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Natural Porphyrins Accelerating the Phototransformation of Benzo[a]pyrene in Water Lijuan Luo, Zhengyu Xiao, Baowei Chen, Fengshan Cai, Ling Fang, Li Lin, and Tiangang Luan Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b05854 • Publication Date (Web): 21 Feb 2018 Downloaded from http://pubs.acs.org on February 22, 2018

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Environmental Science & Technology

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Natural Porphyrins Accelerating the

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Phototransformation of Benzo[a]pyrene in Water

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Lijuan Luo†,‡, Zhengyu Xiao§, Baowei Chen§, Fengshan Cai†, Ling Fang‖, Li Lin†,

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Tiangang Luan†,*

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†

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Guangzhou 510275, China

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‡

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Chinese Academy of Science, Guangzhou 510640, China

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§

State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University,

State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry,

South China Sea Resource Exploitation and Protection Collaborative Innovation Center,

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School of Marine Sciences, Sun Yat-sen University, Guangzhou 510275, China

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‖

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510275, China

Instrumental Analysis and Research Center, Sun Yat-sen University, Guangzhou

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Abstract Phototransformation is one of the most important transformation pathways of organic

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contaminants in the water environment. However, how active compounds enable and

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accelerate the phototransformation of organic pollutants remains to be elucidated. In this

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study, the phototransformation of benzo[a]pyrene (BaP, the first class “human

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carcinogens”) by various natural porphyrins under solar irradiation was investigated,

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including chlorophyll a, sodium copper chlorophyllin, hematin, cobalamin and

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pheophorbide a. Transformation efficiency of BaP varied considerably with chemical

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stabilities of the porphyrins. Porphyrins with a lower stability displayed higher BaP

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transformation efficiencies. BaP transformation had a significant positive correlation with

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the production of singlet oxygen. Identical phototransformation products of BaP were

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observed for all investigated porphyrins, and the main products were identified as BaP-

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quinones, including BaP-1,6-dione, BaP-3,6-dione and BaP-6,12-dione. The mechanism

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of natural porphyrins accelerating the BaP phototransformation in water was proposed to

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proceed via the photocatalytic generation of singlet oxygen resulting in the

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transformation of BaP to quinones.

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Keywords: Chlorophyll; Natural Porphyrins; Benzo[a]pyrene; Phototransformation;

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Singlet oxygen

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2 Environment ACS Paragon Plus

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Introduction

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Benzo[a]pyrene (BaP), one of the polycyclic aromatic hydrocarbons(PAHs) containing

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five fused benzene rings, is widespread in air, water and soil in significant amounts1-2 and

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is included in the US-EPA priority pollutant list.3 On account of the potent mutagenic and

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carcinogenic toxicities, BaP was ranked as the first class “human carcinogens” in the

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World Health Organization (WHO) International Agency for Research on Cancer report.4

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It is a well-studied member of the PAH family and serves as a model compound for

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understanding the degradation of PAHs.5

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BaP can be degraded through either direct or sensitized photochemical reactions.6-7 It

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can absorb surface solar radiation, allowing for the possibility of direct

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photodegradation.8 Moreover, photocatalysis is one of the most attractive methods for

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BaP degradation from the viewpoint of solar energy utilization.9 Our previous study

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found that chlorophyll in green microalgae cells can enhance the phototransformation of

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BaP under simulated solar irradiation in water.10 Chlorophyll is the photosynthetic

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pigment necessary for the photosynthesis in plants, algae and cyanobacteria, which is

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abundant in environments.

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The basic structure of the chlorophyll molecule contains a porphyrin ring coordinated

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to a central metal atom. Many compounds have a similar structure to chlorophyll, such as

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pheophorbide a, hematin, sodium copper chlorophyllin and colalamin, denoted as

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porphyrins. These compounds are different in the metal ions in the center, as shown in

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Figure S1. They are considered natural porphyrins due to natural sources in the

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environment, e.g., sodium copper chlorophyllin is derived from alkaline hydrolysis of

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chlorophyll, where the magnesium atom is replaced with copper. Pheophorbide a, a

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photoproduct of chlorophyll a, lacks the phytyl side chain and central magnesium atom.

