Degradation of tri(2-chloroisopropyl) phosphate by the UV/H2O2 system: Kinetics, mechanisms and toxicity evaluation

Article abstract of DOI:10.1016/j.chemosphere.2019.124388

A photodegradation technology based on the combination of ultraviolet radiation with H₂O₂ (UV/H₂O₂) for degrading tri(chloroisopropyl) phosphate (TCPP) was developed. In ultrapure water, a pseudo-first order reaction was observed, and the degradation rate constant reached 0.0035 min^?1 (R² = 0.9871) for 5 mg L^?1 TCPP using 250 W UV light irradiation with 50 mg L^?1 H₂O₂. In detail, the yield rates of Cl^? and PO₄^3? reached 0.19 mg L^?1 and 0.58 mg L^?1, respectively. The total organic carbon (TOC) removal rate was 43.02%. The pH value of the TCPP solution after the reaction was 3.46. The mass spectrometric detection data showed a partial transformation of TCPP into a series of hydroxylated and dechlorinated products. Based on the luminescent bacteria experimental data, the toxicity of TCPP products increased obviously as the reaction proceeded. In conclusion, degradation of high concentration TCPP in UV/H₂O₂ systems may result in more toxic substances, but its potential application for real wastewater is promising in the future after appropriate optimization, domestication and evaluation.

