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Title: doi:10.1016/j.envint.2006.01.009

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Environment International 32 (2006) 575 – 585
www.elsevier.com/locate/envint

Photochemistry of a major commercial polybrominated diphenyl ether flame
retardant congener: 2,2′,4,4′,5,5′-Hexabromodiphenyl ether (BDE153)
Sierra Rayne a,⁎, Peter Wan a , Michael Ikonomou b
a

b

Department of Chemistry, University of Victoria, PO Box 3065, Victoria, British Columbia, Canada V8W 3V6
Institute of Ocean Sciences, Fisheries and Oceans Canada, 9860 West Saanich Road, Sidney, British Columbia, Canada V8L 4B2
Received 5 September 2005; accepted 6 January 2006
Available online 6 March 2006

Abstract
The photochemistry of a major commercial polybrominated diphenyl ether (PBDE) flame retardant congener, 2,2′,4,4′,5,5′hexabromodiphenyl ether (BDE153), was investigated in acetonitrile, distilled water, and seawater. After a short irradiation period in acetonitrile
at 302nm, the major photoproducts of BDE153 included 2,2′,4,4′,5-(BDE99), 2,2′,4,5,5′-(BDE101), and 2,4,4′,5,5′-(BDE118) substituted pentaBDEs as primary photohydrodebromination products, 2,2′,4,4′-(BDE47), 3,3′,4,4′-(BDE77), 2,3′,4,4′-(BDE66), and 2,2′,4,5′-(BDE49)
substituted tetra-BDEs as secondary photohydrodebromination products, a suite of non-2,3,7,8-substituted mono- through penta-brominated
dibenzofurans, and three tetrabrominated 2-hydroxybiphenyl congeners. By comparison, irradiation in distilled water and seawater gave increased
relative photohydrodebromination contributions and no evidence for the formation of brominated dibenzofurans or 2-hydroxybiphenyls. In all
solvent systems, subsequent degradation of primary and secondary photoproducts under continuing irradiation led to a steadily decreasing reaction
mass balance. The results suggest a short photochemical half-life for BDE153 in aquatic systems, with rapid photohydrodebromination to some of
the most prevalent penta- and tetra-brominated diphenyl ether congeners typically observed in environmental matrices.
© 2006 Elsevier Ltd. All rights reserved.
Keywords: Polybrominated diphenyl ethers (PBDEs); Photochemistry; Environmental fate; Brominated dibenzofurans; Brominated 2-hydroxybiphenyls

1. Introduction
Since the 1970s, polybrominated diphenyl ethers (PBDEs) have come into widespread industrial use as flame retardants in a
variety of technical mixtures (tetra-, penta-, octa-, and deca-brominated) applied to plastics, textiles, and foams used in both
commercial and residential settings, at concentrations up to 30% by weight (Darnerud et al., 2001; de Boer, 2000; Rahman et al.,
2001). Subsequent use and disposal of products containing these compounds has resulted in widespread environmental
contamination (Darnerud et al., 2001; de Boer, 2000; Rahman et al., 2001; Hites, 2004). Mounting bioaccumulatory and
toxicological concerns over these compounds have led to several recent usage bans and voluntary production stoppages in Europe
and North America (Renner, 2000; Pelley et al., 2003; Betts, 2001; Renner and Cooney, 2004; Christen and Petkewich, 2003).

O
Br

Br
∑Br=1–10

⁎ Corresponding author. Department of Civil Engineering Technology, Okanagan College, 1000 K.L.O. Road, Kelowna, British Columbia, Canada. Tel.: +1 250
7625445; fax: +1 250 8625430.
E-mail address: srayne@okanagan.bc.ca (S. Rayne).
0160-4120/$ - see front matter © 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.envint.2006.01.009

576

S. Rayne et al. / Environment International 32 (2006) 575–585

While the acute toxicity of PBDEs is thought to be low relative to other well-known halogenated diaryl ether contaminants such as
chlorinated dioxins and furans and the non-ortho substituted chlorinated biphenyls (de Boer, 2000), the chronic effects may result in
endocrine disruption and immunosuppression, among others (de Boer, 2000; Rahman et al., 2001; Pijnenburg et al., 1995).
Furthermore, the limited toxicological data available for only the most prevalent individual PBDE congeners in environmental
samples (e.g., BDEs 47, 99, and 100) (de Boer, 2000; Rahman et al., 2001), and the demonstrated experience with the widely
differing acute toxicities of individual dioxin, furan, and PCB congeners (toxic equivalent factor [TEF] ranges of > 6 orders of
magnitude) illustrates the need to better understand the environmental fate of this emerging contaminant class.

Br
Br

Br
O

Br

Br

O

O
Br

Br

Br

Br
Br

Br
BDE47

Br
BDE99

Br

Br
BDE100

Despite fairly extensive research into the environmental levels and patterns of PBDEs, relatively little is known regarding their
environmental fate (de Boer, 2000; Renner, 2000; Rayne and Ikonomou, 2002). The use of bromine rather than chlorine in industrial
products is partly to enhance their environmental degradation due to the weaker aryl–bromine bond. Thus, there has been much
speculation as to whether the dominant PBDE congeners typically observed in environmental samples arise from in situ or in vivo
debromination of higher brominated congeners (i.e., hexa- through deca-brominated), or whether they represent historical
contamination from the use of tetra-brominated technical mixtures in the 1970s (Rayne and Ikonomou, 2002).
While there have been previous reports on the photochemistry of the higher brominated diphenyl ethers (Soderstrom et al., 2004;
Eriksson et al., 2004; Raloff, 2003; Hua et al., 2003; Watanabe and Tatsukawa, 1987), mostly with decabromodiphenyl ether
(BDE209) as the starting material, the general lack of comprehensive photoproduct studies or attempts to complete photochemical
mass balances, as well as high concentrations and/or use of exclusively organic solvents, necessitates continuing efforts in this area.

