Identification of Unknown Brominated Bisphenol S Congeners in

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Identification of Unknown Brominated Bisphenol S Congeners in Contaminated Soils as the Transformation Products of Tetrabromobisphenol S Derivatives Aifeng Liu, Jianbo Shi, Zhaoshuang Shen, Yongfeng Lin, Guangbo Qu, Zongshan Zhao, and Guibin Jiang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03266 • Publication Date (Web): 10 Aug 2018 Downloaded from http://pubs.acs.org on August 15, 2018

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Environmental Science & Technology

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Identification of Unknown Brominated Bisphenol S Congeners in

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Contaminated Soils as the Transformation Products of

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Tetrabromobisphenol S Derivatives

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Aifeng Liu 1, Jianbo Shi 2, Zhaoshuang Shen 1, Yongfeng Lin 2, Guangbo Qu 2, Zongshan

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Zhao 1,*, Guibin Jiang 2

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Technology, Chinese Academy of Sciences, Qingdao 266101, P.R. China

CAS Key Laboratory of Biobased Materials, Qingdao Institute of Bioenergy and Bioprocess

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2

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Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for

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* Corresponding author: Dr. Zongshan Zhao

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Tel./Fax: +86 532-80662709

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E-mail address: [email protected] (Z.S. Zhao)

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ACS Paragon Plus Environment


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Abstract Art

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Abstract

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Compared with tetrabromobisphenol A (TBBPA) and its derivatives, the skeletally

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similar chemicals tetrabromobisphenol S (TBBPS) and its derivatives have been rarely

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studied, and very little is known about their structures, environmental occurrence and

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behaviors. In this study, a total of 84 soil samples from a chemical industrial park have been

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collected and analyzed to investigate the occurrence of TBBPS and its derivatives and to

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identify

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(TBBPS-BDBPE), and three byproducts, TBBPS mono(allyl ether) (TBBPS-MAE), TBBPS

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mono(2-bromoallyl ether) (TBBPS-MBAE) and TBBPS mono(2,3-dibromopropyl ether)

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(TBBPS-MDBPE), have been detected with contents ranging from below detection limits to

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1934.6 ng/g dw and with detection frequencies of 21.4-97.6%. In addition, another 5

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unknown TBBPS analogs, tribromobisphenol S (TriBBPS), 2,2’,6’-TriBBPS-MAE

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(TriBBPS-MAE3.2),

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(DBBPS-MAE2.0) and 2,6-DBBPS-MAE (DBBPS-MAE2.6), have been identified in these soil

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samples by untargeted mass spectrometry screening. These unknown analogs have also been

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observed in laboratory transformation experiments of TBBPS-MDBPE conducted under

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reducing conditions. TriBBPS-MAE3.4 and DBBPS-MAE2.6 were more likely to be produced

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than TriBBPS-MAE3.2 and DBBPS-MAE2.0 due to the stereoselectivity of the transformation.

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TriBBPS-MAE3.4 and DBBPS-MAE2.0 were more stable, resulting in higher detection

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frequencies of these compounds in soil samples. Ether bond breakage and debromination

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contributed to the generation of these novel products. The results provide new information on

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the behaviors of TBBPS and its derivatives in the environment.

novel

TBBPS

analogs.

TBBPS,

2,6,2’-TriBBPS-MAE

TBBPS

bis(2,3-dibromopropyl

(TriBBPS-MAE3.4),

3


ether)

2’,6’-DBBPS-MAE


46

1

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Introduction

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Because they delay ignition and reduce the combustion rate in the spread of fire,

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brominated flame retardants (BFRs) have been widely used in plastics, electronics and

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electrical devices. As knowledge about the risks associated with BFRs has improved, the

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production and application of some of these compounds (i.e., polybrominated diphenyl ethers

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(PBDEs), polychlorinated biphenyls (PCBs), and hexabromocyclododecane (HBCD)) have

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been gradually banned. Subsequently, new alternatives have been proposed as substitutes for

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these traditional BFRs in industrial production. Currently, tetrabromobisphenol A (TBBPA) is

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the most widely used BFR, and a skeletally similar chemical, tetrabromobisphenol S

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(TBBPS), has been proposed as a potential alternative to TBBPA 1. Additionally, TBBPS is

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an important raw material for producing the derivative TBBPS bis(2,3-dibromopropyl ether)

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(TBBPS-BDBPE) and certain oligomers containing TBBPS segments in the fields of

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electronic devices, plastics, rubber and textiles 2.

