THE THERMAL DEGRADATION CHARACTERISTICS OF ENVIRONMENTALLY
SENSITIVE PESTICIDE PRODUCTS
by
Debra A. T1rey, Barry Dellinger, Wayne A. Rubey, and Philip H. Taylor
University of Dayton Research Institute
Environmental Sciences Group
Dayton, Ohio 45469-0132
Cooperative Agreement CR-813938-01-0
Co-Project Officers
Donald A. Oberacker and Philip C. L. Lin
Waste Minimization, Destruction, and Disposal Research Division
Risk Reduction Engineering Laboratory
Cincinnati, OH 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
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DISCLAIMER
This report has been reviewed by the Risk Reduction Engineering
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
11
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FOREWORD
Today's rapidly developing and changing technologies and Industrial
products and practices frequently carry with them the increased generation of
materials that if improperly dealt with, can threaten both public health and
the environment. The U.S. Environmental Protection Agency is charged by
Congress with protecting the Nation's land, air, and water resources. Under a
mandate of national environmental laws, the agency strives to formulate and
implement actions leading to a compatible balance between human activities and
the ability of natural systems to support and nurture life. These laws direct
the EPA to perform research to define our environmental problems, measure the
impacts, and search for solutions.
The Risk Reduction Engineering Laboratory Is responsible for planning,
implementing, and managing of research, development, and demonstration
programs to provide an authoritative, defensible engineering basis in support
of the policies, programs, and regulations of the EPA with respect to drinking
water, wastewater, pesticides, toxic substances, solid and hazardous wastes,
and Superfund-related activities.
This publication provides the results of theoretical and laboratory-
scale research which examined thermal breakdown behavior of a variety of
pesticides and one pesticide container material when subjected to heat such as
during open-burning and/or intermediate conditions within an incinerator. The
report contains information important to the technical community concerned
with excess or waste pesticide disposal via burning or incineration.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
ill
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ABSTRACT
The thermal decomposition properties of the active ingredient of 16
pesticides have been theoretically examined. The parameter used to rank their
stability was the temperature required for 99% destruction at a gas phase
residence time of 2.0 s under oxygen starved conditions.
Experimental studies on 5 pesticide related materials were also
conducted under a controlled laboratory testing. Experimental studies of the
high-temperature oxidation and pyrolysis of four key pesticide materials
including the identification and quantification of products of incomplete
combustion (PICs) were conducted. The four pesticides were: Aldicarb and
Phorate (both insecticides), and Atrazine and Alachlor (both herbicides).
These compounds are the active ingredients of Thimet, Temik, Aatrex-Nine-0,
and Lasso II, respectively. A fifth material, a polyethylene blend bag which
is used as an Atrazine container, was also examined.
The examination of the incineration ranking among the 16 subject
pesticides indicated that they should be considered thermally fragile.
However, each pesticide in the controlled laboratory testing decomposes to
yield a large number of reaction intermediates. More intermediates were
consistently produced under pyrolytic conditions. Most of the intermediates
were decomposed by 700°C. Some persisted at'the maximum temperature ,1000'C.
It appears that these materials may be amenable to properly controlled,
high-temperature incineration. It is clear that open-burning of spent
pesticide bags may not significantly reduce their impact on the environment.
It is also concluded that further development of the analytical protocols
associated with the monitoring of decomposition products from pesticide materials
should be conducted.
This report was submitted in fulfillment of Cooperative Agreement No. CR-
813938-01-0 by the University of Dayton Research Institute, under the sponsorship
of the U.S. Environmental Protection Agency. This report covers a period from
October, 1990 to August, 1991, and work was completed as of April, 1992.
iv
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CONTENTS
Foreword 111
Abstract 1v
Figures v1
Tables v11
1. Introduction . 1
2. Conclusions 4
3. Recommendations 5
4. Experimental Procedures 6
4.1 Instrumentation 6
4.2 Sample Introduction 9
5. Results and Discussion 14
References 29
Appendices
1. Pesticide Thermal Stability Data Sheet 31
2. Response Factors for Analytical Standards 48
3. Mass Balance Data 50
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FIGURES
Number Page
1 Close-up schematic of the Insertion-split Interface as 1t 1s
configured 1n the IDAS 8
2 Structures of the active Ingredients of the four pesticides
Investigated 1n this study 12
3 Example chromatogram generated for Alachlor pyrolysls,
phi=10, 4000 ppm, 2s residence time, 1.23 atn 17
4 Weight % remaining curves for parent materials, Alachlor
and Atrazine, generated under ox1dative (phi - 0.5) and
pyrolytic (ph1= 10.0) conditions, 2.0 sec residence time,
4000 and 3000 ppm respectively, and 1.23 atra 18
v1
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TABLES
Number Page
1 Pesticide Thermal Stabll Ity Data 3
2 Volatilization Parameters and Concentration of 0, 1n
the Carrier Utilized to Achieve Target Test Conditions 13
3 Number of Decomposition By-products Observed 14
4 Pesticide Stabllity 15
5 Height % Yield of Products Detected in Aldicarb Oxidation 19
6 Weight % Yield of Products Detected in Aldicarb Pyrolysis 20
7 Weight % Yield of Products Detected in Atrazine Oxidation 21
8 Weight % Yield of Products Detected in Atrazine Pyrolysis 22
9 Weight % Yield of Products Detected in Alachlor Oxidation 23
10 Weight % Yield of Products Detected in Alachlor Pyrolysis 24
11' Qualitative Data of Phorate Oxidation Products 26
12 Qualitative Data of Phorate Pyrolysis Products 27
13 Qualitative Data of Polyethylene Bag Oxidation Products 28
3.1 Aldicarb Oxidation 50
3.2 Aldicarb Pyrolysis 51
3.3 Atrazine Oxidation 52
3.4 Atrazine Pyrolysis 53
3.5 Alachlor Oxidation 54
3.6 Al achlor Pyrolysis 55
vii
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SECTION 1
INTRODUCTION
Each year hundreds of thousands of pounds of pesticides, Insecticides,
herbicides, and fungicides are applied worldwide to control rodents, Insects,
weeds and fungi thought to be a direct threat to human health, or a threat to
livestock and crops raised for human consumption (1). There has recently been
renewed concern over the Impact of applying these chemicals at an ever
expanding rate, both to the environment and to people, whose quality of life
these chemicals have been designed to enhance.
Many studies conducted to address these concerns have evaluated the
persistence and toxicology of pesticide materials in soils and plant and
animal tissues. These studies Indicate that most pesticides themselves are
fragile compounds that are readily transformed in the environment to other
metabolites which may or may not be more toxic or more persistent than the
parent material (2-8).
However, what happens when pesticides are thermally decomposed, as in
the case of open burning of spent bag materials containing trace quantities of
pesticides, as is a common practice for many farmers? Or, what occurs when a
pesticide has been determined through 'persistence and toxicologicaV studies
to no longer be suitable for widespread use and is suddenly banned? The
method of choice for the disposal of these materials in many Instances is
incineration. How will these materials react upon thermal decomposition? A
review of the open literature suggests that there is only limited Information
available (9-12).
Kennedy, et. al., conducted thermal degradation studies of 20 pesticide
materials in the late 1970's: Atrazlne, Bromacil, Carbaryl, Dalapon, DDT,
Dicamba, Dieldrin, Diuron, Dinoseb, DSHA, Malathion, Hemagon, Paraquat,
Piclorara, PMA, Trifluralin, 2,4-D, 2,4,5-T, Vernara, and Zineb (9). The
weight loss of each pesticide with increasing temperature was determined using
a muffle furnace. Degradation studies of each pesticide were also conducted
using sealed ampoules containing the pesticide so that the evolved gases could
be subjected to mass spectral analysis. However, there was no attempt to
separate the gases that entered the mass spectrometer (i.e., all gases were
detected simultaneously), and identification was very crude by today's
standards since compounds were only identified by presence of their
characteristic fragments, and less than 10% of the tentatively identified
compounds were subsequently confirmed. In addition, no attempt was made to
analyze the solid residues that may have remained in the ampoule.
