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This article was downloaded by: [Rayne, Sierra][University Of British Columbia]
On: 23 July 2010
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Journal of Environmental Science and Health, Part A

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pKa values of the monohydroxylated polychlorinated biphenyls (OHPCBs), polybrominated biphenyls (OH-PBBs), polychlorinated diphenyl
ethers (OH-PCDEs), and polybrominated diphenyl ethers (OH-PBDEs)
Sierra Raynea; Kaya Forestb
a
Ecologica Research, Penticton, British Columbia, Canada b Department of Chemistry, Okanagan
College, Penticton, British Columbia, Canada
Online publication date: 23 July 2010
To cite this Article Rayne, Sierra and Forest, Kaya(2010) 'pKa values of the monohydroxylated polychlorinated biphenyls

(OH-PCBs), polybrominated biphenyls (OH-PBBs), polychlorinated diphenyl ethers (OH-PCDEs), and polybrominated
diphenyl ethers (OH-PBDEs)', Journal of Environmental Science and Health, Part A, 45: 11, 1322 — 1346
To link to this Article: DOI: 10.1080/10934529.2010.500885
URL: http://dx.doi.org/10.1080/10934529.2010.500885

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Journal of Environmental Science and Health Part A (2010) 45, 1322–1346
C Taylor & Francis Group, LLC
Copyright
ISSN: 1093-4529 (Print); 1532-4117 (Online)
DOI: 10.1080/10934529.2010.500885

pKa values of the monohydroxylated polychlorinated
biphenyls (OH-PCBs), polybrominated biphenyls
(OH-PBBs), polychlorinated diphenyl ethers (OH-PCDEs),
and polybrominated diphenyl ethers (OH-PBDEs)
SIERRA RAYNE1 and KAYA FOREST2
Downloaded By: [Rayne, Sierra][University Of British Columbia] At: 16:12 23 July 2010

1
2

Ecologica Research, Penticton, British Columbia, Canada
Department of Chemistry, Okanagan College, Penticton, British Columbia, Canada

The SPARC software program aqueous pKa prediction module was validated against corresponding experimental acidity constants
for chlorinated and brominated phenols and the limited experimental aqueous pKa data sets for monohydroxylated polychlorinated
biphenyls (OH-PCBs), polychlorinated diphenyl ethers (OH-PCDEs), and polybrominated diphenyl ethers (OH-PBDEs). pKa values
were then estimated for all 837 monohydroxylated mono- through nona-halogenated congeners in each of the OH-PCB, OH-PCDE,
and OH-PBDE classes, as well as for the monohydroxylated polybrominated biphenyls (OH-PBBs), giving a total of 3348 compounds.
Large intrahomolog pKa variation by up to six units is expected within each contaminant class, with pKa values ranging from about 4
to 11 dependent on the degree and pattern of halogenation. Increasing halogenation generally decreased the average pKa within each
homolog group. Significant intrahomolog differences in pKa values exist between OH-PCB, OH-PBB, OH-PCDE, and OH-PBDE
congeners, including large acidity constant variation between isomers with equivalent halogenation patterns but varying location
of the hydroxy moiety. Congener specific pH dependent investigations into the partitioning and degradation behaviors of these
compounds are necessary, including greater consideration of analyte ionization effects during their extraction and analysis.
Keywords: Polychlorinated biphenyls, polybrominated biphenyls, polychlorinated diphenyl ethers, polybrominated diphenyl ethers,
monohydroxylated derivatives, acidity constants, environmental fate.

Introduction
Polychlorinated biphenyls (PCBs), polybrominated
biphenyls (PBBs), polychlorinated diphenyl ethers
(PCDEs), and polybrominated diphenyl ethers (PBDEs)
(Fig. 1) are established contaminants known to be
widely distributed in the environment.[1−5] Substantial
effort has gone into better understanding the fate and
biological effects of these compounds over the past
several decades. In general, much of the current interest
involves the degradation products of PCBs, PBBs, PCDEs,
and PBDEs, particularly their hydroxylated (OH-PCB,
OH-PBB, OH-PCDE, and OH-PBDE) and methoxylated
(MeO-PCB, MeO-PBB, MeO-PCDE, and MeO-PBDE)
derivatives. In this context, a number of studies have investigated OH-PCB, OH-PBB, OH-PCDE, and OH-PBDE
Address correspondence to Sierra Rayne, Ecologica Research, Penticton, British Columbia, Canada; E-mail:
rayne.sierra@gmail.com
Received March 8, 2010.