Br

Br

Br

Br

Br
Br

O
Br

Br

Br

Br

BDE209
We have previously shown that two mono- and di-para substituted bromodiphenyl ether congeners (BDEs 3 and 15) undergo
exclusive photohydrodebromination to the parent system (diphenyl ether; DE) in aqueous–organic and aqueous–alcoholic solutions
(Rayne et al., 2003). However, the addition of more than two bromine substituents on the diphenyl ether structure may result in novel
photochemical pathways not previously observed with BDEs 3 and 15.

O
Br

O


Br



O

Br

BDE15

BDE3

DE

To help improve our understanding into the fate of brominated diphenyl ethers, we examined the aqueous and organic solution
phase photochemistry of 2,2′,4,4′,5,5′-hexabromodiphenyl ether (BDE153) at concentrations more representative of those observed
in environmental samples (∼10− 9 M). This model congener is a major component of the commercial penta-BDE (e.g., Bromkal 705DE and Great Lakes Chemicals DE-71) and octa-BDE (e.g., Bromkal 79-8DE and Great Lakes Chemicals DE-79) technical
mixtures (Rayne and Ikonomou, 2002).

Br

Br
O
Br

Br
Br

Br
BDE153

S. Rayne et al. / Environment International 32 (2006) 575–585

2. Experimental methods
2.1. Photolyses
Separate 1.3 × 10− 9 M solutions of BDE153 in HPLC grade acetonitrile
(Caledon Laboratories), Milli-Q grade distilled water, and unfiltered seawater
(taken at 1m depth about 5m from shoreline at the Institute of Ocean Sciences
[Patricia Bay, Sidney, BC, Canada] on June 11, 2002) were prepared by
dissolving 2.5 ng in 3mL of solvent. These concentrations are 20-fold lower than
the reported water solubility limit of 2.6 × 10− 8 M for BDE153 (Wania and
Dugani, 2003).
Solutions were not degassed prior to, or during, photolysis and were
expected to contain an equilibrium quantity of dissolved oxygen. Samples were
irradiated in 3mL quartz cuvettes open to the atmosphere and placed 5cm from a
6W 302nm 38cm × 8.1cm × 6.4cm UV lamp (Ultra-Violet Products UVM-57)
mounted horizontally in a secure and consistent placement. With the exception
of the 0- to 60-min duration trials taken at 5-min intervals, all samples were run
in duplicate at each time interval. To compare the relative effects of the 302nm
UV lamp versus solar irradiation, duplicate 1.3 × 10− 9 M solutions of BDE153 in
acetonitrile in a 3mL quartz cuvette were also exposed to solar irradiation for
periods of 0, 3, 6, 9, 12, and 15min between 1:30 and 3:00pm on June 11, 2002,
a clear day with an air temperature of 22 °C. For each solvent system, the 0-min
photolyses were allowed to sit at room temperature (about 20°C) for 60min
prior to workup, thereby acting as thermal blanks for the photochemical studies.
In all cases, no loss of starting material was observed for these 60-min duration
thermal controls. In addition, no potential thermal or photochemical products
were observed in the starting solutions or the thermal controls.

2.2. Sample workup
Following photolysis, all samples were spiked with the following
commercial internal standard solution prior to workup: 25μL of MBDE-MXA
from Wellington Laboratories containing 5μg/mL each of 13C-labelled 2,2′,4,4′tetrabromodiphenyl ether (13C-BDE47), 2,2′,4,4′,5-pentabromodiphenyl ether
(13C-BDE99), and 2,2′,4,4′,6,6′-hexabromodiphenyl ether (13C-BDE155). The
100μL aliquots removed for analysis from aqueous samples were filtered
through a Pasteur pipette containing a 0.2 cm layer of MgSO4 over a 0.2 cm layer
of hexane-rinsed Kimwipes. The MgSO4 was subsequently rinsed with
3 × 250μL of 1 : 1 pesticide grade distilled-in-glass toluene / dichloromethane
for solvent exchange. Both the 100 μL direct aliquots from photolyses in
acetonitrile and the 750μL solvent exchanged extracts in toluene:dichloromethane from the aqueous photolyses were reduced in volume to about 25μL
under gentle heating and a stream of nitrogen, and subsequently transferred to an
amber glass microvial.
For all samples in microvials awaiting analysis, 10μL each of the following
commercial recovery standards were added: EO-5101 from Cambridge Isotope
Laboratories containing 100ng/mL of 13C-labelled 3,3′,4,4′-tetrabromodiphenyl
ether (13C-BDE77) and 150 ng/mL of 13C-labelled 3,3′,4,4′,5-pentabromodiphenyl ether (13C-BDE126); MBDE-MXB from Wellington Laboratories
containing 5μg/mL each of 13C-labelled 2,4,4′-tribromodiphenyl ether (13CBDE28), 2,2′,4,4′,5,6′-hexabromodiphenyl ether (13 C-BDE154), and
2,2′,3,4,4′,5′,6-heptabromodiphenyl ether (13C-BDE171); and 10 μL of a
50μg/mL solution of 13C-labelled 2,3,7,8-tetrabromodibenzo[1,4]dioxin (13C2,3,7,8-TeBDD). Microvials were capped immediately after addition of the
recovery standard and stored at − 20°C in preparation for analysis by highresolution gas chromatography and mass spectrometry (HRGC–HRMS).

2.3. Instrumental analyses
Analyses were performed by HRGC–HRMS using a Micromass Ultima
mass spectrometer equipped with an Agilent 6890 gas chromatograph. For all
analyses, the HRGC was operated in the splitless injection mode, and the
splitless injector purge valve was activated 2min after sample injection. The
volume injected was 1μL of sample plus 0.5μL of air. The HRMS was
operated under positive EI conditions with the filament in the trap
stabilization mode at 600μA, an electron energy of 35eV, and perfluorokerosene used as the calibrant.