Turco, et. al., examined the thermal decomposition of 8 substituted
4,6-bi s(alkylamino)s-triazines: 2-Chloro-4,6-bis-ethylamino-s-triazine
(S i mazi ne), 2-Chl oro-4-ethylami no-6-1sopropylami no-s-tri azi ne (Atrazi ne),
2-Chloro-4,6-bis-isopropyl-amino-s-triazine (Propazine),
2-Methoxy-4-ethylamino-6-tert-butyl amino-s-tri azine,
2-Methyl-4,6-bis-i sopropyl amino-s-triazine,
2-Hydroxy-4,6-bis-ethylamino-s-triazine,
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2-Hydroxy-4-ethylam1no-6-1sopropyl-s-tr1az1ne, and
2-Hydroxy-4,6-b1s-1sopropylamino-s-tr1azine (10). Thermogravametric Analysis
(TGA), Differential Thermal Analysis (DTA), and Differential Thermal
Gravimetry (DTG) techniques were used to determine the temperature at which
the onset of decomposition began, as well as the overall decomposition
profile. This data was used to determine their Arrhenlus decomposition
kinetic parameters. However, no attempt was made to Identify the products of
combustion.
Duvall, et. al., evaluated the thermal decomposition of Kepone, M1rex,
and p,p'-DDT at 1 second residence time 1n air utilizing a quartz flow reactor
(11). Decomposition profiles were determined,, but only United products were
Identified and verified using standards. This study showed that the
pesticides were fragile, (i.e., decomposing to >99X by 700"C), while their
products of incomplete combustion (PICs) were much more stable (persisting at
>900'C).
Durig, et. al., examined the thermal decomposition of six
organophosphorus compounds: Ethylphosphonic dichloride, Methylphosphonic
dichloride, Ethyldichlorophosphine, Ethyldimethylphosphine,
Dimethoxymethylphosphonate, and Ethylphosphonic difluoride (12). A
pyrolysis-GC method was used to decompose the compounds and a flame ionization
detector was used to quantitate the products. Decomposition pathways were
proposed based upon the levels of decomposition observed at various pyrolysis
temperatures; however, no products were identified.
In this study, we have theoretically examined the thermal decomposition
properties of the active ingredient of 16 pesticides and conducted
experimental studies on 5 pesticide related materials. The theoretical
stability evaluations were prepared using available laboratory data, or data
on structurally similar compounds in conjunction with chemical reaction
kinetic theory (13). A summary of this work is presented in Table 1. The
parameters used to rank their stability was the temperature required for 99%
destruction at a gas phase residence time of 2.0 s under oxygen starved
conditions, T«g(2). This parameter has also been used in a ranking of toxic
organic compound incinerability (14). The table also indicates the thermal
stability ranking and the thermal stability class ranking of each of the
pesticides within the hierarchy of the 330 individual compounds and seven
classes currently included in the list ( a ranking of 1 being most stable).
Data sheets on each pesticide are presented in Appendix 1.
This report focuses on detailed experimental studies of the
high-temperature oxidation and pyrolysis of four key pesticide materials
including the identification and quantification of products of incomplete
combustion (PICs). The four pesticides were: Aldicarb and Phorate (both
insecticides), and Atrazine and Alachlor (both herbicides). These compounds
are the active ingredients of Thimet, Temik, Aatrex-Nine-0, and Lasso II,
respectively. A fifth material, a polyethylene blend bag which is used as an
Atrazine container, was also examined. Hopefully, the knowledge gained in
these studies can be used to make more informed decisions concerning future
handling of the pesticides.
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TABLE 1. PESTICIDE THERMAL STABILITY DATA
Compound
DCPA
Al achl or
Acephate
Pron amide
Carbonfuran
Trial! ate
Fonofos
Ethoprop
Chlorprifos
Atrazine
Terbufos
Cyanazine
Azinpho| Methyl
Phorate
Methomyl^
Aldicarb
750
620
595
570
560
550
530
530
510
510
510
500
460
400
200
200
Ranking
105-114
185-189
207
220
226-228
231-234
237-241
237-241
249-251
249-251
249-251
253-258
266-269
276-277
318-320
318-320
mmmmm
Class Division
3
4
5
5
5
5
5
5
5
5
5
5
5
6
7
7
Derived from experimental data obtained from this study
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SECTION 2
CONCLUSIONS
The experimental results of this study are very complex, full
Interpretation of which go far beyond the scope of this program. Some simple
conclusions are, however, readily apparent.
1. Based on the stability of the parent pesticides and their thermal
by-products, it appears that these materials may be amenable to properly
controlled, high-temperature incineration. However, the number yields and
stability of the by-products suggest that open-burning of spent bag materials
containing pesticide residues may not significantly reduce their impact on the
environment.
2. Based on comparison to results of a previously generated ranking of
hazardous waste incinerability, the 16 subject pesticides (with the possible
exception of DCPA) should be considered thermally fragile( i.e., 1^(2) <
600*C).
3. With the exception of Alachlor, there was almost no effect of reaction
atmosphere on pesticide stability. This suggests that the primary mechanisms
of decomposition are unimolecular (e.g., simple bond rupture or more complex
concerted intramolecular reactions).
4. Each pesticide decomposes to yield a large number of reaction
interrediates. More intermediates were consistently produced under pyrolytic
conditions. Most of the intermediates were decomposed by 700*C, however, some
persisted at the maximum temperature in this study, 1000'C. The most stable
organic intermediates were primarily nitrogen containing compounds (i.e.,
nitriles and cyanides).
5. Relatively good mass balances were obtained for three of the pesticides,
suggesting a reasonably complete set of product identifications.
6. Polyethylene bag oxidation intermediates did not appear to be as
environmentally significant as the pesticide intermediates.
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SECTION 3
RECOMMENDATIONS
Based on the complex chemistry observed in these studies it would be
unwise to suggest that we can, on a theoretical basis, predict the by-products
from the open-burning of pesticides not subjected to laboratory testing. The
myriad of potentially toxic by-products that can be formed may represent an
insurmountable challenge if Initial Identifications are attempted In field
tests prior to controlled laboratory testing. Due to the numerous by-products
and complex chemistry observed as the results of the thermal degradation of
pesticides, we offer the following recommendations:
1. Additional laboratory testing of other pesticide products suspected to be
environmentally sensitive should be performed. Results of these studies can
be used to evaluate the environmental Impact of pesticide burning and guide
larger scale evaluation programs.
2. Further development of the analytical protocols associated with the
monitoring of decomposition products from pesticide materials should be
conducted. Many of the by-products observed in our laboratory evaluations are
polar and may be water soluble thus complicating their analysis. Standardized
analytical techniques are not available for many compounds. This can result
in a reduced tendency to analyze for these potentially environmentally
significant species, although analytical techniques may already be available.
3. Thermal decomposition chemistry and kinetics of pesticides should be the
subject of further research such that the open-burning and incineration
behavior of pesticides may be better understood. Organic nitrogen and sulfur
combustion chemistry are largely unexplored fields of apparent environmental
significance.
4. Close coordination between laboratory researchers and field test
researchers should be attempted to ensure that the products identified in the
laboratory are targeted for measurement in the field.
5. Toxicological evaluation of the observed by-products should be performed
to aid in the determination of the environmental risk associated with
open-burning and incineration of pesticides.
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SECTION 4
EXPERIMENTAL PROCEDURES
An exhaustive experimental study of the thermal degradation
characteristics of four pesticides was undertaken. This Included a successful
atom balance for carbon, nitrogen, sulfur, phosphorus and chlorine.
