Diflubenzuron
Decision Document
Richard Troast, Project Manager
Joanne Sanders, Project Manager
Special Pesticide Review Division
Environmental Protection Agency
March 26, 1979
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27498
ACKNOWLEDGEMENTS
EPA Technical Support Team
Frederick Betz, Biologist, EEB, HED
George Beusch, Chemist, RGB, HED
Salvatore Biscardi, Toxicologist, TB, HED
Richard Bozof, Attorney, OGC
Carroll Collier, Chemist, EFB, HED
James Horst, Economist, EAB, TSD
Cara Jablon, Attorney, OGC
Kevin Keaney, Senior Regulatory Policy Analyst, SPED
George Ludvik, Entomologist, ASB, TSD
Joanne Sanders, Project Manager, SPRD
Richard Troast, Project Manager, SPRD
Richard Tucker, Biologist, EEB, HED
U.S. Department of Agriculture and State Land Grant Universities
Helene Cecil, USDA, SEA/FR
Homer Fairchild, USDA, APHIS
G. W. Ivie, USDA, SEA/FR '
Richard Ridgway, USDA, SEA/FR
Charles H. Schaefer, University of California
John. R. Schaub, USDA, ESCS
Patrick J. Shea, USDA, FS
Merle Shepherd, Clemson University
C. Dayton Steelman, Louisiana State University
EPA Environmental Research Laboratory, Athens, Georgia
James W. Falco, Research Chemical Engineer
Lee A. Mulkey, Chemical Engineer
Kenneth F. Hedden, Sanitary Engineer
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Table of Contents
I. Background 1
A. Chemical and Physical Characteristics 1
B. Registered Uses, Production, and Tolerances 1
1. Registered Uses ..1
2. Production 2
3. Tolerances 2
C. Fate in the Physical Environment 3
1. Soil 3
2. Water 5
3. Photochemistry 6
D. Fate in the Biological Environment.... 6
1. Plants 6
2. Animals 8
a. Mammals 9
b. Poultry 11
c. Fish 14
E. Residues 16
F. Regulatory History 22
1. Experimental Use Permits 22
2. Registration and Tolerances 24
a. Cotton 24
b. Soybeans 24
c. Mosquito Control ...25
d. Gypsy Moth 26
e. Douglas Fir Tussock Moth 27
3. Referral for Rebuttable Presumption
Against Registration 27
II. Risk Analysis 28
A. Chronic Effects 26
1. Oncogenicity 28
a. Mouse Study - Oral (Thompson-Hayward) 29
(i) Results 30
(ii) Quality of the Study 36
(iii) Conclusions on the Mouse Study 39
b. Rat Study - Oral (Thompson-Hayward) 40
(i) Results 41
(ii) Quality of the Study 42
(iii) Conclusions on the Rat Study 44
-------
c. 4-Chloroaniline-Oral Study in
Rats and Mice (NCI) 44
d. Overall Conclusions on the Carcinogenic
Risk of Diflubenzuron 46
2. Methemoglobinemia and Sulfhemoglobinemia 47
3- Mutagenicity '. 50
a. Ames Test 50
b. Other Studies 51
4. Hormonal Effects 52
B. Nontarget Effects = 53
1. Aquatic Invertebrates 53
2. Avian Reproductive Effects 57
C. Exposure 58
1. Dietary Exposure 56
2. Mixer-Loader, Applicator and Bystander
Exposure 61
D. Risk Calculations 63
1. Oncogenicity 63
a. Dietary 63
b. Applicators and Bystanders 65
2. Methemoglobinemia and Sulfhemoglobinemia 67
3. Hormonal Effects 67
4. Nontarget Effects 68
III. Benefits • 69
A. Biological Assessment 69
B. Economic Assessment 72
1. Boll Weevil Control 72
2. Boll Weevil Eradication (APHIS) 77
IV. Risk/Benefit Analysis of Alternative Courses of
Action 79
A. Introduction .79
B. Basis for the Development of Regulatory Options...79
C. Alternative Pesticides 82
D. Regulatory Options Selected 85
E. Impact of Regulatory Options 87
1. Option 1. Conditionally Register Diflu-
benzuron for Use on Cotton until January 1,
1984, under the Condition that Required
Studies Are Submitted 87
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2. Option 2. Conditionally Register Diflu-
benzuron until'January 1, 1984, with the
Same Data Requirements Set Forth in Option 1
and Restrictions on Use 90
a. Classify Diflubenzuron as a Restricted
Use Pesticide Requiring Certified
Applicators 91
b. Require the Use of Protective Clothing
during the Mixing, Loading, and
Application of Diflubenzuron. Require
Respirators during Mixing, Loading,
and Ground Application of Diflubenzuron...92
c. Prohibit Application of Diflubenzuron
within the Coastal Zone of the Gulf
States 93
d. Prohibit Application of Diflubenzuron
Near Persons and Dwellings. Prohibit
the Use of Flagmen in the Field 93
e. Prohibit Workers from Entering Treated
Fields until the Day after Application
and the Spray Deposit Has Dried 94
f. Limit Use of Diflubenzuron to Six 1-
Oz.-AI/Acre Applications per Season
with 5- -to 7-Day Intervals between
Applications 94
3. Option 3- Deny the Application for the
Registration of Diflubenzuron for Use
on Cotton 95
V. Recommended Decision 96
Appendices 99
II-l ; 99
II-2 100
Bibliography 101
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I. Background
A. Chemical and Physical Characteristics
Diflubenzuron (N^-[ [(4-chlorophenyl)amirio]carbonyl]-2
T)
6-difluorobenzamide) is the common name for Dimilin ,
V
PH-6040R, and TH-60MOR. It belongs to a new class of
i
chemicals known as insect growth regulators. Diflubenzuron
prevents insect growth by inhibiting the deposition of a
chitin exoskeleton in insect larvae.