Full text of DOI:10.1016/j.chemosphere.2019.124388

Accepted Manuscript
Degradation of tri(2-chloroisopropyl) phosphate by the UV/H O system: Kinetics,
2 2
mechanisms and toxicity evaluation
Huan He, Qiuyi Ji, Zhanqi Gao, Shaogui Yang, Cheng Sun, Shiyin Li, Limin Zhang
PII:
S0045-6535(19)31609-1
DOI:
https://doi.org/10.1016/j.chemosphere.2019.124388
Article Number: 124388
Reference:
CHEM 124388
To appear in: ECSN
Received Date: 24 March 2019
Revised Date: 15 July 2019
Accepted Date: 16 July 2019
Please cite this article as: He, H., Ji, Q., Gao, Z., Yang, S., Sun, C., Li, S., Zhang, L., Degradation of
tri(2-chloroisopropyl) phosphate by the UV/H O system: Kinetics, mechanisms and toxicity evaluation,
2 2
Chemosphere (2019), doi: https://doi.org/10.1016/j.chemosphere.2019.124388.
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Degradation of tri(2-chloroisopropyl) phosphate by the
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UV/H2O2 system: kinetics, mechanisms and toxicity evaluation
Huan He1, Qiuyi Ji1, Zhanqi Gao2, Shaogui Yang1 , Cheng Sun3, Shiyin Li1, Limin Zhang1
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1School of Environment, Nanjing Normal University, Nanjing, Jiangsu 210023, P.R. China
2State Environmental Protection Key Laboratory of Monitoring and Analysis for Organic Pollutants
in Surface Water, Environment Monitoring Center of Jiangsu Province, Nanjing 210036,
P.R. China
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3 State Key Laboratory of Pollution Control and Resources Reuse, School of Environment, Nanjing
University, Nanjing, Jiangsu 210023, P.R. China
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Abstract: A photodegradation technology based on the combination of ultraviolet radiation with H2O2 (UV/H2O2)
for degrading tri(chloroisopropyl) phosphate (TCPP) was developed. In ultrapure water, a pseudo-first order
reaction was observed, and the degradation rate constant reached 0.0035 min-1 (R2=0.9871) for 5 mg L-1 TCPP
using 250 W UV light irradiation with 50 mg L-1 H2O2. In detail, the yield rates of Cl- and PO43- reached 0.19 mg
L-1 and 0.58 mg L-1, respectively. The total organic carbon (TOC) removal rate was 43.02%. The pH value of the
TCPP solution after the reaction was 3.46. The mass spectrometric detection data showed a partial transformation
of TCPP into a series of hydroxylated and dechlorinated products. Based on the luminescent bacteria experimental
data, the toxicity of TCPP products increased obviously as the reaction proceeded. In conclusion, degradation of
high concentration TCPP in UV/H2O2 systems may result in more toxic substances, but its potential application
for real wastewater is promising in the future after appropriate optimization, domestication and evaluation.
Key words：TCPP, UV/H2O2, kinetics, mechanisms, toxic evaluation
Corresponding author. Tel.: +86 25 85891849, Fax: +86 25 85891849
E-mail addresses: yangsg@njnu.edu.cn (SG Yang)
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1. Introduction
Emerging contaminants (ECs) are defined as chemicals that have recently been detected in the
environment, which pose a significant risk to human and ecosystem health. The ECs mainly include
personal care products, pharmaceuticals, pesticides and disinfectants, etc. (Montes et al., 2015). An
important class of ECs are flame retardants (FRs). The materials processed by the FRs can
effectively prevent, delay or terminate the propagation of the flame when attacked by external fire
sources, thereby achieving the flame retarding effect. Phosphorus flame retardants (PFRs), which
have been used for over 150 years, can be divided into three main groups (Veen and Boer, 2012):
organophosphate esters (OPEs), phosphonates, and phosphinates. The existing studies are focused
mainly on tetrabromobisphenol A and other polybrominated diphenyl ethers (PBDEs) (Chow et al.,
2012; Chunyan et al., 2012; Guo et al., 2012; Huang et al., 2013; Cao et al., 2015). However, the
research data of organophosphorus (OPFRs) is very scarce (Antonopoulou et al., 2016).
OPEs are not chemically bound in materials and easily leach into the environment via abrasion,
volatilization and dissolution. As a result, OPEs have been frequently detected in the environment,
such as seawater and groundwater and increasingly in indoor environments (Andresen et al., 2004;
Axel et al., 2011). Tri(chloroisopropyl) phosphate (TCPP), one of chlorinated organophosphate
esters (Cl-OPEs), represents approximately 80% of the chlorinated OPFRs in Europe and is by
volume the most important OPFR (Bollmann et al., 2012). Recent studies have reported that TCPP
is among the most frequently detected emerging pollutants in wastewater effluents in EU at
concentration as high as 24 ꢀg L-1. TCPP has been also detected in surface water, ground water and
drinking water reaching concentrations ranging from few ng L-1 to few ꢀg L-1, even mg L-1 in
wastewater (Bollmann et al., 2012; Cristale et al., 2013; Jun et al., 2014). Physical, biological and
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chemical treatment methods have been used to remove the Cl-OPEs. Adsorbents such as modified
zeolites (Grieco and Ramarao, 2013) and carbon nanotubes (Yan and Jing, 2014) can effectively
adsorb chlorinated organophosphates in water, but cannot achieve the purpose of degradation or
mineralization of Cl-OPEs. The biological method has a low removal rate of the Cl-OPEs. Only
12.3% of tri(2-chloroethyl)phosphate (TCEP) and 11.8% of TCPP can be removed in the University
of Capetown (UCT) process (Pang et al., 2016). Among treatment methods, the advanced oxidation
processes (AOPs) in chemical treatment method are one of the most effective methods for
degrading Cl-OPEs (Watts and Linden, 2009).
The AOPs, including electrochemistry (Loffler et al., 2019), ozonation (Dar et al., 2019),
sonolysis (Choi et al., 2019), UV/H2O2 photolysis (Qiu et al., 2019), photocatalysis (Monteagudo et
al., 2019), and Fenton process (Rostamizadeh et al., 2019), are the most commonly used chemical
methods for water treatment. The potential application of ultraviolet-advanced oxidation processes
(UV-AOPs) to the degradation of OPEs has only begun in recent years. Yuan et al. (2015) have
found that UV/H2O2 was more efficient than ozonation for the degradation of OPEs in a municipal
secondary effluent. The UV/H2O2 process is a conventional advanced oxidation process, based on
the production of hydroxyl radicals (•OH) via the photolysis of H2O2. The hydroxyl radicals (•OH)
are extraordinarily reactive and can attack most organic molecules with very high rate constants
(Andreozzi et al., 1999). Thus, the hydroxyl radicals (•OH) can degrade rapidly and non-selectively
a wide range of organic pollutants in aquatic environment (Khataee et al., 2009). The quantum yield
of •OH production and molar absorption coefficient of H2O2 at 254 nm were 0.5 mol E-1 and 18.6
M-1cm-1, respectively (Morgan et al., 1988; Liao and Gurol, 1995). Hence, the UV/H2O2 process has
been confirmed to be effective in degrading organic pollutants in aquatic environments (Bledzka et
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al., 2010; Ghodbane and Hamdaoui, 2010; Pamela et al., 2010; Zhou et al., 2012).
The removal of OPEs in the UV/H2O2 system has been reported in the literature (Santoro et al.,
2010), but the bis(trimethylsilyl)trifluoroacetamide (BSTFA) derivatization and quantum
calculations are still unclear. Gas chromatography mass spectrometry (GC-MS) and nuclear
magnetic resonance are often used as means of mechanism analysis, but the identification of
intermediates requires verification by quantum calculations (Watts and Linden, 2008). Previous
studies have carried out research on low concentration Cl-OPEs, but there are few studies on high
concentration Cl-OPEs. There is still a knowledge gap on the detailed mechanisms and pathways
involving the degradation of TCPP using UV/H2O2, not to mention the environmental safety of their
degradation products. Besides, the degradation pathway of TCPP in the UV/H2O2 system has not
been reported yet and the toxicity of the intermediates and the toxicity of the degradation system
require further investigation.
The present study aims to degrade high concentration TCPP in the UV/H2O2 system and perform
the kinetics, mechanisms and toxicity analysis. Besides, it also aims to identify the toxic
intermediates of TCPP during its degradation. The intermediates were identified by GC–MS.
Quantum calculation was also carried out to ascertain the position of the TCPP molecule where the
oxidation was firstly initiated. The degradation pathway was estimated based on the intermediate
product. In addition, the toxicity of the intermediates was consulted and the toxicity of the
degradation system was evaluated by luminescent bacteria experiments.
2. Experimental section
2.1. Chemicals
The TCPP was purchased from Aldrich (Milwaukee, WI, USA). H2O2 (30%, v/v) was obtained
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from Fisher Company. HPLC-grade methanol, ethyl acetate, acetonitrile and dimethysulphoxide
(DMSO) were purchased from Tedian Company and used without further purification. The
luminescent bacteria Photobacterium phosphoreum T3 (P. phosphoreum, Strain Number CS233)
was obtained as freeze-dried reagents (0.5 g each bottle) from the Institute of Soil Science, Chinese
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Academy Sciences, Nanjing, China. They were stored at -20
and hydrated prior to testing.
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Ultrapure deionized water was obtained from a Milli-Q water purification system (Milli-Q system,
Millipore, Beldford, MA) and was used in the preparation of all the aqueous solution.
2.2. Experimental Procedures
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The degradation experiments were carried out in a photoreactor (XPA-7, Xujiang Power Plant,
Nanjing, China). XPA-7 multi-tube stirring reaction instrument (Fig. S2) includes light source,
quartz cold trap, quartz test tube, reaction vessel, multi-tube stirring device, rotating device, water
tank, micro water pump, light shield, etc. Samples can be magnetically stirred and evenly
illuminated in a test tube with a uniform rotation around the light source. The UV lamps (250 W)
were manufactured by Shanghai Yaming Lighting Co., Ltd., China. The emitted UV-light flux was
measured by an actinometer made by Beijing Normal University (Beijing, China). Solutions spiked
with 5 mg L-1 of target compound and 50 mg L-1 H2O2 (30%) were irradiated while continuously
mixed. The total solution volume for each exposure was 50 mL.
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2.3. Analytical methods
The residual TCPP was extracted from 1 mL of the UV-H2O2 treated solution with 1 mL of ethyl
acetate by a mixture of liquid and liquid mixture. The extracted analytes were then separated and
assayed by a 7890N gas chromatograph (Agilent Technologies, USA) equipped with a split/splitless
injector, HP-5 capillary column (30 m x 0.32 mm i.d., 0.25 ꢀm film thickness) and flame
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Photometric detector (FPD). The column temperature was set as follows: the initial oven
temperature was 80 °C (for 1 minute), the temperature was raised to 140 °C at a rate of 20 °C min-1
(for 2 min), and then increased at a rate of 4 °C min-1 up to 280 °C (for 6 min). The injector and
detector temperatures were set at 250 °C. Helium (99.999%) was used as a carrier gas at a constant
flow rate of 1.5 mL min-1 and nitrogen (99.999%) was used as a make-up gas at a flow rate of 20
mL min-1. Synthetic air (99.995%) and hydrogen (99.999%) were used as detector gases at flow
rates of 100 and 65 mL min-1, respectively.
Due to the complexity of the intermediate product, the Thermo Fisher Trace gas chromatograph
coupled to a Polaris Q ion trap mass spectrometer (GC/MS, Thermo Fisher, USA) with a DB-5
fused silica capillary column (30 m, 0.32 mm i.d., 0.25 mm film thickness) was used to analyze the
sample. Samples were extracted by SPE column Poly-Sery PSD prior to GC-MS analysis.
All SPE columns were sequentially adjusted with 5 mL of methanol and water at a flow rate of 1
mL min-1 prior to use. The loaded SPE column was then eluted with 5 mL acetonitrile / ethyl acetate
(1:1, V/V). The extracted solution was dried over anhydrous sodium sulfate and concentrated to 1
mL by rotary evaporation. After the solvent was purged with mild nitrogen, trimethylsilylation was
carried out with 0.2 mL of BSTFA at 60 °C for 15 h. The initial temperature of the column oven was
40 °C, and after maintaining at this temperature for 1 minute, it was then heated to 300 °C at a
heating rate of 6 °C min-1. Helium was used as a carrier gas. Mass spectrometry was performed in a
70 eV electron bombardment (EI) mode. Electron impact was used for ionization of the sample.
Some intermediates were identified by the National Institute of Standards and Technology (NIST)
library identification process.
2.4. Calculation of the Frontier electron density and bond dissociation enthalpies (BDEs)
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The ab initio molecular orbital (MO) calculations were carried out using Gaussian 03 program
(Gaussian, Inc.). Structures were fully optimized with the B3LYP/6-311+G* basis set at the level of
the density functional theory (DFT) for all calculations. Then, the Frontier electron densities (FEDs)
of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital
(LUMO) were calculated.
2.5. Toxicity measurements
For the acute toxicity tests, 200 mL of solution before or after reduction/oxidation treatment was
collected. The pH values of all samples were adjusted to 7.0 before the toxicity test. The water
samples were filtered through membrane filter with a porosity of 0.45 µm, and then passed through
a column with non-polar neutral resin (XAD-2). The constituents adsorbed on the column and the
filtered nanoparticles were eluted by methanol, acetone and dichloromethane. The elution was
concentrated to 1 mL by rotary evaporation, dried by the gentle nitrogen and then re-dissolved in 1
mL DMSO. Finally, the samples were stored at −18 ◦C in the dark. Prior to toxicity assessment, the
bacteria P. phosphoreum was reactivated in 1 mL 2.5% NaCl solution and stored in an ice water