concentrations and patterns in commercial mixtures,[6,7]
natural waters[8−10] and biological systems,[11−27] as well
as examined quantitative structure-activity relationships
(QSARs) for various endpoints such as toxicological
effects and biodegradation rate constants.[28−33]
The hydroxylated members of these contaminant classes
contain ionizable phenolic groups whose dissociation will
play a key role in their partitioning behavior in environmental and biological systems.[34] Two common and widely applied partitioning constants in environmental science and
engineering are the air-water partitioning constant (Kaw )
and the octanol-water partitioning coefficient (Kow ). Ionized substrates are generally considered nonvolatile relative to their unionized forms, yielding an effective Kaw of
zero for the ionic form when conducting gas-aqueous phase
modeling exercises. The Kow value (also known as log P for
the molecular form of a compound) is more accurately
reformulated as the Dow (distribution ratio) for ionizable
compounds. The Dow relates the pKa values of ionizible
moieties and the Kow values for the molecular and dissociated forms with the pH, and can differ substantially

Monohydroxylated biphenyls and ethers

1323
Table 1. Comparison between experimental and SPARC estimated pKa values for chlorophenols and bromophenols.

Downloaded By: [Rayne, Sierra][University Of British Columbia] At: 16:12 23 July 2010

Fig. 1. General structures of polychlorinated biphenyls (PCBs),
polybrominated biphenyls (PBBs), polychlorinated diphenyl
ethers (PCDEs), and polybrominated diphenyl ethers (PBDEs).

from the Kow value.[35,36] Consequently, inclusion of pH
dependent partitioning effects is critical towards a reliable
understanding of how OH-PCBs, OH-PBBs, OH-PCDEs,
and OH-PBDEs behave in natural, engineered, and biological systems, and the manner and potency by which they
exert their toxicological effects.
With 837 individual congeners in each of the monothrough nona-halogenated OH-PCB, OH-PBB, OHPCDE, and OH-PBDE classes, there is a need to consider their congener specific partitioning behavior to a
greater level of detail than with the parent nonhydroxylated
analogs. The known strong dependence of phenolic acidity
constants on aryl substitution patterns means that there
are possibly large intrahomolog variations in partitioning
constants such as Dow and Kaw that require consideration
in multimedia modeling efforts, environmental monitoring
programs, and toxicological studies. Furthermore, degradation rates, mechanisms, and products are expected to
be different between the molecular and dissociated forms.
Thus, we have undertaken a comprehensive modeling investigation into the pKa values of all mono- through
nona-halogenated OH-PCB, OH-PBB, OH-PCDE, and
OH-PBDE congeners. Selected congeners are examined in
greater detail to illustrate the large differences in pKa values
depending on hydroxyl group location and halogenation
patterns, and resulting effects on partitioning behavior.

Materials and methods
There are 837 possible monohydroxylated mono-through
nona-halogenated OH-PCB, OH-PBB, OH-PCDE, and
OH-PBDE isomers in each contaminant class. The substitution patterns of all congeners are provided in Appendix
Table 1, which also provides a useful literature reference
for all other potential coupled monoderivatized/monothrough nona-substituted biphenyl and diaryl ether compounds. The total number of congeners in each class is
in agreement with previous reports.[9] SMILES molecular
formats[37,38] were generated for each compound and used
in the physicochemical property estimations.

Compound

Expt. pKa

SPARC pKa

phenol
2-chlorophenol
3-chlorophenol
4-chlorophenol
2,3-dichlorophenol
2,4-dichlorophenol
2,5-dichlorophenol
2,6-dichlorophenol
3,5-dichlorophenol
2,4,5-trichlorophenol
2,4,6-trichlorophenol
2,3,4,6-tetrachlorophenol
pentachlorophenol
2-bromophenol
3-bromophenol
4-bromophenol
2,4-dibromophenol
2,6-dibromophenol
3,5-dibromophenol,
2,4,6-tribromophenol
pentabromophenol

9.99[43,44]
8.56[43]
9.12[43]
9.41[43,44]
7.60[45]
7.80[44−46]
7.30[45]
6.60[45]
8.10[45]
6.90[45]
6.00[45,46]
5.20[45,46]
4.70[45,46]
8.45[43]
9.03[43]
9.37[43]
7.79[47]
6.67[47]
8.06[47]
6.08[47]
4.40[47]