4.1 INSTRUMENTATION
V
All experiments were performed on the Thermal Decomposition Analytical
System (TDAS) which has been described in detail elsewhere (15). The TDAS is
a closed, in-line quartz flow reactor system capable of accepting a solid,
liquid or gas phase sample, exposing the volatilized sample to a highly
controlled thermal environment, and then performing an analysis of the
effluents resulting from this exposure.
Gas-phase samples are swept with carrier gas through heated transfer
lines into a quartz flow reactor where controlled high temperature exposure
occurs. Mean residence times of 0.5 to 6.0 seconds may be achieved. Thermal
decomposition data may be taken over the temperature range 200 to 1050'C.
The effluent resulting from thermal exposure is swept by carrier gas to
an HP 5890 GC where it is cryogenically focused on the head of a capillary
column located inside the GC oven. Later, the oven temperature is raised at a
specified rate and the separated compounds eluting from the column can then be
sent to either the ion source of an HP 5970B mass selective detector (MSO), or
to a flame ionization detector (FID) located within the GC assembly.
Data acquisition and analysis for the TDAS is accomplished with the aid
of an HP 59970 ChemStation and the accompanying system software which Includes
an on-line NIH-EPA mass spectral library. Species with molecular weights
between 16 g/mol (analytical unit limit) and 450 g/mol (transport limit of the
thermal unit) may be analyzed using this system.
In order to successfully execute this ambitious program, it was
necessary to develop a new Interface between the GC and the MSD. This
interface, the insertion-split, was designed as a comproalse between the
typically used 'direct-to-source interface' and the 'open-split interface',
incorporating the meritous aspects of each. For example, the direct-to-source
interface promotes heightened sensitivity for the mass spectrometer because
eluents from the column are deposited directly into the source, just as the
name implies. However, there are many limitations to this type of interface,
one of which directly impacts the type work discussed here. Namely, having
the GC column outlet placed directly in the source of the mass spectrometer
(typically held at 10-6 or 10-7 torr) creates a huge pressure drop across the
column which literally pulls volatile compounds through the latter portion of
the column without allowing for any separation that may be attained by
interaction with the liquid stationary phase. For these experiments it was
paramount that there be separation of such compounds as CO^ CH4 and the light
C2 gases, since these were predicted to be major PICs.
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The open-split Interface provides for the use of uuch larger column
bores and larger sample sizes, but protects the source of the mass
spectrometer from undue wear and tear since much of the column effluent Is
diverted before It enters the source. One of the chief drawbacks of this type
of Interface 1s the loss of sensitivity relative to the direct-to-source
Interface. Since one of the goals of this study was to perform a mass
balance of the data, 1t was Imperative to Isolate and analyze as many of the
products as possible. The Insertion-split Interface provided the best answer
to these two dilemmas.
Essentially the Insertion-split Interface 1s a small-bore transfer tube
placed within a capillary column which 1s surrounded by carrier gas that Is
constantly being swept away. A drawing of this Interface as 1t 1s Installed
in the TDAS is presented in Figure 1. A piece of narrow bore, fused silica
tubing (uncoated but deactivated) is positioned in the source of the mass
spectrometer in much the same way that the capillary column would be
positioned if it were direct-to-source, with a fixed length left on the oven
side of the connection nut (can be a variable length 10-20 era). The end of
this tubing remaining in the oven is then placed inside the outlet end of the
GC capillary column. Obviously, attention must be paid to the inner and outer
dimensions of the two tubes. The film thickness of the capillary column is
also important relative to GC-MS operation. The ends of the transfer tubing
and the capillary column which overlap are housed within a stainless steel
piece of tubing fitted with inlet and outlet gas flows which allow a gaseous
carrier to be purging the area surrounding the junction at all times.
Finally, the entire stainless steel miniaturized housing is firmly mounted
inside the GC oven so as to remain stationary even while the GC oven fan is
running.
Because there is a finite annular gap between the outer wall of the
transfer tubing and the inner wall of the capillary column, and as this
junction is kept pressurized by the addition of flowing helium carrier
surrounding the two overlapping tubes, the outlet to the capillary column now
experiences approximately atmospheric pressure. Thus, light weight materials
are not 'pulled' through the column without being separated as with the
direct-to-source interface. Also, because the transfer tubing is placed
inside the capillary column, transfer of sample fro* column to MS is almost
continuous; there is no axial or open gap in the flowpath of the column
effluent as would be experienced by the open-split interface. This fact helps
to maintain relatively good sensitivity for this Interface despite the fact
that there is some splitting of the sample at the coluan overlap junction.
Before invoking the insertion-split interface for this program
considerable developmental work went into testing the linearity of splitting
for light weight as well as heavy materials (I.e., whether heavy materials
would be preferentially split relative to light weight compounds because of
the axial position they would tend to occupy while traveling through the
capillary column). The insertion-split interface design used a bluff-body
mixing principle at the annular split location as a contingency for this
concern. Test results indicated that indeed the bluff-body design performed
as expected; splitting of a wide-molecular weight test sample was consistently
the same for light, intermediate, and heavy compounds. (The compounds used
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He IN
DIRECT *
TOMS
CAPILLARY
COLUMN
Figure 1. Close-up schematic of the Insertion-split Interface
as 1t 1s configured in the IDAS.
8
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were octane, octadecane, and octacosane In cyclohexane). He also found that
for a given volumetric column flow, linear velocity and head pressure, the
Insertion-split Interface response was always a fixed fraction (approximately
40-50%) of that experienced with the d1rect-to-source Interface. This number
1s of course dependent upon the length and dlaraeter of the transfer tubing
positioned 1n the source of the mass spectrometer.
4.2 SAMPLE INTRODUCTION
Standards of each of four pesticides were received from the National
Repository located at Research Triangle Park, North Carolina. The purity of
each was certified as greater than 98% (i.e., Aldicarb 99.8%, Phorate 98.2%,
Atrazine 99.4%, and Alachlor 99.6%). Aldicarb, Atrazine, and Alachlor were
solids at room temperature, while Phorate was a viscous liquid. The
structures of all four of the compounds are presented in Figure 2. A virgin
Atrazine 90 DF bag (I.e., a bag which had seen no pesticide material) was
received from the project officer.
Target test conditions for the four pesticide active ingredients were
1% mol/mol of pesticide in carrier gas, a gas phase residence time (tr 1 » Z.O
seconds, and two reaction atmospheres: pyrolysis at a fuel/oxygen equivalence
ratio (phi) of 10; and oxidation at phi - 0.5 (100 % excess oxygen). The
Atrazine bag material was run only under oxidative conditions. The
stoichiometric combustion equations for each pesticide are given below.
Equilibrium calculations using the STAIWAN thermodynaimc equilibrium code
indicated that NO, S02, and P04 were the thermodynamically stable combustion
end-products for N, S, and P under our experimental conditions (16).
Aldicarb (TEMIK)
CrHuNa&S + 11.5 02 —> 7 C02 + 2ND + S02 + 7H20
Phorate (Thimet)
C7H1702PS3 + 16.25 02 —> 7 C02 + 3 S02 + P04 + 8.5 H20
Atrazine (AA-TREX Nine 0)
C^HajClNOa + 18.25 02 —> 14 C02 + NO + HC1 + 9.5 H20
Alachlor (LASSO-II)
C8HUC1N5 +.13.75 02 —> 8C02 + 5NO + HC1 + 6.5 H20
Sample delivery for the three solid pesticide active ingredients
(Aldicarb, Atrazine, and Alachlor) in this set of experiments Involved
dissolving the solid material in a suitable solvent and depositing an aliquot
of the solution into a quartz pyroprobe tube. Once the solvent had evaporated
the tube was placed in the platinum coil of a CDS Model 120 Pyroprobe assembly
(Chemical Data System, Inc. ) which was then placed into the insertion region
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of the IDAS. Using temperature programming of both the Insertion region
itself and/or the pyroprobe heating co11» each pesticide was volatilized Into
flowing carrier gas at a specific, reproducible rate (for a given programming
protocol). Separate TGA experiments were performed In flowing air and
nitrogen to aid 1n determining the first approximation of these temperature
protocols.