577

2.3.1. PBDE SIM analyses
Analyses for PBDE photoproducts and unreacted starting material were
performed using a standard 15m DB5-HT column (0.25mm I.D. × 0.1 μm film
thickness) from J&W Scientific with ultra-high purity helium as the carrier gas.
The instrument operated at 10,000× resolution, data were acquired in the
selected ion monitoring (SIM) mode, and the two most abundant isotopic
peaks were monitored for each molecular ion cluster. The temperature program
used under constant pressure (42 kPa) was as follows: hold at 100 °C for 1min;
2°C/min to 140 °C; 4°C/min to 220 °C; 8°C/min to 330 °C; and hold 1.2min.
The splitless injector port, direct HRGC–HRMS interface, and the HRMS ion
source were maintained at 300 °C, 260 °C, and 300 °C, respectively.
Analytical standards were available for identification and quantitation of the
following possible PBDE photoproducts: 2,2′,4,5′-tetrabromodiphenyl ether
(BDE49); 2,2′,4,4′-tetrabromodiphenyl ether (BDE47); 2,3′,4,4′-tetrabromodiphenyl ether (BDE66); 3,3′,4,4′-tetrabromodiphenyl ether (BDE77); 2,2′,4,5,5′pentabromodiphenyl ether (BDE101); and 2,2′,4,4′,5-pentabromodiphenyl
ether (BDE99). A total suite of 41 individual mono- through deca-brominated
diphenyl ether analytical standards was available, but only congeners
representing potential primary or secondary photohydrodebromination products
of BDE153 are listed above.
Analytes were identified only when the HRGC–HRMS data satisfied all of
the following quality assurance/quality control (QA/QC) criteria: (1) two
isotopes of the analyte were detected by their exact masses with the HRMS
operating at 10,000× resolution during the entire chromatographic run; (2) the
retention time of the analyte peak was within 3 s of the predicted time obtained
from analysis of authentic compounds in the calibration standards (where
available); (3) the maxima for both characteristic isotopic peaks of an analyte
coincided within 2s; (4) the observed isotope ratio of the two ions monitored per
analyte were within 15% of the theoretical isotopic ratio; and (5) the signal-tonoise ratio resulting from the peak response of the two corresponding ions was
≥3 for proper quantification of the analyte. Analyte concentrations were
calculated by the internal standard isotope-dilution method using mean relative
response factors (RRFs) determined from calibration standard runs made before
and after each batch of samples was analyzed. Recoveries of individual internal
standards were between 40% and 120% for all analyses. Concentrations of
analytes were corrected for percent recoveries of the internal standards.
2.3.2. PBDF SIM analyses
Analyses for PBDF photoproducts were performed using the HRGC–HRMS
system. A 15m DB5-HT column (0.25mm I.D. × 0.10μm film thickness) from
J&W Scientific with ultra-high purity helium as the carrier gas was used. The
instrument operated at 10,000× resolution, data were acquired in the SIM mode,
and the two most abundant isotopic peaks were monitored for each molecular ion
cluster. The temperature program used under constant pressure (36kPa) was as
follows: hold at 100°C for 2min; 20°C/min to 200°C; and 4°C/min to 314°C. The
splitless injector port, direct HRGC–HRMS interface, and the HRMS ion source
were maintained at 282°C, 260°C, and 300°C, respectively. An analytical standard
was available for 2,3,7,8-tetrabromodibenzofuran (2,3,7,8-TeBDF). The QA/QC
criteria for identification and quantitation of PBDFs analyzed via this method were
equivalent to the criteria outlined above for PBDE SIM analyses.
2.3.3. Brominated 2-hydroxybiphenyl full scan and SIM analyses
Full scan analyses to look for brominated 2-hydroxybiphenyl photoproducts
not having an available standard were performed using a HRGC–LRMS. The
low-resolution mass spectrometer (LRMS) used was a Voyager–Finnigan
(ThermoFinnigan, USA) instrument. A standard 30 m DB5 column (0.25mm I.
D. × 0.25μm film thickness) from J&W Scientific was used with ultra-high
purity helium as the carrier gas. The HRGC–LRMS was operated in the positive
ion mode and at unit resolution over the range from m/z 50 to 725. The GC
temperature program used under constant flow conditions (1 mL/min) was as
follows: hold at 100°C for 2min; 4°C/min to 300°C; and hold for 3min. The
splitless injector port, direct HRGC–LRMS interface, and the LRMS ion source
were maintained at 300 °C, 270°C, and 250°C, respectively.
The extract from the 1-min duration 302 nm irradiation of BDE153 in
acetonitrile revealed three unknown photoproducts with relative molecular ion
cluster areas of 1.1 : 1.8 : 1.0 that were tentatively assigned as tetrabrominated 2hydroxybiphenyls. This compound class assignment was based on analyte elution
times that were significantly greater (about 10min) than the corresponding