9.90
8.34
9.05
9.29
7.48
7.72
7.48
6.79
8.19
6.86
6.17
5.31
4.46
8.36
9.03
9.27
7.72
6.85
8.16
6.21
4.48

pKa values were estimated using SPARC (http://ibmlc2.
chem.uga.edu/sparc/; September 2009 release w4.5.1529s4.5.1529). Hilal et al. have previously validated the SPARC
pKa prediction module for >4000 compounds, yielding
overall root mean squared errors of <0.4 pKa units.[39]
We have also previously validated the SPARC pKa prediction module for carboxylic acids and sulfonamides.[40−42] In
addition to these prior efforts, well established chlorophenol and bromophenol experimental pKa values (Table 1),
as well as the limited experimental pKa database for OHPCBs, OH-PCDEs, and OH-PBDEs (Table 2), were used
to further validate the SPARC estimation program.
Octanol-water partition coefficients (log Kow /log P) and
octanol-water distribution ratios (log Dow ) for selected congeners were generated using SPARC with options for 25◦ C
and an ionic strength of zero. Air-water partition coefficients (log Kaw ) for selected congeners were also estimated
by SPARC in dimensionless units of (mol/L)/(mol/L) using the following default options: total solids concentration
of 1 mg/L comprised of 100% sand distributed entirely with
a charge of +1 and a sand surface area of 100,000 cm2 /g.
Reports on validating the SPARC log P/Dow and Kaw modules are available elsewhere.[48,49] Full congener log P estimates for all compounds in each class were generated using
ALOGPS 2.1 (http://www.vcclab.org/lab/alogps/).[50−55]
In addition to the rigorous log P prediction validations
conducted on ALOGPS by its authors, we have also shown
this program to be competitive with other widely used
software (e.g., KOWWIN, COSMOfrag) for log P estimation of environmental contaminants.[56]

1324

Rayne and Forest

Table 2. Comparison between experimental and SPARC estimated pKa values for OH-PCBs, OH-PCDEs, and OH-PBDEs.

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Compound
4-OH CB 107
4-OH CB 187
4-OH CB 1
2-OH CB 2
4-OH CB 2
4 -OH CB 3
2 -OH CB 9
4 -OH CB 9
2-OH CB 14
4-OH CB 14
4-OH CB 39
3 -OH CB 61
4 -OH CB 61
2 -OH CB 106
6 -OH CB 106
2 -OH CDE 28 (triclosan)
6-OH BDE 47
6 -OH BDE 49
2 -OH BDE 66
6-OH BDE 85
6-OH BDE 90
6-OH BDE 137

Expt. pKa

SPARC pKa

5.4±0.2[14]
4.1±0.2[14]
8.1–8.3[62,63]
8.5[62,63]
8.0–8.1[62,63]
9.6–9.8[62,63]
8.5–9.7[62,63]
9.4–9.5[62,63]
9.5[62,63]
6.9–7.0[62,63]
6.4–6.8[62,63]
10.1[62,63]
9.5–10.4[62,63]
8.1–8.5[62,63]
9.7[62,63]
7.8[58,59]
∼ 7[57]
∼< 6.2[57]
∼< 6.2[57]
∼< 6.2[57]
∼< 6.2[57]
∼< 6.2[57]

5.6
4.7
8.8
9.1
7.9
9.4
10.5
9.5
8.5
6.4
6.3
9.6
9.4
8.8
9.7
8.0
7.3
6.7
6.7
6.6
6.1
5.3

Results and discussion
Method validation
Prior to estimating the pKa values for the monohydroxylated PCB, PBB, PCDE, and PBDE congeners, we validated the prediction approach using established chlorophenol and bromophenol experimental pKa data sets as surrogate models (Table 1). SPARC displays a mean signed
error of 0.00, a mean absolute error of 0.12, and a root
mean squared error of 0.13 pKa units for these 21 phenols. A limited experimental pKa data set is also available
for select OH-PCB, OH-PCDE, and OH-PBDE congeners
(Table 2). We also find good agreement with the SPARC
estimates for these compounds.
Two other studies have reported pKa values for OHPBDE derivatives in mixed methanol:water solutions.
Malmberg[60] reported a pKa of 7.8 for 6-OH BDE 47
in 45% methanol:55% water (v/v). As part of their photochemical studies on mixed chlorinated and brominated
monohydroxy diphenyl ethers, Steen et al.[61] used spectrophotometric methods to obtain pKa values of 8.28 ±
0.02, 7.94 ± 0.03, 7.20 ± 0.02, and 6.29 ± 0.02 for 6-OH
BDE 47, 3-Cl-6-OH BDE 47, 5-Cl-6-OH BDE 47, and 3,5Cl-6-OH BDE 47, respectively, in 60% methanol:40% water
(v/v). Organic cosolvents significantly suppress phenolic
ionization. Thus, these mixed solvent pKa values understandably differ substantially from (i.e., are about 1 to 1.5
units higher than) the corresponding pure aqueous SPARC

