Page 710 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 51

Polychlorinated Biphenyls,

Polybrominated Biphenyls,

Polychlorinated Dibenzo-p-Dioxins,

and Polychlorinated Dibenzofurans

Prasada Rao S. Kodavanti, Matthew C. Valdez, Jae-Ho Yang and Margarita Curras-Collazo

INTRODUCTION Certain approximate stereoisomers in this group, often
collectively referred to as dioxins and dioxin-like com-
Polychlorinated biphenyls (PCBs), polybrominated biphe-
pounds, induce a common suite of effects and have a com-
nyls (PBBs), polychlorinated dibenzo-p-dioxins (PCDDs),
mon mechanism of action mediated by binding of the
and polychlorinated dibenzofurans (PCDFs) belong to a
polyhalogenated aromatic hydrocarbons (PHAHs) ligand to
group of organic compounds that are well-known for their
a specific high-affinity cellular protein. This group of che-
contamination in the global environment, bioaccumulating
micals includes seven PCDD congeners, 10 PCDF conge-
and biomagnifying in the food chain, and exerting toxic
ners, and 12 PCB congeners. While the PBB congeners
effects in wildlife, veterinary animals, and humans
analogous to the 12 PCB congeners could also be consid-
(Huwe, 2002; Schecter et al., 2006; Kodavanti et al.,
ered dioxin-like chemicals, the relatively short commercial
2014a,b; Kodavanti and Loganathan, 2017). PCBs and
lifespan and restricted environmental distribution of PBBs
PBBs were produced commercially for a variety of appli-
generally precludes them from consideration. The proto-
cations, while the PCDDs and PCDFs occur as byproducts
type for the dioxins is 2,3,7,8-tetrachlorodibenzo-p-dioxin
of industrial and natural processes. PCBs and PBBs are
(TCDD). Toxicity and persistence of the PHAHs are deter-
structurally similar, and are formed by substituting chlo-
mined by structure, with lateral substitutions on the ring,
rine or bromine, respectively, for hydrogen on the biphe-
resulting in the highest degree of toxicity. For the PCDDs
nyl molecule (Fig. 51.1). Theoretically, there are 209
and PCDFs, congeners with chlorines in the 2, 3, 7, and 8
possible PCB and PBB congeners considering the five
positions fall into this category. The TCDD-like PCB con-
chlorine- or bromine- binding sites on each ring. Each
geners are the non-ortho- and mono-ortho-substituted com-
congener has been assigned a unique number from 1 to
pounds with no chlorines or no more than one chlorine on
209 in accordance with the rules of the International 0 0
the 2, 2 ,6, or 6 position (Schecter et al., 2006; Kodavanti
Union of Pure and Applied Chemistry. Commercial PCB
et al., 2014a,b).
and PBB products were mixtures of congeners that dif-
The PCDDs, PCDFs, and PCBs are widely distrib-
fered with respect to the number and positions of chlori-
uted into the global environment due to long-range trans-
nation or bromination. PCDDs are composed of two
port and are very resistant to environmental degradation
benzene rings connected by two oxygen atoms and con-
(Kodavanti et al., 2014a,b). As a result, they readily
tain four to eight chlorines, for a total of 75 congeners
accumulate in the food chainwiththe greatest tissue
(Fig. 51.1). PCDFs are also composed of two connected
concentrations in species at the higher trophic levels.
benzene rings. The rings have one oxygen molecule
Residues have been detected in a variety of animal spe-
between them and have four chlorine binding sites avail-
cies, including humans (Safe, 1998; Loganathan and
able on each ring (Fig. 51.1). There are 135 different
Lam, 2012). In some situations, the concentrations of
PCDF congeners (Huwe, 2002; Kodavanti et al., 2014a,b;
these chemicals in the environment are high enough to
Loganathan and Masunaga, 2015).
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00051-9
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