578

S. Rayne et al. / Environment International 32 (2006) 575–585

retention time (RT) windows for tetrabrominated diphenyl ethers and
tetrabrominated dibenzofurans: Unknown #1, RT = 46.91min: m/z = 482 (17%,
M+), 484 (74%, M+ + 2), 486 (100%, M+ + 4), 488 (64%, M+ + 6), 490 (15%,
M+ + 8), 324 (41%, M+ − 2Br), 326 (74%, M+ + 2 − 2Br), 328 (40%, M+ + 4
− 2Br); Unknown #2, RT = 47.67min, m/z = 482 (23%, M+), 484 (77%, M+ + 2),
486 (100%, M+ + 4), 488 (69%, M+ + 6), 490 (20%, M+ + 8), 324 (49%,
M+ − 2Br), 326 (91%, M+ + 2 − 2Br), 328 (46%, M+ + 4 − 2Br); and Unknown #3,
RT = 48.70min, m/z = 482 (11%, M+), 484 (63%, M+ + 2), 486 (100%, M+ + 4),
488 (63%, M+ + 6), 490 (17%, M+ + 8).
Subsequent SIM analyses were performed using the HRGC–HRMS system
on the same photolysis extracts subjected to full scan analyses in order to

confirm the likely identities postulated above based on low-resolution analyses,
and to allow quantitation of the brominated 2-hydroxybiphenyls. Analyses were
performed under the same instrumental conditions as for the full scan analyses,
except that the instrument operated at 10,000× resolution, data were acquired in
the SIM mode, and the two most abundant isotopic peaks were monitored for
each molecular ion cluster. The quantities of the three unknown analytes were
estimated by assuming a RRF of 0.5 for the intensity of the tetrabrominated 2hydroxybiphenyl molecular ion cluster compared to that of 13C-2,3,7,8-TeBDD,
equal to the observed RRF between a tetrachlorinated hydroxybiphenyl and 13C2,3,7,8-tetrachlorodibenzo[1,4]dioxin (13C-2,3,7,8-TeCDD) as described elsewhere (Rayne et al., 2002).

3. Results and discussion
3.1. Photodegradation kinetics and product identification/quantification
Irradiation of a 1.3 × 10− 9 M solution of BDE153 in acetonitrile at 302nm light for 5 min indicated that only about 15% of the starting material
remained, with about 18% of the mass balance accounted for by three penta-BDE and four tetra-BDE photoproducts (Fig. 1a). The contributions of
penta- and tetra-BDEs towards the photochemical mass balance subsequently decreased in an exponential manner over the ensuing 60-min total
irradiation period. Penta-BDE photoproducts reached a mass balance contribution maximum of 14% after 5 min irradiation, after which their
contribution declined to < 0.1% after 60 min irradiation. Similarly, tetra-BDE photoproducts reached a mass balance contribution maximum of 5.9%
after 10 min irradiation, after which their contribution declined to < 0.1% after 60 min irradiation. No other PBDE photoproducts from monothrough tri-substituted were observed at these time scales, thus leaving 70% of the mass balance unaccounted for after only 5 min irradiation, and
> 99% of the mass balance unaccounted for after 60 min irradiation. The efficient photodegradation of BDE153 observed on short time scale
irradiations as performed here is consistent with recent reports suggesting quantum yields ranging from 0.4 to 0.6 (Eriksson et al., 2004; Raloff,
2003) for various tetra- through deca-BDEs, and up to 0.95 for other substituted diphenyl ethers (Scrano et al., 1999). It is also of note that quantum
yields for all diphenyl ethers reported in the literature appear to be significantly influenced by solvent identity.
Levels of the three potential primary debromination products – BDEs 99, 101, and 118 – were observed to reach maximum contributions towards the
mass balance after 5min irradiation of 5.7%, 4.8%, and 3.8%, respectively (Fig. 1b). Concentrations of these analytes subsequently declined under
continued irradiation with pseudo first-order rate constants of 0.22 ± 0.07min− 1 (t1 / 2 = 3.2min; R2 = 0.97; p < 0.0024) for BDE99, 0.22 ± 0.05min− 1 (t1 / 2 =
3.2min; R2 = 0.99; p < 0.00072) for BDE101, and 0.27 ± 0.12min− 1 (t1 / 2 = 2.6min; R2 = 0.94; p < 0.0059) for BDE118. No significant differences
(p > 0.05) were observed between the pseudo first-order rate constants for the photodegradation of BDEs 99, 101, and 118 in acetonitrile.

Br

Br

Br

O

O

Br

Br

Br
Br

Br

Br

BDE101

Br

BDE118

With the decay of these primary debromination products, corresponding increases in concentrations of four secondary debromination
products – BDEs 47, 49, 66, and 77 – reach their maximum contributions towards the mass balance after 10 min irradiation of 1.1%, 1.5%, 1.3%, and
0.3%, respectively (Fig. 1c). Concentrations of these analytes subsequently declined under continued irradiation with first-order rate constants of
0.11 ± 0.02 min− 1 (t1 / 2 = 6.3min; R2 = 0.98; p < 4 × 10− 5) for BDE47, 0.096 ± 0.015 min− 1 (t1 / 2 = 7.2min; R2 = 0.98; p < 2 × 10− 5) for BDE49, 0.11 ±
0.01min− 1 (t1 / 2 = 6.3 min; R2 = 0.99; p < 3 × 10− 6) for BDE66, and 0.12 ± 0.08min− 1 (t1 / 2 = 5.8 min; R2 = 0.89; p < 0.02) for BDE77. No significant
differences (p > 0.05) were observed between the pseudo first-order rate constants for the photodegradation of BDEs 47, 49, 66, and 77 in acetonitrile.

Br

Br

Br

O

Br
O

O

Br
Br

Br

Br

Br
Br

Br

Br
BDE49

BDE66

BDE77

Thus, over the interval from 5 to 10 min irradiation, only about 40% of the reacted mass of the three penta-BDE primary photoproducts can be
accounted for by growth in contribution from the four tetra-BDE secondary photoproducts. As noted above, no other tetra-BDEs were observed in
solution, and the HRGC–HRMS method had sufficient sensitivity and specificity to identify the presence and approximate quantities of any PBDEs
for which analytical standards were not available. Indeed, both BDEs 101 and 118 were initially identified using previously published HRGC

S. Rayne et al. / Environment International 32 (2006) 575–585
100%
20%

579

(a)
Starting material (BDE153)

15%
Penta-BDEs

10%

Percent Contribution Towards Mass Balance

5%

Tetra-BDEs

0%
6%

(b)

5%

BDE99
BDE101

4%
3%
2%
1%

BDE118

0%
1.6%

(c)

