United States
Environmental Protection
Agency
Environmental
Research Laboratory
Athens GA 30613
Research and Development
EPA/600/S3-87/019 Dec. 1987
Project Summary
Measurement of Hydrolysis
Rate Constants for
Evaluation of Hazardous Waste
Land Disposal: Volume 2.
Data on 54 Chemicals
J. J. Ellington, F. E. Stancil, Jr., W. D. Payne, and C. Trusty
To provide input data for a mathe-
matical model to estimate potential
ground-water contamination from
chemicals in land disposal sites, hydrol-
ysis rate constants were determined for
31 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).
Conditions were adjusted to provide
sufficiently precise rate constants to
meet modeling requirements deter-
mined through model sensitivity tests.
In addition to close monitoring of
temperature and pH, precautions were
taken to minimize impact of adventi-
tious processes. Chemical concentra-
tions as a function of incubation time
were measured by gas chromato-
graphy, liquid chromatography, or ion
exchange chromatography. Identities
and purities of the chemicals were
determined by mass spectrometry
supplemented, in some cases, by
infrared spectrometry. Hydrolysis rate
constants are reported for 54
compounds.
This Project Summary was devel-
oped by EPA's Environmental Re-
search 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).
Background
The Hazardous and Solid Waste
Amendments of 1984 to the Resources
Conservation and Recovery Act (PL 98-
616) stipulate that land disposal of
"hazardous wastes" is prohibited unless
the EPA Administrator determines that
prohibition of some wastes is not
required to protect human health and the
environment because those particular
wastes are not likely to reach unaccep-
table levels in ground water as a result
of land disposal. 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
relatively simple model was suggested
that would estimate potential ground-
water contamination for each listed
chemical. The model considers horizon-
tal movement based on advection, dis-
persion, sorption, and transformation.
Hydrolysis is the only transformation
process specifically considered.
Although other transformation pro-
cesses, such as microbial degradation
and chemical reduction, may take place,
they are not presently included in the
model. The model assumes no unsatu-
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rated zone for ground water and assumes
saturated ground-water "zones" ranging
from 3 meters to 560 meters in depth.
The mean depth of those considered is
78.6 meters. Organic carbon contents
used in the model will range from 1%
to 0.1%. The point at which the ground
water must meet standards may vary but
was originally set at 150 meters meas-
ured horizontally from the point of
introduction.
For each chemical considered, the
maximum allowable concentration for
the receiving ground water, 150 meters
"downstream," is entered into the
model, which assumes environmental
characteristics for selected subterranian
systems. 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
ground-water conditions is selected by
as the maximum allowable concentration
in leachates. A chemical may be disposed
of by land only if treatment brings the
leachate concentration down to the level
selected that would not cause ground
water to exceed the acceptable concen-
tration. The modeling approach applies
to landfills, surface impoundments,
waste piles, and land treatment opera-
tions. Land treatment operations may be
addressed in a different manner to allow
for reduction in concentrations resulting
from the land treatment process.
It is necessary to acquire octanol/
water partition coefficients and hydrol-
ysis rate constants for each of the 362
chemicals except for solvents ("fast
track" in the list), which will be treated
as non-degrading, non-sorbing constit-
uents and chemicals already banned by
the State of California (listed as "Cali-
fornia"). These two groups comprise 21
and 44 chemicals, respectively. The
remainder of the 362 chemicals were
separated into three groups by EPA's
Office of Solid Waste: 81 in the "first
third," 121 in the "second third," and
95 in the "third third." This report
provides first- and second-order hydrol-
ysis rate constants for those organic
compounds in the second group for
which satisfactory values were not
developed in an earlier evaluation pro-
cess and describes the laboratory exper-
iments conducted to measure hydrolysis
rate constants. Rate constants for 32
chemicals in the "first third" were
reported in Measurement of Hydrolysis
Rate Constants for Evaluation of Hazard-
ous Waste Land Disposal: Volume 1.
Data on 32 Chemicals. EPA/600/3-86/
043.
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 halide with the loss of halide ion
(-X):
RX + HOH-
-ROH + HX(orH+, X")
The rate of the reaction may be
promoted by the hydronium ion (H+, or
H30+) 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 mechanisms considered in this
study. This allowed direct measurement
of the HaO+ or OH" concentration through
accurate determination of solution pH.
Some chemicals show a pH dependent
elimination reaction:
H X
I I
- C - C -.
H'or
C = C + HX
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.