bath. Subsequently, 0.2 mL of each treated sample and 10 µL reactivated bacteria were added to 2
mL of 3% NaCl solution. After being exposed to sample for 15 min at 15±1 °C, the
bioluminescence was measured by the DeltaTox Analyzer (SDI, USA). DMSO was used as solvent
control. Each degradation reaction sample of TCPP was run in duplicate set. Toxicity was expressed
as the luminescence inhibition ratio and it could be described as Eq. 1:
Sample intensity
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(Eq. 1)
Inhibitionrate (%) = (1 −
) ×100%
Control intensity
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3. Results and discussion
3.1. Performance of TCPP degradation by UV/H2O2 system
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Photolysis of H2O2 was the predominant mode of •OH formation. Hydroxyl radical, with its
relatively high redox potential (2.8 V), is often the oxidant of choice for engineered remediation of
waters pollutants. The potential for •OH formation in UV-irradiated water containing the oxidant
H2O2 has led to the design and implementation of UV/H2O2 for oxidation of unwanted organics at
full-scale water treatment plants. The results in Fig.S1 indicated that no obvious removal of the
TCPP was observed in the UV alone experiment, due to its poor UV absorbance properties in the
UV-C range (λ=200–300 nm). Therefore, at an initial concentration of 50 mg L-1, H2O2 was the only
significant photon absorber (λ=254 nm) in irradiated solutions. As shown in Fig.1, the degradation
of the TCPP approximately followed the pseudo-first-order reaction in kinetics under tested
conditions. The pseudo-first-order rate constant k was measured for the oxidation rate of TCPP,
which was 0.0035 min-1 (R2=0.9871).
TCPP is composed of carbon, hydrogen, oxygen, chlorine, and phosphorus elements. Therefore,
the final degradation products of TCPP should contain CO2, H+, Cl- and PO4 . The simplified
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oxidation pathway for TCPP in the UV/H2O2 system can be described as Eq. 2:
C9H18Cl3PO4 Oxidation→CO2 + H+ + Cl- + PO43− +Intermediates
(Eq. 2)
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The final product of TCPP in the UV/H2O2 system included Cl-, PO4 , CO2 and H+. The
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concentrations of Cl− and PO4 after photooxidation were measured to evaluate the degradation
efficiency of TCPP. Besides, the TOC and pH values were also measured.
3.2. TOC, pH, Cl− and PO43− analysis
3.2.1 TOC removal rate and pH values of TCPP aqueous solution in the UV/H2O2 system
TOC values before and after photooxidation were measured to evaluate the mineralization effect
of TCPP. A Shimadzu TOC-5000A TOC (combustion) analyzer was employed to evaluate the
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mineralization efficiency of target compounds. The removal rate of TOC can be expressed as TOC
(%). In ambient temperature, the reaction time from 0 to 900 min were examined. It can be seen
from Fig. 2A that the TOC removal increased with the increasing of reaction time from 0 to 900 min.
From 720 min to 900 min, the rate of increase in TOC removal rate was significantly faster. At 900
min, the removal rate of TOC reached up to 43.02%, indicating that the UV/H2O2 system had a
certain effect on the degradation of TCPP.
The pH values of the system were measured by suppression of the eluent and achieved with a
Dionex anion ASRS 300 electrolytic suppressor (4 mm) in the auto suppression external water
mode. The pH values after the reaction were depicted in Fig. 2B. From 0 to 180 min, the pH value
of TCPP began to show sharp drops, after that (from 180 min to 900 min) the pH value changed
unremarkably. The initial pH value of TCPP was 8.02 and final pH value was 3.46, indicating that
there was a large amount of H+ production in the UV/H2O2 system, further confirming that TCPP
was degraded.
3.2.2 Concentration of Cl− and PO43− of TCPP aqueous solution in the UV/H2O2 system
The final degradation products of TCPP are supposed to include Cl− and PO43−. The residual
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concentration of Cl− and PO4 can be employed to evaluate the degradation of organic
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contaminants. The concentration of Cl− and PO4 in the UV/H2O2 system can indicate the
degradation degree of TCPP. The formation of Cl− and PO43− in the UV/H2O2 system was analyzed
by a Dionex ion chromatograph (IC, Dionex model ICS 1000) equipped with a dual-piston (in
series) pump, a Dionex IonPac AS11-HC analytical column (4 mm, 250 mm) and a Dionex DS6
conductivity detector.
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From Fig. 2C and 2D, it is obvious that the concentration of Cl- and PO4 increases with the
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increase of the time from 0 to 900 min. The theoretical concentration of Cl- and PO43- was 1.63 mg
L-1 and 1.45 mg L-1, respectively. The formation concentration of Cl- and PO43- was 0.19 mg L-1 and
0.58 mg L-1. That is, the degradation rate of Cl- and PO43- was 11.7% and 40%. The low degradation
rate of Cl means the formation of chlorine-containing compounds, which may cause the solution to
be highly toxic after degradation. The results obtained may also be related to the bond energy.
3.3. Calculation of the frontier electron densities (FEDs) and bond dissociation enthalpies
(BDEs)
The ab initio molecular orbital (MO) calculations were carried out using Gaussian 03 program
(Gaussian, Inc.). Structures were fully optimized with the B3LYP/6-311+G* basis set at the level of
the density functional theory (DFT) for all calculations. Then, the FEDs of the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) were calculated.
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The values of FEDHOMO + FEDLUMO were obtained to predict the reaction sites for radical attack.
The C-H BDEs and O-H BDEs were also calculated to predict the reaction sites for abstracting
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hydrogen reaction initiated by hydroxyl radical. From Table 1, the larger the value of 2FEDHOMO
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the higher the density of the electron cloud, and the easier it is to be attacked by •OH, such as C9
(0.344), C15 (0.591) and Cl 16 (0.349). The larger the value of FEDHOMO2 + FEDLUMO2, the stronger
the activity of the reaction, which means that it is unstable and prone to reaction, such as P1 (0.888).
From Table 2, the smaller the bond energy, the more unstable it is, such as P1-O8 (0.6216) and
C9-C15 (0.6844).
3.4. Degradation pathways of TCPP
The degradation of TCPP mainly included two pathways (Fig. 3). The first pathway included 4
routes. Route I was an •OH addition reaction and a hydrogen extraction reaction to form
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1-chloropropan-2-ol. In route II, Compound 1 was produced by 1-chloropropan-2-ol with
dehydration. Compound 2 was generated by the •OH addition reaction, oxidized to Compound 3,
and further oxidized to Compound 4. Compound 7 was produced by 1-chloropropan-2-ol with
hydrogen abstraction. Compound 5 was generated by hydrogen extraction reaction and Compound
6 was further generated by •OH addition in route III. Route IV generated oxygen by oxidation of
H2O2 and generated Compound 8 by the addition reaction of •OH. The second pathway generated
1-chloropropan-2-yl dihydrogen phosphate by the addition reaction of •OH and H2O, and generated
Compound 11 by attacking C11-Cl 12 and C15-Cl 16 by •OH. 1-chloropropan-2-yl dihydrogen
phosphate generated Compound 9 and Compound 10 by attacking P1-O3 and C5-Cl 6 by •OH,
respectively. From Table 3, the LC50 of Compound 1 is 221 mg L-1, which is much more toxic than
TCPP (LD50=1500 mg kg-1, Wikipedia). Since the pH value was adjusted to 7.0 before the toxicity
test, the effect of hydrogen ions can be ignored. According to the removal rate of the TOC (Fig. 2A),
it can be known that about 57% of the organic molecules were not converted to CO2. From the
calculation of the theoretical and actual values of chloride ions (Fig. 2C) and the degradation rate of
TCPP (Fig. 1), it can be inferred that the intermediates produced chlorine-containing compounds.
When luminescent bacteria are used to detect toxicity, a high concentration of salt must be added to
the test system to maintain their normal survival. Therefore, an increase in the concentration of
chloride ions (Fig. 2C) did not affect the toxicity test. Hence, the toxicity was the result of a
combination of various products or components in the degradation process.
3.5. Toxicity evaluation
The luminescent bacteria toxicity test can effectively detect the acute toxicity of intermediate
products. When these bacteria were in a toxic environment, the light they emit would be suppressed.
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The toxicity of the sample can be quickly and accurately tested according to the change in light
intensity, and the potential toxic substances can be directly detected. That is to say, the higher the
luminescence inhibition rate, the greater the toxicity of the aqueous solution sample. It can be seen
from Fig.4 that as the reaction time increases, the luminescence inhibition rate of the TCPP diluted
20 times and diluted 100 times in the system gradually increases, that is, the toxicity of intermediate
products gradually increases. TCPP has less toxicity studies, but its acute toxicity is smaller than
TCEP, so it has been used as a substitute for TCEP. The LD50 of TCPP is 1500 mg kg-1 and the LC50
of Compound 1 is 221 mg L-1. The intermediate product Compound 1 and other compounds with
unknown toxicity produced by degradation may be the main cause of high toxicity. Among the
detected intermediates, Compound 1 was the only chlorine-containing compound. Since the pH was
adjusted to 7.0 before the toxicity test, the inhibitory effect of H+ on the luminescent bacteria can be
excluded. Chloride ion was a salt necessary for luminescent bacteria, so it did not inhibit the
illumination intensity. Based on the results of incomplete removal of the TOC, it was concluded that
Compound 1 was able to influence the toxicity of the solution to a large extent. As is known to all,
Cl-containing compounds are highly toxic. Thus, in order to reduce the toxicity of aqueous solution,
how to remove Cl-containing compounds from water should be taken into consideration in the next
step. For example, a nanofiltration reverse osmosis unit can be added to the UV/H2O2 system. Yujia
et al. (2019) have found that the early stage products have lower toxicity than TCEP (initial
concentration was 3.51 ꢀM) or their further small molecule products with 185 nm vacuum
ultraviolet based on the toxicology analysis including reactive oxygen species and apoptosis of
Escherichia coli. Based on the proteomics data at molecular and metabolic network levels, the
toxicity of TCEP (initial concentration was 3.5 ꢀM) products was reduced obviously as the reaction
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proceeded (Liu et al., 2018), which was different from the research results of this paper. The main
reason may be that the initial concentration of TCPP in this paper was high (5 mg L-1), the reaction
time was not long enough, so the point of toxicity reduction has not yet been reached.
4. Conclusions
The degradation rate of 5 mg L-1 TCPP in UV/H2O2 system can reach 96% in 900 min. The
degradation of TCPP using UV/H2O2 followed a pseudo-first order reaction with a k of 0.0035
min-1 (R2=0.9871) and •OH was confirmed to be the dominating active radical species. As the
reaction proceeded, TCPP was transformed to several hydroxylated and dechlorinated products.
Based on the luminescent bacteria experimental data, the toxicity of TCPP products was increased
obviously as the reaction proceeded. In conclusion, degradation TCPP at a high concentration (5 mg
L-1) in UV/H2O2 systems may result in more toxic substances, but its potential application for real
wastewater is promising in the future after appropriate optimization, domestication and evaluation.
For example, a nanofiltration reverse osmosis unit can be introduced to the UV/H2O2 system.
Acknowledgments
This research was supported jointly by the National Nature Science Foundation of China (No.
21777067), the Six Talent Peaks Project in Jiangsu Province (No. JNHB-105), National water
pollution control and treatment technology major special subject (No. 2017ZX07202004), the Open
Fund of the State Environmental Protection Key Laboratory of Wetland Ecology and Vegetation
Restoration, Northeast Normal University (No. 130028903) and Introducing Talent Research
Start-up Project of Nanjing Normal University.
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References
Andreozzi, R., Caprio, V., Insola, A., Marotta, R., 1999. Advanced oxidation processes (AOP) for
water purification and recovery. Catal. Today 53, 51-59.
Andresen, J.A., Grundmann, A., Bester, K., 2004. Organophosphorus flame retardants and
plasticisers in surface waters. Sci. Total Environ. 332, 155-166.
Antonopoulou, M., Karagianni, P., Konstantinou, I.K., 2016. Kinetic and mechanistic study of
photocatalytic degradation of flame retardant Tris (1-chloro-2-propyl) phosphate (TCPP). Appl.
Catal. B-Environ. 192, 152-160.
Axel, M.L., Zhiyong, X., Armando, C., Renate, S., Ralf, E., 2011. Organophosphorus flame
retardants and plasticizers in the atmosphere of the North Sea. Environ. Pollut. 159,
3660-3665.
Bledzka, D., Gryglik, D., Olak, M., Gebicki, J.L., Miller, J.S., 2010. Degradation of n-butylparaben
and 4-tert-octylphenol in H2O2/UV system. Radiat. Phys. Chem. 79, 409-416.
Bollmann, U.E., Möller, A., Xie, Z., Ebinghaus, R., Einax, J.W., 2012. Occurrence and fate of
organophosphorus flame retardants and plasticizers in coastal and marine surface waters. Water
Res. 46, 531-538.
Cao, M., Wang, P., Ao, Y., Chao, W., Hou, J., Jin, Q., 2015. Photocatalytic degradation of
tetrabromobisphenol A by a magnetically separable graphene–TiO2 composite photocatalyst:
Mechanism and intermediates analysis. Chem. Eng. J. 264, 113-124.
Choi, C.H., Ko, D.H., Park, B., Choi, Y., Choi, W., Kim, D.P., 2019. Air-water interfacial fluidic
sonolysis in superhydrophobic silicon-nanowire-embedded system for fast water treatment.
Chem. Eng. J. 358, 1594-1600.
14