Some of diflubenzuron's physical characteristics are:
/
Melting point 210-230°C
Molecular Weight 210.7
Appearance " White crystals
Solubility 0.2 mg/liter in water
Partition Coefficient > 50 (dichloromethane/H20)
The structure of diflubenzuron is:
B. Registered Uses, Production, and Tolerances
1. Registered Uses
The only registration for diflubenzuron in the
United States is to control gypsy moths in hardwood forests.
/
EPA issued this registration in 1976.
-1-
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2- Production
Diflubenzuron is manufactured by Phillips-Duphar,
B. V., in the Netherlands. It is imported into the United
States and formulated as a 25% wettable powder by Thompson-
Hayward Chemical Company. The amount of diflubenzuron produced
and imported is a trade secret protected by Section 10 of the
Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), as
amended.
3. Tolerances
The Agency has received three applications for
the registration of diflubenzuron. The proposed uses are
for controlling boll weevils on cotton; green cloverworms,
velvetbean caterpillars, and Mexican bean beetles on soybeans;
and mosquito larvae in temporary flood waters. Under the
Federal Food, Drug, and Cosmetic Act (FFDCA), the Agency
grants tolerances for the amount of the pesticide that may
persist as residues on raw agricultural commodities, feed,
and food. Accordingly, Thompson-Hayward has requested
tolerances for two of the three registrations for which they
have applied:
0.2 ppm in/on cottonseed
0.05 ppm in/on soybeans
0.05 ppm in/on meat, milk, eggs, and meat
byproducts of cattle, goats, hogs, sheep,
and fowl.
-2-
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c' Fate in the Physical Environment
1. Soil
Diflubenzuron degrades in soil with a
half-life in the range of 0.5 to 1 week for technical material
pulverized to 2 micron (u) particles and applied at 1 ppm
(Nimmo and de Wilde, 1975). Particle size and formulation
appear to be critical factors in the rate of degradation in
soil. The work of Nimmo and de Wilde (1973, 1974, 1975)
indicates a ten-fold difference in degradation rates and
persistence in the particle size, which ranges from 2 to
10 u, with the larger particles degrading at a slower rate.
The initial products of soil degradation are 2,6-difluroben-
zoic acid and 4-chlorophenyl urea, which degrade respectively
to 2,6-diflurobenzamide and 4-chloroaniline.
Binding of diflubenzuron degradation products
to soil increases with time. The half-life for the conversion
of 4-chlorophenyl urea and 2,6-diflurobenzoic acid to the
respective chloroaniline and benzamide was 2 to 3 weeks and
4 weeks, respectively (Nimmo and de Wilde, 1973, 1974,
1975). Information on the degradation rate of 4-chloroan-
iline in soil is not available, but it is presumed to
degrade slowly.
-3-
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Soil temperature affects the breakdown
of diflubenzuron. In a report*by Bull and Ivie (1978) there
was a more -rapid breakdown of diflubenzuron in the summer
than in the cooler spring and fall. Winter residues of
diflubenzuron were the most persistent. The data presented
by Bull and Ivie indicate that approximately 16% of the
previous year's diflubenzuron application would remain in
the soil as carryover for the next growing season, presup-
posing the normal agricultural practice of plowing under
crop stubble.
Diflubenzuron is a nonionic pe'sticide with
low water solubility. It shows little mobility in organic
soils (Carringer et al., 1975) and consequently has little
potential to leach from the soils. Very little leaching of
diflubenzuron can be expected to occur under normal field
conditions. Helling (1975) observed that downward movement
decreased as soil organic matter increased. Rieck (undated)
found that the soil metabolite 4-chlorophenyl urea leached
more rapidly than the parent compound.
Booth (undated) reported in Pesticide
Petition 7F1898 that field application of diflubenzuron in a
variety of aquatic environments resulted in residues in
sediment ranging from less than 50 to 200 ppb. Single and
multiple applications were made to both fresh and salt water
ecosystems. About two-thirds of sediment samples showed no
detectable residues « 0.05 ppm).
-4-
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Runoff of diflubenzuron and its metabolites
»
is in part dependent on the organic matter content of the
soil since diflubenzuron will bind into organic soil
matter. Suspended sediment containing diflubenzuron and
4-chloroaniline could be expected to be found in the runoff.
Carringer et al. (1975) reported a partition coefficient
of 4000 between organic matter and water. Thus, for a
soil containing 1% organic matter the overall coefficient
will be 4000/100 or 40:1. This suggests that in typical
river water where the suspended sediment represents only a
small percentage of the total mass, the preponderance of
the diflubenzuron will be in the water phase.
2. Water
Hydrolysis of diflubenzuron yields 4-chlorophenyl
urea and 2,6-diflurobenzoic acid. Diflubenzuron is stable
at neutral or mildly acidic pH levels with half-lives
expected to exceed 2 weeks (Nimmo and DeWilde, 1975). Under
alkaline conditions, tested up to pH 12, the half-life is
reported as being under 2 weeks (Phillips-Duphar, December
8, 1975). Under field conditions diflubenzuron exhibited a
half-life of 1 day in alkaline pastures whereas in neutral
lake water (pH 7) the half-life was 10 to 15 days (Nimmo and
deWilde, 1975).
-5-
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1978). Residues were analyzed in rotational crops grown in
»
soils receiving multiple applications of diflubenzuron.
However, only very low levels (< 0.01 ppm wet weight) were
found in various rotational crops following six to ten
applications of diflubenzuron to cotton at a rate of 1
oz. per acre (Bull and Ivie, 1978).