Before each pesticide series was to begin, approximately 40 quartz tubes
were loaded with sample from the same stock standard solution and solvent was
allowed to evaporate. The tubes were then kept covered at room temperature in
a laboratory hood until just prior to use. It was determined that loading
the quartz tubes in this manner provided the best reproducibillty with regard
to sample size.
Sample delivery for the only liquid active ingredient, Phorate, was more
straightforward than for the three solids. 0.5 ul of the pure liquid was
injected into an insertion region held isothermally at 100 C using a 0.5 ul
full-scale liquid syringe fitted with a 6 inch needle.
The polyethylene bag was run as follows. Approximately 2 mg of bag
material was placed in a quartz pyroprobe tube (loaded with a plug of quartz
wool to keep the piece of polymeric material from falling out). The tube was
then placed in the platinum coil of the CDS Pyroprobe assembly and placed
into the insertion region of the TOAS. As with the solid pesticides,
temperature programming of both the insertion region itself and the pyroprobe
heating coil volatilized the sample into flowing carrier. A separate TGA
experiment was performed in flowing air to aid in determining the first
approximation of this temperature protocol.
The profiles generated using these sample introduction techniques
delivered the maximum possible ppm (mol/mol) concentration of pesticide in the
carrier gas while also delivering a suitable sample size to the analytical
system downstream of the reactor for adequate conversion to products. The
concentration of active ingredients ranged from 0.1 to 0.5% mol/mol in the
carrier, with the sample sizes ranging from 77 to 500 ug. Table 2 presents a
summary of the pesticide concentrations in carrier gas utilized in this study,
the insertion region protocols which delivered these values, and the
accompanying oxygen concentrations required for phi * 0.5.
Degradation of each of the three pesticides was conducted under both
oxygen deficient (fuel/oxygen equivalence ratio of 10) and oxygen rich
(fuel/oxygen equivalence ratio of 0.4 - 0.5) conditions. Approximately 0.5%
oxygen in helium (mol/mol) was available for combustion in the oxygen
deficient conditions (as determined by actual measurement of the reaction
g£)? whereas 1 10% mix of oxygen in a balance of 51% helium/39% nitrogen .was
used for the oxygen rich experiments (these were the values obtained by mixing
compressed air and helium at a one to one ratio vol/vol). Gas mixtures were
prepared by utilizing a gas mixing device developed in-house. Residence time
at temperature for all exposures regardless of atmosphere was held constant at
2 0 seconds, while the reactor temperature was varied over the range 200-
1000'C. Experiments were conducted at 1.23 atm. Sample introduction was
10
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accomplished using the protocols described 1n the proceeding paragraphs.
The effluent resulting from a single reactor exposure (unreacted parent
material and all PICs) was directed to a 60 m, DB-5, 0.32 mm 1.d. column (J&W
Scientific, Inc.) held at -60*C, using liquid nitrogen as coolant.
Individual reaction products were separated by programming the GC oven from
-60 to 290*C @ 10'C/min with a 15 minute hold at -60'C and a 25 minute hold at
290*C. Detection was accomplished with the aid of an HP 59706 quadrapole mass
spectrometer. The mass spectrometer was operated In full-scan mode with an
electron energy of 70 eV and an electron multiplier setting of 1700. To
optimize detection of products, the mass range scanned during the first 20
minutes of the GC program was 10-200 amu, while from 20-80 minutes the mass
range scanned was 10-500 amu. This allowed for maximum detection of light
gasses during the first part of the GC program. Quantitatlon and
identification of products was performed with the aid of an HP ChemStatlon
data system and an on-line HIH-NBS mass spectral library as well as through
manual Interpretation.
Analytical standards for observed products were run wherever possible to
obtain quantitative response factors. Where obtaining a product was either
impossible, extremely difficult, or untimely (i.e., a 6 week or 2 month
waiting period), analytical standards were run for compounds which were in the
same class, or closely related in structure to the compound of interest.
These response factors were then used to estimate the response factors for the
actual products seen in thermal decomposition experiments. Response factors
were typically obtained from 4 or 5 point calibration curves with some
replicate points being performed where possible.
Standards were injected into the TDAS using the same timetable, valve
switching, split ratio, and GC program as were the pesticides. Thus, response
factors generated from the curves could be used directly to perform absolute
quantification of the area responses reported in each data run using the
following equation:
Ng of compound detected - Area Counts of compound/response factor
The 'ng detected' values were then converted using molecular formulas and
molecular weights to yield mass and/or moles of carbon, nitrogen, sulfur,
phosphorus and chlorine. In this way a balance of the atoms at each
temperature could be evaluated. The compiled list of analytical standards run
for this program and the response factors determined in both reaction
atmospheres are given in Appendix 2.
11
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?"• 1
CHj.S-C.CH-N-O-C-NH.CH,
CHS
ALDICARB Cflemik*Insecticide)
N.
xCH2OCHt
\
C-CHaCI
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P H O R ATE (1Mmet*Insectidde)
12
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-------
SECTION S
RESULTS
As expected, the chromatograms generated 1n this study were very
complex, especially at Intermediate destruction temperatures. For example,
the thermal decomposition of Alachlor under oxygen deficient conditions
yielded > 80 different PICs over the temperature range of 275 - 1000'C. This
was the largest number of products formed from an Individual compound that our
laboratory has ever observed. A typical example chroraatogram obtained from
the Alachlor experiments 1s presented in Figure 3.
While the excess oxygen chromatograms were generally less complex than
the pyrolysls ones, a relatively large number of products were nevertheless
detected In these experiments as well. The number of by-products observed for
each of the pesticides 1s summarized in Table 3.
TABLE 3. NUMBER OF DECOMPOSITION BY-PRODUCTS OBSERVED
Pesticide phi - 10 phi - 0.4-0.5
Aldicarb 39 (23) 22 (17)
Phorate 31 (19) 25 (17)
Atrazine 63 (50) 47 (36)
Alachlor 86 (59) 29 (23)
( ) Indicates the number Identified by the mass spectra, remainder listed as
unidentified
The metabolite studies found in the literature reported that these four
pesticides were not persistent in the environment and that they were readily
transformed to other compounds (2-10). Their thermal stability as determined
under the conditions of this study was analogous to this behavior. All four
compounds themselves were labile, disappearing by 600'C under both pyrolytlc
and oxidative conditions. The relative stabilities can be conveniently ranked
by the temperature required for 99% destruction for a 2.0 second residence
time (T«,(2)) (see Table 4). The relative stabilities under both sets of
conditions in this study were: Alachlor > Atrazine > Phorate > Aldicarb.
Aldicarb and Phorate exhibited degradation at the lowest reactor
temperature possible on the TDAS, 200"C. Because no Aldicarb was detected
in the quantitative transport run at 200*C (I.e., it had already been
converted to products), this temperature was assigned as its Tw(2) value. In
14
-------
the case of Phorate, the Tw(2) value Is the temperature at which no Phorate
was detected 1n replicate runs. The detection limit for this compound was
approximately 0.4 % remaining. A more In-depth explanation of the problems
associated with running Phorate are discussed 1n the following section of this
report.
TABLE 4. PESTICIDE STABILITY
aasmmmmmmmmmmmaammmmmmmmammmm
rci
Pesticide phi • 10 pM - 0.4-0.5
Aldlcarb <200 <200
Phorate <400 <275
Atrazine 510 475
Alachlor 620 525
It Is Interesting to note that none of the pesticides displayed a large
dependence upon reaction atmosphere. This observation infers that the
decomposition mechanisms may be dominated by uniroolecular pathways. A more
pictorial representation of this can be seen in the thermal decomposition
composite curves generated for the pesticides, Alachlor and Atrazine, in
Figure 4.
