Isomer distributions of polychlorinated dibenzo-p-dioxins/dibenzofurans formed during de novo synthesis on incinerator fly ash

Article abstract of DOI:10.1021/es971077z

Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) emitted from municipal waste incinerators appear to have a chlorination pattern that is quite constant across various samples and conditions. This suggested that these patterns may be controlled by thermodynamic properties of the individual PCDD/F congeners, such as the free Gibbs energy of formation (Δg°(f,T)). This would make prediction of the isomer composition of a particular sample (and hence its TEQ value) possible, based on values of ΔG°(f,T). A laboratory scale study was carried out with activated carbon on fly ash as the source of PCDD/F formation. Although it was found that the isomer distributions within homologues were independent of the reaction time (proof of thermodynamic control), other observations (lack of equilibrium/isomerization between isomers and lack of similarity between isomer distributions measured and predicted by ΔG°(f,T)) contradicted the possibility of thermodynamic control. Hence, this study could not confirm that de novo formation of PCDD/F could explain thermodynamically controlled isomer distributions in incinerators. Some recommendations for further work- time-based studies with precursors, isomerization studies with single congeners, and more data on ΔG°(f,T) values of PCDD/F-were made. Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) emitted from municipal waste incinerators appear to have a chlorination pattern that is quite constant across various samples and conditions. This suggested that these patterns may be controlled by thermodynamic properties of the individual PCDD/F congeners, such as the free Gibbs energy of formation (ΔG°_f,T). This would make prediction of the isomer composition of a particular sample (and hence its TEQ value) possible, based on values of ΔG°_f,T. A laboratory scale study was carried out with activated carbon on fly ash as the source of PCDD/F formation. Although it was found that the isomer distributions within homologues were independent of the reaction time (proof of thermodynamic control), other observations (lack of equilibrium/isomerization between isomers and lack of similarity between isomer distributions measured and predicted by ΔG°_f,T) contradicted the possibility of thermodynamic control. Hence, this study could not confirm that de novo formation of PCDD/F could explain thermodynamically controlled isomer distributions in incinerators. Some recommendations for further work - time-based studies with precursors, isomerization studies with single congeners, and more data on ΔG°_f,T values of PCDD/F - were made.

Full text of DOI:10.1021/es971077z

Environ. Sci. Technol. 1998, 32, 1888-1893
would be governed by thermodynamic properties of the
Isomer Distributions of
Polychlorinated Dibenzo-p-dioxins/
Dibenzofurans Formed during De
Novo Synthesis on Incinerator Fly
Ash
individual PCDD/ F isomers. A distribution that was very
dependent on kinetic parameters would more likely differ
between incinerators. Knowledge of the factors that deter-
mine the isomeric composition of PCDD/ F effluents is crucial,
since the TEQ value of a specific emission depends on the
presence of the 2,3,7,8-substituted congeners.
Values of ∆H°f,T and ∆G°f,T for the various PCDD/ F
congeners were reported by a number of authors (5-11).
These thermodynamic data could then be used to compare
isomer distributions measured in effluents and predicted by
theory. Typical isomer distributions within homologues from
various combustion sources showed a certain degree of
similarity with predictions based on values of ∆G°f,T, although
results differed per homologue (8, 11).
The concept of thermodynamic control of PCDD/ F isomer
distributions within homologues required more proof than
a correlation between isomer distributions measured (in real
incinerators) and predicted by values of ∆G°f,T. In addition,
time independence of the distributions and the existence of
some kind of equilibrium between the isomers (e.g., through
isomerization) would have to be verified. Both the influence
of time and possible equilibration could be studied readily
on a laboratory scale. The small scale offered the advantage
of better control of reaction conditions. For instance, a time
study in a municipal waste combustor would be more
difficult, since the fly ash sampled for several hours would
have a poorly defined time history.
We carried out a series of experiments to investigate to
what extent the isomer distributions of PCDD/ F within
homologues were thermodynamically controlled. We chose
carbon as the reactant in this study since de novo formation
of PCDD/ F is a slow process (hours), which made it possible
to vary the reaction time over a wide range. Time, tem-
perature, [H2O], [HCl], and [O2] were varied to study the
influence of these parameters on the isomer distributions.
Time dependence of the isomer distributions, the extent to
which equilibrium exists, and a comparison between isomer
distributions measured and predicted are reported.
