United States
Environmental Protection
Agency
Hazardous Waste Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-86/076 Feb. 1987
v>EPA Project Summary
Soil, Clay, and Caustic Soda
Effects on Solubility, Sorption,
and Mobility of
Hexachlorocyclopentadiene
S. F. Joseph Chou and Robert A. Griffin
This study on the aqueous chemistry,
sorption, and mobility of hexachlorocy-
clopentadiene (C-56) in soil materials
was initiated to provide information on
its behavior in the environment, partic-
ularly on its movement through soil at
land disposal facilities for hazardous
wastes. Studies showed that the solu-
bility of C-56 in water, soil extracts, and
sanitary landfill leachates ranged from
1.03 to 1.25 ppm. Sodium hydroxide
(caustic soda) and sodium chloride de-
creased the solubility of C-56 in water
as the salt concentration increased;
sodium hypochlorite slightly increased
the solubility of C-56; and sodium
perchlorate had no significant effects
due to increasing salt concentration on
the solubility of C-56. A caustic brine
composed of a mixture of the salts was
intermediate in decreasing solubility.
The half-life of C-56 in water was
about three months at both 22°C and
35°C, indicating little temperature de-
pendence. C-56 is very photosensitive,
and its half-life was less than four min-
utes in aqueous solution and less than
1.6 minutes in hexane or methanol so-
lution. Studies also indicated that pH
did not significantly affect the C-56 hy-
drolysis rate in aqueous solution; how-
ever, iron caused an increase in the hy-
drolysis rate. At least 12 products of
photolysis and hydrolysis were
identified. Pentachlorocyclopentenone,
hexachlorocyclopentenone, pen-
tachloropentadienoic acid, cis- and
transpentachlorobutadiene, and tetra-
chlorobutenyne were the major prod-
ucts identified.
The presence of salts in solution dra-
matically affected the sorption of C-56;
brine, NaCI, and NaOH caused an in-
crease in sorption while NaOCI caused
a decrease in sorption. There was also a
high direct correlation between the
total organic carbon (TOO content of
soils and the amount sorbed.
C-56 remained immobile in the soils
when leached with water, landfill
leachate, or caustic brine but was
highly mobile when leached with or-
ganic solvents. In a soil column leach-
ing study, some hydrolysis products of
C-56 were much more mobile than
C-56, indicating they might migrate and
generate environmental problems.
This Project Summary was devel-
oped by EPA's Hazardous Waste Engi-
neering Research Laboratory, Cincin-
nati, OH, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Environmental concerns have created
a demand for information on land dis-
posal of toxic organic substances such
as hexachlorocyclopentadiene (C-56 or
"hex" waste). C-56 is a highly toxic
compound that produces systemics of
unknown mechanism in mammals and
has been reported to have caused sig-
nificant decreases in survival of fathead
minnows at concentrations as low as
7.3 ppb.
C-56 has no end uses of its own but is
commercially important as a chemical
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intermediate for producing chemical
feed stocks, pesticides, adhesives,
resins, and other related products. The
present environmental concern is the
disposal of large quantities of industrial
wastes containing C-56. A major source
of C-56 wastes comes from manufactur-
ing chlorinated insecticides.
The phenomenon of salting-out a
nonelectrolyte from an aqueous solu-
tion by adding salt is well known. Thus,
the high salt content of the caustic soda
brine waste water would be expected to
cause changes in the aqueous solubility
of C-56. Because sorption of C-56 by soil
materials is a function of concentration,
knowledge of how the solubility
changes with brine concentration is im-
portant to accurately predict attenua-
tion and mobility.
C-56 is extremely volatile and pho-
toreactive in sunlight. Near-surface half-
lives of C-56 in aquatic systems are less
than 10 minutes. C-56 shows an unex-
pected tendency to undergo the Diels-
Alder reaction with many dienophiles at
temperatures between 20°C and 200°C.
It condenses even with simple olefins
which normally do not react with dienes
and with polynuclear aromatic hydro-
carbons. Thus, the apparent disappear-
ance of C-56 from the environment
should not be construed to mean that it
is always degraded to smaller
molecules; it may condense into larger
molecular weight compounds. Al-
though C-56 has been used in the chem-
ical industry for decades, there is a
dearth of information on the environ-
mental impacts of the compound on
aquatic or soil systems.