Tables 5 through 10 present the specific products detected in the
decomposition studies of Aldicarb, Atrazine, and Alachlor in the fora of
Weight % Yield (relative to parent) for each atmosphere. Many of the products
detected in these experiments may be environmentally significant.
Due to the viscosity of Phorate, the small volume available for sampling
(i.e., only 50 ul in a 1.5 mL vial volume), and the short 'shelf-life' of
Phorate once exposed to the atmosphere, the reproducibility of injection was
not good. Replicate and triplicate injections at each reaction condition
resulted in relative standard deviations of as much as +- 36%. For this
reason, only qualitative analysis of the Phorate decomposition products are
listed in Tables 11 and 12. All areas of peaks that were not identifiable by
their mass spectra are summed under the heading 'Unidentified'.
Results obtained from the Atrazine bag oxidation experiments are
presented in the same manner as Phorate data in Table 13 (i.e., as qualitative
analysis of the decomposition products). The act of volatilizing the polymer
in the insertion region necessarily makes 'Height % Yield (relative to
parent)' type data meaningless. As with Phorate, areas of peaks which we were
unable to identify are summed under the heading 'Unidentified'. The products
seen from this series of experiments v/ere the same ones observed in previous
15
-------
studies conducted 1n this laboratory In which polyethylene and
polyethylene/polypropylene blends were thermally decomposed (17).
Mass balance for the pesticide experiments was achieved with a fairly
good degree of success. Some temperature data points were clearly outliers,
while most data points were within •»•- 30% of the 100% recovery mark. A
listing of the atom balances for C, N, S, or Cl where appropriate are
presented In Appendix 3. Because of the high degree of uncertainty associated
with the Phorate data, no atom balances were attempted.
16
-------
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Alachlor Oxidation
Alachlor Pyrolysis
Atrazine Oxidation
. Atraa'ne Pyrolysis
300
400
500
600
700
Temperature (°C)
Figure 4. Weight % remaining curves for parent materials, Alachlor
and Atrazine, generated under oxidative (phi * 0.5) and
pyrolytic (phi* 10.0) conditions, 2.0 sec residence time,
4000 and 3000 ppra respectively, and 1.23 atia.
18
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TABLE 11. QUALITATIVE DATA OF PHORATE OXIDATION PRODUCTS
Temperature CO
Compound 200 250 275
Phorate XXXX XXX
Ethanol XXXX
Ethanthiol XXXX
Methanethiol XXX
1,2,4-Trithiolane XXX
1,1-Thio-bis-ethane XXX
l,l'-[Methylenebis(thio)]-bis-ethane XXX
1,3,5-Trithiane XXX
0,0-Diethyl-S-pentenyl-phosphorodithioc acid XXXX XXXX
0,0-Di ethyl -S-alkyl-phosphorodithioac acid isomers XXXX XXXX
1,2,4-Trithiolane XXX
Ethyl -thio-acetic acid XXX
Di ethyl distil fide XXX
2,2'-Dithio-bis-ethanol XXX
Ethyl -(l-methyl-propyl)-disul fide XXX
Sulfur dioxide X XX XX
Carbon monoxide X XX XX
Carbon dioxide X XX XX
Sulfuric acid
-------
TABLE 12. QUALITATIVE DATA OF PHORATE PYROLYSIS PRODUCTS
Compound
Temperature CO
200 250 300 325 350 375 400
Phorate XXX
Ethanthiol XX
1,1'-[Methylenebis(thio)]-bis-ethane
Carbon dioxide X
Ethanol
Thiirane
Methyl-thio-ethane
Tetramethylphosphine
1,1-Thio-bis-ethane
Ethyldisulfide
Dimethyldisulfide
Heptyl-thiophene
1,3,5-Trithiane
Sulfur dioxide
Carbon disulfide
X
X
XXX XXXX XXXX XXX
XXXX XX XXXXX
XX
XX XX
XX XXX
X X
XXXX XXXX
XX
XXX
XXX
XXX
XX
XX
XXX
XXX
XX
XXX
XX
XX
XX
XX
Unidentified
XXX XXX XX XX
1) 'X' depicts an area count response such that 10,000 < X < 100,000
2) 'XX' depicts an area count response such that 100,000 < X < 1,000,000
3) 'XXX' depicts an area count response such that 1,000,000 < X < 10,000,000
4) 'XXXX' depicts an area count response such that 10,000,000 < X <
100,000,000
5) The value for 'Unidentified' is a summation of the areas of all
unidentified peaks at that temperature
27
-------
TABLE 13. QUALITATIVE DATA OF POLYETHYLENE BAG OXIDATION PRODUCTS
Temperature CO
Compound 300 400 500 600 700 750
Acetone XXX1'4XXX XXX XX
2-Oxopropanal X XXX
3,5-Dipropy1-l,2,4-trioxolane XX XX XX
D1hydro-2-methyl- 3(2H)furanone XX XX XX
l-Acetyloxy-2-butanone X
Pentenal X
Hexenal XX XXX XX XX
Dihydro-2(3H)-furanone XX XX XXX XX
Dihydro-2,5-furan-dione XX
C6 Alkyl-cyclohex-anone XX XX
C7 Alkyl ketone XX XXX
6-Methyl-octadecane XX XX
Hexadecane XX XX XX
6-Methyl-octadecanal XX XX
Carbon dioxide XXX XXX XXX XXX XXX XXX
Carbon monoxide XX XX XX XX XXX XXX
2,5-Furandione XX XX XX
Butanedial XXX XX XX
Benzene E XXX
Unidentified5 XXXX XXXX XXXX XXX
1) 'X' depicts an area count response such that 10,000 < X < 100,000
2) 'XX' depicts an area count response such that 100,000 < X < 1,000,000
3) 'XXX' depicts an area count response such that 1,000,000 < X < 10,000,000
4) 'XXXX' depicts an area count response such that 10,000,000 < X <
100,000,000
5) The value for 'Unidentified' is a summation of the areas of all
unidentified peaks at that temperature
28
-------
SECTION 6
REFERENCES
1. J. E. Huff and J. K. Haseman, "Exposure to Certain Pesticides May Pose
Real Carcinogenic Risk," C & E News, pp. 33-36, January 7, 1991.
2. N. R. Andrawes, H. W. Dorough, and D. A. Lindquist, "Degradation and
Elimination of Temik in Rats," Journal of Economic Entomology, Vol. 60
No. 4, pp. 979-987, August 1967.
3. L. Ou, K. S. V. Edvardsson, and P. S. C. Rao, "Aerobic and Anaerobic
Degradation of Aldicarb in Soils, J. Agric. Food Chem., 33, pp.
72-78, 1985. » » HH
4. P. R. Boshoff and V. Pretorius, "Determination of Phorate and Its
Metabolites by Mixed Phase Gas Chromatography," J. Agric. Food Chem ,
Vol. 27, No. 3, pp. 626-630.
5. S. Y. Szeto and M. J. Brown, "Gas-Liquid Chromatographic Methods for the
Determination of Disulfoton, Phorate, Oxydemetron-methyl, and Their
Toxic Metabolites in Asparagus Tissue and Soil," J. Agric. Food Chem.,
30, pp. 1082-1086, 1982.
6. L. Q. Huang, "Pesticide and Industrial Chemical Residues," J. Assoc
Anal. Chem., Vol. 72, No. 2, pp. 349-354, 1989.
7. I. Viden, Z. Rathouska', J. Davidek, and J. Hajslova, "Use of Gas Liquid
Chromatography/Mass Spectrometry for Triazine Herbicide Residues
Analysis in Forage and Milk," Z. Lebensm Unters Forsch, 185, pp. 98-105,
8. W. E. Pereira, C. E. Rostad, and T. J. Leiker, "Determination of Trace
Levels of Herbicides and Their Degradation Products in Surface and
Ground Waters by Gas Chromatography/Ion Trap Mass Spectrometry,"
Analytica Chimica Acta, 228, pp. 69-75, 1990.