pKa values of 7.27, 6.60, 5.76, and 5.14. As such, the existing environmental photochemical interpretations[61] regarding the relative reactivities of the phenol and phenolate forms for these compounds will likely need to be reconsidered using expected monomeric aqueous pKa values
rather than the higher reported experimental mixed aqueous:organic solvent acidity constants.
Estimated OH-PCB, OH-PBB, OH-PCDE,
and OH-PBDE pKa values
Having validated the pKa estimation approach, we then
calculated pKa values for each of the 837 monohydroxylated mono- through nona-halogenated PCB, PBB,
PCDE, and PBDE classes (i.e., a total of 3348 compounds)
(Fig. 2). With increasing homolog group for each class
of compounds, the pKa generally declines, but there is
wide intrahomolog variability (up to 6 pKa units) in the
acidity constants for all homolog/class combinations.
Minimum and maximum pKa ranges for each compound
class are as follows: OH-PCBs, 4.6 to 10.7; OH-PBBs, 4.6
to 10.8; OH-PCDEs, 4.1 to 9.2; and OH-PBDEs, 4.2 to
9.3. Consequently, while higher substituted congeners are
more likely to have lower pKa values requiring explicit
dissociative consideration of the phenolate group in
engineered and natural systems and in vivo, all homolog
groups for all four classes of compounds contain members
whose pKa values are estimated to be sufficiently low
that at least partial dissociation is expected in biological
and environmental matrices. A full listing of all OH-PCB,
OH-PBB, OH-PCDE, and OH-PBDE structures and
estimated pKa values is provided in Appendix 1. Given
the fundamental importance the acidity constants play in
our improved understanding of how these contaminants
behave in the environment, additional experimental testing
of this pKa data set (particularly with appropriately chosen
end members) appears to be a research priority for the field.
Thus, for accurate reporting of OH-PCB, OH-PBB, OHPCDE, and OH-PBDE concentrations and patterns in environmental and biological samples, the matrix must be
acidified to about pH 2 prior to any extractions to ensure
all potential congeners are captured by the method. This
process has not been followed in all studies. For example,
some groups have initially extracted biological materials
with pure and mixed organic solvents such as hexane, acetone, and MTBE prior to a subsequent strong base extraction that is intended to fractionate the phenolic derivatives
from neutral compounds. However, the partition coefficients for OH-PCB, OH-PBB, OH-PCDE, and OH-PBDE
congeners will vary substantially depending on the pKa ,
biasing analyte collection efficiency during the initial organic solvent extraction process.
Using the ALOGPS 2.1 software program, we estimated
log P values for the molecular forms of all 3348 OH-PCB,
OH-PBB, OH-PCDE, and OH-PBDE congeners (Fig. 3
and Appendix 2). There is little intrahomolog difference in

1325

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Monohydroxylated biphenyls and ethers

Fig. 2. SPARC estimated pKa values for all 837 congeners in each of the (a) OH-PCB, (b) OH-PBB, (c) OH-PCDE, and (d) OH-PBDE
classes. Halogenation homolog group divisions are shown as vertical dashed lines.

the log P values regardless of halogen and/or hydroxy substitution patterns. However, the log Dow values of the corresponding dissociated phenolate anions are not expected
to display such intrahomolog homogeneity. As an example, we have used SPARC to estimate the pH dependent

log Dow values for the six OH-PCB 43 congeners (Fig. 4).
These congeners have the following estimated pKa values
ranging over >4 units: 4-OH CB 43, 5.58; 6-OH CB 43,
7.74; 3 -OH CB 43, 8.14; 4 -OH CB 43, 8.59; 5 -OH CB
43, 9.07; and 6 -OH CB 43, 9.63. Whereas the location

Rayne and Forest

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1326

Fig. 3. ALOGPS 2.1 estimated log P values for the molecular forms of all 837 congeners in each of the (a) OH-PCB, (b) OH-PBB, (c)
OH-PCDE, and (d) OH-PBDE classes.

of the hydroxyl group on OH-PCB 43 has little influence
on the log Dow for the molecular form (i.e., the log P
or log Kow in common terminology) at pH<5 (±0.5 log
Dow difference among all six congeners), at a marine pH

of 8.1 there is a 3-unit log Dow difference between the
least hydrophobic congener (4-OH CB 43; log Dow ∼3.5)
and the most hydrophobic congener (5 -OH CB 43; log
Dow ∼6.5).

