800 400

Wavenumber/cm-1

350

400

450

500

550

f

350 300

e-

0.4

0 500 1000 1500 2000

pr

Ex/nm

0.6

d

oo

450

b

400

Abs

300

Em/nm

wheat straw rape straw

0.8

250

0.2

250

200

300

400

500

600

700

λ/nm

800

200 200

250

300

350

400

450

500

550

Em/nm

al

Fig.2

a

rn

1.0

0.7

C/C0

0.8

DOC=0 DOC=10 mg/L DOC=20 mg/L DOC=40 mg/L DOC=60 mg/L DOC=80 mg/L

0.6 0.5 0

1

b

1.0 0.9

Jo u

0.9

Ct/C0

Pr

0.0

0.8 0.7

DOC=0 DOC=10 mg/L DOC=20 mg/L DOC=40 mg/L DOC=60 mg/L DOC=80 mg/L

0.6 0.5

2 T(h)

3

4

0

1

2 T(h)

3

4

Journal Pre-proof Fig.3

a

0.9

0.9

0.8

0.8

0.7 As As+MeOH As+NBT As+FFA 1

0.5 2 T(h)

3

4

8

0

2.0

c

wheat straw rape straw

2 T(h)

3

4

d

wheat straw rape straw

H2O2(μM)

e-

1.2 0.8

Pr

4

.

OH/μM

1

1.6

6

2

0.4

1

2

T (h)

3

0

4

1

2 T (h)

rn

0

0.0

al

0

Jo u

Fig.4 1.0 0.9

a

0.7 pH=5 pH=6 pH=7 pH=8

0.5 0

b

0.8 0.7 pH=5 pH=6 pH=7 pH=8

0.6 0.5 1

2 T(h)

4

0.9

0.8

0.6

3

1.0

Ct/C0

Ct/C0

f

0

As As+MeOH As+NBT As+FFA

0.6

oo

0.5

0.7

pr

0.6

b

1.0

Ct/C0

Ct/C0

1.0

3

4

0

1

2 T(h)

3

4

Journal Pre-proof

pr

oo

f

Fig.5

Jo u

rn

al

Pr

e-

Fig.6

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Fig.7

Journal Pre-proof Declaration of competing interests The authors declare that they have no known competing financial interests or personal

Jo u

rn

al

Pr

e-

pr

oo

f

relationships that could have appeared to influence the work reported in this paper.

Journal Pre-proof

Jo u

rn

al

Pr

e-

pr

oo

f

Graphical abstract

Journal Pre-proof

Highlights 

Straw-derived dissolved organic matter (S-DOM) exhibited spectroscopic features.



Hydroxyl radicals dominated the photooxidation of As(III) mediated by S-DOM.



The oxidation efficiency of As(III) was inhibited in the presence of NO3− while

Jo u

rn

al

Pr

e-

pr

oo

f

enhanced in the presence of Fe(III).