R U U D A D D I N K , *
H A R R I E A . J . G O V E R S , A N D K E E S O L I E
Department of Environmental and Toxicological Chemistry,
Amsterdam Research Institute for Substances in Ecosystems,
University of Amsterdam, Nieuwe Achtergracht 166,
1018 WV Amsterdam, The Netherlands
Polychlorinated dibenzo-p-dioxins (PCDD) and dibenzo-
furans (PCDF) emitted from municipal waste incinerators
appear to have a chlorination pattern that is quite constant
across various samples and conditions. This suggested that
these patterns may be controlled by thermodynamic
properties of the individual PCDD/F congeners, such as the
free Gibbs energy of formation (∆G°f,T). This would make
prediction of the isomer composition of a particular
sample (and hence its TEQ value) possible, based on values
of ∆G°f,T. A laboratory scale study was carried out with
activated carbon on fly ash as the source of PCDD/F
formation. Although it was found that the isomer distributions
within homologues were independent of the reaction time
(proof of thermodynamic control), other observations (lack
of equilibrium/isomerization between isomers and lack
of similarity between isomer distributions measured and
predicted by ∆G°f,T) contradicted the possibility of
thermodynamic control. Hence, this study could not confirm
that de novo formation of PCDD/F could explain thermo-
dynamically controlled isomer distributions in incinerators.
Some recommendations for further workstime-based
studies with precursors, isomerization studies with single
congeners, and more data on ∆G°f,T values of PCDD/
Fswere made.
Experimental Section
Experimental conditions are described in Table 1. Details
on apparatus, mixing and heating, cleanup, and analysis were
described as follows: set 1 in ref 12, set 2 in ref 13, set 3 in
ref 14, set 4 in ref 15, set 5 in ref 15, and set 6 in ref 16. All
experiments were carried out with a mixture of activated
carbon and fly ash from a municipal waste incinerator in
Zaanstad, The Netherlands. All native organic material had
been removed from the fly ash before mixing it with the
activated carbon. All runs were carried out with the mixture
placed as a fixed bed in a glass/ quartz tube that was heated
in a furnace. A gas stream passed through the fly ash bed
during all experiments, except in set 2. Evaporated PCDD/ F
were collected in a cold trap. PCDD/ F from the fly ash and
cold trap were combined in the sample cleanup. T4CDD-
OCDD and T4CDF-OCDF were quantified on a GC/ MS with
a SP 2331 column. This column separated the 134 tetra-
hepta congeners into 102 peaks, giving a detailed picture of
the isomer distributions within the homologues (16). All
experiments were carried out twice.
Introduction
Formation of polychlorinated dibenzo-p-dioxins (PCDD) and
polychlorinated dibenzofurans (PCDF) during municipal
waste incineration was discovered in 1977 (1). The presence
of these compounds on incinerator fly ash has led to
laboratory-scale modeling of the formation process. Recent
reviews summarized the most important trends and results
(2, 3).
One striking aspect of the formation of PCDD/ F was the
similarity of the isomer distributions within homologues that
was usually found in various waste incinerator fly ashes (4).
Given the large variety of reaction conditions that must exist
(e.g., feed, residence time, temperature), this observation
suggested that the final distributions within homologues
Results and Discussion
As can be seen in Table 1, we carried out six sets of
experiments. Since data on the amount of PCDD/ F, [PCDD]:
[PCDF] ratios, and homologue distributions have been
* Corresponding author present address: Department of Chemical
Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180;
phone: 518-276-2741; fax: 518-276-4030; e-mail: addinr@rpi.edu.
