Geoscience Reference
In-Depth Information
Chlorinated aromatics, including monochlorobenzene (MCB), o-dichloroben-
zene (o-DCB), and p-dichlorobenzene (p-DCB), are the major chlorinated aromatic
species produced on an industrial scale. MCB is used as both a chemical interme-
diate and a solvent. As an intermediate, it is used to produce chloronitrobenzene,
pesticides, and pharmaceutical products. In solvent applications, MCB is used in the
manufacture of isocyanates. Its high solvency allows it to be used with many types of
resins, adhesives, and coatings. The o-DCB is used primarily for organic synthesis,
especially in the production of 3,4-dichloroaniline herbicides. Like MCB, it can be
used as a solvent, especially in the production of isocyanates. It is also used in motor
oil and paint formulations. The p-DCB is used as a moth repellent and for the control
of mildew and fungi. It also is used for odor control. It is a chemical intermediate for
the manufacture of pharmaceuticals and other organic chemicals.
4.2.2 Brominated Flame Retardants
The term brominated flame retardant (BFR) incorporates more than 175 different
types of substances, which form the largest class of flame retardants; other classes
are phosphorus-containing, nitrogen-containing, and inorganic flame retardants
(Birnbaum and Sttaskal
2004
). The major BFR substances in use today (depicted
in Fig.
4.6
) are tetrabromobisphenol A (TBBPA), hexabromocyclododecane
(HBCD), and mixtures of polybrominated diphenyl ethers (PBDEs) (namely,
decabromodiphenyl ether (DBDE), octabromodiphenyl ether (OBDE), and pent-
abromodiphenyl ether (pentaBDE)).
BFRs have been added to various products (e.g., electrical appliances, building
materials, vehicle parts, textiles, furnishings) since the 1960s, in growing rates
(15-fold from the mid-1960s to 2003; DePierre
2003
). BFRs usually are classified
as semivolatile and hydrophobic, but these properties vary due to the large
diversity of this group of compounds.
BFRs tend to accumulate in organic-rich media, such as soils and sediments,
and lipid-rich biotic tissues and are expected to biomagnify in food chains
(DePierre
2003
). Two incidents in the 1970s brought attention to the toxic
potential of BFR. The first incident was in a farm in Michigan in 1974, where
polybrominated biphenyls were mixed accidentally with animal feed. As a result,
individuals living on affected farms and consumers of contaminated farm products
were exposed to these compounds for months before the mistake was discovered.
The outcomes of the contamination were loss of livestock and long-term impact on
the health of farm families (Birnbaum and Sttaskal
2004
; Dunckel
1975
). The
second case involved tris(2,3-dibromopropyl)phosphate (tris-BP), which is a
mutagen and causes cancer and sterility in animals; it was found to be absorbed
from fabric by people (Blum et al.
1978
). These two BFRs were phased out, as a
consequence (Birnbaum and Sttaskal
2004
).
The potential toxicity of these compounds is considered here for the PBDE
group and HBCD, which are among the most ubiquitous BFRs to date. PBDEs