ACCEPTED MANUSCRIPT
Chow, K.L., Man, Y.B., Zheng, J.S., Liang, Y., Tam, N.F.Y., Wong, M.H., 2012. Characterizing the
optimal operation of photocatalytic degradation of BDE-209 by nano-sized TiO2. J. Environ.
Sci. 24, 1670-1678.
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
Chunyan, S., Jincai, Z., Hongwei, J., Wanhong, M., Chuncheng, C., 2012. Photocatalytic
debromination of preloaded decabromodiphenyl ether on the TiO2 surface in aqueous system.
Chemosphere 89, 420-425.
Cristale, J., García, V.A., Barata, C., Lacorte, S., 2013. Priority and emerging flame retardants in
rivers: Occurrence in water and sediment, Daphnia magna toxicity and risk assessment.
Environ. Int. 59, 232-243.
Dar, A.A., Wang, X.H., Wang, S.Y., Ge, J.L., Shad, A., Ai, F.X., Wang, Z.Y., 2019. Ozonation of
pentabromophenol in aqueous basic medium: Kinetics, pathways, mechanism, dimerization
and toxicity assessment. Chemosphere 220, 546-555.
Ghodbane, H., Hamdaoui, O., 2010. Decolorization of antraquinonic dye, C.I. Acid Blue 25, in
aqueous solution by direct UV irradiation, UV/H2O2 and UV/Fe(II) processes. Chem. Eng. J.
160, 226-231.
Grieco, S.A., Ramarao, B.V., 2013. Removal of TCEP from aqueous solutions by adsorption with
zeolites. Colloid Surface A. 434, 329-338.
Guo, Y., Lou, X., Xiao, D., Xu, L., Wang, Z., Liu, J., 2012. Sequential reduction–oxidation for
photocatalytic degradation of tetrabromobisphenol A: Kinetics and intermediates. J. Hazard.
Mater. 241-242, 301-306.
Huang, A.Z., Wang, N., Lei, M., Zhu, L.H., Zhang, Y.Y., Lin, Z.F., Yin, D.Q., Tang, H.Q., 2013.
Efficient Oxidative Debromination of Decabromodiphenyl Ether by TiO2-Mediated
15