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Hematin is abundant in living animal’s blood. Cobalamin, also called vitamin B12, a

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cobalt porphyrin, could be synthetized by algae and bacteria.11 These porphyrin

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compounds exist in natural water because they enter into environmental systems with the

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death of plants or animals. Herein, chlorophyll a is the most common porphyrin in the

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aquatic environment, which is usually used to monitor water quality. The concentration

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of chlorophyll a was up to be 434.3 mg m-3 during an algal bloom.12

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Studies on the photocatalytic degradation of organic pollutants with porphyrins were

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much reported,13-14 which were mainly focused on the modification and preparation of

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porphyrins.15-16 However, the effect of natural porphyrins on the photocatalytic

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degradation of PAHs in natural environments has not been deeply explored in the

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literature. The fate of BaP in the natural environment remains to be understood, in

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particular in the presence of porphyrins from natural sources. The main objective of this

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study was to understand the roles of natural porphyrins in the phototransformation of BaP,

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and elucidate the phototransformation mechanism of BaP induced by porphyrins under

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simulated solar irradiation in water. The effect of environmental parameters, such as pH

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value, salinity, dissolved organic matters (DOM) on the BaP phototransformation process

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containing porphyrins were also investigated.

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Materials and Methods

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Chemicals. Standards of BaP (99.6%), acetone (99.5%), methanol (≥99.9%),

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benzene (99.8%), phenol (98%) and furfuryl alcohol (FFA, 97.5%) were obtained from

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Sigma-Aldrich (St. Louis, MO, USA). Benzo[a]pyrene D12 (BaP-D12, 99%) was

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obtained from Dr. Ehrenstorfer (Germany). Chlorophyll a (98.1%) was purchased from

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Wako Pure Chemical Industries, Ltd. (Japan). Cobalamin (>95.0%) was purchased from

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Tokyo chemical industry Co., Ltd. (Japan). Hematin (97%) was purchased from Alfa

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Aesar Chemicals Co., Ltd. (China). Sodium copper chlorophyllin was made in CNW,

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China. Pheophorbide a was from J&K Scientific Ltd. (China). Six transformation

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products of BaP, 1-hydroxybenzo[a]pyrene (1-OH-BaP, >96%), 3-

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hydroxybenzo[a]pyrene (3-OH-BaP, >99%), benzo[a]pyrene-cis-4,5-dihydrodiol (BaP-

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cis-4,5-diol, >99%), benzo[a]pyrene-1,6-dione (BaP-1,6-dione, >99%), benzo[a]pyrene-

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3,6-dione (BaP-3,6-dione, >99%) and benzo[a]pyrene-6,12-dione (BaP-6,12-dione, >99%)

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were supplied by Middlewest Research Institute (NCI Chemical Resource, Kansas, MO,

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USA). Ethyl acetate (99.8%), sodium chloride and anhydrous sodium sulfate were

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provided by Farce Chemical Supplies (China). High-purity water was supplied by a Milli-

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Q water system (Millipore, Eschborn, Germany).

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The stock solutions of chlorophyll a and pheophorbide a were prepared by dissolving

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the appropriate amounts of chlorophyll a and pheophorbide a in 90% ethanol (v/v) with

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concentrations of 200 and 1000 mg L-1, respectively, and stored in the dark at 4 °C. For

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sodium copper chlorophyllin and cobalamin, stock solutions were prepared by dissolving

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appropriate amounts of solid powder in Milli-Q water at a concentration of 1000 mg L-1.

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The hematin solution was prepared with 0.1 mol L-1 NaOH at a concentration of 1000 mg

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L-1.

