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United States
Environmental Protection
Agency
Environmental Research
Laboratory
Athens GA 30613
Research and Development
EPA/600/S3-88/028 Sept. 1988
&EPA Project Summary
Measurement of Hydrolysis
Rate Constants for
Evaluation of Hazardous
Waste Land Disposal:
Volume 3. Data on 70
Chemicals
J. Jackson Ellington, Frank E. Stancil, Jr.,
William D. Payne, and Cheryl D. Trusty
To provide input data for a
mathematical model to estimate poten-
tial ground-water contamination from
chemicals in land disposal sites,
hydrolysis rate constants were measured
for 70 regulated chemicals under careful-
ly controlled conditions. Hydrolysis rates
were measured under sterile conditions
at precisely controlled temperatures and
at three hydrogen-ion concentrations (ph
3, 7, and 11). Conditions were adjusted
to provide sufficiently precise rate con-
stants to meet modeling requirements,
as determined through model sensitivi-
ty tests. In addition to precise control of
temperature and pH, precautions were
taken to minimize impact of adventitious
processes. Chemical concentrations as
a function of incubation time in the con-
stant temperature bath were measured
by gas chromatography, liquid chroma-
tography, or ion exchange chromatogra-
phy. Identities and purities of the
chemicals were determined by mass
spectrometry supplemented, and in
some cases, by infrared spectrometry.
Four chemicals (DL-rrans-4-
chlorostilbene oxide, benzyl chloride, 2,
4-dichlorophenoxyacetic acid methyl
ester, and lindane) were used as stan-
dard reference compounds (SRCs) to en-
sure reproducibility of analytical opera-
tions and control of parameters that af-
fect hydrolysis rates of chemicals in an
aqueous environment. The methyl ester
and lindane were used as SRCs in the pH
ranges of 8 to 9.5 and 9.5 to 11, respec-
tively. Benzyl chloride and the stilbene
oxide were used in conjunction with
neutral and acidic hydrolysis rate deter-
minations, respectively. Determinations
of the hydrolysis rates of the SRCs
repeated at varying temperatures and
pHs over a 2-year period yielded coeffi-
cients of variation of less than 12% in the
measurements.
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 order-
ing information at back).
Introduction
The Hazardous and Solid Waste Amend-
ments of 1984 to PL 98-616 (RCRA)
stipulate that land disposal of "hazardous
wastes" is prohibited unless the EPA Ad-
ministrator 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 unacceptable levels in
groundwater as a result of land disposal.
The amendments define hazardous waste
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as any of 362 specific compounds (either
part of or inclusive of Appendix VIII com-
pounds). In compiling this list, major con-
siderations were the toxicity and quantity
of the waste material generated annually.
In implementing the 1984 Hazardous and
Solid Waste Amendments to the Resource
Conservation and Recovery Act (RCRA),
EPA's Office of Solid Waste (OSW) will app-
ly a decision rule based on a mathematical
model of chemicals under consideration
that considers horizontal underground
movement of a chemical in a contaminated
aquifer offsite to a withdrawal point based
on advection, dispersion, sorption, and
chemical hydrolysis. Application of the
model requires as input the second- or first-
order hydrolysis rate constants for those
chemicals containing hydrolyzable func-
tional groups.
It is necessary to acquire hydrolysis rate
constants for each of the 362 chemicals ex-
cept for solvents ("fast track" in the list),
which will be treated as non-degrading,
non-sorbing constituents and chemicals
already banned by the State of California
(listed as "California"). These two groups
comprise 21 and 44 chemicals, respective-
ly. The remainder of the 362 chemicals
were separated for regulation into three fac-
tions 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 pro-
vides first- and second-order hydrolysis rate
constants for all those organic compounds
in the first and second "thirds" plus an ad-
ditional 12 chemicals of interest (Table 1)
for which satisfactory values were not
developed in an earlier evaluation process.
It also describes the laboratory experiments
conducted to measure hydrolysis rate
constants.
The Environmental Protection Agency
has proposed that manufacturers and pro-
cessors of the remaining 31 "third third"
chemicals be required, under Section 4 of
the Toxic Substances Control Act (TSCA),
to perform testing for chemical fate in-
cluding determination of hydrolysis rate
constants.
Hydrolysis Measurements
A typical hydrolysis experiment consisted
of preparing a spiking solution of the com-
pound of interest, preparing buffer solu-
tions, transferring spiked buffer to individual
"rate point tubes" (15-ml sealed ampules),
then monitoring disappearance over time
by analyzing individual tubes and determin-
ing the amount of compound remaining.