Cottonseed was analyzed in two different studies
after the plants had been sprayed with diflubenzuron. In a
greenhouse study, leaves of cotton plants were sprayed three
times with labeled diflubenzuron. After 45 days, radioactivity
equal to 53 to 94 ppb diflubenzuron was found in the cotton-
seed. The authors, Mansager and Still (unpublished), attempted
to extract and identify the radioactivity but were unsuccessful.
However, they concluded that, since no extractable residue
was released, the radioactivity was not due to diflubenzuron
but to a contaminant (USDA/State, 1978). This,study was not
repeated.
A field study by Bull and Ivie (1978) also demonstrated
low radioactive residues « 0.01 ppm) in cottonseed. This
study employed six to ten applications of labeled diflubenzuron.
The authors made no attempt to identify the radioactive
materials (USDA/State, 1978).
-7-
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3. Photochemistry
Diflubenzuron was photochemically stable on leaf
surfaces under natural sunlight (Bull and Ivie, 197&). In
studies with soil and water mixtures, negligible degradation
was measured under natural light (Phillips-Duphar, December
19, 1973; October 7, 1974).
D. Fate in the Biological Environment
1. Plants
Diflubenzuron applied to various types of plant
leaves was neither absorbed into the plant nor degraded on
the leaf surface (USDA/State, 1978). However, it appeared
that diflubenzuron adsorbed, onto the plant leaf surface
within the initial 24 to 48 hours after application.
Once the material was adhered to the leaf surface, only
wind-abrasion, rain-washing, or the fall of senescent leaves
moved the material into the soil. Only negligible amounts
of diflubenzuron were measured, as total radioactivity, in
leaves, stems, bolls, and other fruiting structures of the
plant (USDA/State, 1978).
Uptake of diflubenzuron from soils has been measured
in several plant species. Most of the material found,
measured by total radioactivity, was in the aerial portions
of the growing plants. Lesser amounts of diflubenzuron or
its metabolites were found in the root structures (USDA/State,
-6-
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EPA scientists have analyzed the residue data
presented by Thompson-Hayward (Pesticide Petition 7F1898)
and concluded that the use of diflubenzuron at 1 oz. per
acre before cotton bolls open may lead to occasional trace
residues of diflubenzuron on the undelinted cottonseed.
However, the possible contaminative residues in delinted
cottonseed and processed commodities derived from cottonseed
would be below detectable levels of 0.05 ppm. They anticipated
no detectable residues of diflubenzuron metabolites in
either cottonseed or processed commodities from cottonseed
(Hummel, 1976a).
2. Animals
This section is based on a review of the literature
submitted by a USDA/State team in the report "Effects of
•D
Diflubenzuron (Dimilin ) on Non-Target Avian and Aquatic
Organisms and Its Fate in the Environment" (USDA/EPA/State,
1978), the USDA/EPA/State Assessment Team report "Potential
Exposure of Diflubenzuron to Birds, Non-Target Aquatic
Organisms and Humans" (USDA/EPA/State, 1978), and reports
compiled by the Residue Chemistry Branch of the Office of
Pesticide Programs on the data submitted by Thompson-Hayward
(Pesticide Petition 7F1898).
-8-
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a. Mammals
Metabolism studies with diflubenzuron have
been perfo'rmed in rats, cows, and sheep. Rats administered
14
C-labeled diflubenzuron excreted 70 to 95% of the
dose in the urine and feces within 6 days of administration.
Radioactivity remaining in the carcasses was quantified as
5% of the dose. No unmetabolized diflubenzuron was found in
the urine. Metabolites identified were 2,6-diflurobenzoic
acid and 4-chlorophenyl urea. Other compounds were present
but were not characterized (USDA/State, 1978).
Diflubenzuron was metabolized and almost
totally excreted by cows and sheep. About 0.2% of the dose
fed to cows was found in their milk. Metabolites excreted by
both species include 4-chlorophenyl urea; 2,6-difluorobenzamide;
and 2,6-difluro-3-hydroxyl-diflubenzuron; 2,6-diflurobenzoic
acid; and the glycerine conjugate of 2,6-difluorobenzoic
acid (USDA/State, 1978).
Further studies on the metabolism of diflu-
benzuron indicated that microsomal activity may be responsible
for the metabolism of the molecule. Labeled diflubenzuron
-9-
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was metabolized by sheep livetr microsomes into 2,6-difluro-
benzoic acid, 2,6-diflurobenzamide, 4-chlorophenyl urea,
4-chloroacetanilide, 4-chloroaniline and the N,N-dimethyl
derivative of 4-chloroaniline (USDA/State, 1978).
The Agency reviewed a 28-day feeding study
in which 250, 5, 0.5 and 0.05 ppm diflubenzuron was fed to
lactating dairy cattle. This study indicated that milk did
not contain detectable residues of diflubenzuron except at
the two highest feeding levels of 5 and 250 ppm. Difluben-
zuron residues were measured as 0.013 and 0.22 ppm, respec-
tively. At the lower feeding levels, 0.05 and 0.5 ppm, any
diflubenzuron residues were below 0.3 and 1.4 ppb, respectively.
In the only segment of the study designed to show decline
levels, the 5 ppm dose, a withdrawal period of 4 days
reduced any diflubenzuron levels below the detection
limit, 1.6 ppb (Hummel, 1977b). Chromatographic analyses of
the detectable residues in milk indicated that the residues
found were not diflubenzuron. However, there was no indication
of what metabolites were present (USDA/State, 1978).
Analyses of tissue extracts indicated that
in the liver, the metabolite 2,6-diflurobenzoic acid was
predominantly found, but diflubenzuron, 4-chlorophenyl urea,
and 4-chloroaniline were also found. Residue levels,
-10-
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expressed as the parent compound diflubenzuron, were measured
at all feeding levels (Table 1-1). A 7-day withdrawal
period did not reduce the residues (Hummel, 1977b)~.
b. Poultry
White Leghorn and Plymouth Rock-Rhode
Island Red Cross hens excreted 80-90/& of the diflubenzuron
administered to them within 3 days (Opdycke et al., 1976).
