Characterization of Brominated Disinfection Byproducts Formed

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Environmental Processes

Characterization of Brominated Disinfection Byproducts Formed During the Chlorination of Aquaculture Seawater Juan Wang, Zhineng Hao, Fengqiong Shi, Yongguang Yin, Dong Cao, Ziwei Yao, and Jing-fu Liu Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b05331 • Publication Date (Web): 27 Apr 2018 Downloaded from http://pubs.acs.org on April 27, 2018

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Environmental Science & Technology

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Characterization of Brominated Disinfection Byproducts

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Formed During the Chlorination of Aquaculture Seawater

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Juan Wang,

†‡

†

†

†

†

Zhineng Hao, Fengqiong Shi, #Yongguang Yin, Dong Cao, Ziwei Yao, §

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†#

and Jingfu Liu *

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†

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research

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Center for Eco-Environmental Sciences, Chinese Academy of Sciences, P. O. Box

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2871, Beijing 100085, China

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‡

Institute of Environment and Health, Jianghan University, Wuhan 430056, China

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#

University of Chinese Academy of Sciences, Beijing 100049, China

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§

National Marine Environmental Monitoring Center, 42 Linghe Street, Shahekou

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District, Dalian 116023, China

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* Corresponding author: E-mail: [email protected]

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Fax: +86-10-62849192

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ACS Paragon Plus Environment


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TOC/Abstract Art

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Abstract:

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Although brominated disinfection byproducts (Br-DBPs) have been reported to

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form from reactions between bromide, dissolved organic matter (DOM) and

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disinfectants, their formation during the disinfection of aquaculture seawater via

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chlorination has been rarely studied. Herein, after 5 days of disinfection of raw

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aquiculture

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trichloroisocyanuric acid (TCCA) and chlorine dioxide (ClO2), 181, 179 and 37

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Br-DBPs were characterized by ultra-high-resolution Fourier transform ion cyclotron

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resonance mass spectrometry (FT-ICR MS). Sunlight irradiation of the chlorinated

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aquaculture seawater with TCCA and NaDDC was found to reduce the formation of

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Br-DBPs, possibly due to the photodegradation of the important HBrO/HClO

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intermediate and the degradation of formed Br-DBPs. The formation of Br-DBPs

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chlorinated by ClO2 increased under sunlight irradiation. The number of Br-DBPs

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formed during chlorination processes agreed well with the total organic bromine

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(TOBr) content measured by inductively coupled plasma mass spectrometry

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(ICP-MS). Most of the Br-DBPs were highly unsaturated and phenolic compounds,

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which were primarily generated through electrophilic substitution by bromine coupled

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with other reactions. In addition, some emerging aromatic Br-DBPs with high relative

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intensities were also assigned, and these compounds might be highly lipophilic and

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could potentially accumulate in marine organisms. Our findings call for further focus

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on and investigation of the Br-DBPs produced in chlorinated aquaculture seawater.

seawater

samples

with

sodium

dichloroisocyanurate

44 3


(NaDDC),


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INTRODUCTION

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Chlorine-containing disinfectants, such as chlorine, sodiumhypochlorite and

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chloramines, are commonly used in water disinfection treatments due to their

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outstanding performance in the removal of microorganisms, degradation of

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micropollutants, discoloration, and attenuation of taste and odor.1-4 However, these

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disinfectants can lead to the formation of harmful disinfection byproducts (DBPs)

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through reactions among the disinfectants, halide ions and natural organic matter

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(NOM).1, 5, 6 In general, brominated DBPs (Br-DBPs) are more concerned because of

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their higher cytotoxicity and genotoxicity relative to their chlorinated analogues.7, 8

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Trichloroisocyanuric acid (TCCA) and sodium dichloroisocyanurate (NaDDC),

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which are thought to be cleaner and safer than traditional disinfectants, have been

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used as alternative disinfectants for water disinfection, and their consumer demand

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has increased annually,9-11 which accounted for 8% of the disinfectants used in the