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Photoreaction procedure. The photoreactions were performed under white light

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irradiation at a light intensity of 50 µmol photons s-1 m-2, which was provided by a series

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of cool white fluorescent lamps. The spectrum is from 310 to 750 nm in the wavelength,

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resembling the solar spectrum. The pH value of the reaction system was adjusted using

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0.1 mol L−1 NaOH and 0.1 mol L−1 HCl, and was determined using a pH meter (Sartorius

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PB-10, Germany). The salinity of the solutions was adjusted with 5 mol L−1 NaCl. A

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series of 250 mL conical flasks were prepared, and 100 mL of sterile water was added

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into each flask. The stock solution of BaP was spiked, and the initial concentration was

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1.0 mg L-1. The solutions of porphyrins were added at a concentration of 1.0 mg L-1.The

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flasks without porphyrins were used as the control. The flasks were then shaken on a 6


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rotary shaker at 160 rpm at 22 ± 2 °C. Triplicate flasks from each of the treatments were

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retrieved at different time intervals, and the residual amounts of BaP and the

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transformation products were determined.

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BaP extraction and analysis. BaP was extracted with ethyl acetate by liquid-

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liquid extraction according to the methods described by Ke et al.17 BaP-D12, the

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surrogate standard for the quantification of BaP, was added in the initial extraction. The

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extracts were concentrated to nearly dry by rotary evaporation and then re-dissolved in

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methanol. The final volume was adjusted to 2 mL and stored at 4 ◦C for further analysis.

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The BaP samples were analyzed with an Agilent Technologies 7890 gas

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chromatograph (GC) equipped with a 5975 mass spectrometer (MS). An HP-5MS fused

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silica capillary column coated with 5% phenylmethyl polysiloxane (30 m length, 0.25

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mm i.d., 0.25 µm film thickness; Wilmington, DE, USA) was used. An Agilent auto

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liquid sampler was used for sample injection, and the injection volume was 1.0 µL.

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Helium was the carrier gas with a constant flow rate of 1.0 mL min-1. The injection mode

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was splitless, and the injector and detector temperatures were 280 °C. The GC column

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temperature was programmed from 120 °C to 290 °C at a rate of 30 °C min-1, held for 1

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min, then increased from 290 °C to 300 °C at the rate of 5 °C min-1, and held at 300 °C

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for 6 min. The samples were analyzed in selected ion monitoring (SIM) mode. The limit

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of detection (LOD), defined as a signal of three times the noise level, was 2.81 µg L-1. 7



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Photodegradation of porphyrins. As porphyrins would be photodegraded

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under light irradiation, the concentrations of porphyrin were determined at Day 1, 4, 7

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and 10. The chlorophyll a concentration was calculated according to the method

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described by Huang and Cong.18 The method of alkaline hematin D-575 was used to

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determine the concentration of hematin.19 For the other porphyrins, the absorbance of the

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supernatant was measured at maximum absorption wavelength of 404, 667 and 356 nm

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for sodium copper chlorophyllin, pheophorbide a and cobalamin respectively by a UV-vis

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spectrophotometer. And then their concentration was analyzed with spectrophotometer

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(Unico UV-2600).

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Detection of •OH and 1O2. The photo production of •OH and 1O2 was

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determined in the solutions of the porphyrins following the methods described by Luo et

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al.10 In the determination of 1O2, the initial concentration of FFA in the aqueous solution

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was changed to 500 µmol L-1.

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Determination of BaP transformation products. After GC-MS analysis, the

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sample extracts were exposed to identify the possible BaP intermediates. An aliquot of

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0.2 mL of the sample extract was diluted with methanol, and the volume was adjusted to

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1 mL. High-performance liquid chromatography (HPLC) combined with atmospheric

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pressure ionization mass spectrometry (APCI-MS) was selective and sensitive for the

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determination of the BaP transformation products. The Thermo Scientific LC system

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consisted of an Accela 1250 pump and an Accela autosampler. The separation of BaP

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transformation products were performed on a Hypeisil GOLD column (100 mm × 2.1

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mm, i.d.; 1.9 µm particle size, Thermo Scientific). The column (temperature 35 °C) was

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eluted for 8 min at a flow rate of 300 µL min-1 with a binary gradient of water: methanol

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(25:75, v/v) for 4 min, followed by the same gradient at a ratio of 10: 90 for 2 min and

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then returned to the initial gradient of 25: 75 for 2 min. The injection volume was 10.0

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µL.

