United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA/600/S3-86/043 Apr. 1987
SEPA Project Summary
Measurement of Hydrolysis Rate
Constants for Evaluation of
Hazardous Waste Land Disposal:
Volume 1. Data on 32 Chemicals
J. Jackson Ellington, F. E. Stancil, Jr., and W. D. Payne
To provide input data for a mathe-
matical model to estimate potential
groundwater contamination from chem-
icals in land disposal sites, hydrolysis
rate constants were determined for 26
regulated chemicals under carefully
controlled conditions. Hydrolysis rates
were measured under sterile conditions
at precisely controlled temperatures and
at three pH levels, 3, 7, and 11. Condi-
tions were adjusted to provide suf-
ficiently precise rate constants to meet
modeling requirements determined
through model sensitivity tests. In addi-
tion to close monitoring of temperature
and pH, precautions were taken to
minimize impact of adventitious pro-
cesses. Chemical concentrations as a
function of incubation time were mea-
sured by gas chromatography, liquid
chromatography, or ion exchange chro-
matography. Identities and purities of
the chemicals were determined by mass
spectrometry supplemented, in some
cases, by infrared spectrometry.
Hydrolysis rates for three standard
reference compounds (chlorostilbene
oxide for acid, 2,4-D methyl ester for
base, and benzyl chloride for neutral
conditions) were measured repetitively
to assess the effect of undetected
changes in experimental conditions.
Pseudo-first order rate constants deter-
mined for benzyl chloride at 28.0°C
over 8 months had a coefficient of varia-
tion (C.V.) of 9.0%. Values determined
at higher temperatures (36.4, 45.0, and
52.9 C) and extrapolated back to
28.0°C had a C.V. of 18.0%. Second-
order rate constants for the 2,4-D
methyl ester and for 4-chlorostilbene
oxide determined under similar condi-
tions (28.0°C, 8 mo.) had C.V.'s of
14.7% and 14.0%, respectively.
Hydrolysis rate constants were deter-
mined experimentally for the following
26 compounds: warfarin, aldrin,
brucine, dieldrin, disulfoton, endosulfan
I, endosulfan II, fluoroacetic acid
sodium salt, 2-methyllactonitrile, fam-
phur, acrylamide, acrylonitrile, c/s-1,4-
dichloro-2-butene, trans-1,4-dichloro-2-
butene, 4,4-methylene-6/s-(2-chloroani-
line), pentachloronitrobenzene, pro-
namide, reserpine, thiourea, uracil
mustard, ethyl carbamate, 2,3-dichloro-
propanol, 1,3-dichloropropanol, 1,2,3-
trichloropropane, 1,2,3-trichloroben-
zene, and 1,2,4-trichlorobenzene. Rate
data also were reported for: nitro-
benzene, mitomycin C, chloromethyl
methyl ether, 1,2-dibromo-3-chloropro-
pane, and ethylene dibromide.
All compounds except thiourea were
hydrolyzed to some extent under the
varying conditions of pH and tempera-
ture employed. Hydrolysis rate con-
stants reported at 25°C ranged from
approximately 1 hr° to 1 x 107 hr1.
Half-lives correspondingly ranged from
a few minutes to centuries.
This Project Summary was developed
by EPA's Environmental Research
Laboratory, Athens, GA, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
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Background
The Hazardous and Solid Waste
Amendments of 1984 to the Resource
Conservation and Recovery Act (PL 98-
616) stipulate that land disposal of
hazardous waste is prohibited unless the
EPA Administrator determines that pro-
hibition of some wastes is not required to
protect human health and the environ-
ment because those particular wastes
are not likely to reach unacceptable levels
in groundwater as a result of land dis-
posal. The amendments define hazardous
waste as any of 362 specific compounds
(either part of or inclusive of Appendix
VIII compounds). In compiling this list,
major considerations were toxicity of the
material and quantity of waste material
generated annually.
To provide a practical tool for deter-
mining which listed hazardous materials
may be disposed of by land disposal and
under what conditions, the use of a rela-
tively simple model was suggested that
would estimate potential groundwater
contamination for each listed chemical.