From 0.3 to 0.8? of the dose was found in the eggs 12 days
after treatment. Most of the labeled compound in these eggs
was unmetabolized diflubenzuron. Tables 1-2 and 1-3 list
the residues found in the hens and their eggs. Major
diflubenzuron metabolites -were 2,6-diflurobenzoic acid,
4-chlorophenyl urea, and 4-chloroaniline.
Additional studies cited in the USDA/EPA
State report (USDA/EPA/State, 1978) also indicated that, in
poultry, labeled diflubenzuron was secreted into the eggs
and retained in muscle, liver, fat, and kidney tissue.
In addition, the metabolite 4-chlorophenyl urea was identified
in the eggs and kidney. Additional work with unlabeled
diflubenzuron gave essentially similar findings and provided
an indication that different strains of chickens differed
somewhat in their ability to accumulate residues of difluben-
zuron. Leghorn chickens accumulated diflubenzuron residues in
eggs at twice the levels found in New Hampshire strain
chickens.
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Table 1-1. Liver Residues of Diflubenzuron
Feeding Level (ppm)
0.05
0.5
5.0
250.0
Residues Found (ppm)
0.01
0.08
0.54
6.00
Table 1-2.
Total Activity Expressed as Diflubenzuron
Found in Chickens.
Commodity
Feeding Level, ppm
0.05
0.5
Fat
Kidney
Liver
Breast Muscle
Leg Muscle
Whole Egg
0.0175
0.0026
0.0026
0.0017
0.0016
0.0029
0.033
0.013
0.044
<0.005
<0.005
0.100
1.160
0.338
0.453
0.054
0.099
0.833
-12-
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Table 1.3. Components of Diflubenzuron Expressed as 1% of
Total Activity Ethyl Acetate Extractable
Difluben-
Commodity zuron
4-CPU 2,6-DFBA
Nori-Extrable
Extractable
(Not identified)
Fat
Leg Muscle
Liver
Kidney
Egg
100
66.3
Breast Muscle 63.4
18.6
23.8
68.8
0
13
22.1
49.8
40.0
11.2
0
6-8
9.2
7.4
0
3.7
1.
_o
5.3
19.0
5.2
36.2
0
16.3
0
-13-
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c. Fish
Booth et al. (1976) studied the accumulation
and fate of' diflubenzuron in rainbow trout and bluegill
sunfish in water treated with 1.0 ppm C-labeled material.
After 20 days, about 60$ of the total radioactive residues
in fish meat was 4-chloroaniline, 12 to 15% was difluobenzoic
acid, and 1 to 5% was 4-chlorophenyl urea. Intact diflubenzuron
comprised 1 to 2% of total meat residues. A rapid depletion
of these residues was reported. Apperson et al. (1978) also
reported accumulations of diflubenzuron with maximum residues
of 355 ppb in white crappie from a lake treated with 5 ppb
diflubenzuron.
The analysis of the residues found in the
Booth study is reported in Table 1-4. The data shows that
fish (trout and bluegill) metabolize diflubenzuron to
4-chloroaniline. The unidentified component was material
which did not migrate in the chromatography and was not
further characterized (Hummel, 1976).
-14-
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TABLE 1-4. Residues of Diflubenzuron and Metabolites in Rainbow Trout and
Bluegill Sunfish
Percent of Extractable Residue
- Rainbow Trout Bluegill Sunfish
Component Water Fish Water Fish
Day 9 Day 20 Day 20 Day 9 Day 20 Day 20
Diflubenzuron 83 74 19 41 19 14
2,6-Difluorobenzoic acid 1 3 19 20 37 30
4-Chlorophenyl urea 1 4 16 10 23 7
4-Chloroaniline 15 17 29 29 16 21
Unidentified 0 2 17 0 5 28
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Table 1-5 shows £he general metabolic pathway
for diflubenzuron in soil, water, plants, and animals. The
pathway is common for the production of 4-chloroaniline
and 2,6-diflurobenzoic acid in all situations (Opdyck et al.,
1976; Philips-Duphar, December 1, 1975, and December 22,
1975; Booth et al., 1976; Bull and Ivie, 1978; and Nimmo and
de Wilde, 1975). The metabolism beyond 4-chloroaniline was
reported by Metcalf et al. (1975) in a model ecosystem, to
include 4-chloroacetanilide and the 4-chloro-N,N-dimethyl-
aniline. The production of 4-chlorophenyl hydroxylamine and
4-chloronitrobenzene in animals was theorized by O.K. Offringa
of Phillips-Duphar in a statement filed by Thompson-Hayward
Chemical Company (1977).
E. Residues
In order to estimate the potential levels of di-
flubenzuron which may be found in local rivers in treated
areas, EPA researchers constructed a computer-simulated model
of cotton and soybean fields to estimate the agricultural
runoff from four applications of 4 or 3 or 2 or 1.5 oz.
diflubenzuron/acre on cotton (Falco et al., 1979). Key
assumptions in the simulation included: 1) all diflubenzuron
was applied to cotton in late June and early July, and was
degraded by October, 2) cotton grown in irrigated areas was
not considered, even though the affected acreage is extensive,
-16-
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Table 1-5. Metabolic Pathway of Diflubenzuron
Diflubenzuron
[
4-chlorphenyl urea
C ]
I
0.1
4-chloroaniline
4-chloroacetanilide
2,6-diflurobenzoic acid
^ ]
2,6-diflurobenzamide
4-chloro-NN-dimethylaniline
C»
I
4-chlorophenyl hydroxylamine (proposed)
I
4-chloronitroso benzene (proposed)
C /=\ 3
ON *•
-17-
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because the possibility of runoff from these areas is low,
3) rainfall was based on data for Beeville, Texas, 4)
rainfall in Beeville, Texas, was representative of rainfall
occurring throughout the cotton areas analyzed, 5) difluben-
zuron is sprayed throughout a river basin on a simultaneous
and uniform treatment schedule.