9. M. V. Kennedy, B. J. Stoganovic, and F. L. Shuman, Jr., "Chemical and
Thermal Aspects of Pesticide Disposal," J. Environ. Quality, Vol. 1, No
1, pp.. 63-65, 1972.
10. Turco, M. Cirstea, E. Chivulescu, E. Dragusin, "Thermal Decomposition of
2-Substituted 4,6-bis(alkylamino) s-triazines," Rev. Chim. (Bucharest),
29(2), pp. 109-13, 1978. '
11. D. S. Duvall and W. A. Rubey, "Laboratory Evaluation of High-Temperature
Destruction of Kepone and Related Pesticides," EPA 600/2-76-299,
December 1976.
29
-------
12. J. R. Durig, D. F. Smith, and D. A. Barren, "Thermal Decomposition
Studies of Some Organophosphorus Compounds," J. of Anal, and Appl.
Pyrolysis, 16, pp. 37-48, 1989.
>
13. S. W. Benson and H. E. O'Neal, "Kinetic Data on Gas-Phase Unimolecular
Reactions," NSRDS-NBS 21, National Bureau of Standards, Washington, D.
C., 1970.
14. P. H. Taylor and B. Dellinger, "Development of a Thermal Stability Based
Index of Hazardous Waste Incinerability," Fiscal Year 1990 Report
Prepared for US-EPA Cooperative Agreement CR-813938-01-0, C. C. Lee,
Project Officer, October 1990.
15. W. A. Rubey, "Design Considerations for a Thermal Decomposition
Analytical System (TDAS)," Report prepared for U. S. Environmental
Protection Agency, EPA-600/2-8-098, August 1980.
16. W. C. Reynolds, "STANJAN Equilibrium Program, Version 3.0," Department
of Mechanical Engineering, Stanford, University, Stanford, CA, 1986.
17. D. A. Tirey, R. C. Striebich, and W. A. Rubey, "High Temperature
Pyrolysis and Oxidation of Waste Plastics," Final Report prepared for
Westinghouse Savannah River Laboratory, Aikon, SC, August 1990.
30
-------
APPENDIX 1
PESTICIDE THERMAL STABILITY DATA SHEET
Empirical Formula:
Molecular Weight
IUPAC Name:
ALOCHLOR
(LASSO-n HERBICIDE)
C14H20C1NO2
270 g/mol
2-CWoro-2',6t-dielhyl-N-(methoxy-methyl)-acetanilkle
Structure:
-C2HS
C2HS
Data Source
1. Pure compound (Phi = 0.05)
2. Pure compound (Phi = 10)
Evaluation:
Recommendation:
Ranking:
T99 (2K°Q Comment
525 No evidence of POHC reformation.
620 No evidence of POHC reformation.
Only apparent low energy unimotecular decomposition
pathway is C-N fission.
677 1. C-N fission, rough estimates of rate parameters yield
log A = 16.0 1/s and Ea = 68 kcal/moL
Ea based on C6H5CH2-NHCH3 bond strength of
68.7 kcal/moL
If radical chains are present, H abstraction from two ethyl
groups may also contribute to destruction.
C-N fission (forming resonance-stabilized intermediate)
and H abstraction appear to be the rate-controlling
decomposition channels. 90°C difference in observed
and unimokcular T99 prediction indicates that significant
radical chains contribute to destruction.
620 Data Source No. 2.
31
-------
Empirical Formula:
Molecular Weight
IUPAC Name:
Structure:
ATRAZINE
(Aatrex Herbicide)
216 g/mol
2<;hlcro^
-------
ALDICARB
(Temik Insecticide)
Empirical Formula:
Molecular Weight
IUPAC Name:
Structure:
190 g/mol
2-Methyl-2-(melhylthio>propionaldehyde-o-
(methylcarbamoyO-oxime
CM,
CH3-S-C-CH=N-0-C-NH-CH3
CHg
Data Source
1. Thermal Stability Ranking
2. Pure compound (Phi - 0.05)
3. Pure compound (Phi = 10)
Evaluation:
T99(2X°Q
Comment
Recommendation:
Ranking:
510 Based on C-S bond energy estimate of 59 kcal/mol and
FY 90 Status Report estimated Arrhenlus parameters of
log A - 16.0 1/s and Ea = 56 kcal/moL This is now
believed to be in error.
<200 No evidence of POHC reformation.
<200 No evidence of POHC reformation.
There are at feast two tow energy unimokcular
decomposition pathways: S-C fission and C-N fission.
For this compound, there are 2 C-S routes and 1 C-N
route.
775 1. C-N fission. Rough estimates of rate parameters yield
log A = 16.0 1/s and Ea £75 kcaWaoL
Ea based on bond strength of CfcHsCH^NHCHa of
68.7±1 kcal/moL Since C-N fission for this compound
does not form resonance-stabilized radical, Ea must be
substantially larger than 69 kcal/moL
673 2. C-S fission. D°(C2Hs-S) = 7O5 kcaVmoL Rough
estimates of Arrhenius parameters yield tog A= 1631/1
and Ea = 69 kcai/moL
If radical chains are present. H abstraction from methyl
groups may ako contribute to destruction.
C-S fission, C-N fission, and H abstraction may contribute
to complex decomposition mechanism. Large
descrepancy between observed and predicted
unimokcular T<99 suggests additional low-energy
reaction channels arc occurring. Must analyze reaction
products.
<200 Data Source No. 3.
33
-------
Empirical Formula:
Molecular Weight
IUPAC Name
ACEPHATE
(Orthene 75 WP Insecticide)
183g/mol
o^-Dirnelhyl-acetyl-phosphoranuothioate
Structure:
CH3S>J>
>PNCCH3
CU0' H 3
E>ata Source
No literature data available
Evaluation:
NA
691
Recommendation:
Ranking:
600
Comment
NA
Only apparent tow-energy decomposition channel is C-S
fission. P-S bond may also be weak;
C-S fission. D0(C2,Hs-S) « 70 .5 kcal/mol. Rough
estimates of Arrhenius parameters yield log A = 16.0
Ifs and Ea = 69 kcal/mol.
there is no available information to estimate the strength
of the P-S bond.
If radical chains are present. H abstraction from methyl
and methoxy groups may contribute to destruction,
C-S fission, C-H fission, and H abstraction may contribute
to complex decomposition mechanism. Estimate of
ranking is more uncertain compared to the other
insecticides and herbicides evaluated
Theoretical estimate.
34
-------
Empirical Formula:
Molecular Weight
HJPACName
Structure:
AZINPHOS METHYL
(Guthion WP Insecticide)
317 g/tnol
o^-Dimelhylphosphorodithioate-s-ester-
3^mercaptomelhyl)-lA3-benzotriaan-4{3H)-one
Data Source
No literature data available
Evaluation:
Recommendation:
Ranking:
199 (2X°Q Comment
NA NA
Low energy channels dominated by C-S fission.
P-S bond may also be weak.
551 C-S fission, rough estimates of rate parameters
yield tog A = 16.0 1/s and Ea » 59 kcaVmoL
Ea based on bond strength of C6H5CH2-SCH3 of
59.4±2 kcalAnol.
There is no available data to estimate strength of P-S
bond.
If radical chains are present, H abstraction from methoxy
group may also contribute to destruction.
C-S fission (forming resonance-stabilized intermediate)
and H abstraction may be rate-controlling decomposition
channels.