The principal objectives of this re-
search were to determine the attenua-
tion mechanisms and capacity of se-
lected clay minerals and soils for C-56,
to determine the effects of caustic brine
on the attenuation and solubility of
C-56, to study the aqueous chemistry of
C-56, and to develop a chemical model
to predict C-56 migration through soil
materials.
Experimental Materials
A reagent grade C-56 was obtained
from Pfaltz and Bauer, Inc., Stamford,
CT, and was used without further purifi-
cation. An analytical standard of C-56
(lot #0213) was also obtained from EPA
in Research Triangle Park, NC. Both ma-
terials were identical and the purity was
about 98 percent. Water, soil extracts,
and landfill leachates of varying content
of dissolved organic carbon (TOO were
collected and analyzed. The samples
used in the C-56 solubility studies and
their respective TOC values are given in
Table 1. TOC values in water samples
ranged from 0.32 to 271 ppm; this al-
lowed us to determine if solubility dif-
ferences occurred as a result of dis-
solved organic matter in water.
The sorbents used in the sorption and
mobility studies were four clay miner-
als, seven soils, a clean sand, and some
low temperature ashed soils and muck.
The carbonaceous sorbents Ambersorb
XE-348 and activated bone carbon were
also selected for study because of their
potentially high sorption capacity for
C-56 from aqueous solution.
Results
Solubility of C-56 in Waters
and Leachates
The solubility of C-56 in distilled
water, deionized water, tap water,
Sugar Creek water, soil extracts, and
landfill leachates varied from 1.03 ppm
in Sugar Creek water to 1.25 ppm in Du-
Page landfill leachate. The results are
given in Table 1.
Effect of Dissolved Salts on the
Solubility
The effect of several soluble salts on
the solubility of C-56 was treated by fit-
ting the solubility data to the
Setschenow equation:
S0
log -g- = Km
where S0 is the solubility (ppm) of C-56
in tap water and S its solubility (ppm) in
a salt solution of concentration m (mole/
L). Representative data for C-56 plotted
according to the Setschenow equation
are shown in Figure 1. Of the three salts
studied, sodium hydroxide and sodium
chloride decreased the solubility of C-5.
in tap water and sodium hypochlorif
slightly increased its solubility. Th
three salt mixtures (brine) were intei
mediate in depressing C-56 solubility
Sodium perchlorate did not signifi
cantly affect the solubility of C-56. Th
results indicated that there was ai
anion effect and that the effect of th
individual salts upon C-56 solubility wa
additive.
Photolysis and Hydrolysis
C-56 was found to be photoreactive
The rate of photolysis in aqueous solu
tion and organic solvents followed
first-order reaction. Values of the first
order rate constant (K), the half-life (tl7 ;
and correlation coefficient (r2) betweli
concentrations and times for the photol
ysis of C-56 in solution exposed to sun
light, long-wave UV, and short-wave IP
light are given in Table 2. Representa
tive first-order degradation plots of C-5i
photolysis in tap water exposed to long
and short-wave UV light are given ii
Figure 2. C-56 photolyzed much faster ii
hexane than in tap water or methano
•4-\
.5
0
Salt
Figure
0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6
Concentration (mole/L) ISGS1983
1. Elfect of dissolved salts on the
water solubility of C-56 at 22°C
± 1°C—plot according to the
Setschenow equation.