The model considers horizontal move-
ment based on advection, dispersion,
sorption, and transformation. Hydrolysis
is the only transformation process specifi-
cally considered. Although other trans-
formation processes, such as microbial
degradation and chemical reduction, may
take place, they are not presently included
in the model. The model assumes no
unsaturated zone for groundwater and
assumes saturated groundwater "zones"
ranging from 3 meters to 560 meters in
depth. The mean depth of those con-
sidered is 78.6 meters Organic carbon
contents used in the model will range
from 1% to 0.1%. The point at which the
groundwater must meet standards may
vary but was originally set at 150 meters
measured horizontally from the point of
introduction
For each chemical considered, the
maximum allowable concentration for the
receiving groundwater, 150 meters
"downstream," is entered into the model,
which assumes environmental charac-
teristics for selected subterrainian sys-
tems. The concentration of leachate
leaving the disposal site is computed for
various conditions of rainfall, soil type,
pH, etc. A computed leachate concentra-
tion that would cause unacceptable
groundwater conditions is selected by
the Office of Solid Waste (OSW) maximum
allowable concentration in leachates. A
chemical may be disposed of by land only
if treatment brings the leachate con-
centration down to the level selected that
would not cause groundwater to exceed
the acceptable concentration. The model-
ing approach applies to landfills, surface
impoundments, waste piles, and land
treatment operations. Land treatment
operations may be addressed in a dif-
ferent manner to allow for reduction in
concentrations resulting from the land
treatment process.
It is necessary to acquire octanol/water
partition coefficients and hydrolysis rate
constants for each of the 362 chemicals
except for solvents ("fast track" in the
list), which will be treated as non-degrad-
ing, non-sorbing constituents and chem-
icals already banned by the State of
California (listed as "California"). These
two groups comprise 21 and 44 chemi-
cals, respectively. The remainder of the
362 chemicals were separated into 3
groups by OSW: 81 in the "first third,"
121 in the "second third," and 95 in the
"third third." This report provides first-
and second-order hydrolysis rate con-
stants for those organic compounds in
the first group for which satisfactory
values were not developed in an earlier
evaluation process and describes the
laboratory experiments conducted to
measure hydrolysis rate constants.
Hydrolysis Kinetics
Hydrolysis of organic compounds refers
to reaction of the compound with water
in which bonds are broken and new
bonds with HO- and H- are formed. A
common example is the reaction of an
alkyl hahde with the loss of halide ion
(-X).
RX+HOH
->ROH + HX(orH+, X)
The rate of the reaction may be pro-
moted by the hydronium ion (H+, or H3O+)
or the hydroxyl ion (OH"). The former is
referred to as specific acid catalysis and
the latter as specific base catalysis. These
two processes, together with the neutral
water reaction, were the only mecha-
nisms considered in this study. This al-
lowed direct measurement of the H30+ or
OH concentration through accurate
determination of solution pH.
Some chemicals show a pH dependent
elimination reaction:
H X
H+ or
-C-C
OH
In this study, only the disappearance of
substrate was monitored with no attempts
to identify mechanisms.
All processes referred to above are
included where the rate of hydrolysis is
given by the equation,
d[C]
kh[C] =
dt (1;
kA[H+][C] + kB[OH ][C] + k£ [H20][C]
where [C] is the concentration of reactanl
and kh is the pseudo-first-order rate
constant at a specific pH and temperature,
kA and kB are second-order rate constants
and kN' the pseudo-first-order rate con-
stant for the acid, base, and neutral
promoted processes, respectively. The
water concentration is essentially not
depleted by the reaction and is much
greater than [C], thus kN'[H20] is a con-
stant (kN).
Equation 1 assumes each individual
rate process is first order in substrate,
thus kh can be defined as:
Using the autoprotolysis equilibrium
expression
KW = [H+][OH1 (3]
equation 2 may be rewritten as
KBKW
-
[Hi
(4)
Equation 4 shows the dependence of kh
on [H+] and on the relative values of kA,
KB, and KN.