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Although TBBPS and its derivatives have been widely produced and used in industrial

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applications, only a few reports have recently become available on their environmental

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occurrence, behavior and risks 3. The concentrations of TBBPS and TBBPS-BDBPE in the

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wastewater from a BFR factory was reported to be as high as 10 µg/L 4. Furthermore,

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TBBPS-BDBPE has been frequently detected in herring gull eggs collected from colonies at

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the Laurentian Great Lakes 2, 5 and in seafood from the Bohai Sea, China 6, where the highest

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measured concentration was 55.5 ng/g liquid weight. Some emerging TBBPS analogs, such

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as

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(TBBPS-MBAE) and TBBPS mono(2,3-dibromopropyl ether) (TBBPS-MDBPE), have been

TBBPS

mono(allyl

ether)

(TBBPS-MAE),

TBBPS

4


mono(2-bromoallyl

ether)

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identified as byproducts of TBBPS-BDBPE in mollusk samples from the Bohai Sea 7. In

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addition, software predictions demonstrate that TBBPS-BDBPE can be transformed into

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skeletally similar chemicals, including TBBPS and TBBPS-MDBPE 7.

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Similar to the formation of OH-PBDEs through the degradation of PBDEs 8, the

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degradation or transformation of TBBPS and its derivatives may also lead to the generation

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of unknown metabolites, which may exhibit higher toxicity to wildlife and humans than the

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precursors. To date, more than 100 metabolites or transformation products of TBBPA

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generated from debromination 9, β-scission (cleavage at the central carbon atom)

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hydroxylation

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health risks of some of these metabolites, such as tribromobisphenol A (TriBBPA),

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dibromobisphenol A (DBBPA), monobromobisphenol A (MBBPA), TBBPA sulfate, and

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TBBPA glucoside

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severe toxicity than TBBPA in microtox and algal assays

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microorganisms can be drastically reduced by increasing the degree of degradation or

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mineralization of TBBPA 20-22. Given the structural similarity between TBBPA, TBBPS and

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their derivatives, it is logical to hypothesize that TBBPS and derivatives are subject to

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comparable environmental transformation processes mentioned above

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less knowledge is available about the metabolites or transformation products of TBBPS and

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its derivatives whether from model experiments or field investigations 3.

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, and O-methylation

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10

,

have been identified. The potential ecological and

14-18

, have been evaluated. TriBBPA, DBBPA and MBBPA exhibited more 19

. Generally, the acute toxicity to

3, 6

. However, much

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In this study, we aimed to identify the unknown compounds related to TBBPS and its

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derivatives in contaminated soil samples from a chemical industrial park. Transformation

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experiment of TBBPS-MDBPE under reducing conditions was carried out to further verify 5



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the detected unknown compounds and the possible degradation mechanisms. The

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identification of the unknown compounds possibly generated from TBBPS and its derivatives

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in both field and model experiments would be beneficial for the study of their environmental

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fate and ecological risks.

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2 Materials and chemicals

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2.1 Chemicals and reagents

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TBBPS (98%) and TBBPS-BDBPE (99%) was purchased from ANPEL Laboratory

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Technologies Inc. (Shanghai, China) and used without further purification. TBBPS-MAE,

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TBBPS-MDBPE and TBBPS-MBAE were synthesized and further purified according to the

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reported method 7. Cyanocobalamin (CCA, Vitamin B12) was obtained from Sigma-Aldrich.

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Sodium citrate and titanium(III) chloride solution (15 mL, 20% w/v, in 2 N HCl) were

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purchased from Acros Organics. Methanol, hexane and methylene dichloride (DCM) were all

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HPLC grade. Water was generated by a Milli-Q advantage A10 system.