As a result of the assumptions used to make the
model, it is likely that the predicted concentrations of
diflubenzuron are too high and that the duration of the
predicted concentrations is too short. However, the
researchers estimated that the error would not exceed one
order of magnitude.
Table 1-6 shows the maximum diflubenzuron and
4-ehloroaniline levels predicted at the mouths of the
modeled rivers. Table 1-7 shows the predicted average
concentrations of diflubenzuron and 4-chloroaniline at the
mouths of the modeled rivers during the summer months.
Table 1-8 shows the average summer concentration of
diflubenzuron in sediment at the mouth of the modeled
rivers.
EPA chemists reviewed the model and pointed out that
the 4-chloroaniline levels predicted by the model probably
were much less than actual levels to be expected because the
model did not account for 4-chloroaniline formation in soil
-18-
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TABLE I-b. Maximum Daily Diflubenzuron and 4-Chloroaniline
Concentrations at the Mouth of Each River from
Use on Cotton
Diflubenzuron4-Chloroaniline
Concentration Concentration
from Cotton from Cotton
Application Application
Basin Year ug/1 ug/1
Mississippi
Atchafalaya
Tombigbee
Brazos
Colorado
Nueces
Rio Grande
1971
1971
1972
1974
1971
1975
1971
1.9
2.2
0.22
3.7
13. B
25.0
109.3
7.8
IB. 5
O.B5
11.9
22.0
3.3*
bb.b
Note:These are the projected residues from four
1.5-oz. applications.
•Occurred in 1973-
-19-
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Table I-?.
Average Summer Concentrations of Difluben-
zuron and 4-Chloroaniline at the Mouth of
Each River from Use on Cotton
Diflubenzuron 4-Chloroaniline
Concentration Concentration
Basin Year ug/1 ug/1
Mississippi
Atchafalaya
Tombigbee
Brazos
Colorado
Nueces
Rio Grande
1971
1972
1973
1974
1975
1971
1972
1973
1971
1972
1973
1974
1975
1973
1974
1975
1971
1972
1973
1974
1975
1973
1974
1975
1971
1972
1973
1974
1975
0.20
0.09
0.11
0.06
0.05
0.2B
0.13
0.11
0.03
0.05
0.05
0.01
0.01
0.49
0.71
0.29
1.5
1.3
0.41
0.20
O.Ob
1.3
0.08
1.2
b.4
0.49
0.23
0.41
0.01
0.94
0.41
0.49
0.26
0.20
1.7
0.75
0.52
0.06
0.07
0.07
0.02
0.02
0.90
1.3
0.45
1.3
1.2
0.35
O.lb
0.07
O.OB
0.05
O.OB
1.5
0.12
0.05
0.10
0.004
NOTE:
1.5-oz. applications,
-20-
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Table 1-8. Average Summer Concentrations of
Diflubenzuron in Sediment at the
Mouth of Each River from Use on Cotton.
Diflubenzuron
Concentrations
Basin
Mississippi
Atchafalaya
Tombigbee
Brazos
Colorado
Nueces
Rio Grande
Year
1971
1972
1973
1974
1975
1971
1972
1973
1971
1972
1973
1974 -
1975
1973
1974
1975
1971
1972
1973
1974
1975
1973
1974
1975
1971
1972
1973
1974
1975
ug/gm
0.39
0,17
0.21
0.12
0.09
0.56
0.26
0.22
0.07
0.09
0.09
0.03
0.03
0.96
1.40
0.56
2.88
2.59
0.81
0.39
0.16
2.51
1.63
2.37
12.6
0.96
0.46
0.81
0.03
NOTE: These are the projected residues from
four 1.5-oz. applications
-21-
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before runoff (Collier and Severn, 1978). This 4-chloroaniline
formed in the soil would be additive to the 4-chloroaniline
formed in the water. The 4-chloroaniline values calculated
are reported in Table 1-9.
F. Regulatory History
1. Experimental Use Permits
The Agency issued an Experimental Use Per-
mit (EUP) in 1976 to allow for efficacy testing of diflu-
benzuron on large plots of cotton. A temporary tolerance
of 0.2 ppm on cottonseed was issued in conjunction with
the EUP to permit the sale of the seed.
After the 1976 season was completed, the
EUP lapsed and Thompson-Hayward requested an extension for
the 1977 season. The Agency approved Thompson-Hayward1s
application for the 1977 season but stipulated that the seed
could not be used for food because of adverse toxicological
findings. In 1978, Thompson-Hayward once again applied for
an extension of the EUP with a temporary tolerance. The
Agency granted both the EUP and the tolerance after it
performed a risk estimate which indicated that the use for
which the permit was requested would not have a significant
adverse effect on human health.
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Table 1-9. Predicted Levels of 4-Chloroaniline in Five Representative Rivers
Diflubenzuron*
River Cone, ug/1
Mississippi
Atchafalaya
Tombigbee
Brazos
Colorado
0.55
0.80
0.2b
0.95
3.2
4-Chloroan-
iline Cone.
ug/1 (calc)
0.25
0.40
0.14
0.48
1.6
4-Chloroan-
iline Potential Ingestion **
Range ug/1 exposure ug/yr
0.1-1
0.2-2
0.05-0.5
0.2-2
0.5-5
18-180
36-360
9-90
36-36
90-900
•Highest average summer concentration of diflubenzuron predicted from four appli-
cations at 2 oz/acre for cotton and four applications at 1 oz/acre for soybeans.