BDE49

1.2%
BDE66

0.8%
BDE47

0.4%
BDE77

0%
0

10

20

30

40

50

60

Irradiation Time (min)

Fig. 1. Contributions of (a) unreacted starting material (BDE153; ○, solid line), the sum of penta-BDE photoproducts (□, dashed line), and the sum of tetra-BDE
photoproducts (♦, dash-dot-dot line); (b) individual penta-BDE photoproducts BDE99 (○, solid line), BDE101 (□, dashed line), and BDE118 (♦, dash-dot-dot line);
and (c) individual tetra-BDE photoproducts BDE49 (○, solid line), BDE47 (□, dashed line), BDE66 (♦, dash-dot-dot line), and BDE77 (▲, dotted line) towards the
overall photochemical mass balance for BDE153 over a 60-min irradiation period at 302nm in acetonitrile.

relative retention time (RRT) models (Ikonomou and Rayne, 2002; Rayne and Ikonomou, 2003a,b). At the time of preliminary identification, an
analytical standard was not available for BDE101; subsequent purchase and analysis of this standard conclusively identified BDE101 as predicted
by the HRGC–RRT models.
Further photolyses were conducted at 1-min intervals over the first 5-min irradiation period in three different solvent systems (acetonitrile,
distilled water, and seawater) to better understand the primary photochemistry of BDE153 and the influence of solvent identity. While solvent
effects on the quantum yields of PBDE photochemistry have been previously reported (Raloff, 2003; Eriksson et al., 2004), little previous mention
has been made as to the solvent effects on the relative distributions of photoproducts. In addition, photolyses of BDE153 on these shorter time scales
was intended to help close the incomplete photochemical mass balance that was observed after 5 min irradiation, where about 70% of the mass
balance had remained unaccounted for in acetonitrile. Similar difficulties in completing a photochemical mass balance for the higher brominated
diphenyl ethers both in solution and adsorbed on solids (e.g., sand, silica gel) have been previously reported (Watanabe and Tatsukawa, 1987;
Eriksson et al., 2004; Soderstrom et al., 2004). To compare the experimental irradiation intensity with that under solar illumination, a suite of trials in
acetonitrile were also exposed to natural sunlight at 3-min intervals over a duration of 15 min.
Under these four irradiation conditions at reduced time scales, the influence of water content and solar radiation on the rate of decay for BDE153
were evident. In acetonitrile, loss of starting material followed pseudo first-order kinetics with a rate constant of 0.43 ± 0.10 min− 1 (t1 / 2 = 1.6 min;
R2 = 0.98; p < 0.0011; Table 1). In distilled water, a reliable rate constant for the decay of BDE153 could not be calculated, as the lack of
quantification of this analyte at t = 1min irradiation resulted in a non-significant (p > 0.05) regression between natural log-transformed concentration
(mass balance contribution) and time for the remaining 2–5 min data set.
Water appears to favor photohydrodebromination for an as yet unidentified reason. For example, in distilled water, when 60% of starting material
has reacted after 2 min irradiation, about 29% of the total mass balance (and about 50% of the reacted mass balance) can be accounted for by
debromination products (Table 2). Conversely, in acetonitrile, debromination never accounts for more than 20% of the reacted mass balance (and
about 16% of the total mass balance). As well, increased water content may also be expected to favor photonucleophilic aryl–bromine substitution
by water to yield hydroxylated PBDEs. The increasing contribution of the photohydrodebromination pathway in water – and improved mass
balance – suggests this reaction is not favored, consistent with our previous findings on the aqueous photochemistry of BDEs 3 and 15 (Rayne et al.,

580

S. Rayne et al. / Environment International 32 (2006) 575–585

Table 1
Percent contributions towards the photochemical mass balance of starting material (BDE153) and the penta- and tetra-BDE photoproducts over a 5-min irradiation
period at 302 nm in acetonitrile
1min
BDE153
BDE99
BDE101
BDE118
BDE47
BDE77
BDE66
BDE49
a
b
c

51.8 ± 10.9%
3.8 ± 0.8%
3.2 ± 0.6%
2.3 ± 0.4%
0.06% b
n/a
0.06% b
0.12% b

2min
a

b

39.1%
5.5%
4.5%
3.5%
0.18%
0.06%
0.18%
0.24%

3min

4 min

5min

19.6 ± 0.9%
5.8 ± 0.2%
4.9 ± 0.1%
3.7 ± 0.2%
0.36 ± 0.06%
0.06%
0.42 ± 0.06%
0.48 ± 0.01%

14.8 ± 1.3%
n/a c
4.8 ± 0.4%
3.8 ± 0.4%
0.48 ± 0.06%
0.12 ± 0.06%
0.54 ± 0.06%
0.72 ± 0.01%

9.9 ± 2.2%
5.0 ± 0.6%
4.3 ± 0.4%
3.5 ± 0.4%
0.48 ± 0.06%
0.18 ± 0.06%
0.66 ± 0.06%
0.78 ± 0.01%

Error bars indicate the range of duplicate trials.
Analyte not quantified in duplicate sample.
Analyte not quantified in either of the duplicate samples.