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2.2 Sample collection

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Topsoil (0-5 cm depth) and subsoil (30-40 cm depth) samples (42 pairs, 84 samples)

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were collected from a chemical industrial park. The detailed sampling information has been

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reported elsewhere

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stored at -20 °C until analysis. The subsoil samples were preserved in bags filled with

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nitrogen gas.

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2.3 Sample pretreatment

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. The soil samples were freeze-dried, ground, sieved (100 mesh) and

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The soil samples (1 g) were extracted with DCM (20 mL) for 30 min by ultrasonic

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extraction three times. The extracts were combined, concentrated with a rotary evaporator, 6


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solvent-exchanged to 0.5 mL DCM/hexane (1/1, v/v), and further cleaned by gel permeation

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chromatography (GPC, biobeads S-X3, 2.5 cm i.d. × 40 cm length). After the extracts were

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loaded, the GPC column was first rinsed with 100 mL of DCM/hexane (1/1, v/v), and then

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the extracts were eluted with 150 mL of DCM/hexane (1/1, v/v), further concentrated and

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solvent-exchanged to 1 mL of methanol for high-resolution mass spectrometry (HRMS)

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analysis.

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2.4 Instrumental analysis

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Ultra-high-performance liquid chromatography (Ultimate 3000) coupled with Orbitrap

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Fusion Tribrid mass spectrometer (UHPLC-Orbitrap-HRMS, Thermo Fisher Scientific,

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U.S.A.) was used for qualitative and quantitative analyses under the recommended conditions

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7

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TBBPS, TBBPS-MAE, TBBPS-MBAE and TBBPS-MDBPE 7. A ZORBAX ODS column

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(3.0×150 mm, 5 µm, Agilent) was used for the analysis of TBBPS-BDBPE

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instrumental parameters and gradient elution conditions were reported elsewhere

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briefly described in the Supporting Information.

. An Extend C18 column (2.1×50 mm, 1.8 µm, Agilent) was selected for the analysis of

23

. The detailed 7, 23

and are

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TBBPS, TBBPS-BDBPE, TBBPS-MAE, TBBPS-MBAE and TBBPS-MDBPE were

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detected in the soil samples by UHPLC-Orbitrap-HRMS by comparison to standards and

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quantified using external standard method. Trials of applying atmospheric pressure chemical

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ionization mass spectrometry (APCI-MS) and atmospheric pressure photoionization mass

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spectrometry (APPI-MS) for analysis of TBBPA derivatives (structure similar to

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TBBPS-BDBPE) displayed low sensitivity 6. In untargeted mass spectrometry of positive

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electrospray ionization (ESI+) in preliminary experiments, no obvious brominated chemicals 7



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related to TBBPS-MDBPE have been observed. As these phenolic chemicals are easily

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ionized under negative electrospray ionization (ESI-) mode (Table 1) and generated high

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response signals, the compounds were identified by their m/z values at the highest isotopic

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abundance of [M-H]-. The isotope ratios of the detected TBBPS, TBBPS-MAE,

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TBBPS-MBAE and TBBPS-MDBPE compounds in the soil samples were 1:4:6:4:1,

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1:4:6:4:1, 1:5:10:10:5:1 and 1:6:15:20:15:6:1, respectively (Table 1), coinciding with Br

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numbers of 4, 4, 5 and 6 in these four compounds. TBBPS-BDBPE was also detected by ESI

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mass spectrometry 6 due to ether bond ionization and the formation of the [M-C3H5Br2]- ion

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under full scan mode. However, the ionization efficiency of TBBPS-BDBPE was much lower

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than that of the phenolic chemicals, thus resulting in a lower sensitivity.

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2.5 Reductive transformation

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In this study, the transformation of TBBPS-MDBPE was performed under reducing

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conditions created by cyanocobalamin (CCA) and titanium(III) citrate solutions. CCA in the

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super-reduced state (CCAs) is proposed to be an effective alternative to an anaerobic

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dehalogenation bacterium for studying the degradation metabolism of halogenated

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compounds

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diphenyl ether

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(DPTE)

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an alternative strategy for studying the anaerobic degradation or transformation mechanism

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of TBBPS-MDBPE in our study. Due to the low ionization efficiency 28, 29 of TBBPS-BDBPE

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and its possible metabolites, TBBPS-MDBPE was chosen as the representative initial

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chemical for studying the transformation of TBBPS derivatives.