460 Theoretical estimate.
35
-------
Empirical Formula:
Molecular Weight
lUPACName
Structure:
CARBONFURAN
(Furadan Insecticide)
C12H15N03
221 g/mol
23-Dihydro-2^-
-------
Empirical Formula:
Molecular Weight
IUPAC Name:
Structure:
CHLORPRIFOS
(Lorsban Insecticide)
351 g/mol
o,o-Diethyl-o-(3^,6-trichloro-2-pyridyl)-
phosphorolhioate
0-P-(OC2H5)2
S
Data Source
No literature data available
Evaluation:
Recommendation:
Ranking:
T99(2X°Q
NA NA
Comment
Low energy channels dominated by six-center
elimination of ethylene (two channels)
570 Rough estimate of Arrhenius parameters yield
log A = 12.8 1/s and Ea = 48 kcalAnoL These
rate parameters are based on measurement of six-center
ethylene elimination from CH3COOC2H5 as given in
Table 3.12 of S.W. Benson Thermocbemical Kinetics.
If radical chains are present, H abstraction from ethoxy
group may also contribute to destruction.
Six-center ethylene elimination is very likely to dominate
the destruction of this compound. Small contribution
from H abstraction may also contribute.
510 Theoretical estimate.
37
-------
Empirical Formula:
Molecular Weight
RJPAC Name;
Structures:
CYANAZINE
(Bladcx DF Hcrbicide/Extrazine n Herbicide)
C9Hi3CIN6
240 g/mol
2-U4-CWoro-6XeihylamirKj)-s-triazin-2-yl]amino]-
2-melhylproprionitrile
!-C-(CH3)2
Data Source
No literature data available
Evaluation:
T99(2X°Q
NA
Comment
Recommendation:
Ranking:
659
NA
Initiation dominated by C-N fission.
For the cyanazine compound there are 2 such pathways
with the N—C-(CH3)2 (CN) being slightly faster due to
the formation of a resonance-stabilized radical
Rough estimates of rate parameters yield
log A = 16.3 1/s and Ea = 68 kcaVmoL
Ea based on bond strength of CeHsCHz-NHCHs of
68.7±1 kcal/mol
If radical chains are present. H abstraction from methyl
and ethyl groups may contribute to destruction.
Decomposition mechanism likely dominated by C-N
fission with a small contribution from H abstraction.
500 Should be slightly less stable than ATRAZINE.
38
-------
Empirical Formula:
Molecular Weight:
lUPACName
Structure:
DCPA
(Dacthal W75 Herbicide)
332 g/mol
DimethyI-23,5,6-tetracnlorolerephthalate
COOCH3
COOCH3
Data Source
No literature data available
Evaluation:
T99(2X°Q
NA
Comment
Recommendation:
Ranking:
NA
Six-center molecular elimination not available as in longer
chain phlhalates.
If radical chains are present, H abstraction from methyl
may contribute to destruction.
Kinetic information on the primary decomposition
channels for this compound can only be estimated
by analogy with dimethylphthalate (TQ9 = 775°Q.
750 Theoretical estimate.
39
-------
Empirical Formula:
Molecular Weight
IUPAC Name
Structure:
ETHOPROP
(Mocap Granules Insecticide)
242 g/mol
o-Elhyl-s^-dipropylphosphorodithioate
C2H50-P-(S-C3H7)2
O
Data Source
No literature data available
Evaluation:
Comment
Recommendation:
Ranking:
NA
591
NA
Six center elimination of ethylene only apparent low*
energy decomposition pathway. P-S bond may also be
weak.
Rough estimate of Arrhenius parameters yield
log A = 12.5 1/s and Ea = 48 kcai/mol. These
rate parameters are based on measurement of six-center
ethylene elimination from CH3COOC2H5 as given in
Table 3.12 of S.W. Benson Thermochemical Kinetics.
There is no available data to estimate strength of P-S
bond.
If radical chains are present. H abstraction from n-propyl
groups may also contribute to destruction.
Six-center ethylene elimination is very likely to dominate
the destruction of this compound with significant
contribution from H abstraction.
530 Theoretical estimate.
40
-------
Empirical Formula:
Molecular Weight:
IUPAC Name
Structure:
FONOFOS
(Dyfonatc Insecticide)
246 g/mol
o-Ethyl-s-phenyl-ethyl-phosphorodilhioate
Data Source
No literature data available
Evaluation:
Recommendation:
Ranking:
T99(2)(°Q
NA NA
Comment
Only apparent tow-energy decomposition channel is six-
center elimination of ethylene. P-S bond may also be
weak.
591 Rough estimates of Arrhenius parameters for six-center
elimination are log A = 12.5 and Ea = 48 kcal/moL These
rate parameters are based on measurement of six-center
ethylene elimination from CH3COOC2H5 as given in
Table 3.12 of S.W. Benson Thermochemical Kinetics.
There is no available data to estimate strength of P-S
bond.
H abstraction from ethyl group may also contribute to
destruction.
Six-center ethylene elimination and H abstraction may be
rate-controlling decomposition channels.
530 Theoretical estimate.
41
-------
Empirical Formula:
Molecular Weight
niPAC Name
METHOMYL
(Lannate Insecticide)
162 g/mol
s-Meutyl-N-{(methylcarbamoyO-oxy] -thioacetimidate
Structure:
ff
CH3-C=N-O-C-N-CH3
S-CH5
Data Source
Thermal Stability Ranking
FY 90 Status Report
Evaluation:
Recommendation:
Ranking:
T99 (2X°Q Comment
510 Based on C-S bond energy estimate of 59 kcal/mol and
estimated Arrhenius parameters of log A - 16.0 1/s and
Ea = 56 kcal/mol This is now believed to be in error.
C-S fission (two pathways) and C-N fission are believed
to be dominant decomposition routes.
775 1. C-N fission. Rough estimates of rate parameters yield
log A » 16.0 IVs and Ea £75 kcal/moL
Ea based on bond strength of CgHsCH^NHCHs of
68.7±1 kcal/mol. Since C-N fission for this compound
does not form resonance-stabilized radical, Ea must be
substantially larger than 69 kcal/moL
673 2. C-S fission. D°(C2Hs-S) = 70.5 kcaVmol. Rough
estimates of Arrhenius parameters yield log A = 163 I/*
and Ea = 69 kcal/moL
If radical chains are present, H abstraction from methyl
groups may also contribute to destruction,
C-S fission, C-N fission, aad H abstraction may contribute
to complex decomposition mechanism. Expected to be
slightly less stable than ALDICARB doe to the larger
number of extractable H atoms.
<200 Based on experimental data for ALDICARB.
42
-------
Empirical Formula:
Molecular Weight
IUPAC Name
Structure:
PRONAMIDE
(Kerb WP Herbicide)
256 g/mol
N-(l,I-
-------
Empirical Formula:
Molecular Weight
IUPAC Name
Structure:
PHORATE
(Thimck Insecticide)
260 g/mol
O,O-Diethyl-S-(ethylthio)methyl phosphorodilhioate
s
II
(C2H5O)2-P-S-CH2-S-C2Hs
Dala Source
1. Pure compound (Phi = 0.05)
2. Pure compound (Phi = 10)
Evaluation:
Recommendation:
Ranking:
T99 (2X°Q Comment
<400 No evidence of POHC reformation.
<400 No evidence of POHC reformation.
570 Possible six-center molecular elimination similar to that
observed for esters. Rough estimates of Arrhenius
parameters for the two degenerate channels yield
log A - 12.8 1/s and Ea = 48 kcal/mol. These rate
parameters are based on measurement of six-center
ethylene elimination from CH3COOC2H5 as given in
Table 3.12 of S.W. Benson Thermochemical Kinetics."
Other low energy channels may include C-S fission
(three channels) and P-S fission.
645 D° (C2H5-S) = 70.5 kcai/mol. Rough estimates of
Arrhenius parameters yield log A = 16.6 1/s and
Ea = 69 kcal/mol.
There is no available information to estimate the strength
of the P-S bond.
If radical chains are present. H abstraction from ethyl
and ethoxy groups win contribute to destruction.