ACCEPTED MANUSCRIPT
Photocatalysis in Aqueous Environment. Environ. Sci. Technol. 47, 518-525.
Jun, L., Nanyang, Y., Beibei, Z., Ling, J., Meiying, L., Mengyang, H., Xiaowei, Z., Si, W., Hongxia,
Y., 2014. Occurrence of organophosphate flame retardants in drinking water from China. Water
Res. 54, 53-61.
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
Khataee, A.R., Vatanpour, V., Ghadim, A.R.A., 2009. Decolorization of C.I. Acid Blue 9 solution by
UV/Nano-TiO2, Fenton, Fenton-like, electro-Fenton and electrocoagulation processes: A
comparative study. J. Hazard. Mater. 161, 1225-1233.
Liao, C.H., Gurol, M.D., 1995. Chemical oxidation by photolytic decomposition of hydrogen
peroxide. Environ. Sci. Technol. 29, 3007-3014.
Liu, J., Ye, J., Chen, Y., Li, C., Ou, H., 2018. UV-driven hydroxyl radical oxidation of
tris(2-chloroethyl) phosphate: Intermediate products and residual toxicity. Chemosphere 290,
225-233.
Loffler, T., Clausmeyer, J., Wilde, P., Tschulik, K., Schuhmann, W., Ventosa, E., 2019. Single entity
electrochemistry for the elucidation of lithiation kinetics of TiO2 particles in non-aqueous
batteries. Nano Energy 57, 827-834.
Monteagudo, J.M., Duran, A., San Martin, I., Carrillo, P., 2019. Effect of sodium persulfate as
electron acceptor on antipyrine degradation by solar TiO2 or TiO2/rGO photocatalysis. Chem.
Eng. J. 364, 257-268.
Montes, N., Otero, M., Coimbra, R.N., Méndez, R., Martínvillacorta, J., 2015. Removal of
tetracyclines from swine manure at full-scale activated sludge treatment plants. Environ.
Technol. 36, 1966-1973.
Morgan, M.S., Trieste, P.F.V., Garlick, S.M., Mahon, M.J., Smith, A.L., 1988. Ultraviolet molar
16