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aquaculture in China.12 During water disinfection, TCCA and NaDDC release

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hypochlorous acid (HOCl), which is the vital component of disinfection.9, 12 Chlorine

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dioxide (ClO2), another alternative disinfectant, has been extensively used in water

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disinfection, accounted for 20% of the disinfectants used in the aquaculture in

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China,12 due to its lower potential to form DBPs.13-16 Nevertheless, the use of these

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alternative disinfectants can still result in the formation of Br-DBPs. For example, the

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oxidation of Br− by HOCl produces hypobromous acid/hypobromite (HOBr/OBr−),

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which can subsequently react with the electron-rich moieties of NOM, such as

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phenols and olefins, to form Br-DBPs.1, 5, 17 4


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Currently, studies on the formation of Br-DBPs have mainly focused on the

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disinfection of drinking water and swimming pools, and very few studies have

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examined the disinfection of aquaculture seawater.18 However, the generation of

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Br-DBPs during aquaculture seawater disinfection should not be under estimated

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because of the extremely high concentration of bromide (67 mg L−1) in aquaculture

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seawater relative to that in freshwater sources (< 2 mg/L).4,

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seawater disinfection have shown that considerable amounts of Br-DBPs were

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generated in chlorinated seawater,18, 19 most of which contained aromatic structures.19

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More importantly, DBPs containing aromatic structures, which are more lipophilic

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with higher log P values (2.40−5.01) than aliphatic halogenated DBPs

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(0.43−1.79),20-22 more efficiently permeate cells and accumulate in marine

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organisms.20,23-25 For instance, high levels of polybrominated diphenyl ethers and

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brominated phenols were found in the blood of fish and wildlife from the Baltic Sea24,

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26

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and cats through the ingestion of pet food.26 In addition, nitrogenous DBPs, which are

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generally more toxic than carbonaceous DBPs,27 can also be produced in

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nitrogen-containing water during chlorination treatment and potentially accumulate in

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aquatic organisms.4,27 For instance, 2,2-dichloroacetamide has been confirmed to

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accumulate in zebrafish and cause metabolic damage.28

5

Recent studies on

and in seafood,23 and these compounds were also determined to accumulate in dogs

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Given that the disinfection of aquaculture seawater is performed under the

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conditions of the natural environment, the effects of sunlight irradiation on the

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formation of Br-DBPs should be considered. Previous studies have reported that 5



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sunlight can cause the formation of organobromine compounds due to the production

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of reactive halogen species (RHS) in seawater.29, 30 Furthermore, sunlight can also

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lead to the degradation of HClO/ClO− and HBrO/BrO− to Cl− and Br−,31 as well as the

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degradation of these generated Br-DBPs,32,33 which would decrease the amount of

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DBPs produced. Therefore, studies on the formation of Br-DBPs during the

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disinfection of aquaculture seawater both in the dark and under sunlight irradiation are

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very important.

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Due to its extremely high mass accuracy and resolution, ultra-high-resolution

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Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) coupled

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with electrospray ionization (ESI) has been utilized as an emerging technique for

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identifying the complicated molecular compositions of NOM34, 35 and DBPs during

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water treatment.19, 36-38 Although FT-ICR MS is not able to quantify these compounds

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because of variations in the ionization efficiency of ESI under different conditions,

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the relative intensity (RI) of a peak, which is calculated by comparing the intensity of

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a specific peak with that of the most intense peak, can partially reflect the content of

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the specific substance.39 Inductively coupled plasma mass spectrometry (ICP-MS) has

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been employed as a sensitive tool for quantifying the total organohalogen content in

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seawater and human urine.40, 41

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The objective of this research was to study the formation of Br-DBPs in

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aquaculture seawater chlorinated by TCCA, NaDDC and ClO2 by utilizing

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ESI-FT-ICR MS. Special attention was paid to the impact of light irradiation, which

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strongly affects Br-DBP formation, by performing the disinfection of aquaculture 6


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seawater in the field where sunlight irradiation can vary tremendously. In addition, the

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total organic bromine (TOBr) concentration, a parameter used to evaluate the bulk

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organic bromine level in chlorinated aquaculture seawater, was measured by ICP-MS.