Based on the very limited avaflabk data, six-center
elimination is believed to be the dominant
decomposition channel
400 Theoretical estimate. Should be more stable than
TERBUFOS due to the greater strength of C-H bonds in
methyl versus ethyl groups
44
-------
Empirical Formula:
Molecular Weight:
IUPAC Name
Structure:
TERBUFOS
(Counter Syslcmmic Insecticide)
C9H2102PS3
288 g/mol
s-(((l,l-dimethylethyl)thio)methyl)-o,o-diethyl-
phosphorodithioate
s
II
(C2H50)2-P-S-CH2-S-C-(CH3)3
Data Source
No literature data available
Evaluation:
Recommendation:
Ranking:
799 (2)(°Q Comment
NA NA
570 Possible six-center molecular elimination similar to that
observed for esters. Rough estimates of Arrhenius
parameters for the two degenerate channels yield
log A = 12.8 1/s and Ea = 48 kcalAnoL These rate
parameters are based on measurement of six-center
elhylene elimination from CH3COOC2H5 as given in
Table 3.12 of S.W. Benson Thermochemical Kinetics."
Other low energy channels may include C-S fission (two
channels) and P-S fission.
645 D° (C2H5-S) = 70.3 kcal/mol. Rough estimates of
Arrhenius parameters yield log A = 16.6 1/s and
Ea = 69 kcal/mol.
There is no available information to estimate the strength
of the P-S bond.
If radical chains are present, H abstraction from methyl
and ethoxy groups will contribute to destruction.
Based on the very limited available data, six-center
elimination is believed to be the dominant
decomposition channel
500 Theoretical estimate. Should be of comparable stability
compared to PRORATE.
45
-------
TRIALLATE
(Far-Go Granules Herbicide)
Empirical Formula:
Molecular Weight
IUPAC Name:
Structure:
305 g/mol
s^3^'-Trichloroallyl)-diisopropyl-thiocarbarnate
Data Source
1. Pure compound in air
Evaluation:
Recommendation:
Ranking:
T99 (2X°Q Comment
516 Data fit to pseudo-first order decay. A = 6.8E8 1/s and
Ea = 31kcal/mol.
Low-energy channels believed to be dominated by
C-N fission, C-S fission, and 4-center HC1 elimination.
For this compound, there are 2 C-N routes, 1 C-S route,
and 1 HC1 elimination route,
755 1. C-N fission. Rough estimates of rate parameters yield
log A = 16.3 1/s and Ea 275 kcal/mol.
Ea based on bond strength of CgHsCH^NHCHs of
68.7±1 kcal/mol. Since C-N fission for this compound
does not form resonance-stabilized radical, Ea must be
substantially larger than 69 kcal/mol.
691 2. C-S fission. De(C2Hs-S) = 70.5 kcal/mol. Rough
estimates of Arrhenius parameters yield log A = 16.01/s
and Ea = 69 kcal/mol.
751 3. HC1 elimination, using 23-dicMoropropane by
analogy (sp2 hybridized Q, tough estimates of Arrhenios
coefficients are log A = 13.8 and Ea =* 63 kcal/moL
If radical chains are present. H abstraction from methyl
groups may also contribute to destruction.
C-S fission. C-N fission, four-center HC1 elimination, and
H abstraction may all contribute to this very complex
decomposition mechanism.
550 Should be slightly more stable than Data Source No. 1.
-------
APPENDIX 2
RESPONSE FACTORS FOR ANALYTICAL STANDARDS
A complete list of the compounds run as analytical standards in this
program is presented below:
Response Factors
Compound
Carbon Monoxide
n-Propane
Acetonitrile
Carbon Dioxide
2-Methyl-propane
Propanenitrile
Hydrogen Chloride
n-Butane
2-Methyl-propenenitrile
Methane
.2-Methyl-Butane
Butanenitrile
Ethane
n-Pentane
2-Butenenitrile
Ethylene
2-Methyl-pentane
2-Chloro-propeneni tri1e
Acetylene
n-Hexane
2-Butenedinitrile
Sulfur Dioxide
2,4-Dimethylpentane
2-Methyl-propanenitrile
n-Heptane
Toluene
n-Octane
p-Xylene
n-Propylbenzene
n-Decane
n-Butylbenzene
n-Dodecane
n-C12
n-C13
n-C14
n-C15
Alachlor
Atrazine
Oxidative
50
400
428
50
500
527
100
450
300
100
175
546
181
190
554
200
227
381
175
232
331
100
230
538
180
350
180
375
355
181
450
190
190
181
186
184
1000
1200
Pyrolytic
100
600
350
100
844
527
100
627
350
200
232
546
234
230
554
240
227
381
200
232
331
350
230
538
180
350
180
375
355
181
450
190
190
181
186
184
1000
1200
47
-------
Response Factors
Compound 0x1 dative Pvrolvtlc
Diphenylamine 500 500
Quinollne 500 500
4-Chloro-aniline 500 500
N,N-Dimethylan11ine 450 450
Thloacetanride 125 125
Naphthalene 350 350
Aniline 500 500
Benzonitrile 350 350
Benzene 352 352
Acenaphthene 500 500
Acenaphthylene 500 500
Anthracene 500 500
Fluoranthene 450 450
Fluorene 450 450
Phenanthrene 400 400
Pyrene 500 500
48
-------
APPENDIX 3
MASS BALANCE DATA
TABLE 3.1. ALDICARB OXIDATION
Weight X
Temp.fC) C N S
275 109.1 75.3 140.8
300 93.2 70.1 122.6
350 97.2 72;3 124.6
400 90.1 75.9 115.9
450 114.0 105.1 127.9
500 99.3 97.3 103.4
550 96.2 91.7 114.1
600 103.8 124.9 112.6
650 96.0 97.9 131.2
49
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sszsss
TABLE 3.2. ALDICARB PYROLYSIS
inssssessa
Weight %
H S
300 106.1 73.4 140.5
350 82.6 62.0 111.8
400 104.1 73.0 140.4
450 93.9 54.4 118.9
500 123.6 91.7 130.0
550 120.4 101.3 78.3
600 116.7 105.7 65.4
650 93.5 93.2 74.9
700 94.9 97.6 106.9
750 99.5 106.7 126.7
800 96.0 97.4 132.0
850 103.0 93.9 151.0
900 106.9 84.4 93.3
950 94.6 104.9 106.0
1000 115.7 92.7 109.2
50
-------
TABLE 3.3. ATRAZINE OXIDATION
= ======= = =3
Temp.CC)
275
300
350
400
450 "
475
500
550
600
650
700
800
100
109
104
95
156.9
89.0
135.
103
107
.7
.4
.3
108.1
89.1
42.2
N
100.9
109.9
104.6
94.3
119.1
48.4
79.4
89.9
116.0
153.2
161.0
54.6
Weiqht %
£1
100.9
100.9
104.6
94.5
93.5
52.6
48.0
112.8
98.9
97.4
99.2
103.1
51
-------
TABLE 3.5. ALACHLOR OXIDATION
BssxaraajsaaaaasaaasaaaBBacasaea
Height %
Temp.CC) C N £1
275 101.2 101.1 101.1
300 98.2 99.1 97.1
350 95.4 97.2 94.2
400 101.6 105.7 91.9
450 79.5 89.0 91.4
500 93.7 101.9 76.0
550 88.9 80.0 97.6
600 84.3 37.2 100.9
650 81.2 141.5 112.8
700 94.4 93.3 106.2
-------
TABLE 3.6. ALACHLOR PYROLYSIS
Weight %
Temp.CC) C N £L
300 101.2 101.3 101.3
400 96.6 97.8 94.2
450 102.5 105.4 96.4
475 100.3 107.2 88.0
500 122.7 136.6 95.0
525 135.8 138.3 102.3
550 95.0 94.3 69.7
600 91.9 83.2 126.4
650 99.9 81.0 118.7
700 69.3 52.0 100.6
750 80.4 53.2 90.1
800 69.6 51.5 69.4
850 78.9 60.3 78.2
900 70.9 78.8 94.3
950 73.5 102.7 100.7
1000 63.5 109.9 95.3
54
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