Geology Reference
In-Depth Information
PBDE structure
TBBPA
CH
3
CH
3
O
Br
Br
xBr
HO
yBr
OH
Br
Br
Figure 8 Generic structure of the polybrominated diphenyl ether (PBDE) and the
structure of tetrabrominated bisphenol-A (TBBPA). Note the x and y on the
PBDE structure represent the number of bromine atoms around each phenyl
ring (where x
¼
1-5 and y
¼
1-5). The maximum number of 5 bromine atoms
on each ring results in the fully brominated, decabrominated diphenyl ether
electrical equipment in general, and are also used extensively as additives
in textiles and flexible foams, whereby they are dissolved in the polymer
before it is formed into shape or blown into its foam structure. As a
result, PBDEs, will, over time, volatilise from the equipment or furnish-
ing into which they have been added. TBBPA, on the other hand, is
primarily used as a reactive flame retardant i.e. it is covalently bound
into mainly epoxy and polycarbonate resins used in the manufacture of
printed circuit boards within electronic equipment.
6.6.3.1 Demand for BFRs. PBDEs are grouped into homologues ac-
cording to the number of bromine atoms around the phenyl rings and are
available commercially as three different formulations; pentaBDE, oct-
aBDE and decaBDE, whereby the penta- and octaBDE contain between 10
and 20 individual congeners and the decaBDE formulation largely com-
prising of the single congener, decabrominated diphenyl ether. Worldwide
demand of PBDEs is high, and is estimated to be 7500 t for pentaBDE,
3760 t for octaPBDE and 56100 t for decaBDE for 2001,
46
although
quantities of the pentaBDE and octaPDE are likely to change following a
ban by the European Union and a voluntary phase-out by one of the main
industrial producers in the US. Concern arises due to PBDE occurrence in
human blood and breastmilk, with evidence of increasing PBDE levels in
wildlife.
44
The physical-chemical properties of the PBDEs are analogous to
'legacy' persistent organic pollutants such as polychlorinated biphenyls
(PCBs), previously used in the electrical industry. For example, PBDEs are
semi-volatile (although the decabrominated congener is considered non-
volatile at ambient temperatures) with log K
ow
values of 5.9-6.2 for tetra-
BDE, 6.5-7.0 for pentaBDE, 8.4-8.9 for octaBDE and 10 for decaBDE;
46
evidence of their propensity for movement in the environment and ability
to strongly partition to fats/lipids.
It is estimated that worldwide demand for TBBPA in 2001 was some
120,000 tonnes
47
and concern over this chemical (and related phenols) has
arisen due to its occurrence in sewage sludge, aquatic sediments and fish.
