Page 729 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

694 Section |IX Gases, Solvents and Other Industrial Toxicants

VetBooks.ir influence metabolism of chemicals endogenous to the levels of a food chain. PFOS has been shown to biocon-
centrate from water into benthic invertebrates by three
body as well as that of foreign chemicals. Compared to
orders of magnitude and to bioaccumulate in top predators
chlorine atoms, bromine atoms are in general lost more
easily from the molecule (more “reactive”), rendering by 5- to 20-fold (Kannan et al., 2005a). PFCs are also
PBDEs more susceptible to various types of degradation detected in wildlife and human tissues. Bald eagles, river
and metabolism than PCBs (Table 52.1). Trace analysis otters, and bottlenose dolphins accumulate PFOS in their
of these commercial mixtures for other brominated con- livers at microgram per gram tissue concentrations
taminants revealed the presence of PBBs and PBDFs, but (Senthilkumar, 2005; Houde et al., 2006). Furthermore,
not PBDDs, at levels above the limit of detection (Hanari fluorinated acids are even found in ocean waters, Arctic
et al., 2006). It is known that PBDEs, upon pyrolysis at ice, and Antarctic environment and biota (Yamashita
900 C, release PBDFs and PBDDs, and the amount of et al., 2011). Physical and chemical properties of PFCs

these contaminants depends on the conditions of pyrolysis are summarized in Table 52.2. PFCs are ubiquitous in the
(Buser, 1986; Thoma et al., 1986; Shaw et al., 2010). environment and bioaccumulate in animals and humans;
their toxic properties are being revealed (Gill et al., 2004;
Stein et al., 2014).
Perfluorinated Compounds
Perfluorinated compounds have ionic and neutral charac-
ters. Because of their thermodynamically strong covalent TOXICOKINETICS
carbon fluorine bonds, these compounds were initially Brominated Flame Retardants
considered as nontoxic and nonmetabolizable. It is appar-
ent that the carbon fluorine bond has maximum energy The major pathway of TBBPA exposure is through diet,
compared to other bonds. Most of them were also consid- despite its low levels in the average diet in the United
ered to have little volatility. PFCs with considerable vola- States. The bioavailability of TBBPA in circulation is very
tility are fluorotelomer alcohols (FTOHs or hydroxylated low even after administration of a high dose to rats due to
PFCs), which together with some sulfonamide-based rapid metabolism, indicating its low potential to bioaccu-
PFCs may undergo transformation in the environment to mulate and cause toxic effects (Shaw et al., 2010). TBBPA
form more persistent PFOA or similar perfluoroalkyl car- or its metabolites such as TBBPA-glucuronide, a diglucur-
boxylic or sulfonic acids (Buck, 2015). PFCs are water onide, and a mixed glucuronide-sulfate were detected in
soluble in the several parts per million range (Table 52.2). bile and were excreted predominantly in feces; however,
PFCs with unique surface modification properties readily metabolites were also found in urine (Hakk et al., 2000).
bind to surfaces including blood globulins (Kodavanti After intravenous injection into rats, TBBPA was also
et al., 2008). rapidly cleared, and the majority of the intravenous dose
The stability of the carbon fluorine bond contributes was also recovered in the feces (Kuester et al., 2007).
to the persistence of PFCs in the environment and their Kinetic studies in rodents and humans suggest low absorp-
ability to bioaccumulate and biomagnify in higher trophic tion of TBBPA from the gastrointestinal tract and rapid

TABLE 52.1 Physical and Chemical Properties of Polybrominated Diphenyl Ethers
Property PBDEs (penta-, octa-, and deca-PBDE)
Physical state at room temperature Pale yellow liquid to white powder
Molecular weight 564 959.2
Water solubility (μg/L at 25 C) 1

Boiling point ( C) ,300 to .400
Melting point ( C) 85 306

Vapor pressure at 25 C (mmHg) 2.2 3 10 27 to 9 3 10 210

Log K ow 5.7 8.27
3
Henry’s law constant (atm m /mol) 7.5 3 10 28 to 1.2 3 10 25
Source: Data from ATSDR (Agency for Toxic Substances and Disease Registry), 2004. Toxicological Profile for
Polybrominated Diphenyl Ethers and Polybrominated Biphenyls (ATSDR, 2004) and De Wit, C.A., 2002. An
overview of brominated flame retardants in the environment. Chemosphere, 46, 583 624 (De Wit, 2002).