= kh[C] = kA[H+][C] + kB[OH"][C]
dt +kN'(H20][C] (1)
where [C] is the concentration of reactant
and kh is the pseudo-first-order rate
constant at a specific pH and tempera-
ture, kA and kB are second-order rate
constants and k.n' the pseduo-first-order
rate constant for the acid, base, and
neutral promoted processes, respec-
tively. The water concentration is essen-
tially not depleted by the reaction and
is much greater than [C], thus kN'[H20]
is a constant (kN).
Equation 1 assumes each individual
rate process is first order in substrate,
thus kh can be defined as:
kh =
kN
(2)
(3)
equation 2 may be rewritten as
kh = kA[H+] + M_w + kN (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 temper-
ature can be calculated from equation 5,
where kh is the observed rate.
tl/2 -
_ 0.693
(5)
Using the autoprotolysis equilibrium
expression
Contributing Factors in
Determination of Hydrolysis
Rate Constants
A typical hydrolysis experiment con-
sisted of preparing a spiking solution of
the compound of interest, preparing
buffer 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
determining percentage of the substrate
remaining.
Spiking solutions were prepared by
dissolving the substrate in acetonitrile,
methanol, or water. The concentration
was such that 0.1 ml diluted to 100 ml
with buffer gave a substrate concentra-
tion that was 1x10"5M 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.
Immediate analysis of one tube estab-
lished the 100% response peak (To).
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 per-
formed in triplicate.
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The EPA repositories at Research
Triangle Park, NC, and Las Vegas, NV,
were the first choice for chemicals on
which hydrolysis rates were measured.
Commercial 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 two
phosphate esters and methyl
methacrylate.
Solvents used were "distilled in glass,"
Burdick and Jackson solvents either gas
chromatograph of HPLC grade, as
required by the method of analysis.
An Orion Research EA920 pH meter*
equipped with an Orion Research
810300 Ross combination electrode was
used for all pH measurements. National
Bureau of Standards (NBS) reference
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
adjusted 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 M
potassium hydrogen phthalate was
diluted to 0.005 M and final pH adjust-
ment made with 0.1 M HCI. The pH 7
buffer was prepared from 0.1 M potas-
sium dihydrogen 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 JVI NaOH.
Buffer stability was tested initially at
0.001 M. Thus, pH 5 and pH 7 buffers
held their respective pHs for the test
period. The pH 9 buffer (0.001 M)
decreased to pH 8.07 after 24 hours and
to pH 7.50 after 96 hours. Buffer at a
concentration of 0.005 IM remained
constant at 9.10 ± 0.03 pH units for 25
days. Containers for the experiment were
screw cap test tubes. Autoclaved (COa
free) water was used.
Forma Scientific refrigerated and
heated baths (Model 2095} were used for
•Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use
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. Temper-
atures were measured with American
Society for Testing and Materials (ASTM)
thermometers, calibrated by NBS proce-
dures and NBS-certified master ther-
mometers. 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, and Z-Ultrapure cartridges.
Water obtained from this unit had a
resistance of greater than 16 meg ohms.
This double deionized water was auto-
claved for 30 min/liter and allowed to
cool before use. The sterile water was
stored in a sterile-cotton-plugged con-
tainer until used. All hydrolysis runs
were conducted in screw cap tubes. Data
from smear plate counts on agar indi-
cated 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 performed 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.
Control 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 sen-
sitivity and specificity
2. solvent extraction stopped hydrol-
ysis and allowed multiple injec-
tions over extended periods of time
3. solvent extraction also lessened
problems caused by compound
sorption to glass
4. methodology allowed direct aque-
ous injection of water soluble
compounds that were not amena-
ble 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
several compounds. Linearity of detector
response in the concentration range of
analysis for each chemical was estab-
lished to ensure reliable concentration
versus time plots.
Standard Reference
Compounds
Standard reference compounds are
compounds that are used as quality
assurance standards and as references
in inter-laboratory generation of hydrol-
ysis data. Repetition of rate constant
measurement for these compounds over
the course of the reporting period
established baseline information for
evaluating experimental techniques and
for all aspects of quality assurance.