As a good approximation, the second-
order rate constants for acid hydrolysis
and for base hydrolysis can be calculated
by dividing the pseudo-first order rate
constant obtained at the appropriate pH
by the hydronium ion or hydroxyl ion
concentration, respectively. The half-life
of a chemical at a given pH and tempera-
ture can be calculated from equation 5,
where kh is the observed rate.
0.693
(5)
Contributing Factors in
Determination of Hydrolysis
Rate Constants
A typical hydrolysis experiment con-
sisted of preparing a spiking solution ol
the compound of interest, preparing buf-
fer solutions, transferring spiked buffer
to individual "rate point tubes" (15-ml
Teflon lined, screw cap, or sealed
ampules), then monitoring degradation
by sacrificing individual tubes and deter-
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mining percentage of the substrate
remaining.
Spiking solutions were prepared by
dissolving the substrate in acetonitnle,
methanol, or water. The concentration
was such that 0 1 ml diluted to 100 ml
with buffer gave a substrate concentration
that was 1x105M or was 50% of the
water solubility or less
Initial hydrolysis runs were performed
at pH 3, 7, and 11 Buffers were prepared
at these pHs then measured at the
temperature of the hydrolysis run. Each
run consisted of five or six tubes. Im-
mediate analysis of one tube established
the 100% response peak (T0). Analysis of
a second tube within 3 to 6 hours gave a
good estimate of sampling frequency for
the remaining tubes.
The initial hydrolysis runs were used to
set pH and temperature conditions for
subsequent rate determinations. The rate
determinations were normally performed
in triplicate; however, some compounds
required more replicates (aldrin, dieldrin)
and some less (2-methyllactonitrile).
The EPA repositories at Research Tri-
angle Park, NC, and Las Vegas, NV, were
the first choice for chemicals on which
hydrolysis rates were measured. Com-
mercial chemical companies were the
second sources The chemicals used for
determining rate constants were analyzed
by mass spectrometry for confirmation of
the stated identity. The generated mass
spectral data were used to confirm
identities of chemicals. GC/FTIR was
used to characterize the 1,2,3- and 1,2,4-
isomers of trichlorobenzene.
Solvents used were "distilled in glass,"
Burdick and Jackson solvents either gas
chromatograph of HPLC grade, as re-
quired by the method of analysis
An Orion Research EA920 pH meter
equipped with an Orion Research
A810300 Ross combination electrode
was used for all pH measurements
National Bureau of Standards (NBS) ref-
erence standards were used to calibrate
and check the pH meter. The pH meter
had a stated accuracy of ±0.02 units. The
temperature compensation probe was
used for all measurements. The pH was
measured at the temperature of the
hydrolysis rate measurement and ad-
justed with base or acid to obtain the
desired pH.
Buffer stock solutions were prepared
at 0 1 M using sterile water as described
above. To prepare pH 3 buffer, 0.1 IM
potassium hydrogen phthalate was diluted
to 0 005 M and final pH adjustment made
with 0.1 M HCI. The pH 7 buffer was
prepared from 0.1 M^ potassium dihy-
drogen phosphate diluted to 0.005 M
with final pH adjustment using 0.1 M
NaOH. Buffers for pHs 9 and 11 were
made by diluting 0.1 M sodium phosphate
heptahydrate to 0.005 M with final pH
adjustment using 0.1 M NaOH.
Buffer stability was tested initially at
0.001 M. Thus, pH 5 and pH 7 buffers
held their respective pH's for the test
period. The pH 9 buffer (0.001 M) de-
creased to pH 8.07 after 24 hours and to
pH 7.50 after 96 hours. Buffer at a con-
centration of 0.005 M remained constant
at 9.10 ± 0.03 pH units for 25 days.