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The mass spectrometric analyses were performed using a Thermo Scientific TSQ

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Quantum Ultra mass spectrometer equipped with an APCI source. The measurements

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were performed in positive ion mode at 400 °C vaporizer temperature, 350 °C capillary

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temperature, 40 psig sheath gas pressure and 5 psig aux gas pressure. The discharge

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current was set at 4.0 µA. The mass spectrometer was operated under select reaction

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monitoring (SRM) mode. The identification of BaP intermediates was confirmed by

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comparing their retention times and characteristic mass spectra with the standard

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compounds. The retention times, qualitative and quantitative ions, and collision energies

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for the standards of the BaP transformation products are shown in Table S1.

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Effect of DOM on BaP phototransformation. In order to study the effect of DOM on BaP phototransformation in natural environment, the natural water was

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collected from the Pearl River (23°06′24.22″ N, 113°17′30.49″ E). After being filtered

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with 0.45 µm filter, the water samples were stored in the dark at 4 °C. The TOC in these

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samples was determined using TOC analyzer (Aurora 1030, OI Analytical Company).

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Statistical analysis. The mean and standard deviation values of triplicates were

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calculated. Kinetics of BaP transformation and porphyrins degradation were calculated

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using first-order equation.20 The effect of pH and salinity on BaP transformation was

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compared by one-way analysis of variance (ANOVA). If the ANOVA results were

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significant at p ≤ 0.05, Turkey’s multiple comparisons as post-hoc tests were applied to

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determine where the differences occurred. The relationship between the BaP

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transformation percentages and the concentrations of 1O2 were tested by correlation

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analysis and the Pearson coefficient was calculated. The statistical analyses were

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performed using SPSS 16.0. Linear correlation between 1O2 concentrations and BaP

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degradation percentages were also conducted using Origin 8.5. With respect to linear

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regression, the data was checked to meet the normal distribution.

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Results and Discussion

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Effect of chlorophyll a on BaP phototransformation under dark and

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light conditions. The effects of chlorophyll a on BaP phototransformation under dark

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and light conditions are shown in Figure 1. Under dark conditions, chlorophyll a had no

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effect on the transformation of BaP during 7 days irradiation. The BaP transformation

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percentages in the treatment of chlorophyll a and the control (sterile water without

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chlorophyll a) were 9.4% and 10.1% at Day 7, respectively. Under light irradiation, the

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concentration of BaP decreased dramatically during the first 4 days in the chlorophyll a

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solution, and up to 95.8% of the BaP was transformed at Day 4. However, only 11.8% of

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the BaP was phototransformed in the control flasks at Day 7, indicating that chlorophyll

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accelerated the phototransformation of BaP observably under light irradiation and that

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light was the essential element during the reaction.

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Effect of porphyrins on BaP phototransformation. Chlorophyll has a

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porphyrin structure as its molecular core and contains a metal atom at its center, which is

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structurally similar to sodium copper chlorophyllin, hematin, pheophorbide a and

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cobalamin (Figure S1). These four porphyrins were applied to compare with chlorophyll

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a in the phototransformation of BaP under light irradiation (Figure 2). Among the

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porphyrins, the removal of BaP, based on the residual amounts in the medium, increased

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in the order of chlorophyll a > cobalamin > pheophorbide a > hematin > sodium copper

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chlorophyllin. Chlorophyll a had the highest capability to transform BaP, and sodium

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copper chlorophyllin had the least capacity to transform BaP. The BaP removal in the

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solution of sodium copper chlorophyllin was even lower than that in the controls.

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The first-order kinetics of BaP transformation in the presence of different porphyrins

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was calculated. Rate constants (k) and half-lives (t1/2) are shown in Table S2. Correlation

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coefficients (R2) were in the range of 0.8827 to 0.9828 in four porphyrins except sodium

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copper chlorophyllin, which demonstrated that BaP phototransformation in the solution

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of chlorophyll a, hematin, pheophorbide a and cobalamin was in good accordance to the

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first-order kinetic reaction. The first-order phototransformation rate of BaP ranged from

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0.0061 to 0.395 d-1 and varied greatly with the types of porphyrins.