Table 1. Solubility of C-56 at 22°C ± 1 °C After 15 Hours Equilibrium in Waters and Landfii
Leachates Using Centrifugation Technique
Waters and Leachates
TOC of Waters and
Leachates (ppm)
Concentration (mg/L
Distilled water
Deionized water
Tap water
Sugar Creek water
Bloom field soil extract
(soil:tap water = 1:3)
Catlin soil extract
(soil:tap water = 1:3)
Blackwell sanitary landfill
leachate
DuPage Sanitary landfill
leachate
0.32
0.50
1.31
7.62
16.00
49.80
235.00
271.00
1.11
1.14
1.08
1.03
1.06
1.20
1.19
1.25
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Table 2. First-Order Rate Constant (K), Half-Life (t1/2), and Regression Coefficient (r2) for the
Photodegradation of C-56 in Distilled Water, Methanol, and Hexane Under Sun-
light, Long-Wave UV Light (L-UV), and Short-Wave UV Light (S-UV)
K (min ^) 1 1/2 (min)
Treatment
C-56 in water
C-56 in methanol
C-56 in hexane
Sun
0.24
0.30
0.45
L-UV
0.30
0.32
0.45
S-UV
0.019
0.006
0.013
Sun
3.47
2.32
1.55
L-UV
2.28
2.17
1.55
S-UV
36.47
115.50
53.31
Sun
1.00
1.00
1.00
r2
L-UV
1.00
0.99
1.00
S-UV
1.00
1.00
0.99
.
0.9
I 0.61
| °o:l-
.§ 0.2"
§ 0.1
£ 0.09
§0.06
,§ 0.03
o.or.
Tap Water
Short-Wave UV
468
Time (min)
10 12 14
ISGS 1983
Figure 2.
First-order degradation plot of
tap water soluble C-56 exposed
under long- and short-wave UV
light.
The half-life due to photolysis of C-56 in
water exposed to long-wave UV or sun-
light was less than 3.5 minutes (Fig-
ure 2). The half-life of C-56 in water in
the dark was about three months at
both 22°C and 35°C, indicating little tem-
perature dependence. Although pH did
not significantly affect the C-56 hydroly-
sis rate in aqueous solution, the pres-
ence of iron caused an increase in the
hydrolysis rate. At least 12 products of
photolysis and hydrolysis were identi-
fied. Pentachlorocyclopentenone and
hexachlorocyclopentenone were the
major products found in distilled water.
Cis- and trans-pentachlorobutadiene,
tetrachlorobutenyne, and pentachloro-
pentadienoic acid were the major prod-
ucts identified in mineralized water.
Pentachlorocyclopentenone which is
unstable under high temperature condi-
tions in hexane solution and in water
was dimerized and then converted to
hexachloroindone. A postulated degra-
dation pathway of C-56 is shown in Fig-
ure 3.
Sorption by Soil Materials,
Activated Carbon, and
AmbersorbR Carbonaceous
Sorbent
All data were fitted by linear regres-
sion to the log form of the empirical
Freundlich adsorption equation:
log ^ = log Kf + N log C
where x = p.g of compound sorbed;
m = weight of sorbent (g);
C = equilibrium concentration of the so-
lution (p-g/mL); and Kf and N are con-
stants. Values of Kf and N were obtained
from the regression_equations as the in-
tercepts at a concentration of 1 ppm and
the slope, respectively. The Freundlich
parameters and the correlation coeffi-
cient (r2) between the amount of C-56
sorbed by a unit of sorbent and the
equilibrium concentration of C-56 are
shown in Table 3. The molar K (KF) was
calculated from mass K (Kf) by using the
equation described by Osgerby:
Kf (mass) x Mol wtN
«F
Bryce> muck + Catlin (1:1) > #5 soil >
Catlin > Flanagan > Bloomfield > Ava.
Aqueous Degradation Pathway
C-56
Cl Cl
Pentachloro-2- Hexachloroindone
Cyclopentenone
Cl O
Tetrachloro-
Pentadienoic
Acid
Hexachloro-3- C(/> c,'
Cyclopentenone \_
Cl
*
J-//C/
Cl
Pentachloro- Ct'f^ Cl
Pentadienoic Acid (^ COOH
Cl
C02
Cis-Pentachloro-
Butadiene
c
Cl Cl
-^ Cl CI^CI-HCI
Cl
Cl
H
Trans- Tetrachloro-
Pentachloro- Butenyne
Butadiene
ISGS 1982
Figure 3. Proposed pathway for the degradation of C-56 in aqueous solution.
-------
Table 3. Freundlich KF, N, Correlation Coefficient (r2), and Molar KF for Sorption C-56 by Various Sorbents from Tap Water Aqueous Solution
at 22°C 1
Freundlich parameters
Sorbents
N
KF
(nmole<1-">mLng-1)
Carbon Sorbents
Activated carbon
Ambersorb
Soil Materials
16,854
2,706
0.60
0.63
0.9982
0.9736
"Average amount of C-56 sorbed by unit of sorbent (pg/g) (omitted from regression in Figure 4).