ACCEPTED MANUSCRIPT
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
absorptivities of aqueous hydrogen peroxide and hydroperoxyl ion. Anal. Chim. Acta 215,
325-329.
Pamela, C.A., Mohamed Gamal, E.D., Smith, D.W., 2010. Degradation of bromoxynil and
trifluralin in natural water by direct photolysis and UV plus H2O2 advanced oxidation process.
Water Res. 44, 2221-2228.
Pang, L., Yang, P.J., Zhao, J.H., Zhang, H.Z., 2016. Comparison of wastewater treatment processes
on the removal efficiency of organophosphate esters. Water Sci. Technol. 74, 1602-1609.
Qiu, W.H., Zheng, M., Sun, J., Tian, Y.Q., Fang, M.J., Zheng, Y., Zhang, T., Zheng, C.M., 2019.
Photolysis of enrofloxacin, pefloxacin and sulfaquinoxaline in aqueous solution by UV/H2O2,
UV/Fe(II), and UV/H2O2/Fe(II) and the toxicity of the final reaction solutions on zebrafish
embryos. Sci. Total Environ. 651, 1457-1468.
Rostamizadeh, M., Jalali, H., Naeimzadeh, F., Gharibian, S., 2019. Efficient Removal of Diclofenac
from Pharmaceutical Wastewater Using Impregnated Zeolite Catalyst in Heterogeneous Fenton
Process. Phys. Chem. Res. 7, 37-52.
Santoro, D., Raisee, M., Moghaddami, M., Ducoste, J., Sasges, M., Liberti, L., Notarnicola, M.,
2010. Modeling Hydroxyl Radical Distribution and Trialkyl Phosphates Oxidation in UV-H2O2
Photoreactors Using Computational Fluid Dynamics. Environ. Sci. Technol. 44, 6233-6241.
Veen, I.V.D., Boer, J.D., 2012. Phosphorus flame retardants: Properties, production, environmental
occurrence, toxicity and analysis. Chemosphere 88, 1119-1153.
Watts, M.J., Linden, K.G., 2008. Photooxidation and subsequent biodegradability of recalcitrant
tri-alkyl phosphates TCEP and TBP in water. Water Res. 42, 4949-4954.
Watts, M.J., Linden, K.G., 2009. Advanced Oxidation Kinetics of Aqueous Trialkyl Phosphate
17