Four chemicals (DL-frans-4-
chlorostilbene oxide, benzyl chloride,
2,4-dichlorophenoxyacetic acid methyl
ester, and lindane) were used as stand-
ard reference compounds (SRCs) to
ensure reproducibility and control of two
parameters, temperature and pH, that
affect hydrolysis rates of chemicals in an
aqueous environment. The acetate and
lindane were used as SRCs in the pH
ranges of 8 to 9.5 and 9.5 to 11,
respectively. Benzyl chloride and the
stilbene oxide were used in conjunction
with neutral and acidic hydrolysis rate
determinations, respectively. Determina-
tions of the hydrolysis rates of the SRCs
were repeated at varying temperatures
and pHs over a 15-month period. Each
SRC is amenable to analysis by both gas
chromatography and liquid chromatog-
raphy. During the study, the rates for the
SRCs were determined on four gas
chromatographs and three liquid chro-
matographs by four chemists. For these
determinations the greatest variability
from the mean at the 95% confidence
limit was ±12% for the acetate. The
mean and uncertainty at the 95% con-
fidence level was: stilbene oxide (17.0
± 2.0 M"1 mm"1), benzyl chloride [ (7.2
± 0.5) X 10~4 mm"1], acetate (699 ± 77
M"1 min'1), and lindane (3.3 ± 0.1 M"1
min"1).
Reproduction of the hydrolysis con-
stants of the SRCs at the established
concentrations, pHs, and temperatures
insured that the experimental conditions
for each set of compounds were accep-
table and that the rate constants for the
compounds 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
determinations. Hydrolysis data for the
second and third set of compounds will
be reported in subsequent volumes.
Hydrolysis Rate Constants
A summary sheet was prepared for
each chemical. The summary sheet
contained information pertinent to the
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 generated 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
constants 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
parameters. A temperature correction
was applied to all calculations involving
kw or [OH~). When statistical tests of the
data indicated the hydrolysis was inde-
pendent 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.
Table 1. Hydrolysis Rate Constants and Half-Lives at 25°C Laboratory Determined Rate Data
CAS Number
591-08-2
75-05-8
53-96-3
492-80-8
1 15-02-6
305-03-3
57-74-9
494-03-1
91-58-7
126-99-8
5344-82-1
542-76-7
50-18-0
72-54-8
20830-81-3
2303-16-4
111-44-4
78-87-5
297-97-2
Compound
n-(Aminothioxomethyl)-
acetamide
Acetonitrile*
2 -A cetylaminofluorine
Auramine*
Azaserine
ChlorambuciP
Chlordane (cis isomer)
Chloronaphazine"
Beta- Chlornaphthalene
2-Chloro-1. 3 -butadiene"
1 -(O-Chlorophenyl)thiourea
3-Chloropropanenitrile
Cyclophosphamide"
ODD fp,p' isomer)
Daunomycin
Diallate
Dichloroethyl ether*
1 ,2-Dichloropropane
0.0-Diethyl-O-pyranzinyl
Rate Constants
Acid Neutral
/W~1 hr'' hr"1
[1.7±0.2)XW*
2.3 X 10~*
5.5 3.9X10'*
328 ±20 (2.6 ± 0.4) X 10'*
0.4
3.2 X 10'3
(9. 5 ± 2.8) X )0'e
Base
M'1 Air'1
7.50 ±0.09
5.8 X W'3
6X10'3
6.8 ±0.7
4.3 XW3
Calculated
Half-Life
atpH7
4.6 yr
>1 50,000 yr
34 yr
74 d
99 d
1.7 hr
>197,000 yr
216hr
8.3 yr
Polymerizes in absence of inhibitors (no hydrolysis)
(9.8 ±3.0)X10'7
(1.3 ±0.1)X10~4
7.1 X 10'*
(2.8±0.9)XW'e
(9.7 ±0.5) XW'5
(1.2±0.7)XWS
3.2 X 10~2
(5.0±0.2)XW*
(1.0±0.06)XW3
0.1 4 ±0.03
12.071 ±1,960
5.2
10
0.9 ± 0.4
4.3 X 10~*
7.3 ±0.7
81 yr
22 d
41 d
28 yr
298 d
6.6 yr
22 hr
15.8 yr
29 d
phosphorothioate
55-91-4
Diisopropyl fluorophosphate*
3.8
7.2 X 10'
28
96 hr
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Table 1.