2003). The lack of observable photonucleophilic bromine substitution by a hydroxyl group for BDEs 3, 15, and 153 in water seems to rule out
heterolytic aryl–bromine bond cleavage as a significant photodegradation pathway for PBDEs in aquatic systems.
In seawater, the photodegradation rate constant of BDE153 decreases to 0.15 ± 0.03 min− 1 (t1 / 2 = 4.6 min; R2 = 0.99; p < 0.00065; Table 3). The
cause of the decreased rate constant in seawater relative to acetonitrile is presently unknown, but could be due to competitive light absorption by
other dissolved and particulate species and/or partitioning of BDE153 onto hydrophobic dissolved or particulate organic carbon (thereby shielding
the starting material from irradiation). An improved photochemical mass balance for BDE153 was achieved in seawater. After 1min irradiation,
about 93% of the total mass balance (and 65% of the reacted mass balance) can be accounted for by starting material (80%), penta-BDE primary
photoproducts (12%), and tetra-BDE secondary photoproducts (1%). The wide range of good hydrogen donating substrates in seawater (Larson and
Weber, 1994; Schwarzenbach et al., 2003) is a potential explanation for the observed preferential photohydrodebromination in this solvent system
relative to distilled water and acetonitrile.
A reliable rate constant for the decay of BDE153 in acetonitrile under solar irradiation could not be calculated (p > 0.05; Table 4), although the
mass balance for debromination products suggests a different contribution of reaction pathways than under 302nm irradiation. The available solar
wavelengths appear to favor non-debromination photochemical pathways in acetonitrile. Under solar irradiation with significant loss of starting
material (80–85% after 3 min exposure), < 1% of the mass balance was observed as debromination products in the form of penta-BDEs. There was
no evidence of secondary photochemical formation of tetra-BDEs from the minor amounts of primary penta-BDE photoproducts under solar
irradiation in acetonitrile.
The results for solar irradiation (namely, the apparent wavelength effect of BDE153 photochemistry relative to the 302nm irradiations)
complicate potential conclusions based on the photolyses in seawater. The results from irradiation of BDE153 in seawater at 302nm would prima
facie suggest that in marine systems, BDE153 may undergo almost exclusive and rapid photohydrodebromination resulting in some of the most
prevalent penta- and tetra-BDE congeners (e.g., BDEs 47 and 99) observed in aquatic systems (Darnerud et al., 2001; de Boer, 2000; Rahman et al.,
2001; Hites, 2004; Rayne and Ikonomou, 2002). However, the observed difference in photoproduct profiles for photolyses of BDE153 in
acetonitrile under 302nm and solar illumination suggest simple generalizations cannot yet be made. Although water appears to promote
photohydrodebromination (evidenced from trials in both distilled water and seawater), the solar wavelengths may allow access to additional
photochemical pathways such as homolytic and/or heterolytic aryl–ether cleavage, or aryl–bromine bond heterolysis.
3.2. Photochemical formation of PBDFs and brominated 2-hydroxybiphenyls
To better understand the potential contributions of non-photohydrodebromination pathways towards the photochemistry of BDE153, the extracts
from photolyses in acetonitrile (both under 302nm and solar irradiation for the 1- to 5-min intervals, and under 302nm irradiation for the 5- to 60-

Table 2
Percent contributions towards the photochemical mass balance of starting material (BDE153) and the penta- and tetra-BDE photoproducts over a 5-min irradiation
period at 302 nm in distilled water

BDE153
BDE99
BDE101
BDE118
BDE47
BDE77
BDE66
BDE49
a
b
c

1min

2min

3min

4min

5min

n/a a
7.1 ± 0.4%
5.3 ± 0.1%
4.7 ± 0.8%
0.38 ± 0.21%
0.19 ± 0.16%
0.48 ± 0.34%
0.38 ± 0.21%

41.0 ± 6.1% b
10.8 ± 0.9%
7.9 ± 1.3%
7.2 ± 0.2%
0.82 ± 0.28%
0.40 ± 0.25%
1.13 ± 0.62%
0.95 ± 0.34%

27.0 ± 0.6%
11.8 ± 0.8%
8.9 ± 1.3%
7.9 ± 0.1%
1.53 ± 0.64%
0.80 ± 0.57%
2.23 ± 1.26%
1.80 ± 0.66%

38.5 ± 17.7%
8.7 ± 0.6%
6.5 ± 1.1%
5.7 ± 0.3%
1.36 ± 0.51%
0.70 ± 0.43%
1.99 ± 0.99%
1.65 ± 0.46%

32.7% c
7.6 ± 0.8%
7.2 ± 0.2%
4.9 ± 0.7%
0.94 ± 0.15%
0.37 ± 0.04%
1.23 ± 0.07%
1.25 ± 0.31%

Analyte not quantified in either of the duplicate samples.
Error bars indicate the range of duplicate trials.
Analyte not quantified in duplicate sample.

S. Rayne et al. / Environment International 32 (2006) 575–585

581

Table 3
Percent contributions towards the photochemical mass balance of starting material (BDE153) and the penta- and tetra-BDE photoproducts over a 5-min irradiation
period at 302 nm in seawater a
1min
BDE153
BDE99
BDE101
BDE118
BDE47
BDE77
BDE66
BDE49
a
b
c

2min
c

b

80.1%
4.9 ± 1.8%
3.4 ± 1.0%
3.5 ± 1.3%
0.38 ± 0.10%
0.22 ± 0.09%
0.48 ± 0.17%
0.35 ± 0.13%

66.2 ± 4.6%
4.3 ± 0.5%
3.1 ± 0.3%
3.2 ± 0.4%
0.47% c
0.26 ± 0.01%
0.66% c
0.49 ± 0.03%

3min

4min

5 min

60.0 ± 3.2%
4.1 ± 1.8%
3.1 ± 1.3%
3.2 ± 1.4%
0.74 ± 0.39%
0.48 ± 0.30%
1.08 ± 0.61%
0.80 ± 0.45%

48.2 ± 23.1%
4.3 ± 0.8%
3.0 ± 0.5%
3.3 ± 0.7%
1.03 ± 0.31%
0.65 ± 0.19%
1.57 ± 0.42%
1.22 ± 0.27%

43.5 ± 21.8%
3.6 ± 0.9%
2.5 ± 0.6 %
2.8 ± 0.8%
0.82 ± 0.17%
0.57 ± 0.16%
1.24 ± 0.35%
0.95 ± 0.23%