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Monohydroxylated biphenyls and ethers

Fig. 4. SPARC estimated pH dependent (a) log Dow and (b) log
Kaw values for the six monohydroxy PCB 43 congeners. Vertical
dashed lines are shown at pH 5.5 (average precipitation), 7.4
(physiological), and 8.1 (marine).

Interestingly, whereas there is only a small difference
(<0.5 units) in the log Dow values of the molecular forms,
under highly alkaline conditions there is a larger (∼2
log Dow units) differentiation in the hydrophobicity of
the dissociated species. This pH dependent log Dow behavior is analogous to that reported experimentally for
related compounds such as chlorinated and brominated
phenols and tetrabromobisphenol A.[64−66] We also note
that good agreement in the following log P estimates
for these six compounds was found between SPARC and
ALOGPS (log Dow values cannot be readily estimated by
ALOGPS): 4-OH CB 43, SPARC=6.21, ALOGPS=5.91;
6-OH CB 43, SPARC=6.00, ALOGPS=5.85; 3 -OH CB
43, SPARC = 6.25, ALOGPS = 5.89; 4 -OH CB 43,
SPARC = 6.46, ALOGPS = 5.94; 5 -OH CB 43, SPARC =
6.46, ALOGPS = 5.91; and 6 -OH CB 43, SPARC=6.18,
ALOGPS=5.86.
Consequently, since isotopically labelled internal standards are not available and employed for all possible OHPCB, OH-PBB, OH-PCDE, and OH-PBDE congeners in
the source material, the literature database of concentrations and patterns likely needs to be evaluated on a case-

1327
by-case basis for data quality, which greatly complicates
comparing concentrations and patterns between different
investigations. Furthermore, in vivo partitioning behavior
between various tissues (i.e., blood, liver, lipids, muscle, etc.)
will not be constant within or between homolog groups or
classes. As such, some OH-PCB, OH-PBB, OH-PCDE, and
OH-PBDE congeners with lower pKa values may preferentially reside in hydrophilic/proteinophilic tissues, whereas
less acidic members may prefer more lipidic environments.
Thus, single tissue assessments differentially distort any
implied body burdens, and toxicological studies should be
focused on the congeners most likely to preferentially partition into the matrix of interest.
For example, in their studies of OH-PBDEs in surface
waters and precipitation, Ueno et al.[10] stated that – with
a precipitation pH of about 4 to 5 in their sampling region
– the OH-PBDE target analytes would be undissociated
and thereby efficiently sorbed by XAD-2 resin. Among the
reported OH-PBDEs in Ueno et al.,[10] we estimate the following pKa values: 3 -OH BDE 7, 9.11; 4 -OH BDE 17,
8.18; 6 -OH BDE 17, 8.13; 2 -OH BDE 28, 8.08; 3 -OH
BDE 28, 7.57; 6 -OH BDE 49, 6.73; 2 -OH BDE 68, 6.90;
6-OH BDE 47, 7.27; 3-OH BDE 47, 6.12; 5-OH BDE 47;
4 -OH BDE 49, 6.66; 4-OH BDE 42, 6.67; 6-OH BDE 90,
6.09; 6-OH BDE 99, 5.89; 4-OH BDE 90, 5.20; 2-OH BDE
123, 6.09; 6-OH BDE 85, 6.64; and 6-OH BDE 137, 5.25.
These OH-PBDEs have estimated acidity constants ranging over 3.9 log units, suggesting inconsistent partitioning/extraction behavior may have occurred during sampling and analysis. At a precipitation pH of 5, 6-OH BDE
137 is expected to be about 39% ionized, whereas 3 -OH
BDE 7 would be effectively entirely in the molecular form.
With OH-PBDE pKa values estimated to range from 4.2 to
9.3 for these compounds, some congeners will be effectively
ionized while others will be effectively unionized in near
neutral surface waters, necessitating a site- and compoundspecific approach to sampling, analysis, and data intepretation.
As noted previously, internal standards must be chosen to best approximate the expected partitioning behavior during sample processing. The estimated intrahomolog
pKa variation of up to several units appears to prevent
use of single recovery standards in each homolog, unlike
some analytical approaches employed for the parent PCBs,
PBBs, PCDEs, and PBDEs which can reasonably rely on
approximately similar partitioning behavior during extraction for all members of a homolog group. For reliable analytical data, each OH-PCB, OH-PBB, OH-PCDE, and
OH-PBDE target analyte must have a corresponding internal standard that mimics the target’s expected partitioning
behavior, which itself is dependent on both the phenol ionization and the number of halogens on the aromatic rings.
Similarly, the effective Kaw values for these compounds
will also be pH dependent (Fig. 4). Using the six OH-PCB
43 congeners again as a representative case study, 4-OH CB
43 has a significantly higher estimated log Kaw (by about