CASNumber
60-51-5
541-53-7
62-50-0
96-45-7
111-54-6
640-19-7
118-74-1
67-72-1
757-58-4
465-73-6
303-34-4
58-89-9
109-77-3
148-82-3
16752-77-5
80-62-6
70-25-7
75-55-8
56-84-2
86-88-4
7598-73-9
615-53-2
152-16-9
1 1 7-84-0
298-02-2
1120-71-4
94-59-7
107-49-3
62-55-5
137-26-8
(continued)
Compound
Dimethoate"
2.4-Dithiobiuret
Ethyl methanesulfonate*
Ethylene thiourea
Ethylene-Bis-(Dithio-
carbamic Acid) [as in
disodium salt, Nabam]
2-Fluoroacetamide
Hexachlorobenzene
Hexachloroethane
Hexaethyl tetraphosphate*
Isodrin
Lasiocarpine
Lindane
Malononitrile
Melphalan*
Methomyl*
Methyl methacrylate
N-Methyl-N-nitro-N-nitroso-
guanidine'
2-Methylaziridine*
Methylthiouracil
Alpha-Naphthaylthiourea
N-Nitroso-N-ethylurea'
N-Nitroso-N-
methylurethane"
Octamethylpyrophosphoramide*
Di-n-Octylphthalate*
Phorate*
1,3 -Propane sultone*
Safrole
Tetraethyl pyrophosphate*
Thioacetamide*
Thiram
Rate Constants
Acid Neutral Base
M-1 hr~i hr-1 /VT1 hr"
1.7 X10'4 756
(7.1 ± 1.3JX10'3
1.5X10'2
Zero hydrolysis observed after 90 days at 90°C and pH (3, 7, 9)
848 0.01
(3.3±0.3)X10'S
Zero hydrolysis observed after 1 3 days at 85°C and pH (3, 7, 11)
Zero hydrolysis observed after 1 1 days at 85°C and pH(3. 7, 111
9.3 X 10'2
1.7X10'*
(4.9±0.1)X10'S 9.8 ±0.1
(1.2±0.2)XW4 198 ±6
(1.35 ± 0.42} X 10~3 806 ± 45
0.15
8.9X10'S 210
200 ± 47
4.9 2.7X1 O'2 9.5X10*
4.0 X10'3 8.0 X10'3
(9.7±2.7)X10~*
(8.0 ± 2.4) X 10's 9.9 X 10'2
63 0.19 5.3X10"
9.5 2.9 X 10~* 2.9 X 103
0.23 ±0.03 1X10~"
7.4
7.2 X 10'3
8.2X10'*
Zero hydrolysis observed after 26 days at 85°C and pH (3, 7. 11)
9.3 X W*
(6.0 ± 0.06) X 10'2 (8.6 ±1.1)X 10's 1.4 ± 0.09
5.0 X10'3 4,153 ±80
Calculated
Half-Life
atpH7
118hr
98 hr
46 hr
69 hr
2.4 yr
7.5 hr
46 yr
1.6 yr
206 d
20.2 d
4.6 hr
262 d
3.9 yr
19 hr
87 hr
8.2 yr
361 d
0.96 hr
24 hr
3,400 yr
107 yr
96 hr
8.5 hr
7.5 hr
336 d
5.3d
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Table 1. (continued)
CAS Number
8001-35-2
126-68-1
Compound
Toxaphene
0,0,0-Triethylester
Rate Constants
Acid Neutral Base
(8.0 ± 2.2) X 10~e 3.2 ± 2.2
(2.0 ±0.2) X ?0~5
Calculated
Half-Life
atpH7
10 yr
3.9 yr
2524-09-6
126-72-7
phosphorothioic A cid
O.O.S-Triethylester
phosphorodithioic Acid
Tris(2,3-Dibromopropyl-
phosphate
X2.0±0.2>XW~S
(1.0 ± 1.1) X 70~5
78
<3.9 yr
4.4 yr
^Values were extracted from literature references for the particular chemical. The neutral hydrolysis rate for thioacetamide was determined at
Athens-ERL.
The EPA authors, J. Jackson Ellington (also the EPA Project officer, see below)
and Frank E. Stancil, Jr., are with Environmental Research Laboratory,
Athens, GA 30613; William D. Payne is with Technology Applications, Inc.,
Athens, GA 30613; and Cheryl Trusty is with University of Georgia. Athens,
GA 30602.
The complete report, entitled "Measurement of Hydrolysis Rate Constants for
Evaluation of Hazardous Waste Land Disposal: Volume 2. Data on 54
Chemicals," (Order No. PB 87-227 344/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 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
Official Business
Penalty for Private Use $300
EPA/600/S3-87/019
0000129 PS
It- 60604
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