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1 8 8 8 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 32, NO. 13, 1998
S0013-936X(97)01077-8 CCC: $15.00
1998 Am erican Chem ical Society
Published on Web 05/12/1998

TABLE 1. Reaction Conditions Used in the Experiments
set 1: variation of reaction tim e
4.0 g of 97.5% fly ash and 2.5% carbon; T ) 300 °C; 30, 60, 120, 240, or 360 m in; 17 m L/m in technical air;
H2O added by passing flow through im pinger, but not quantified
set 2: variation of reaction tim e
2.0 g of 98% fly ash and 2% carbon; T ) 348 °C; 50, 110, or 230 m in; no flow through the fly ash bed
set 3: variation of tem perature
2.0 g of 93% fly ash, 2% carbon and 5% NaCl; T ) 298, 348, or 398 °C; 60 m in; N2 53 m L/m in, O2 6.5 m L/m in;
H2O added by passing flow through im pinger, but not quantified
set 4: with and without water
2.0 g of 98% fly ash and 2% carbon; T ) 348 °C; 60 m in; N2 103 m L/m in, O2 12 m L/m in, H2O (vapor) 0 or 27 m L/m in
set 5: with and without HCl
2.0 g of 98% fly ash and 2% carbon; T ) 348 °C; 60 m in; N2 103 m L/m in, O2 12 m L/m in or N2 99 m L/m in, O2 12 m L/m in,
HCl 0 or 5 m L/m in
set 6: variation of percentage of O2
2.0 g of 96.4% fly ash, 1.5% carbon and 2.1% NaCl; T ) 348 °C; 50 m in; N2 200-207 m L/m in, O2 2, 4, 10, or 20 m L/m in
FIGURE 1. P5CDD isomer distribution for set 1. Explanation of peak numbers: 43 ) 1,2,4,7,9 + 1,2,4,6,8; 44 ) 1,2,3,6,8; 45 ) 1,2,4,7,8; 46
) 1,2,3,7,9; 47 ) 1,2,4,6,9 + 1,2,3,4,7; 48 ) 1,2,3,7,8; 49 ) 1,2,3,6,9; 50 ) 1,2,4,8,9 + 1,2,4,6,7; 51 ) 1,2,3,4,6; 52 ) 1,2,3,6,7; 53 ) 1,2,3,8,9.
described elsewhere (12-15), we focused in this paper on
the isomer distributions produced in these experiments. Sets
1 and 2 were designed to study the influence of the reaction
time on the isomer distributions. In set 2, no flow was present
during the experiments, the bed was heated in an open tube,
and O2 could enter by diffusion as described elsewhere (13).
Figure 1 depicts the influence of time on the P5CDD
distribution in set 1. The peak numbers on the horizontal
axis refer to the elution order of the various isomers on the
SP 2331 GC column. Note that not all isomers could be
separated due to coelution. For each experiment within a
set, all the homologue distributions were calculated by setting
the sum of each homologue to 100% and calculating the
relative contribution of each peak. The mean values for the
P5CDD homologue of set 1 are shown in Figure 1, the error
bars representing the range. The trend found was that the
P5CDD isomer distribution was independent of the reaction
time. Differences found as result of increasing reaction times
were small and in the same order of magnitude as the
variation between duplicate experiments. Similar results
were found for all other homologues in both sets 1 and 2 (not
shown). The shortest time used was 30 min (set 1). Shorter
reaction times were difficult with de novo type reactions
since short time scale runs produced too little PCDD/ F.
The time independence of PCDD/ F formation (from
carbon) suggested thermodynamic control of the isomer
distributions, although nothing could be said about reaction
times <30 min. If the isomer distributions were thermo-
dynamically controlled, some kind of equilibrium/ steady
state had to exist. This would be the case if isomerization
of PCDD/ F after formation was fast relative to other reactions,
creating an equilibrium between all possible substitution
patterns within a homologue. We investigated this possibility
by reacting 1,2,3,4,7,8-H6CDD on fly ash. However, no
isomerization was observed. Also, the dechlorination
products of this particular isomersT4CDD and P5CDD
isomerssdid not isomerize. A more detailed account of these
experiments was given in ref 17. The absence of isomer-
ization with this single H6CDD compound suggested that
isomerization of PCDD/ F after formation was not an
important pathway on this fly ash. Therefore, no equilibrium
through isomerization would exist. These observations
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FIGURE 2. Experimental and theoretical values for T CDD and P5CDD isomer distribution. Explanation of peak numbers: T CDDs (peaks
4
4
1-14): 1 ) 1,3,6,8; 2 ) 1,3,7,9; 3 ) 1,3,7,8; 4 ) 1,3,6,9 + 1,2,4,7 + 1,2,4,8; 5 ) 1,2,6,8; 6 ) 1,4,7,8; 7 ) 2,3,7,8; 8 ) 1,2,3,4 + 1,2,3,7 + 1,2,3,8
+ 1,2,4,6 + 1,2,4,9; 9 ) 1,2,3,6 + 1,2,7,9; 10 ) 1,2,7,8 + 1,4,6,9; 11 ) 1,2,3,9; 12 ) 1,2,6,9; 13 ) 1,2,6,7; 14 ) 1,2,8,9. P5CDDs (peaks 43-53):
43 ) 1,2,4,7,9 + 1,2,4,6,8; 44 ) 1,2,3,6,8; 45 ) 1,2,4,7,8; 46 ) 1,2,3,7,9; 47 ) 1,2,4,6,9 + 1,2,3,4,7; 48 ) 1,2,3,7,8; 49 ) 1,2,3,6,9; 50 ) 1,2,4,8,9
+ 1,2,4,6,7; 51 ) 1,2,3,4,6; 52 ) 1,2,3,6,7; 53 ) 1,2,3,8,9.