"The potential ingestion exposure may then be calculated as follows Cassuming that
water treatment works have no effect on the 4-chloroaniline concentration):
0.1-1.0 ug/1 4-Chloroaniline x 21/day x 90 days per season = 18-180 ug/yr
ingestion of 4-Chloroaniline. These data are included in the table.
-23-
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c. Mosquito Control
»
The original registration filed by Thompson-
Hayward indicated the possible accumulation of residues in
fish and potable water (Pesticide Petitions 6H5130, 6F17731).
Therefore, a tolerance was necessary for potable water and
fish to allow residues in these items. EPA scientists
concluded that the data did not provide a basis for the
establishment of permanent tolerances for these major
reasons: the tolerance must be addressed in terms of
diflubenzuron and its metabolites for fish and potable
water, the analytical methodology for enforcement of the
tolerance is inadequate, further characterization of
residues may be needed once levels of residue in fish meal
are established, studies reflecting residues of diflubenzuron
in additional fish and shellfish are needed, and data from
processed food products derived from fish are needed
(Hummel, 1976).
Thompson-Hayward subsequently submitted a
version of the proposed revised label for diflubenzuron
that eliminated the need for tolerances. The proposed label
limits application to temporary rain pools; drainage ditches
and lagoons from dairy, poultry, and swine-holding areas;
overflow; and intermittently flooded sites associated with
urban and residential areas. Aerial application of diflubenzuron
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2. Registration and Tolerances
a. Cotton
Use of diflubenzuron on cotton requires a
tolerance for residues on cotton seed. EPA scientists,
in reviewing the data presented by Thompson-Hayward in
Pesticide Petition 7F1898, concluded that diflubenzuron
residues would not exceed the requested tolerance provided
appropriate rotational crop restrictions and restrictions on
grazing and feeding of treated foliage were placed on the
product label. However, unresolved toxicological issues
precluded granting the requested tolerance at the time of
EPA's review of Thorapson-Hayward's petition.
b. Soybeans
Diflubenzuron use on soybeans requires a
tolerance for diflubenzuron residues in soybeans. The
data submitted to EPA does not yet provide a basis for
establishment of a tolerance because the issue of whether
the diflubenzuron residues concentrate in soybean hulls and
soapstock is unresolved. EPA has determined that the
concentration of diflubenzuron in the hulls and soapstock
requires a Feed Additive Tolerance. The registrant is
questioning this conclusion. Consequently, until this issue
is resolved, no further review will be conducted on this
application.
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is proposed. The EPA has notified Thompson-Hayward that
»
deficiencies exist in the application which preclude issuance
of a registration for this use (Gee, 1979). Data requirements
include environmental fate of the diflubenzuron in water and
sediment and efficacy data for the granular formulation.
Labeling changes required by the Registration Division
include removal of aerial application instructions.
Consequently, as with soybeans, this use will not receive
further review at this time.
d. Gypsy Moth
Diflubenzuron was registered to control
gypsy moths in forests in 1976. This use is limited to
application by State and Federal personnel. Currently,
there are two separate programs designed to control the
spread of the gypsy moth: an eradication program and a USDA
control program. The Animal Plant Health Inspection Service
(APHIS) uses diflubenzuron in an eradication program to
control outbreaks of gypsy moth in geographical locales
distinct from the original infestation. The Forest Service
of USDA and state governments use diflubenzuron to control
active infestations within the area of the original outbreak.
This use, registered for forests only, will not be dealt
with further until a Generic Standard is proposed for this
chemical.
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e. Douglas Fir Tussock Moth
The Forest Service of USDA had an experimental
use permit (EUP) for diflubenzuron to control the Douglas
Fir Tussock Moth, a pest of the Pacific Northwest forests.
At present no application is on file with the Agency for
this proposed use. Consequently, although diflubenzuron has
a potential use for control of the Douglas Fir Tussock Moth,
no decisions with respect to the registration of the compound
for this use can be made in this document.
3. Referral for Rebuttable Presumption Against
Registration
Diflubenzuron was referred to the Special
Pesticide Review Divison for rebuttable presumption against
registration review in October 1977 because the^compound was
suspected to cause tumors and chronic blood effects in
humans (methemoglobinemia and sulfhemoglobinemia), testosterone
depression in domestic animals, reproductive effects in
birds (diminished egg production and reduced hatching), and
effects to nontarget organisms (acute toxicity to crustaceans
from direct application to water, and acute and chronic
toxicity to crustaceans from runoff from treated fields
(Campt, 1977)).
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•II. Risk Analysis
A. Chronic Effects
1. Oncogenicity
Thompson-Hayward Chemical Company presented
two chronic feeding studies conducted by Huntingdon Laboratory
in support of its application for the registration of difluben-
zuron: "Effects of DU 11230? in Dietary Administration to
Rats for 10M Weeks" (Huntingdon, 1976) and "Tumorigenicity
of DU 112307 to Mice" (Huntingdon, 1977). These studies were
reviewed by EPA's Carcinogen Assessment Group (CAG).
CAG also considered in its cancer assessment a National
Cancer Institute (NCI) chronic feeding study in which
4-chloroaniline, a metabolite of diflubenzuron found in
mammalian systems, was administered to rats and mice.
CAG concluded that the Thompson-Hayward studies
suffered from several severe deficiencies in design which
greatly reduced their sensitivity with respect to the
detection of a carcinogenic response. These deficiencies
preclude any interpretation of the results of these studies
as evidence of a negative response. In addition, CAG
concluded, based on the diagnoses of several pathologists,
that the Thompson-Hayward mouse study provides suggestive
evidence of a carcinogenic response in lymphoreticular
tissues.