Analyte not quantified in either of the duplicate samples.
Error bars indicate the range of duplicate trials.
Analyte not quantified in duplicate sample.

min intervals), distilled water, and seawater were also analyzed for the presence of polybrominated dibenzofurans (PBDFs). Only the sample
irradiated at 302nm for 1 min in acetonitrile provided evidence of photochemical PBDF formation. In this sample, eight distinct mono- through
penta-BDF analytes were observed with the following contributions towards the mass balance: one penta-BDF at 1.2%; one tetra-BDF at 2.2%; two
tri-BDFs at 2.0% and 1.2%, respectively; three di-BDFs at 1.4%, 1.4%, and 1.2%, respectively; and one mono-BDF at 4.2%.
The PBDF analytes accounted for about 15% of the total mass balance, and about 30% of the reacted mass balance. These results are similar to
previous reports on the photochemistry of BDE209, which followed photohydrodebromination and photochemical PBDF production down through
the various homologue groups to the corresponding mono- and di-bromo analytes. Once photohydrodebromination of BDE209 had proceeded to
the dominantly hexa-BDE stage, a significant increase in contribution from the tetra- and penta-BDFs was observed (Watanabe and Tatsukawa,
1987). Thus, it appears that hepta- through deca-BDEs do not photochemically rearrange into PBDFs, but rather prefer to undergo
photohydrodebromination to the hexa-BDE level. Our results, and those of Watanabe and Tatsukawa (1987), suggest that the photochemical
pathway leading to PBDF production is a significant contributor for PBDEs with ≤6 bromine substituents.
The identity of the penta-BDF primary photoproduct can be assigned to 1,2,4,7,8-PeBDF, as no other penta-BDF congeners are likely to be
formed by photochemical means from BDE153. With the observed absence of 2,3,7,8-TeBDF, for which an analytical standard was available, there
appears to be no formation of the highly toxic 2,3,7,8-substituted PBDFs through either the primary or secondary photolysis of BDE153. Of note,
toxicological work suggests 2,3,7,8-TeBDF may be more acutely toxic than the well-known 2,3,7,8-tetrachlorodibenzo[1,4]dioxin (2,3,7,8-TeCDD;
Hornung et al., 1996).

Br
O
Br

Br

Br

Br

Br

O

Br
Br

Br
1,2,4,7,8-PeBDF

2,3,7,8-TeBDF

As mentioned above, there have been previous reports of PBDF formation from hexa-through deca-BDEs (Raloff, 2003; Watanabe and
Tatsukawa, 1987), but the identities of individual PBDF congeners were not provided in either study. The analogous photochemical formation of
chlorinated dibenzofurans from chlorinated diphenyl ethers in about 10% yield was suggested to occur via the triplet state (Choudhry et al., 1977),
Table 4
Percent contributions towards the photochemical mass balance of starting material (BDE153) and the penta- and tetra-BDE photoproducts over a 15-min irradiation
period under solar illumination in acetonitrile

BDE153
BDE99
BDE101
BDE118
BDE47
BDE77
BDE66
BDE49
a
b
c

1min

2min

3 min

4min

5 min

22.7 ± 10.9% a
0.32 ± 0.06%
0.37 ± 0.08%
0.17 ± 0.02%
nd c
nd
nd
nd

15.4% b
0.33 ± 0.05%
0.20 ± 0.19%
0.17 ± 0.02%
nd
nd
nd
nd

13.8 ± 0.9%
0.31 ± 0.01%
0.29 ± 0.01%
0.17 ± 0.01%
nd
nd
nd
nd

14.1 ± 1.3%
0.40 ± 0.04%
0.39 ± 0.02%
0.23 ± 0.02%
nd
nd
nd
nd

16.2 ± 2.2%
0.43 ± 0.02%
0.39 ± 0.01%
0.25% b
nd
nd
nd
nd

Error bars indicate the range of duplicate trials.
Analyte not quantified in duplicate sample.
Analyte concentration below method detection limit in both duplicate samples.

582

S. Rayne et al. / Environment International 32 (2006) 575–585

BDE153
Penta-BDEs
Tetra-BDEs
Penta-BDFs
Tetra-BDFs
Tri-BDFs
Di-BDFs
Mono-BDFs
TB-2-HBPs
0%

20%

40%

60%

80%

100%

Percent Contribution Towards Mass Balance

Fig. 2. Contributions towards the photochemical mass balance of BDE153 after 1-min irradiation in acetonitrile at 302nm by penta- and tetra-BDEs, mono- through
penta-BDFs, and tetrabrominated 2-hydroxybiphenyls (TB-2-HBPs).

and similar findings were also reported for hydroxychlorodiphenyl ethers (Freeman and Srinivasa, 1983). In addition, the work of Watanabe and
Tatsukawa (1987) on BDE209 photochemistry in 8 : 1 : 1 hexane/benzene/acetone seems to confirm this reactivity pattern for PBDEs. The heavyatom effect (Turro, 1991) – where the efficiency of inter-system crossing to the triplet state is enhanced through the addition of higher molecular
weight substituents – would also tend to favor the preferential photochemical formation of PBDFs from PBDEs compared to the corresponding
reaction for chlorinated diphenyl ethers. Thus, the 30% yield of PBDFs observed for the photolysis of BDE153 is consistent with a triplet state
reaction providing higher yields of these products versus the chlorinated diphenyl ethers (having 10% conversion to chlorinated dibenzofurans).
The 1-min photolysis extracts following irradiation at 302nm in acetonitrile, distilled water, and seawater were also subjected to full-scan
HRGC–HRMS analyses. In the acetonitrile photolysis extract, three tetrabrominated 2-hydroxybiphenyls were identified in contributions of 2.9%,
4.7%, and 2.6% towards the photochemical mass balance. No evidence of brominated 2-hydroxybiphenyls was observed in the extracts from the
distilled water and seawater photolyses after 1 min irradiation.

