Geology Reference
In-Depth Information
6.6.3.2 PBDE and TBBPA Photochemistry. For aryl-halides, the
bromine-carbon bond is not as strong as the chorine-carbon bond, with
a typical bond-dissociation energy of the bromine-carbon bond of 301
kJ mol
1
compared to 360 kJ mol
1
for the chlorine-carbon bond.
48
Therefore, unlike PCBs, many PBDEs are more susceptible to loss of the
halogen atoms and photochemical decomposition has been recognised
as an important route for both debromination and transformation for
various PBDE congeners present in the wider environment. Several
studies have investigated the photochemical degradation of PBDEs
46,49
to determine rates of degradation and identify photodegradation by-
products in aqueous solutions under simulated light conditions. Figure 9
shows the absorption spectra (e) of seven PBDE congeners dissolved in
tetrahydrofuran (several of the higher brominated congeners are only
sparingly soluble in MeOH/H
2
O) and exposed to a UV-light source in
the study of Eriksson et al.
46
Clearly the higher brominated congeners
absorb light at longer wavelengths, possessing higher l
max
values than
less brominated congeners. As such, the rate of degradation of PBDEs
by UV light in the sunlight region was found to be dependent on the
(
×
10
-4
)
2.5
3000
2500
2.0
2000
5
1.5
6
8
1500
2
1.0
1
3
1000
7
4
0.5
500
0
0
290
300
310
320
330
340
350
λ ( (
nm)
Figure 9 Absorbance spectra (expressed as e, the molar absorbance coefficient) of seven
PBDE congeners. The line numbers ar: (1) BDE-209; (2) BDE-206; (3)
BCDE-203; (4) BDE-183; (5) BDE-155; (6) BDE-85; (7) BDE-77; line 8
represents the UV light irradiance in units of J s
1
cm
2
(or W cm
2
)
From Eriksson et al.
46
courtesy of the American Chemical Society