Spiking solutions were prepared by
dissolving the compound in acetonitrile,
methanol, or water. The concentration was
such that 0.1 ml diluted to 100 ml with buf-
fer gave a test compound concentration
that was 1x10-s/W or was 50% of the water
solubility or less.
Initial screening hydrolysis runs were per-
formed at three pH levels (3, 7, and 11). Buf-
fer pH was measured at the temperature
of the hydrolysis run. These initial
hydrolysis runs were used to set pH and
temperature conditions for subsequent rate
constant measurements. The measure-
ments of rate constants were normally per-
formed in triplicate; however, some com-
pounds required more replicates and some
less.
Standard Reference Compounds
(SRCs)
Chemical standards of known concentra-
tion have long been used for assuring
reliability of quantitative chemical analyses,
calibrating instruments, and measuring
recoveries of analytes from various
matrices. In a manner analogous to using
chemicals of known concentration as stan-
dards for concentration measurement,
chemicals whose hydrolysis rate constants
have been measured with established
precision by one experimenter or group can
be used as SRCs by other experimenters
in establishing and maintaining quality con-
trol in rate measurements.
Four compounds were used as SRCs for
this study, one each for acid and neutral
hydrolysis, and two for base hydrolysis.
Reproduction of the hydrolysis rate con-
stants of the SRCs at the established con-
centrations, pHs, and temperatures en-
sured that the experimental conditions were
reproducible ahcTnefped 'evaluate the ac-
curacy and precision of measurements for
the other compounds.
Frequency Distribution of
Hydrolysis Rate Constants
The frequency distribution of the
measured/extrapolated half-lives for 127 of
the 362 OSW compounds is represented
in Figure 1. The actual hydrolysis rate con-
stants for these compounds can be found
in Tables 1 and 2 and reference 1 of the
complete text. The 127 chemicals covered
a wide range of chemical classes and
chemical reactivity within each class. Thus,
the distribution in Figure 1 (60% of half-
lives < 3 years) might be considered as be-
ing representative of organic compounds
in general.
Table 1.
Hydrolysis Rate Constant and Half-Lives at 25°C for Selected Compounds
CAS Number
108-90-7
628-89-7
107-07-3
594-20-7
95-50-1
541-73-1
106-46-7
24009-05-0
608-93-S
319-94-8
95-94-3
88-06-2
Compound
Chlorobenzenea
2-(2-Chloroethoxy) ethanol
2-Chloroethanol (41, 42)
2, 2-Dichloropropane
1, 2-Dichlorobenzenea
1,3-Dichlorobenzenea
1,4-Dichlorobenzenea
1-Hydroxychlordeneb
Pentachlorobenzenea
Pentachlorocyclohexene (gamma PCCH)
1, 2,4,5-Tetrachlorobenzenea
2,4,6-Trichlorophenolc
Rate Constants
Acid Neutral
(32+0.1) x 10-5
4.5 x 10-6
(4.7 ±0.2) x 10-2
3.0 x 10-5
(2.3±3.5) x 10-7
Base
<09
36.0
<0.9
<0.9
<0.9
<1 X 10-4
<09
74 + 3
<0.9
Calculated
Half-life at
pH 7, 25°C
> 900 yr
3yr
9.9 yr
15 hr
> 900 yr
> 900 yr
> 900 yr
200,000 yr
> 900 yr
2.1 yr
> 900 yr
>40 yr
a= Based on assumed base mediated 1% disappearance after 16d at 85°C and pH 9.70 (pH 11.26 at room temperature).
b = Based on assumed base mediated 5°/o disappearance after 48d at 85°C and pH 9.51 (pH 11.04 at room temperature).
c = Based on assumed 5% disappearance after 330 hr at 85°C.
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Figure 1.
0-1 hr 1-24hr 1 -30 d 1-12 mo 1-3 y
Half-Life (25°C, pH 7)
Half-lives of OSW compounds.
3-5 y 5-10 Y >10y
The EPA authors J. Jackson Ellington (also the EPA Project Officer, see below),
and Frank E. Stancil. Jr., are with the Environmental Research Laboratory,
Athens, GA 30613; William D. Payne is with Technology Applications, Inc.,
Athens GA 30613; and Cheryl Trusty is with the University of Georgia, Athens,
GA 30613.
The complete report, entitled "Measurement of Hydrolysis Rate Constants for
Evaluation of Hazardous Waste Land Disposal: Volume 3. Data on 70
Chemicals," (Order No. PB 88-234 042/AS; Cost: $12.95, 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
College Station Road
Athens, GA 30613
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