ACCEPTED MANUSCRIPT
374
375
376
377
378
379
380
381
382
383
384
385
Flame Retardants and Plasticizers. Environ. Sci. Technol. 43, 2937-2942.
Yan, W., Jing, C., 2014. Sorption behavior of organophosphate esters on carbon nanotubes with
different surface oxidation. Environ. Chem. 33, 1692-1699.
Yuan, X., Lacorte, S., Cristale, J., Dantas, R.F., Sans, C., Esplugas, S., Qiang, Z., 2015. Removal of
organophosphate esters from municipal secondary effluent by ozone and UV/H2O2 treatments.
Sep. Purif. Technol. 156, 1028-1034.
Yujia, C., Jinshao, Y., Ya, C., Han, H., Hongling, Z., Huase, O., 2019. Degradation kinetics,
mechanism and toxicology of tris(2-chloroethyl) phosphate with 185 nm vacuum ultraviolet.
Chem. Eng. J. 356, 98-106.
Zhou, C., Gao, N., Deng, Y., Chu, W., Rong, W., Zhou, S., 2012. Factors affecting ultraviolet
irradiation/hydrogen peroxide (UV/H₂O₂) degradation of mixed N-nitrosamines in water. J.
Hazard. Mater. 231-232, 43-48.
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Figure Captions
Fig.1. The degradation efficiency and kinetics of TCPP from 0 to 900 min in the
UV/H2O2 system (CTCPP= 5 mg L-1, CH2O2=50 mg L-1, PUV=250 W)
3−
Fig.2. The (A) TOC removal (B) pH values (C) Cl− concentration and (D) PO4
concentration of TCPP from 0 to 900 min in the UV/H2O2 system (CTCPP= 5 mg L-1,
CH O2=50 mg L-1, PUV=250 W)
2
Fig.3. Two pathways of TCPP (A and B)
Fig.4. Luminescence inhibition rate of degraded TCPP for 20 times diluted and 100
times diluted