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This is the first study to identify and characterize the Br-DBPs generated in

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chlorinated aquaculture seawater using FT-ICR MS, and the results should be helpful

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for assessing the safety of the use of chlorine-containing disinfectants in aquaculture

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seawater.

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MATERIALS AND METHODS

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Chemicals and Water Sample Preparation. NOM (serial No. 2R101N) was

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purchased from the International Humic Substances Society (St. Paul, MN, US).

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Methanol (Optima grade) and formic acid (99%) were purchased from Fisher

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Scientific (Shanghai, China). Sodium bromide (≥ 99.5%) was purchased from

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Sigma-Aldrich (Saint Louis, MO, US). TCCA (analytical grade) and NaDDC

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(analytical grade) were purchased from Aladdin Reagent Company (Shanghai, China).

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Chlorine dioxide (ClO2) was purchased from Xiya Reagent Company (Shandong,

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China). Ultrapure water (18.2 MΩ) was obtained from a Milli-Q gradient system

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(Millipore, MA, US).

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Artificial seawater (ASW) was prepared according to the formula of

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Mendez-Díaz and Shimabuku,40 and the components were given in supporting

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information (Table S1). ASW was kept in darkness before exposure to disinfectants.

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Raw seawater samples (RSW), below the 30 cm of the water surface, which might

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undergo weak sunlight irradiation, were collected from aquaculture seawater farms in 7



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the northwest Huanghai Sea (N 39º48′ 2.81″, E119º26′36.42″), ambient temperature

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of 16 °C, then filtered through a 0.45 µm pore-size cellulose acetate membrane to

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remove the suspended particles, and stored in the dark at room temperature. RSW

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samples were immediately used after being taken from field seawater, thus microbial

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degradation and production had little effect on DOM compositions. The pH, Br− and

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dissolved organic carbon (DOC) content of RSWs was 8.2, ~0.82 mM and ∼4.0 mg C

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L−1, respectively, and the other characteristics of RSWs were listed in Table S1.

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Chlorination Experiment. The chlorination of RSW/ASW samples in the dark

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was performed in 1 L amber glass bottles wrapped with aluminum foil. The DOC and

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pH values of the ASW were 3.0 mg C L−1 and 8.0, respectively. All the initial

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concentrations of TCCA, NaDDC and ClO2 were 0.71 mg L−1 (available chlorine),

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which was approximately the recommended dosage for aquaculture disinfection. Then,

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all the samples were submerged in a 20 L water bath to maintain the reaction

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temperature at 25 ± 2 °C. At the same time, the water samples were magnetically

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stirred at 300 rpm to simulate the motion of aquaculture seawater. Control

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experiments were performed under the same conditions without disinfectants. Before

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chlorination, a 250 mL aliquot of the solution was sampled from each seawater

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sample. After 1, 3 and 5 d of chlorination, a 250 mL aliquot of the solution was

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sampled, and the reaction was immediately quenched by adding excess Na2S2O3 (100

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µM). In parallel, water samples were chlorinated under sunlight irradiation according

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to the same procedures performed in the dark, except that the samples were irradiated

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in a sunlight simulator (Beifanglihui Company, SN-500, Beijing, China), equipped 8


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with three 2500 W air-cooled Xe lamps. Specifically, UV-light with wavelengths

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below 290 nm was attenuated by insetting glass cutoff filters (2 cm below Xe lamps),

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and the light intensity was held steady at 550 W m−2. The emission spectrum of the

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simulated sunlight is given in the Supporting Information (Figure S1).