formed an argument against thermodynamic control of
isomer distributions during de novo formation on our fly
ash.
assumed 600 K as the average temperature of our experi-
ments. With all ∆G°f,600K values for the isomers within a
homologue available, the equilibrium composition, assuming
isomerization between all the isomers, could be calculated
(8). As with the experimental isomer distributions, the sum
of the homologue was set to 100%, and all relative contribu-
tions were determined. The variation of the theoretical
isomer distributions within the temperature range of our
experiments was negligible. When a peak represented more
than one isomer in Figures 2-6, their theoretical values were
added to make a direct comparison with the experimental
value possible.
Experiments carried out in sets 3-6 (Table 1) were aimed
at studying the influence of parameters other than time on
the isomer distributions within homologues. We varied
temperature, [H2O], [HCl], and [O2]. The results of these
experiments were obvious: little variation was seen in the
isomer distributions (not shown, calculated in the same
manner as the distributions in Figure 1). Since no particular
reaction parameter influenced the isomer patterns, we
decided to calculate the average value for each peak over all
experiments in all sets. Results are shown in Figures 2-6.
For peak 1 in Figure 2, representing 1,3,6,8-T4CDD, 26 values
from each experiment in sets 1-4 were averaged. For this
peak, the values in sets 5 and 6 were not available, since the
formation of T4CDD in these experiments was too low,
perhaps due to increased levels of chlorine favoring formation
of higher chlorinated congeners (set 5) or decreased O2 (set
6). The error bars represent the standard deviation. The
average percentage ( standard deviation shows the natural
boundaries of this particular isomer on the fly ash used. For
all isomers, the standard deviation varied between 10 and
300% relative to the average percentage, with an average of
50%.
If our experimental and theoretical isomer distributions
would be (very) similar, this would constitute an important
argument in favor of thermodynamic control of these
distributions during de novo formation. The theoretical
approach showed that with thermodynamic control all
PCDD/ F congeners were formed. There would be no
homologue that was dominated by a single isomer, except
perhaps the H7CDF, where the 1,2,3,4,6,7,8-isomer would
constitute 70% of the homologue. A similar trend was seen
with our experimental distributions, and to that extent there
was a similarity between experiment and theory. However,
with each of the homologues there were important differences
between the experimental and theoretical values. In Figure
2, peaks 1 and 2 were significantly lower than predicted by
∆G°f,600K. Other peaks (8-10) were higher in the experiment
than predicted by theory. Peak 15, in Figure 3, should be the
major component according to theory but was instead quite
small. On the other hand, most isomers within T4CDF were
predicted to be low, which was the case in the experiment.
In Figure 2, peak 43 was too low in the experiment when
compared with theory. In Figure 4, peaks 54 and 55 were
much lower measured than predicted. Figure 5 had peak 77
as a major component, but it was still lower than predicted
The theoretical values depicted in Figures 2-6 were based
on calculations of ∆G°f,T for all tetra-hepta CDD/ F. Cal-
culations by Thompson (9, 10) and Unsworth et al. (8) gave
values of ∆G°f,T that were quite comparable. Also, the values
of ∆G°f,T within a certain homologue were quite close for
all isomers within that homologue. Those reported by Shaub
(5-7) showed large variations within homologues, which
seemed unrealistic for a set of isomers. We therefore decided
to use the data reported in ref 8 and additional data made
available to us based on the same technique (18). We
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FIGURE 3. Experimental and theoretical values for T CDF isomer distribution. Explanation of peak numbers: 15 ) 1,3,6,8; 16 ) 1,3,7,8 +
4
1,3,7,9; 17 ) 1,3,4,7; 18 ) 1,4,6,8; 19 ) 1,2,4,7; 20 ) 1,3,6,7; 21 ) 1,3,4,8; 22 ) 1,3,4,6 + 1,2,4,8; 23 ) 1,2,4,6; 24 ) 1,2,6,8 + 1,2,3,7 + 1,4,7,8;
25 ) 1,3,6,9; 26 ) 2,3,4,9 + 1,2,3,4; 27 ) 1,2,3,8 + 1,4,6,7 + 2,4,6,8 + 1,2,3,6; 28 ) 1,3,4,9; 29 ) 1,2,7,8; 30 ) 1,2,6,7 + 1,2,7,9; 31 ) 1,4,6,9;
32 ) 1,2,4,9; 33 ) 2,3,6,8; 34 ) 2,4,6,7; 35 ) 1,2,3,9 + 2,3,4,7; 36 ) 1,2,6,9; 37 ) 2,3,7,8; 38 ) 2,3,4,8; 39 ) 2,3,4,6; 40 ) 2,3,6,7; 41 ) 3,4,6,7;
42 ) 1,2,8,9.