OH

Br

Br
∑Br=4

Together with the contributions of unreacted starting material (51.8%) and penta- and tetra-BDE debromination products (9.5%), approximately
86% of the mass balance can now be accounted for after 1min irradiation in acetonitrile (Fig. 2). Of note is the apparent absence of the primary
2′,3,4′,5,5′,6-hexabromo-2-hydroxybiphenyl product expected from a photo-Fries rearrangement of BDE153 (Scheme 1), and the absence of any of
its expected secondary pentabrominated 2-hydroxybiphenyl photohydrodebromination products that would give rise to the observed
tetrabrominated 2-hydroxybiphenyls. Mono- through tri-brominated-2-hydroxybiphenyls were also not observed in the extract, although their
presence may have been masked through co-elution with other analytes or impurities. These analytes could potentially account for the remaining
14% of the photochemical mass balance.
That aryl–ether cleavage may be an important pathway in the photochemical fate of brominated diphenyl ethers has been previously suggested
for BDE209. Watanabe and Tatsukawa (1987) reported the production of tetra- and penta-bromobenzenes during the photolysis of BDE209,
showing that aryl–ether cleavage takes place from starting material. However, in this previous study, the use of hexane as the dominant solvent
likely favors rapid hydrogen abstraction from any photogenerated phenoxyl and aryl radicals compared to potential reaction with dissolved oxygen
(in the case of aryl radicals) or radical coupling to give hydroxylated biphenyls (as under the experimental conditions presented here). The apparent
absence of brominated biphenyls and dihydroxybiphenyls from bimolecular radical coupling (from different molecules of starting material) in the
current study versus the work of Watanabe and Tatsukawa (1987) is likely due to the low concentrations used in the present investigations
(∼ 10− 9 M). Our low concentrations of starting material would favor preferential hydrogen abstraction from either acetonitrile, impurities in the
distilled water, or a variety of natural products in the seawater. In addition, the reaction of dissolved oxygen with aryl radicals to yield bromophenols
would be promoted under the present conditions.
Br

Br

Br
O

Br

Br

O



Br
O

+
Br

Br
Br

Br

+

Br

Br
Br

Δ

Br

Br

H
Br

Br
Br

Br

OH Br
Br

Br

Br

Br

Scheme 1. Mechanism for the primary photo-Fries rearrangement of BDE153 yielding 2′,3,4′,5,5′,6-hexabromo-2-hydroxybiphenyl.

S. Rayne et al. / Environment International 32 (2006) 575–585

O

Br

O
Br

Br

Br

hν(-HBr or Br2)

583

hν(ortho Photo-Fries rearrangement)

OH Br

hν(-HBr or Br2)

Br
Br Br

Scheme 2. Interconnected photochemical pathways of ortho-substituted PBDEs, PBDFs, and ortho-brominated 2-hydroxybiphenyls.

The advanced photohydrodebromination of PBDFs and 2-hydroxybiphenyls after 1 min irradiation in acetonitrile, while these analytes were
not observed in aqueous systems, may be dependent on either or both of the following mechanistic details. The corresponding photochemical
pathways may be absent or significantly reduced when water is present. In addition, water may enhance the conversion to – and subsequent
photohydrodebromination of – PBDFs and 2-hydroxybiphenyls, such that any of these compounds formed during the initial stages of
photolysis are then rapidly debrominated to the parent systems before the first analytical time scale. Although authentic standards were
available for the parent 2-hydroxybiphenyl and dibenzofuran analytes, there was no evidence of these analytes in the photolysis extracts as
investigated by SIM and full-scan GC–MS analyses. However, the presence of these analytes would readily be masked by “noise” from the
background hydrocarbon impurities present in photolysis extracts when target analytes are present at nanomolar concentrations, and thus, their
presence cannot be ruled out.
Evidence for enhanced photohydrodebromination of PBDFs and 2-hydroxybiphenyls (relative to PBDEs) comes from a previous
report on the photochemistry of BDE209, which suggested a similarly rapid PBDF photohydrodebromination pathway (Eriksson et al.,
2004). In addition, PBDFs are known to have rapid debromination kinetics with high quantum yields and greater molar extinction
coefficients at wavelengths > 280nm (Watanabe et al., 1994; Lenoir et al., 1991). As well, hydroxylic solvents (or their presence as
cosolvents) are known to favor the photo-Fries rearrangement (Ogata et al., 1970). Because water favors the photo-Fries rearrangement
and appears to increase the photohydrodebromination kinetics of PBDFs, it is possible that rapid photochemical conversion to PBDFs
and 2-hydroxybiphenyls – and subsequent photohydrodebromination prior to the first analytical time scale – may help explain the
apparent absence of these compound classes in our experimental aqueous systems.
An additional complexity in elucidating the primary and subsequent photochemistry of BDE153 is the interconnected nature of the
photochemical pathways leading to the PBDE, PBDF, and brominated 2-hydroxybiphenyl products (Scheme 2). Di-ortho substituted dithrough hexa-BDEs may form the corresponding PBDFs through loss of two bromine atoms (formal loss of Br2). As well, formal
loss of HBr from mono-ortho substituted di- through hexa-BDEs may also lead to production of the corresponding PBDFs. That
1,2,4,7,8-PeBDF is formed from BDE153, while 2,3,7,8-TeBDF is not, suggests that photochemical loss of HBr may be preferred over
loss of Br2.

Br
O

Br

Br

Br
Br
1,2,4,7,8-PeBDF
30%


Br

Br

Br

O
Br

Br
Br
Br
BDE153


20%

Br

Br

O


Br

+
Br

Br
BDE99

Br

Br

O
+
Br

Br
Br
Br
BDE101

20%

OH Br
Br
ΣBr=4
Scheme 3. Observed primary photoproducts of BDE153.

O
Br
Br
Br
BDE118


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