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Additional evidence that diflubenzuron may pose
a carcinogenic risk to humans is provided by the NCI study
on 4-chloroaniline in which an increase in mesenychymal
tumors in the spleen of male rats and hemangiomatous tumors
in mice appeared to be associated with the administration
of the test compound. A more detailed discussion of these
studies, their results, and their deficiencies is provided
below. The source of this discussion is the CAG report on
diflubenzuron (hereafter "CAG Report") (Albert, 1979).
a. Mouse Study - Oral (Thompson-Hayward)
Mice (CFLP) of known litter origin were
randomly distributed according to body weight in five test
groups of 52 males and 52 females in each group. Four mice
were housed in each cage. The diet was powdered laboratory
food mixed with the required amounts of diflubenzuron (DU
112307 batch P 7227). Dietary levels of 0, H, 8, 16, and 50
ppm diflubenzuron were fed for 80 weeks to groups 1-5,
respectively. All animals were examined daily for signs of
ill health, toxicity, and behavioral changes. Food and
water consumption were recorded. On completion of the
treatment period, all the surviving mice were killed with
C02. Gross pathology was done on all animals. All
abnormalties were recorded including appearance and size.
Microscopic examination was routinely performed on lymph
-29-
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nodes (cervical and mesenteric), liver, spleen, ovaries,
thyroid, adrenals, pituitary glands, and all macroscopically
observed lesions suggestive of neoplasia. Blood and bone
marrow smears were made.
(i) Results
A significant increase in lymphoreticular
tumors (lymphosarcoma, reticulum cell sarcoma, myeloid leu-
kemia) according to Fisher's exact test (p=0.0l4) was diag-
nosed originally by Huntingdon Laboratory in the group of
female mice treated with 16 ppm diflubenzuron compared to
controls. No significant increase of lymphoreticular tumors
was found in any other treatment group of female mice or in
any treatment group of male mice.
In addition, according to the Huntingdon
Laboratory's original diagnosis, lymphosarcomas in female mice
were found as early as 14 weeks in the 16 ppm treatment group,
6 and 37 weeks in the 50 ppm treatment groups, and 44 weeks in
the control group. This suggests a carcinogenic response with
a decrease in latency period as doses increase.
Huntingdon Laboratory reassessed the
histopathology results for lymphoreticular tumors (Huntingdon,
1975) and presented results slightly different from those in
its original submission. A comparison of the original
diagnosis with the reassessment is summarized in Table II-1.
-30-
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Dr. D. Goodman of Clement Associates
performed an histopathologie evaluation of all slides from
all female mice. Her conclusion was that diflubenzuron was
noncarcinogenic in this study. However, according to her
diagnoses, there was a significant increase of lymphoreticular
tissues tumors in the 16 ppm group of female mice as compared
to controls by Fisher's exact test (p=0.035).
Thompson-Hayward Chemical Company requested
Clement Associates to convene an independent panel of patholo-
gists to review the diagnosis of lymphoreticular tumors in the
female mice from the Huntingdon study. The panel consisted of
Drs. D. Goodman, R. Squire, S. Vesselinovitch, and A. Rogers.
The panel reviewed animal tissue from all
female mice in all dose groups previously diagnosed by
Huntingdon Laboratory as having hematopoietic tumors, plus
all additional female mice from the 0, 16, and 50 ppm dose
groups that were found to have hematopoietic tumors by
either Dr. Goodman or Dr. Vesselinovitch. This panel
concluded that there was no evidence of a carcinogenic
effect in the lymphoreticular tissues from female mice in
this study. However, according to their diagnoses, there
was a significant increase of lymphoreticular tissue tumors
in female mice dosed at the 16 ppm level as compared to
controls by Fisher's exact test (p=0.035).
-32-
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The first report indicated that the tissue in some cases had
autolyzed and that a histopathological evaluation was not
performed.. Inexplicably, the second report included the
histopathology for these tissues.
Table II-l
Total Number of Lymphoreticular Tissue Tumors in
Male and Female Mice (Huntingdon Laboratory)
Groups 0 ppm 4 ppm 8 ppm 16 ppm
Original Diagnosis
Males
Females
Revised Diagnosis
Males
Females
8
7
9
9
3
11
5
10
6
10
7
12
9
15 (peO.019)
9
15 (p=0.0577)
5
13
6
13
As can be seen, Huntingdon, in its reevalua-
tion, changed its original finding of a significant increase
by Fisher's exact test of lymphoreticular tumors in the 16
ppm treatment group, into an insignificant increase.
Because of this revision, further review of microscopic
slides from the study was done by several pathologists at
the request of either the registrant or EPA.
-31-
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Dr. N. Dubin, consultant to CAG, reviewed all
available tissues from female mice in the 0, 16, and 50 ppm dose
•groups. He stated that there was no evidence for the carcin-
ogenicity of diflubenzuron. However, according to his diag-
noses there was a borderline response at 16 ppm (Fisher's exact
test P=0.059).
A panel consisting of Drs. Werner Kirsten,
James Varinman, and Diana Variakojis of the Department of
Pathology at the University of Chicgo Medical School reviewed
31 related cases (approximately 300 slides) from the study.
These cases were selected for either background baseline
lesions (which had uniform positive or negative findings) or
for confirmation of the presence (or absence) of lymphore-
ticular tumors where pathologists had not previously
been able to completely agree. The diagnoses of Dr. Kirsten's
panel, when combined with the unanimous findings of the other
pathologists, demonstrated a significant response by Fisher's
exact test in both the 16 and 50 ppm treatment groups.
(P=0.0050 and P=0.04, respectively).
The data from all the pathological diagnoses
other than those of the Kirsten panel are summarized in Table
II-2. The Data from the Kirsten panel are summarized in Table
II-3.
-33-
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Table II-2. This table shows the incidence of lymphoreticular tumors in female
mice and the statistical significance values by Fisher's exact test between
control and respective treatment groups.