FIGURE 4. Experimental and theoretical values for P5CDF isomer distribution. Explanation of peak numbers: 54 ) 1,3,4,6,8; 55 ) 1,2,4,6,8;
56 ) 2,3,4,7,9; 57 ) 1,3,4,7,9; 58 ) 1,3,4,7,8 + 1,2,3,6,8; 59 ) 1,2,4,7,8; 60 ) 1,3,4,6,7 + 1,2,4,7,9; 61 ) 1,2,4,6,7; 62 ) 1,2,3,4,7 + 2,3,4,6,9; 63
) 1,3,4,6,9; 64 ) 1,2,3,4,8 + 1,2,3,7,8; 65 ) 1,2,3,4,6; 66 ) 1,2,3,7,9; 67 ) 1,2,3,6,7; 68 ) 1,2,4,6,9 + 2,3,4,8,9; 69 ) 1,3,4,8,9; 70 ) 1,2,3,6,9; 71
) 2,3,4,6,8; 72 ) 1,2,3,4,9; 73 ) 1,2,4,8,9; 74 ) 2,3,4,7,8; 75 ) 1,2,3,8,9; 76 ) 2,3,4,6,7.
by ∆G°f,600K
.
Figure 6 showed that peaks 97 and 98 were
agreement between experiment and theory. From these
figures, only this homologue would appear to have a
thermodynamically controlled isomer distribution.
reversed in formation as compared to theory. However, for
the four H7CDF isomers (99-102) there was a remarkable
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FIGURE 5. Experimental and theoretical values for H CDD and H CDF isomer distribution. Explanation of peak numbers: H CDDs (peaks
6
6
6
77-83): 77 ) 1,2,4,6,7,9 + 1,2,4,6,8,9 + 1,2,3,4,6,8; 78 ) 1,2,3,6,7,9 + 1,2,3,6,8,9; 79 ) 1,2,3,4,7,8; 80 ) 1,2,3,6,7,8; 81 ) 1,2,3,4,6,9; 82 ) 1,2,3,7,8,9;
83 ) 1,2,3,4,6,7. H CDFs (peaks 84-96): 84 ) 1,2,3,4,6,8; 85 ) 1,3,4,6,7,8 + 1,3,4,6,7,9; 86 ) 1,2,4,6,7,8; 87 ) 1,2,4,6,7,9; 88 ) 1,2,3,4,7,8 +
6
1,2,3,4,7,9; 89 ) 1,2,3,6,7,8; 90 ) 1,2,4,6,8,9; 91 ) 1,2,3,4,6,7; 92 ) 1,2,3,6,7,9; 93 ) 1,2,3,4,6,9 + 1,2,3,6,8,9; 94 ) 1,2,3,7,8,9; 95 ) 1,2,3,4,8,9;
96 ) 2,3,4,6,7,8.
FIGURE 6. Experimental and theoretical values for H CDD and H CDF isomer distribution. Explanation of peak numbers: H CDDs (peaks
7
7
7
97-98): 97 ) 1,2,3,4,6,7,9; 98 ) 1,2,3,4,6,7,8. H CDFs (peaks 99-102): 99 ) 1,2,3,4,6,7,8; 100 ) 1,2,3,4,6,7,9; 101 ) 1,2,3,4,6,8,9; 102 ) 1,2,3,4,7,8,9.
