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Environmental Processes
Photolytic transformation products of decabromodiphenyl ethane (DBDPE) Alexandra Klimm, Daniela Brenner, Bianca Lok, Jannik Sprengel, Kerstin Krätschmer, and Walter Vetter Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b01231 • Publication Date (Web): 07 May 2019 Downloaded from http://pubs.acs.org on May 8, 2019
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Photolytic transformation products of decabromodiphenyl ethane (DBDPE)
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Alexandra Klimm1, Daniela Brenner1, Bianca Lok1, Jannik Sprengel1, Kerstin Krätschmer1,2,
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Walter Vetter1*
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1Institute
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Germany
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2European
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79114 Freiburg, Germany
of Food Chemistry, University of Hohenheim, Garbenstraße 28, D-70599 Stuttgart,
Union Reference Laboratory (EU-RL) for halogenated POPs in Feed and Food, D-
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* Corresponding author
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Walter Vetter
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Phone: +49 711 459 24916
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Fax: + 49 711 459 24377
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Email:
[email protected] 17 18 19
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Abstract: The photolytic transformation of decabromodiphenyl ethane (DBDPE) - a current-
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use brominated flame retardant (BFR) and major substitute of the structurally related
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decabromodiphenyl ether - was investigated in different solvents (toluene, dichloromethane,
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chlorobenzene and benzyl alcohol). The transformation rate followed pseudo first order
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kinetics, with increasing half-life (t1/2) in the order of toluene (t1/2 = 4.6 min), chlorobenzene
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(t1/2 = 14.0 min), dichloromethane (t1/2 = 27.9 min) and benzyl alcohol (t1/2 ~60 min). Formation
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and amount of transformation products varied depending on the solvent used. A detailed study
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of the hydrodebromination products allowed to tentatively assign all three possible nonaBDPEs
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(BDPE 207, 208, and in benzyl alcohol only BDPE 206) and three predominant octaBDPE
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congeners (BDPE 197, 201 and 202). Next to the reported BDPEs, formation of several oxygen
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containing transformation products (OxyTPs), dominated by octabrominated OxyTP, was
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verified by GC-Orbitrap-HRMS analysis. Use of HPLC and Florisil column enabled the
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separation of OxyTPs and BDPEs, and the polybrominated OxyTPs were most likely tricyclic
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compounds with almost planar structure.
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INTRODUCTION
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Since the 1970s, several brominated flame retardants (BFRs) have been added or bonded to
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combustible materials in order to increase fire resistance. 1,2 Yet, environmental concerns have
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eventually led to the classification of several BFRs as persistent organic pollutants (POPs) by
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listing them in the Annex of the Stockholm Convention. 3–6 BFRs listed as POPs in Annex A
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are currently tetra- and pentabromodiphenylether (commercial pentabromodiphenylether),
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hexa-
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hexabromobiphenyl (all 2009), hexabromocyclododecane (2013) and most recently
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decabromodiphenyl ether (commercial mixture, consisting mainly of decaBDE (BDE 209),
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2017). These BFRs were gradually substituted with “novel” BFR (NBFRs). These BFRs were
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gradually substituted with “novel” BFR (NBFRs). A major substitute of decaBDE is
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decabromodiphenyl ethane (DBDPE) which was introduced in the early 1990s. 5–9 Its structure
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is quite similar to BDE 209, but the ethane bridge between the aromatic rings makes it slightly
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more hydrophobic than BDE 209.10 DBDPE was found to be bioaccumulative and thus has the
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potential to reach the food chain.10 It was detected in air 6, tree bark 7, lakes, sewage sludge,
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marine and surface sediments 8,9,11–13, car dust 2 and indoor dust.14,15 DBDPE was found to be
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cytotoxic impairing the hormone system.16–18 Yet, the environmental behavior of DBDPE has
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not been adequately investigated. 5
and
heptabromodiphenylether
(commercial
octabromodiphenyl
ether),
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It seemed plausible that some information of the environmental properties of DBDPE
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may be derived from the structurally related BDE 209. For instance, BDE 209 was found to be
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susceptible to UV light resulting in the loss of bromine and the possibility of
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rearrangements.19,20 As a result, decaBDE can photodegradate to lower brominated PBDEs,
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polybrominated dibenzo-p-dioxins (PBDDs) and polybrominated dibenzofurans (PBDFs)
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which are known to be more toxic compared to the higher brominated structure.21–24 Hence
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photochemical transformation appears to be an important elimination pathway not only for 3 ACS Paragon Plus Environment
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PBDEs,25–28 but also for DBDPE although DBDPE was considered safer as it did not generate
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highly toxic PBDD/Fs under pyrolysis conditions.29,30 Nadjia et al. (2014) described its
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photodegradation in tetrahydrofuran (THF) as a very fast pseudo first order kinetic reaction
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having a photolytic efficiency of 63% within the first 3 min of irradiation.10 Wang et al. (2012)
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determined that reductive bromination was the main process leading to three nonaBDPEs as
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well as octaBDPEs and heptaBDPEs.23 However, structures of the transformation products have
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not been assigned thus far. In addition, Kajiwara et al. (2008) investigated the photolysis of
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BDE 209 and DBDPE in plastic using natural sunlight. Reductive debromination was observed
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in the case of BDE 209 but not for DBDPE. These, differences indicated that more research
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was required on degradation products of DBDPE.31
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The goal of this study was to determine the transformation products of DBDPE during
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the photolytic transformation in different solvents. For this purpose, DBDPE was irradiated
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with UV-light using a medium-pressure mercury-vapor lamp to study the transformation
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kinetics as well as the formation of transformation products depending on irradiation time and
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solvent used. High amounts of transformation products were fractionated by means of reversed-
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phase high performance liquid chromatography (RP-HPLC). Based on gas chromatography
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coupled with electron capture negative ion mass spectrometry (GC/ECNI-MS), comparisons
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with other substance classes, the formed transformation products were studied, including
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several novel, oxygen-containing transformation products.