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Photodegradation of porphyrins. During the light irradiation, porphyrins

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bleached as time increased. As shown in Table S3, porphyrin photodegradation

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conformed to the first-order kinetic reaction (R2 = 0.7459 ～ 0.9997). The

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photodegradation rates of five porphyrins ranged from 0.050 to 0.798 d-1, with an order of

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chlorophyll a > pheophorbide a > cobalamin > hematin > sodium copper chlorophyllin.

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We found that BaP phototransformation rate was substantially related to chemical

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stability of the porphyrin present in reaction solution. Generally, the lower stability of the

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porphyrin, the higher BaP transformation rate.

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Under light irradiation, chlorophyll a degraded fastest with the half-life of 0.87 d

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(Table S2). To determine the effect of degraded chlorophyll a on the phototransformation

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of BaP, chlorophyll a was irradiated under light for 4 days, and then BaP was spiked. As

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shown in Figure S2, 97.75% of BaP was removed at Day 4. The rate constant was 0.658 12


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d-1, faster than that of the original chlorophyll a (Table S2). The result suggested that the

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photodegradation products of chlorophyll a also accelerated the phototransformation of

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BaP. According to literatures, Chlorophyll a first lost phytol, magnesium and

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carbomethoxy groups forming pheophorbide a.21 and then the tetrapyrrole macrocyclic

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ring cleaved, formed methyl vinyl maleimide, methyl ethyl maleimide, a C-E-ring

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derivative and hematinic acid,22-23 the final products were low molecular weight acids,

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such as glycerol, lactic, citric, succinic, malonic acids and alanine.24 To determine which

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products played important roles in the BaP transformation, further research is needed.

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Photoproduction of •OH and 1O2. Reactive oxygen species (ROS), in particular

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hydroxyl radical (•OH) or singlet oxygen (1O2), play important roles in the

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phototransformation of organic pollutants.25-28 Therefore, the formation of •OH and 1O2

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was determined in our studies. The results are shown in Figures S3 and 3a. The

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production of the •OH in the chlorophyll a treatments was lower than 2 × 10-2 µmol L-1

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(Figure S3). The chlorophyll concentrations and exposure time had insignificant effects

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on the production of the •OH. In our previous study, the phototransformation of BaP

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increased with the chlorophyll concentration,10 which was inconsistent with the

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production of the •OH. This result suggests that the •OH did not play an important role in

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the process.

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The concentration of 1O2 was approximately four orders of magnitude higher than •OH

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in the presence of porphyrins. The generation of 1O2 increased with the time, the

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concentration of 1O2 increased in the order of chlorophyll a > cobalamin > pheophorbide

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a > hematin > sodium copper chlorophyllin after 7 days of irradiation (Figure 3a). The

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order was consistent with the BaP phototransformation efficiency among the five

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porphyrins shown in Figure 2. The results indicate that the phototransformation of BaP

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was closely related to the production of 1O2. According to the linear regression analysis,

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BaP phototransformation percentages was positively related to 1O2 concentrations (r =

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0.9261, p < 0.001, Figure 3b). The correlation analysis between the BaP transformation

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percentage and the concentration of 1O2 in each porphyrin treatment was also tested, and

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the results are listed in Table S3. The results show that BaP transformation had a

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significant positive correlation with the production of 1O2 (p < 0.05), except in the control

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treatment, suggesting that 1O2 played a major role in the phototransformation of BaP.