28,371
4,381
Houghton Muck B
Muck B ashed 1 day
Muck B ashed 6 days
Muck B ashed 38 days
Bryce silty loam
Muck A + Catlin silt loam (1:1)
#5 soil
Catlin silt loam
Catlin ashed 22 days
Flanagan silt clay loam
Bloomfield loamy sand
Ava silt clay loam
Ava ashed 19 days
Ca-bentonite
Illite
Montmorillonite
Kaolinite
1,045
910
637
64
385
284
97
54
4.74*
30
14
9
1.18*
32
24
18
4.4
0.80
0.76
0.71
0.68
0.86
0.76
0.66
0.93
0.95
0.55
0.94
0.63
0.55
0.60
0.58
0.9822
0.9759
0.9641
0.9506
0.9946
0.9971
0.9725
0.9982
0.0140
0.9943
0.9085
0.9148
0.0392
0.9838
0.9991
0.9928
0.9924
1,366
1,235.8
924.5
97
462
388
151
59
4.7*
32
25
10
1.2*
52
43.1
30.3
7.6
This suggests a relationship between
the organic matter content of these soils
and their sorption capacity for C-56. The
sorption of C-56 on four clays followed
the series: Ca-bentonite > illite > mont-
morillonite > kaolinite. C-56 was
strongly sorbed by activated carbon
and Ambersorb XE-348. The sorption
constants (Kf) for activated carbon and
Ambersorb XE-348 were 16,854 and
2,706, respectively. The results indi-
cated that activated carbon and Amber-
sorb XE-348 were much more effective
than most earth materials in removing
C-56 from water.
Effect of Earth Material TOO on
Sorption
The relationship between the total or-
ganic carbon (TOC) content of 15 earth
materials used as sorbents and sorption
of C-56 (Table 3) was investigated. The
molar K (KF) plotted as a function of TOC
(percentages) is shown in Figure 4. A
high correlation (r2) between KF and
TOC (%) was found with a linear regres-
sion relation of:
KF = 42.65 TOC (%)
(r2 = 0.972)
Koc = 4,265
The slope of the line from Figure 4
yields a new sorption constant (Koc) nor-
malized for the organic carbon content
of the soils. The K^ determined for C-56
was approximately 4,265. The results
indicated that the sorption properties of
soil materials for C-56 can be predicted
relatively accurately when the TOC con-
tent of the involved earth materials is
known. However, only a few soil materi-
als was used to develop the equation
and the relationship between sorption
and types of organic matter is unknown.
Even though the overall relationship is
highly significant, serious discrepancies
Kf = 42.65 TOC
r2 = 0.97
= 4,265
30
TOC(%)
Figure 4.
Kr vs. TOC for C-56 sorption by
15 soil materials.
between predicted and actual sorption
for a given soil may occur. Therefore,
caution should be used in interpreting
and using these results.
Effect of Soluble Salts on
Sorption
The results showed that all the salts
and brine dramatically affected sorp-
tion. The change in sorption followed
the inverse trend of the Setschenow
parameters (K). Salts causing the great-
est depression in solubility also caused
the largest increase in sorption and vice
versa. The effect of soluble salts on C-56
solubility appears to be related to its
sorption by soil materials.
Mobility of C-56 in Soils:
Determination by Soil TLC
The mobility of C-56 in soils, ex
pressed as Rf values, is summarized ir
Table 4. According to the results, C-56
stayed immobile in all soils wher
leached with tap water, caustic brines
or landfill leachate. However, C-56 was
highly mobile when leached with or
ganic fluids such as acetone/water mix
tures, acetone, methanol, or dioxane
The mobility of C-56 increased wher
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Table 4. Mobility of Hexachlorocyclopentadiene in Several Soil Materials Leached With Various Solvents as Measured by Soil TLC
Rf Value'
Soil
Materials
Muck soil
Catlin silt
loam
Flanagan silt
clay loam
Ava silt clay
loam
Bloomfield
limestone
Ottawa sand
Caustic
12-4-3
/VD*'*
0.00
ND
0.00
0.00
ND
Brine (%)**
3-1-0
ND
0.00
ND
0.00
0.00
ND
Tap
water
0.00
0.00
0.00
0.00
0.00
ND"
Landfill
leachate
0.00
0.00
0.00
0.00
0.00
0.00
Acetone/
water (1:1)
0.09
0.79
0.84
0.87
0.87
0.90
Methanol
0.05
0.88
0.89
0.89
0.97
ND
Acetone
0.14
0.97
0.99
0.99
0.98
ND
Dioxane
0.64
0.99
0.99
0.96
0.99
0.98
'Computed from statistical peak analysis of data by using values of 1st moment for grouped data.