Containers for the experiment were screw
cap test tubes. Autoclaved (C02 free)
water was used
Forma Scientific refrigerated and
heated baths (Model 2095) were used for
temperatures in the range of 2 to 70°C
(±0.02°C) A lauda C-20 oil bath with a
stated control accuracy of ±0.01 °C and a
fine control range of ±0.2°C was used
for temperatures above 68°C. Tempera-
tures were measured with American
Society for Testing and Materials (ASTM)
thermometers, calibrated by NBS proce-
dures and NBS-certified master thermom-
eters. The thermometers were calibrated
in 0.1 °C increments.
Water used in the experiments was
unchlorinated ground water that was first
processed through a high capacity reverse
osmosis unit and a deionizer unit. This
"house" deionized water was further
purified by passage through a Barnstead
Nanopure II deionizer, 4-module unit with
Pretreatment, High Capacity, andZ-Ultra-
pure cartridges. Water obtained from this
unit has a resistance of greater than 16
meg ohms This double deionized water
was autoclaved for 30 min/liter and al-
lowed to cool before use. The sterile
water was stored in a sterile-cotton-
plugged container until used. All hy-
drolysis runs were conducted in screw
cap tubes. Data from smear plate counts
on agar indicated growth as being less
than 1 colony per milliliter through 9
days at 25°C and pH of 5, 7, and 9.
Sterility checks on the water were per-
formed intermittently.
Buffer solutions also were checked for
bacterial growth. Buffer solutions, pre-
pared as described above, were trans-
ferred at room temperature to screw cap
test tubes. One-half were flame trans-
ferred, the other half without flaming. A
sample (1 ml) from each tube was plated
daily, for 9 concurrent days on TGE agar.
After a 48-hour incubation, no growth
was found. This confirmed sterility. Con-
trol checks during hydrolysis runs showed
no growth.
Methods of Analysis
Generally gas chromatography was the
first method of choice for four reasons:
1) instrument provided required sensi-
tivity and specificity
2) solvent extraction stopped hydrolysis
and allowed multiple injections over
extended periods of time
3) solvent extraction also lessened
problems caused by compound
sorption to glass
4) methodology allowed direct aqueous
injection of water soluble com-
pounds that were not amenable to
other methods of analysis
High performance liquid chromato-
graphy (HPLC) was used extensively; ion
chromatography and the diode array UV-
detector were used in the analysis of
sodium fluoroacetate and thiourea, re-
spectively. Hydrogen cyanide released by
the decomposition of 2-methyllactonitrile
was monitored by EPA Method 335.
Linearity of detector response in the
concentration range of analysis for each
chemical was established to ensure reli-
able concentration versus time plots.
Standard Reference Compounds
Standard reference compounds are
compounds that are used as quality as-
surance standards and as references in
inter-laboratory generation of hydrolysis
data. Repetition of rate constant measure-
ment for these compounds over the
course of the reporting period established
baseline information for evaluating ex-
perimental techniques and for all aspects
of quality assurance. Three compounds
were selected; one for each process: acid,
base, and neutral hydrolysis. Each stan-
dard reference compound is also amen-
able to analysis by both gas chromato-
graphy and liquid chromatography.
Reproduction of the hydrolysis constants
of the SRCs at the established concentra-
tions, pHs, and temperatures insured that
the experimental conditions for each set
of compounds were acceptable and that
the rate constants for the OSW com-
pounds could be determined with required
precision and accuracy. A range of
pseudo-first-order hydrolysis rates for all
SRCs and second-order rate constants
for the acidic and basic reference com-
pound were established from these deter-
minations. Hydrolysis data for the second
and third set of compounds will be re-
ported in subsequent volumes.
Hydrolysis Rate Constants
A summary sheet was prepared for
each chemical. The summary sheet con-
tained information pertinent to the
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analysis of each chemical, and included
source, purity, and analytical method.
Also included on the sheet was informa-
tion on pH, temperature, pseudo-first-
order and second-order rate constants,
half-lives, and correlation coefficients (r2).
Where a literature reference for the
hydrolysis of a compound was obtained,
the summary sheet contained the second-
order rate constant if applicable and first-
order rate constants at 25°C. For several
of the compounds, lab data were gen-
erated in this study to fill in gaps in the
literature.