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Water Sample Pretreatment. The water samples were pretreated according to

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the procedure reported by Mendez-Díaz and Shimabuku.40 In brief, the water samples

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were preferentially acidified to approximately pH 2.0 by adding formic acid

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dropwise, and then the samples were concentrated and desalted by SPE. The main

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steps of sample pretreatment were as follows:(i) Bond Elut PPL SPE cartridges (6 mL,

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1 g, Agilent Technologies, Folsom, CA) were sequentially rinsed with two cartridge

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volumes of methanol and acidified ultrapure water (pH ∼ 2.0, acidified with formic

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acid); (ii) the acidified water samples were pumped through cartridges at a flow rate

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of ∼5 mL min−1 to accumulate the target compounds, after which the cartridges were

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desalted by rinsing with two cartridge volumes of acidified ultrapure water; (iii) the

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cartridges were dried with nitrogen gas and eluted with two cartridge volumes of

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methanol. The eluate was divided into 2 equal portions, freeze-dried and stored at

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-20 °C in the dark. One portion of the freeze-dried samples was diluted with a

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methanol/water solution (v/v, 50/50) to 1 mL for the detection of Br-DBPs. To

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measure the TOBr and TOC, the other portion of the freeze-dried sample was

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dissolved in 19 mL of ultrapure water, and then trace halide ions were removed by

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filtrating the sample through a Ba/Ag/H cartridge (2.5 mL, 2.2‒2.6 meq/cartridge,

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Dionex/Thermo Scientific, Sunnyval, Cal.). Before the measurement of the TOBr, 5% 9



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NH4OH (v/v) was added to the sample to minimize the accumulation of bromide in

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the spray chamber or on the nebulizer.

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FT-ICR MS analysis. A Bruker SolariX 15 Tesla (FT-ICR MS) was used to

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analyze the extracted Br-DBPs. The diluted sample was injected into the electrospray

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source at 2 µL min−1 using a syringe pump. The ESI voltage was set to -3.8 kV, and

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the mass range was set at m/z 150‒1000 Da. Ions were accumulated in the hexapole

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ion trap for 0.2 s before being introduced into the ICR cell. Three hundred mass

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spectra were averaged per sample. Each sample was measured three times to ensure

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the

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cross-contamination and sample carryover, the injection syringe and lines were

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washed three times with 3 volumes of 50:50 methanol/water (v/v) between each

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injection. Blank methanol was measured frequently and showed no signs of sample

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carryover with the exception of a few m/z peaks that always appeared in the blanks,

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which were attributed to the SPE resin and residues present in the methanol and the

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instrument. A sodium formate solution (10 mM) and a known homologous series of

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NOM were used to externally calibrate the instrument with a mass error of < 0.2 ppm

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and to internally recalibrate the mass spectra, respectively.

reproducibility

and

reliability

of

the

measurement.

To

minimize

194

Bruker Daltonics data analysis software version 4.0 was used to identify and

195

assign molecular formulas to the peaks with a signal-to-noise ratio (S/N) > 5. The

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molecular

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C1−50H0−100O0−40N0−3S0−2Br1-3 with the restrictions H/C < 2.2 and O/C < 1.2.42-44 The

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mass resolution was 4.5×105‒2.1×106 (for molecular weight between 200‒500 Da)

formulas

were

calculated

based

on

10


element

combinations

of

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and 3.2×105‒4.5×105 (for molecular weight between 500‒700 Da), and the mass error

200

between the measured and calculated chemical formula was < 1 ppm. Because of the

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equal abundances of the 79Br and 81Br isotopes, the brominated compounds could be

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easily distinguished. Since FT-ICR MS has ultrahigh resolution for detecting Br-DBPs,

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the isotopic peaks for target compounds can be easily distinguished from adjacent

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peaks according to the isotopic simulation (Figure S2). Therefore, validation of the

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assigned Br-containing molecular formulas by isotope simulation was useful and

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reliable.36

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To visually display the distribution and components of these Br-DBPs, a van

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Krevelen diagram was constructed from the H/C and O/C ratios. The compounds

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were divided into five groups based on the modified aromaticity index (AI_mod) and

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the H/C ratio35 as follows: polycyclic aromatics (AI_mod > 0.66); polyphenols (0.5

Characterization of Brominated Disinfection Byproducts Formed

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