27

23, 24

. For example, the anaerobic degradation of toxaphene

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, chlorinated ethane

and TBBPA-MDBPE

23

24

, brominated

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, 2,3-dibromopropyl-2,4,6-tribromophenyl ether

by CCAs has been reported. Therein, it was also used as

8


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Typically, the solutions were prepared according the following procedure. First, CCAs

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was prepared according to previous methods 23. Briefly, in an anaerobic chamber, titanium(III)

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citrate (0.2 M) was prepared by adding sodium citrate (50 mL, 0.4 M, pH = 7.0) to a

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titanium(III) chloride solution (15 mL, 20% w/v, in 2 N HCl). The mixed solution was diluted

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to 100 mL with deionized water after adjusting the pH to 8.0 using Na2CO3 (2 M). CCAs was

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prepared by dissolving CCA in this titanium(III) citrate solution at two concentrations, 800

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and 80 µM, which are denoted CCAs-1 and CCAs-2, respectively. Many chlorinated

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chemicals have been transformed using CCAs at about 80 µM

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CCAs-2 were used separately to transform TBBPS-MDBPE (20 µg) over six time periods (10

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min, 20 min, 30 min, 60 min, 2 h and 24 h). Solutions of titanium(III) citrate (1 mL, 0.2 M)

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and CCA (1 mL, 800 µM) were also separately applied to the treatment of TBBPS-MDBPE

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(20 µg) to compare with the CCAs performance. All the solutions were extracted with DCM

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(5 mL) three times, concentrated into 1 mL of methanol and analyzed by HRMS to

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characterize the transformation products.

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2.6 Quality control and quality assurance

23, 25, 30

. Both CCAs-1 and

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The recoveries of TBBPS, TBBPS-BDBPE, TBBPS-MAE, TBBPS-MBAE and

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TBBPS-MDBPE from soil samples ranged from 85% to 95%. The method detection limits

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(MDLs) were defined as the minimum amount of analyte producing a peak with S/N = 3/1.

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MDLs were 2, 10, 0.05, 0.1 and 0.8 ng/g dw for TBBPS, TBBPS-BDBPE, TBBPS-MAE,

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TBBPS-MBAE and TBBPS-MDBPE, respectively. The TBBPS-related byproducts and

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transformation products were identified by Orbitrap-HRMS at a resolution of 120 000 and a

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mass error of 75%, Spearman’s rank

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correlation test was performed between each combination of the following factors of the soil

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samples: the compound content, total organic content (TOC) and pH

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was below 0.05, the linear regression between two tested variables was regarded as

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significant. Contents below the detection limit were treated as half of the detection limit.

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3

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3.1 Occurrence of TBBPS and TBBPS derivatives in soil samples

23

. When the p value

Results and discussion

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The analytical results of TBBPS, TBBPS-BDBPE and their byproducts in soil samples

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are shown in Table S1 and summarized in Table 2. TBBPS and three byproducts,

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TBBPS-MAE, TBBPS-MBAE and TBBPS-MDBPE, were detected at high detection

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frequencies of 94.0%, 95.2%, 40.5% and 97.6%, respectively (Table 2). Due to high method

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detection limit (MDL) of TBBPS-BDBPE, its detection frequency (21.4%) was relatively

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lower. TBBPS-BDBPE showed the highest content (1934.6 ng/g dw) because of its possible

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direct discharge from BFR plants. TBBPS-MDBPE, one of the most important byproducts of

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TBBPS-BDBPE, exhibited the second highest level (detectable contents of 3.6-1149.9 ng/g

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dw). The detectable contents of TBBPS-MAE and TBBPS-MBAE were 0.5-624.8 ng/g dw

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and 0.4-17.1 ng/g dw, respectively, much higher than those detected in mollusk samples from 10


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the adjacent sea region 7. In both mollusk and soil samples, TBBPS-MDBPE was the most

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frequently detected TBBPS byproduct. Although the contents of TBBPS and TBBPS-BDBPE

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were much lower than those of TBBPA and its derivatives (

Identification of Unknown Brominated Bisphenol S Congeners in

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