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After absorbing light, the porphyrins reach triplet states, and energy is transferred to

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ground state oxygen, resulting in the formation of 1O2 by a spin reversal process of one

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electron in O2.29

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BaP transformation products. To confirm the role of ROS in BaP

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phototransformation and the transformation pathway, the BaP intermediates were

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determined. Identical transformation products were observed for all investigated 14


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porphyrins and the main products were identified as BaP-quinones, including BaP-1,6-

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dione, BaP-3,6-dione and BaP-6,12-dione (Figure 4). The concentration of the products

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increased with the irradiation time, suggesting that the products accumulate in the

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medium. Chlorophyll a had the highest BaP transformation production, and sodium

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copper chlorophyllin had the least production, which was consistent with the BaP

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phototransformation efficiency in Figure 2. A low amount of BaP-cis-4,5-diol was found

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in the solutions with porphyrins; however, the signal to noise ratio was less than 3, which

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was under the detection limit. Cis-dihydroxy BaP is known as the biodegradation

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metabolite,10,30-31 which is rarely present in phototransformation process. Monohydroxy

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BaP was also tested; however, none of 1-OH-BaP, 3-OH-BaP or their isomers were

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detected. In this research, BaP-quinones were the major products of BaP, which is

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different from human cells. BaP is metabolized to BaP-dihydrodiols, phenols and tetraols

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via cytochrome P450 enzymes, one-electron oxidation, and dihydrodiol dehydrogenase in

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human cells.32-33

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Recently, density functional theory calculations was used to elucidate the degradation

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mechanism of PAHs initiated by •OH in the presence of O2 and NOx,34-36 and the

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dominant degradation products of BaP were OH-BaP, NO2-BaP, 7,10-BaP-dione, as well

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as several ring-opened products.35 All the above mentioned products were not detected in

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this study, suggesting that the phototransformation of BaP by porphyrins in the water was

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proceeded via other mechanisms rather than •OH. BaP-1,6-dione, BaP-3,6-dione and

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BaP-6,12-dione were the main transformation production of BaP, indicating that 1O2

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initiated the phototransformation of BaP. The mechanism of porphyrins catalyzing the

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phototransformation of BaP was proposed as porphyrins photooxidized BaP to quinones

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via the photocatalytic generation of 1O2.

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The BaP transformation products were converted into BaP parent according to the

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mass balance calculation and the result is shown in Figure 5. Nearly all the disappeared

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BaP was transformed into quinones, and the recovery percentages were 93.6-105.4%,

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indicating that the benzene ring of BaP cannot be broken and is just accumulated as

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quinones in the medium. The concentrations of BaP photoproducts increased with BaP

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degradation over the 7-days irradiation. This implied that these products were more stable

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than parent BaP. BaP-1,6-dione was the major product among the three quinones in the

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high transformation efficiencies treatments, such as chlorophyll a, pheophorbide a and

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cobalamin (Figure S4), while BaP-3,6-dione maintain the similar relative percentages in

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the all porphyrins solution during 7 days irradiation. This result was inconsistent with a

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previous study, where BaP-3,6-dione was found as the dominant product of BaP under

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different light irradiation conditions.31

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PAHs require activation to electrophilic metabolites exert their mutagenic or carcinogenic effects in human cells.33 As a result, BaP-quinones are more toxic than the

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parent BaP.37-38 The environmental risk of BaP would be increase in the present of natural

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porphyrins, which could not be ignored in the water environment. On the other hand, the

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rate limiting steps of the high molecular weight PAH degradation is the introduction of

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molecular oxygen into aromatic ring as demonstrated in previous studies.39-40 The

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phototransformation of BaP by porphyrins could candidate as the first step for the initial

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oxidization of BaP and thereafter transformation products were further degraded using

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other degradation methods. It is believed that combined advantages of different

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transformation or degradation processes could accelerate the photodegradation of BaP or

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other PAHs.

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Effect of pH, salinity and DOM on BaP phototransformation. In natural

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water environments, the phototransformation of organic pollutants are influenced by

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environmental parameters, such as pH, salinity and DOM. The effect of pH, salinity and

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DOM on BaP phototransformation represented with porphyrins was conducted in this

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research. Chlorophyll a was selected for the study, since it had the highest capability to

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transform BaP and it is the most common porphyrin in the natural environments.

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The BaP phototransformation efficiency increased as the pH value increased. The

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transformation efficiency of BaP was highest at pH 12.0, and was low under strong acidic

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condition (Figure 6a). It could be explained that the photostabilities of porphyrins were

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dependent on the pH value, and the high pH value could enhance the photodegradation of 17



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porphyrins.41-42 As a result, it might led to high production of 1O2, and then the highest

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BaP phototransformation efficiency was occurred at pH 12.0.