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MATERIALS AND METHODS
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Chemicals
and
Reagents.
Decabromodiphenyl
ethane
(1,2-bis(2,3,4,5,6-
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pentabromophenyl)ethane, DBDPE, CAS no. 84852-53-9, purity O5$?4N9 was from Tokyo
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Chemical Industry (Tokyo, Japan). Benzyl alcohol (99%, chlorine-free), diethyl ether (>97%),
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toluene
(HPLC
grade),
pyridine
8O55?5N9
and
the
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silylating
agent
(N,O-
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bis(trimethylsilyl)trifluoroacetamide (BSTFA) and trimethylchlorosilane (TMCS), 99:1 (v/v))
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were obtained from Sigma-Aldrich (Steinheim, Germany). Chlorobenzene 8O55?#N9 and
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anhydrous sodium sulfate were from Carl Roth (Karlsruhe, Germany) while 2,6-di-tert-butyl-
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p-cresol 8O55NQ BHT) was purchased from Fluka Analytics (Seelze, Germany).
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Dichloromethane 8O55?1N9 and n-hexane 8O5#N for pesticide residue analysis) were from Th.
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Geyer (Renningen, Germany). and liquid nitrogen from Westfalen (Münster, Germany).
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Acetonitrile 8O55?#N9 was obtained from KB Bernd Kraft (Duisburg, Germany) and Florisil
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(0.150-0.250 mm, 60-100 mesh) was from Merck (Darmstadt, Germany). 2,2´,4,4´,5,5´-
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hexachlorobiphenyl (PCB 153, purity 99.9%) was ordered from Dr. Ehrenstorfer (Augsburg,
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Germany). 3,3’,4,5’-Tetrachloro-4’-biphenylol (4’-OH-PCB 79, O55?4N9 was from LGC
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Standards (Wesel, Germany).
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Standard solutions. Solutions of DBDPE were prepared by dissolving (i) 1.23 mg
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DBDPE in 25 mL toluene, (ii) 1.13 mg DBDPE in 25 mL chlorobenzene and (iii) 1.36 mg
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DBDPE in benzyl alcohol, respectively. Sample (iii) was additionally heated to 60 °C. The three
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stock solutions were diluted 1:20 in the respective solvent. Sample (iv) was prepared by placing
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~2.08 mg DBDPE in 25 mL dichloromethane. The sample was heated to 40 °C and
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ultrasonicated for 15 min. Then, the supernatant of the saturated solution was removed and the
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stock solution was diluted 1:4 for further experiments.
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UV irradiation experiments in different solvents. UV irradiations were performed
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according to von der Recke and Vetter32. In brief, DBDPE solutions (1.2 mL) were transferred
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into water-cooled (18±0.2) quartz cells (type QS 0.500, Carl Zeiss, Oberkochen, Germany),
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which were kept at in a distance of 8 cm to the light source (medium-pressure mercury-vapor
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lamp, 150 W, type TG 150, Heraeus Noblelight, Hanau, Germany, UV-spectra of the lamp and
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DBDPE see Figure S1, Supporting Information). During the irradiation, 100 µL-aliquots were
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taken after 0, 3, 5, 10, 20, 40, 60, 120 and 180 min (end of the experiment) and placed in 1.5 mL 5 ACS Paragon Plus Environment
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amber vials with 200 µL insert. Control samples were treated the same way with the lamp
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turned off. The internal standard -PDHCH (107 ng in 10 µL iso-octane) was added and the
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sample solutions were subjected to gas chromatography/mass spectrometry (GC/MS) analysis.
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No mentionable transformation of DBDPE was observed in the control samples (