Data from all the summary sheets were
used to derive the values in Table 1.
These values are the calculated rate con-
stants at 25°C. The rate constants were
assumed to increase a factor of 10 for
each 20°C increase in temperature above
25°C. This corresponds to an activation
energy of about 20 kcal/mole. When
applicable, extrapolated values (25°C)
were obtained using activation param-
eters. A temperature correction was
applied to all calculations involving kw or
[OH"]. When statistical tests of the data
indicated the hydrolysis was independent
of pH, hydrolysis values from the extremes
of pH (acid and/or base) were included in
calculating the neutral hydrolysis rates
reported in Table 1. Confidence limits
were calculated from the mean and
standard deviation values and are the
values reported in Table 1.
TaWe 1. Hydrolysis Pate Constants at 25° C
Warfarin
Aldrin
Brucine
Dieldrin
Disulfoton
Endosulfan 1
Endosulfan II
Fluoroacetic Acid
Sodium Salt
2-Methyllactonitrile
Nitroglycerine"
Famphur
Aery/amide
Acrylonitrileb
Mitomycin Ca
Chloromethyl methyl ether3
J,2-D/bromo-3-chloropropanea
Ethylene Dibromide"
cis- 1 ,4-Dichloro-2-butene
trans- 1 ,4-Dichloro-2-butene
4,4-Methylene-bis-(2-chloroaniline)
Pentachloronitrobenzene
Pronamide
Fteserpine
Thiourea
Uracil Mustard
Ethyl Carbamate
2.3-Dichloro- 1 -propanol
1 ,3-Dichloro-2-propanol
1,2,3- Trichloropropane
1,2,3- Trichlorobenzene
1,2,4- Trichlorobenzene
Acid
M-'hr'
1.4x1&4
5.9 xia3
(8.1±2.7)xlO-3
(7.4±3.9)x10-3
<3.6x102
(4.2±0.3)x102
(2.9±3)x10-4
4.3x1 a3
0.82
Rate Constants
Neutral
hr-'
4.9 x J&6
£?.S±2.3)x10"5
(7.5±3.3)x106
(2.8±0.4)x104
(3.2±2.0)x10'3
(3.7±2.0)x10-3
<1.7x10'6
4.47
(25±9)x10"4
<(2.1±2.1)x10-6
3.7x1 0'4
21
9.9x1 0'6
(9.1±1 1)x10'3
(9.0±0.5)x10-3
<9x10'8
(2.8±0.7)x10'5
<1.5x105
(4.5±1.8)x10-5
<5.3x107
0.57±0.08
<2.6x10'7
(5.3±0.8)x10'5
(3.1±0.2)x10'3
(1.8±0.6)x10-6
(1.6±1.3)x10's
(2.3±.9)x105
Base
M-'hr'
0.026
0.21
5.99
C/.0±0.7)x104
(1.5±0.9)x104
77±11
5.0
(6.1±6.5)x10-1
3.0±1.7
20.6
7.4x1 0'2
9.8±10.9
(2.05±0.2)x105
1.1x10'1
20.6±2.2
854±87
9.9x1 0'4
a Values were extracted from literature references in Section 1. The second-order alkaline hyrolysis rate constant for Mitomycin C was determined a
Athens ERL.
b Calculated from alkaline second-order rate constant assuming zero neutral contribution.
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The EPA authors J. Jackson Ellington (also the EPA Project Officer, see below),
Frank E. Stancil. Jr.. and William D. Payne are with the Environmental
Research Laboratory. Athens. GA 30613.
The complete report, entitled "Measurement of Hydrolysis Rate Constants for
Evaluation of Hazardous Waste Land Disposal, Volume I," (Order No. PB 87-
140 349/AS; Cost: $18.95, 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:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Athens. GA 30613
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
POSTAGE & FEES PAH
EPA
PERMIT No G-35
Official Business
Penalty for Private Use $300
EPA/600/S3-86/043
CHICAGO
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