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Table 1
The frontier electron densities and bond dissociation enthalpies
2
FEDHOMO
+
2
2
2
Atom
FEDHOMO
FEDLUMO
2FEDHOMO
2
FEDLUMO
0.888
0.147
0.273
0.180
0.371
0.259
0.414
0.147
0.185
0.084
0.496
0.344
0.028
0.043
0.321
0.180
0.008
P1
O2
0.010
0.007
0.006
0.001
0.001
0.000
0.001
0.106
0.172
0.001
0.000
0.000
0.000
0.002
0.295
0.174
0.007
0.878
0.140
0.267
0.179
0.370
0.259
0.412
0.041
0.013
0.083
0.496
0.344
0.028
0.041
0.025
0.006
0.001
0.021
0.014
0.011
0.001
0.002
0.001
0.003
0.212
0.344
0.002
0.001
0.000
0.000
0.004
0.591
0.349
0.013
O3
C4
C5
Cl 6
O7
O8
C9
C10
C11
Cl 12
C13
C14
C15
Cl 16
C17

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Table 2
Bond energy in TCPP
Bonds
Bond energy
1.5388
0.8370
0.8192
0.6216
0.9151
0.9787
0.9395
1.0036
0.9066
0.9793
0.9435
1.1589
0.6844
0.9685
0.9685
1.0041
0.9685
P1-O2
P1-O3
P1-O7
P1-O8
O3-C4
C4-C5
C5-Cl 6
C4-C13
O7-C10
C10-C11
C11-Cl 12
O8-C9
C9-C15
C15-Cl 18
C9-Cl 17
C10-C14
C15-Cl 16

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Table 3
The intermediate products of TCPP in the UV/H2O2 system
No
.
tR
Toxicity LD50
(Rat,oral)
Name
EI-MS spectrum ions
Possible structure
(min)
41 (999); 39 (741); 76
(390); 38 (153); 78
221 mg L-1
(LC50, mouse,
inhalation)
1
8.08
(Z)-1-chloroprop-1-ene
(128); 40 (114); 37 (110);
49 (73); 75 (51uk); 27
(50)|
207 (999); 147 (816); 298
(762); 73 (611); 283
(237); 208 (209); 299
(196); 209 (150); 135
(139); 133 (133)
2
8.63
Propane-1,2-diol
20000 mg kg-1
73 (999); 117 (696); 147
(691); 45 (182); 75 (142);
191 (126); 66 (122); 148
(112); 190 (99); 74 (92)
147 (999); 73 (924); 148
(165); 45 (150); 74 (88);
149 (84); 66 (80); 72 (69);
190 (65); 59 (58)
2-hydroxypropanoic
acid
3
9.85
3543 mg kg-1
4
9.19
Oxalic acid
7500 mg kg-1

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99 (999); 125 (682); 43
(354); 41 (183); 141
NA
5
26.72
Triisopropyl phosphate
(160); 45 (153); 27 (87);
123 (76); 42 (74); 39 (70)
99 (999); 125 (585); 41
O
P
Diisopropyl hydrogen
phosphate
(478); 43 (337); 42 (287);
O
OH
6
19.06
NA
91 (283); 65 (155); 45
O
(103); 40 (90); 139 (84)
147 (999); 75 (864); 73
(745); 45 (301); 117
(265); 43 (249); 131
5045 mg kg-1
7
7.41
Propan-2-ol
(169); 133 (163); 148
(145); 59 (143)
207 (999); 147 (816); 298
(762); 73 (611); 283
8
8.96
Phosphorous acid
NA
(237); 208 (209); 299
(196); 209 (150); 135
(139); 133 (133)
299 (999); 73 (464); 300
(252); 314 (184); 301
(132); 45 (112); 133 (84);
9
14.62
Phosphoric acid
1530 mg kg-1

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211 (64); 75 (52); 147 (52)
73 (999); 18 (601); 299
(441); 256 (220); 75
1-hydroxypropan-2-yl
dihydrogen phosphate
10 20.04
NA
(184); 211 (181); 117
(157); 45 (145); 17 (138);
227 (133)|
73 (999); 131 (267); 227
(204); 211 (199); 75
(188); 130 (184); 285
(160); 299 (152); 117
(130); 115 (118)
Bis(1-hydroxypropan-2-
yl) hydrogen phosphate
11 23.20
NA
*Most of the toxicity data were obtained from Wikipedia (http://en.wilipedia.org/wiki/); NA means the
toxicity data are not available.

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3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
1.0
0.8
0.6
0.4
0.2
0.0
0
200 400 600 800 1000
Time (min)
0
200
400
600
800
1000
Time (min)
Fig.1. The degradation efficiency and kinetics of TCPP from 0 to 900 min in the UV/H2O2 system (CTCPP= 5 mg
L-1, CH 2=50 mg L-1, PUV=250 W)
2
O

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50
40
30
20
10
0
TOC
8
7
6
5
4
3
pH
A
B
0
200
400
Time (min)
600
800
Cl-
1000
0
200
400
Time (min)
600
800
1000
0.6
0.5
0.4
0.3
0.2
0.1
0.0
PO43-
0.20
0.15
0.10
0.05
0.00
C
D
0
200
400
600
800
1000
0
200
400
600
800
1000
Time (min)
Time (min)
Fig.2. The (A) TOC removal (B) pH values (C) Cl− concentration and (D) PO43− concentration of TCPP from 0 to
900 min in the UV/H2O2 system (CTCPP= 5 mg L-1, CH 2=50 mg L-1, PUV=250 W)
2
O

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(A)
(B)
Fig.3. Two pathways of TCPP (A and B)

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20 times diluted
100 times diluted
100
80
60
40
20
0
0
200
400
600
800
1000
Time (min)
Fig.4. Luminescence inhibition rate of degraded TCPP for 20 times diluted and 100 times diluted