"NaCI - NaOCI - NaOH (in tap water).
"'ND = Not determined.
leached with acetone/water mixtures as
the percentages of acetone increased in
water. Mobility of C-56 in soil was pro-
portional to the solubility of C-56 in the
solvent and to the soil organic content.
C-56 was significantly more mobile in
sandy soil than in muck soil.
The above findings are significant in
C-56 waste disposal. To decrease the
risk of C-56 migration from a landfill,
C-56 wastes should not come in contact
with leaching organic solvents or highly
organic leachates. This study also sug-
gests that migration of C-56 through soil
as vapor transport may be ah important
mechanism.
So/7 Column Leaching Study
In this study, a sample of Bloomfield
loamy sand heavily spiked with C-56 to
simulate a spill was leached with 192
inches of tap water. We found that
0.0005 percent of the applied com-
pound was leached from the soil
column. This loss suggests that C-56
will not be readily leached from even
highly contaminated soils by percolat-
ing water. However, some hydrolysis
products apparently have higher solu-
bility in water than C-56 and were much
more mobile in soil. From this study, it
was concluded that the secondary prod-
ucts of C-56, rather than C-56 itself,
might migrate and cause environmental
problems.
Recommendations
The results of this study showed that
C-56 was photoreactive and subject to
hydrolysis and sorption reactions. How-
ever, the disappearance of C-56 from
the environment does not mean that it
is always degraded to smaller
molecules or sorbed to soil particles.
C-56 has also been shown to condense
into compounds of larger molecular
weight. To determine the full environ-
mental impacts of C-56 on aquatic sys-
tems, further study of the toxicity and
mobility of C-56 breakdown and/or con-
densation products is essential.
Almost no attenuation of C-56 by soils
occurred when soil contaminated with
C-56 was leached with organic solvents.
To decrease the risk of potential migra-
tion of C-56 from a landfill, C-56 wastes
and organic solvents should not be dis-
posed of in the same landfill location
and C-56 waste should not come in con-
tact with leaching organic solvents or
highly organic leachates. Additional re-
search is also needed to determine the
chemical transformation of C-56 in soils,.
in real environmental settings, espe-
cially in landfills where buried C-56
wastes may come in contact with or-
ganic solvents, acids, or iron drums.
The results and conclusions derived
from this study deal specifically with at-
tenuation and mobility of C-56 in the liq-
uid phase. Vapor phase transport
through soil pores was ignored; for
compounds such as C-56 which have an
appreciable vapor pressure—this
means of migration may be a significant
mechanism for redistribution. More in-
formation is needed to assess the mag-
nitude of this means of migration for all
organic wastes including C-56.
The full report was submitted in par-
tial fulfillment of Grant No. R806335 by
the Illinois State Geological Survey. The
report, entitled "Soil, Clay, and Caustic
Soda Effects on Solubility, Sorption,
and Mobility of Hexachlorocyclopenta-
diene," was published as Environmen-
tal Geology Note 104 by the Illinois
State Geological Survey.
The Principal Investigators, S. F. Joseph Chou and Robert A. Griffin, are with the
Illinois State Geological Survey, Champaign. IL 61820.
Mike H. Roulier is the EPA Project Officer (see below).
The complete report, entitled "Soil, Clay and Caustic Soda Effects on Solubility,
Sorption, and Mobility of Hexachlorocyclopentadiene," (Order No. PB 84-116
060; Cost: $11.95, subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Hazardous Waste Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
-------
62501091
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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