7
The results of our investigation showed that the isomer
distributions within homologues were independent of the
reaction time for de novo formation. This constituted an
important argument for thermodynamic control of the
chlorination pattern of PCDD/ F. Stieglitz et al. reported on
a change in isomer distributions as function of time with
original fly ash that had not been pretreated and still
contained all organics formed on its surface during the
incineration (19). Since these authors had both carbon and
small organic precursors on their fly ash to form PCDD/ F,
thermodynamically controlled isomer distributions within
homologues from carbon could be disturbed by the formation
of certain specific isomers from precursors (e.g., from
chlorophenols). On the other hand, the lack of isomerization
of 1,2,3,4,7,8-H6CDD on our fly ash suggested that no
equilibrium between the various isomers within a homologue
existed. Also, the similarity between isomer distributions
measured in our experiments and predicted by theory was
limited, except for the H7CDF. In summary, there appeared
to be arguments both in favor and against thermodynamic
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1 8 9 2 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 32, NO. 13, 1998

(2) Addink, R.; Olie, K. Environ. Sci. Technol. 1995, 29 (6), 1425-
1435.
(3) Altwicker, E. R. J. Hazard. Mater. 1996, 47, 137-161.
(4) Schramm, K. W.; Wehrmeier, A.; Lenoir, D.; Henkelmann, B.;
Hahn, K.; Zimmermann, R.; Kettrup, A. Organohalogen Compd.
1996, 27, 196-200.
(5) Shaub, W. M. Thermochim. Acta 1982, 55, 59-73.
(6) Shaub, W. M. Thermochim. Acta 1982, 58, 11-44.
(7) Shaub, W. M. Thermochim. Acta 1983, 62, 315-323.
(8) Unsworth, J. F.; Dorans, H. Chemosphere 1993, 27 (1-3), 351-
358.
(9) Thompson, D. Chemosphere 1994, 29 (12), 2545-2554.
(10) Thompson, D. Chemosphere 1994, 29 (12), 2583-2595.
(11) Zimmermann, R.; Wehrmeier, A.; Lenoir, D.; Schramm, K. W.;
Kettrup, A. Organohalogen Compd. 1996, 27, 237-242.
(12) Addink, R.; Drijver, D. J.; Olie, K. Chemosphere 1991, 23 (8-10),
1205-1211.
control of isomer distributions within homologues during
de novo formation.
As reported in the Introduction, the isomer distributions
measured in incinerator effluents appeared to thermody-
namically controlled (4). This study could not confirm that
this was caused by the formation of PCDD/ F from carbon,
since de novo formation modeled on a laboratory scale
yielded arguments both in favor and against thermodynamic
control. Further study is needed since thermodynamic
properties of PCDD/ F could be an easy tool to predict the
isomer composition (and hence TEQ value) of a particular
sample. Time-based studies with small organic precursors
could yield information on changes in isomer distributions
under distinctly kinetically controlled conditions. And once
the reactant is gone, would the resulting PCDD/ F isomer
distributions move toward a more thermodynamically fa-
vored distribution? Experiments with single PCDD/ F con-
geners could be used to investigate conditions that favor
equilibration and isomerization. Further data on ∆G°f,T
values of PCDD/ F could be used to make a more reliable
comparison between experimental and theoretical isomer
distributions.
(13) Addink, R.; Olie, K. Environ. Sci. Technol. 1995, 29 (6), 1586-
1590.
(14) Addink, R.; Paulus, R. H. W. L.; Olie, K. Environ. Sci. Technol.
1996, 30 (7), 2350-2354.
(15) Addink, R.; Bakker, W. C. M.; Olie, K. Organohalogen Compd.
1992, 8, 205-208.
(16) Ryan, J. J.; Conacher, H. B. S.; Panopio, L. G.; Lau, B. P. Y.;
Hardy, J. A. J. Chromatogr. 1991, 541, 131-183.
(17) Addink, R.; Antonioli, M.; Olie, K.; Govers, H. A. J. Environ. Sci.
Technol. 1996, 30, (3), 833-836.
Acknowledgments
Thermodynamic data on PCDD and PCDF were supplied by
Dr. John F. Unsworth, Shell Research Ltd., Thornton Research
Center, Chester, U.K.
(18) Values supplied by J. F. Unsworth.
(19) Stieglitz, L.; Vogg, H. Chemosphere 1987, 16 (8-9), 1917-1922.
Received for review December 12, 1997. Revised manuscript
received March 27, 1998. Accepted April 1, 1998.
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ES971077Z
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