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The range of salinity in this study was from 0 to 1.0 mol L-1, which covered the salinity

315

levels normally found in the aquatic environment. As shown in Figure S5, the salinity had

316

an insignificant effect on the phototransformation of BaP in chlorophyll a-

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containingsolution (p > 0.05). The effect of chlorophyll a concentration on the BaP

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phototransformation was investigated in our previous research.10 The results showed that

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BaP phototransformation efficiency increased initially with an increase of chlorophyll a

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concentration, but declined when the concentration reached 3.0 mg L-1.

321

The water samples from the Pearl River are rich in DOM, and the TOC was measured

322

as 23.5 ± 2.5 mg L-1. As shown in Figure 6b, the BaP phototransformation was inhibited

323

by DOM when compared with pure water in Figure 1. The half-life of BaP in the water of

324

the Pearl River was 57.8 d, which was much longer than that in pure water (38.9 d in

325

Table S2). The suppression of PAHs by DOM was attributed to light screening, reactive

326

species quenching, PAHs binding.43-45 With the addition of chlorophyll a into the water

327

of the Pearl River, the half-life of BaP was shortened to 15.2 d, indicating that

328

chlorophyll a was still able to accelerate the phototransformation of BaP in the natural

329

water containing the high level of DOM. The effect of DOM on the phototransformation

330

of organic pollutants was much reported.46-47 However, the effect of DOM on the natural

18


Page 18 of 32

Page 19 of 32


331

porphyrin-involved transformation of organic pollutants was relatively few considered,

332

especially for the carcinogenic BaP.

333

Environmental Implication. Natural porphyrins, e.g., chlorophyll a, could be

334

decidedly resulted in the phototransformation of organic contaminants in the aquatic

335

environment under sunlight irradiation, BaP in our case. This transformation was initiated

336

by the formation of singlet oxygen from the photolysis of porphyrins. Our study

337

highlights the important roles of biologically-originated compounds in the transformation

338

of organic contaminants in the real aquatic environment. Understanding such a

339

transformation including determination of identities and toxicity of transformation

340

products and relative contribution to the total transformation could render a high

341

possibility to accurately assess the risks of organic pollutants to aquatic ecosystem and

342

the public.

343

Associated content

344

Supporting information

345

The supporting information is available free of charge on the ACS Publications website.

346

Table of retention time, qualitative and quantitative ions, and collision energy for the

347

standard of BaP transformation products, rate constants (k) and half-lives (t1/2) of BaP

348

phototransformation and porphyrins photodegaradation, correlation analysis between 19



349

the BaP transformation percentage and the production of 1O2, figure of the structures

350

of five porphyrins, effect of degraded chlorophyll a on BaP phototransformation,

351

effect of chlorophyll a concentration on the production of •OH, relative percentages

352

of BaP transformation products in different porphyrins treatments during 7 days

353

irradiation, and effect of salinity on BaP phototransformation by chlorophyll a at Day

354

4 are available.

355

Author information

356

Corresponding author

357

*E-mail: [email protected], Telephone: +86-20-84112958; Fax: +86-20-84037549

358

Notes

359

The authors declare no competing financial interests.

360

Acknowledgements

361

This research was financially supported by the National Natural Science Foundation of

362

China (NSFC, No. 21707175, 21625703, 41473092, 21777198), State Key Laboratory of

363

Organic Geochemistry (OGL-201504).

364

References

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506 507

24


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Page 25 of 32


508

Figure captions

509 510 511

Figure 1 Effects of chlorophyll a on BaP phototransformation under dark and light conditions. C0 is the initial concentration of BaP, and C is the concentration of BaP at the sampling time.