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1328
2 log units) for the molecular form (i.e., at pH values <2
units below the respective pKa values; K◦aw ) than its 6-OH,
3 -OH, 4 -OH, 5 -OH, and 6 -OH counterparts. This expected differential K◦aw behavior for the molecular forms
likely reflects the shielding effect of the two adjacent chlorine substituents on the hydroxy group in the 4-OH CB
43 isomer, which hinders hydrogen bonding between the
aqueous solvent and the hydroxy moiety, thereby favoring
partitioning into the gas phase. By comparison, the other
congeners only have one (6-OH and 3 -OH CB 43) or no
(4 -OH, 5 -OH, and 6 -OH CB 43) adjacent chlorine substitutents that can shield the hydroxy group, and thus they
all display log K◦aw values that differ by less than about
0.5 log units from each other. With a lower pKa value, 4OH CB 43 begins to display the effects of pH dependent
air-water partitioning behavior at much lower pH values
(∼5.5) than the other congeners (∼8 to 10). At a marine
pH of 8.1, the difference in effective Kaw (Kaw,eff ) values
between 4-OH CB 43 and the other congeners has been
reduced to between 0.5 and 1 order of magnitude. Consequently, when assessing air-water partitioning of hydroxylated PCBs, PBBs, PCDEs, and PBDEs, pH dependent
models and both reliable pKa and K◦aw values need to be
used to ensure Kaw,eff are accurately estimated for the pH
value(s) of interest, thereby allowing the relative mobilities
of various congeners to be correctly depicted.
In addition, different photolytic rates, mechanisms, and
product profiles are well established for the molecular versus dissociated forms of simple halogenated phenols.[67]
The limited experimental photochemistry work on OHPBDEs indicates more rapid photodegradation rates from
the phenolate form,[57] analogous to their halophenol relatives. Thus, photochemical studies in organic solvents [68]
that suppress ionization will not yield relevant qualitative
or quantitative data for analytes expected to be at least
partially ionized under ambient aqueous conditions. Other
biotic and abiotic degradation processes will also likely display pH dependent rates, products, and mechanisms. As a
result, rigorous environmental degradation and waste treatment investigations of OH-PCBs, OH-PBBs, OH-PCDEs,
and OH-PBDEs must explicitly take pH dependent ionization of the phenolic group into consideration during their
studies.

Conclusion
Aqueous pKa values were estimated for all monohydroxylated mono- through nona-halogenated OH-PCB,
OH-PBB, OH-PCDE, and OH-PBDE congeners. Substantial intrahomolog variability of up to 6 units in pKa
values is expected within each compound class, along
with generally decreasing trends in pKa with increasing
halogenation, reflecting an influence from both the degree
and pattern of halogen substitution. The widely varying
pKa values between individual OH-PCB, OH-PBB,

Rayne and Forest
OH-PCDE, and OH-PBDE necessitates congener specific
pH dependent investigations into the partitioning and
degradation behaviors of these compounds, and greater
consideration of analyte ionization effects during their
extraction and analysis. While octanol-water and air-water
partitioning coefficients for the unionized forms are not
expected to vary widely within each homolog group,
large intrahomolog pKa variation is predicted to result
in significantly different partitioning behaviour under
realistic environmental and biological conditions for the
ionized forms depending on halogenation pattern.

Acknowledgments
We thank an anonymous reviewer for valuable suggestions
that improved the quality of the manuscript.

References
[1] Hutzinger, O.; Safe, S.; Zitko, V. The Chemistry of PCBs; CRC Press:
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