512 513

Figure 2 Effects of porphyrins on BaP phototransformation under light irradiation

514 515 516 517

Figure 3 (a) Singlet oxygen production in the treatments of porphyrins under light irradiation, (b) Correlation between the singlet oxygen production and the BaP transformation percentage

518 519 520 521 522

Figure 4 Concentration of BaP transformation products in the treatments of (a) control, (b) chlorophyll a, (c) sodium copper chlorophyllin, (d) hematin, (e) pheophorbide a and (f) cobalamin under light irradiation. 1,6-dione, 3,6-dione and 6,12-dione represent BaP-1,6dione, BaP-3,6-dione and BaP-6,12-dione, respectively.

523 524 525

Figure 5 Percentage of BaP residual and its transformation products after treatments with porphyrins. The percentage of BaP-quinone was obtained by the equation:

526

pBaP - quinone （%）=

527 528

BaP-quinone (µg), MWBaP is the molecular weight of BaP (252), MWBaP-quinone is the molecular weight of BaP-quinone (282), and mBaP-initial is the initial mass of BaP (µg).

m BaP −quinone × MW BaP × 100% , where mBaP-quinone is the mass of MW BaP −quinone × m BaP -initial

529 530 531

Figure 6 (a) Effect of pH on BaP phototransformation in chlorophyll a solution after 4 days irradiation, (b) Effect of DOM on BaP phototransformation under light irradiation

532

25



533

Page 26 of 32

Figure 1

Control-dark Chlorophyll a-dark Control-light Chlorophyll a-light

1.2

1.0

C/Co

0.8

0.6

0.4

0.2

0.0 0

1

2

3

4

5

Time (day) 534 535 536

26


6

7

Page 27 of 32

537


Figure 2

538 1.2 Control Sodium copper chlorophyllin Hematin Pheophorbide a Cobalamin Chlorophyll a

1.0

C/Co

0.8

0.6

0.4

0.2

0.0 0

1

2

3

4

5

6

Time (day) 539 540 541

27


7


542

Page 28 of 32

Figure 3

a

b

Control Sodium copper chlorophyllin Hematin Pheophorbide a Cobalamin Chlorophyll a

100

BaP degradation percentage (%)

500

Singlet oxygen (µmol/L)

400

300

200

100

0

y = -0.2378x + 0.1648 r = 0.9261

80

60

40

20

0 0

1

2

3

4

5

6

7

0

Time (day)

100

200

300

400

Singlet oxygen (µmol/L)

543 544

28


500

Page 29 of 32

545


Figure 4

Concentration (µg/L)

(a) 600

Concentration (µg/L)

(b) 600

500

500

400

400

300

300

200

200

100

100

0

(c) 600

1,6-dione

3,6-dione

6,12-dione

Sodium copper chlorophyllin

0

(d) 600

500

500

400

400

300

300

200

200

100

100

0

(e) 600 Concentration (µg/L)

Day 1 Day 4 Day 7

Control

1,6-dione

3,6-dione

6,12-dione

0

(f) 600

Pheophorbide a

500

500

400

400

300

300

200

200

100

100

0

1,6-dione

3,6-dione

6,12-dione

0

Chlorophyll a

1,6-dione

3,6-dione

6,12-dione

3,6-dione

6,12-dione

3,6-dione

6,12-dione

Hematin

1,6-dione

Cobalamin

1,6-dione

546 547 548

29



549

Page 30 of 32

Figure 5 BaP-6,12-dione BaP-3,6-dione BaP-1,6-dione BaP 100

Percentage (%)

80

60

40

20

0 D1 D4 D7

Control

D1 D4 D7

D1 D4 D7

Chlorophyll a

Sodium copper chlorophyllin

D1 D4 D7

D1 D4 D7

D1 D4 D7

Hematin

Pheophorbide a

Cobalamin

550 551 552

30


Page 31 of 32

Figure 6

b

1.0

1.0

0.8

0.8

0.6

0.6

C/C0

a

C/C0

553


0.4

0.4

0.2

0.2

0.0

Pearl River water Pearl River water + chlorophyll a

0.0 2

4

6

8

10

12

0

1

pH

2

3

4

Time (day)

554 555

31


5

6

7


TOC Art 152x101mm (120 x 120 DPI)


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Natural Porphyrins Accelerating the ... - ACS Publications

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