Diflu-
benzuron
Dosage Dr. I.N.
Group Dubin
Clement
Associates
(Dr. Squire
& Panel
Huntingdon
Laboratory
(original)
Huntingdon
Laboratory
(revised)
Dr. D. Goodman
0 ppm
Ib ppm
50 ppm
12/49
IB/43
p=0.05Bb
17/49
p=0.1751
B/49
15/43
p=0.0345
10/49
p=0.3645'
7/49
15/143
p=0.0190
13/50
p=0.1117
9/49
15/43
p=0.057«
13/50
p=0.2352
B/49
15/43
p=0.0345
10/49
p=0.3b45
-34-
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Table II-3
Dr. Kirsten's
Diflubenzuron Group Positive
Dosage for Lymphoreti-
Group cular Tumors (a)
Previous
Pathologists
Unanimous for
Lymphoreticular
Tumors (b)
Total Positive
Diagnoses Attributed
Dr. Kirsten's Panel (c)
0 ppm
Ib ppm
3/12
2/7
3/27
14/35
b/49
lb/43 H
50 ppm
(Dr. Kirsten
only reviewed
positive cases)
4/9
10/40 (Clement Assoc.
Drs. Squire, Goodman,
etc.) or
10/41 (Dr. Dubin &
Huntingdon)
14/49,
p=0.035 or
14/50
p=0.0430
a/ Slides were selected for review on the basis of conflicting diagnoses.
b/ Slide to which all pathologists agreed on positive diagnosis.
c/ Assuming that the Kirsten's panel would have agreed to the unanimous diagnosis
of positive findings by pathologists listed in Table II-2.
£/ Statistically significant values were calculated according to Fisher's exact test.
-35-
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(ii) Quality of the Study
The mouse study suffered from several
severe deficiencies which greatly reduced its sensitivity
for detecting a carcinogenic response. These deficiencies
are discussed in detail in the CAG Report. Briefly summarized,
these deficiencies are as follows:
1. There is no indication that the maximum
tolerated dose (MTD) was used in this experiment. According
to the National Cancer Institute Guidelines for Carcinogenic
Bioassay in Small Rodents (Sontag et al., 1976), the MTD is
defined as "the highest dose of the test agent given during
the chronic study that can be predicted not to alter the
animal's normal longevity from effects other than carcino-
genicity." It is important that the MTD be used to maximize
the ability to detect a carcinogenic response.
Several steps need to be taken in determining
the MTD. One important step is to conduct a subchronic test
on both sexes of the test animal to be used in the chronic
study. The highest dose of the test agent to be used in the
subchronic study should be the maximum dose which has not
been demonstrated to cause toxic effects in properly con-
ducted acute studies. According to these procedures Hun-
tingdon Laboratory should have used doses possibly as high
as 50,000 ppm in the diet on both sexes of mice in its
-36-
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subchronic study. Instead,^it used only male mice in the
subchronic study and used a highest dose of only 50 ppm in
the test. On this basis, it chose 50 ppm as the MTD to be
used in the chronic study. If the subchronic study had been
properly conducted, the MTD might have been demonstrated to
be several orders of magnitude higher.
It appears that the Huntingdon Laboratory
selected 50 ppm as the MTD for the chronic test because it
observed foci of liver cell necrosis in three of eight male
mice that received 50 ppm diflubenzuron for 6 weeks in the
subchronic study. However, the fact that no liver necrosis
was found in the mice administered 50 ppm over 80 weeks in
the chronic study suggests that the liver lesions found in
the subchronic study were not caused by the diflubenzuron,
but rather had some other etiology. In addition, if several
doses higher than 50 ppm had been administered in the
subchronic study, an absence of liver necrosis at the
higher dose levels would have demonstrated that the liver
necrosis found at the 50 ppm level was not caused by the
test agent.
It should be noted that two Thompson-Hayward
consultants, Dr. Robert A. Squire and Dr. Jack L. Radomski,
have questioned (Appendices II-1 and II-2) whether the MTD
was used in this study. In fact, Dr. Radomski was of the
-37-
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opinion that the highest doge used in the chronic study was
substantially lower than the MTD.
2. Another deficiency of the mouse study
is that only seven tissues (lymph nodes, spleen, liver,
thyroid, ovaries, adrenal gland, and pituitary gland) were
routinely examined microscopically. The NCI guidelines
specify over 30 tissues and organs that should be routinely
examined microscopically. Many of the organs not examined
microsopically were examined macroscopically. However, this
procedure alone is inadequate since many small tumors could
have been missed. It should be noted that the lungs were
excluded from routine microscopic examination even though
this is frequently found to be a target tissue.
3. There is no indication in the report
of the chronic mouse study that the doses of diflubenzuron
administered to the mice were verified by chemical analysis
of the diet of the treated mice during the course of the
experiment. Thus, there is some question as to whether the
mice were in fact administered the doses indicated in the
report.
4. The experiment was of suboptimal
length (80 weeks). The mice should have been administered
diflubenzuron at least 104 weeks before sacrifice. If the
study had been conducted longer, a greater number of tumors
may have been observed.
-38-
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b- Rat Study - Oral (Thompson-Hayward)
Sprague-Dawley rats of the CD strain
(five groups) each composed of 45 female and 45 male rats
constituted the main group for the carcinogenic study. The
15 male and 15 female rats which constituted the satellite
group to the toxicity study were randomly distributed
according to body weight into five test groups. Rats were
housed five to a cage. Animal room temperature and humidity
were controlled at 21° + 2°C and 50% +_ .0%, respectively.
Lighting was controlled to give 12 hours light and 12 hours
dark per 24 hours. The diet was powdered laboratory food
mixed with the designated amount of diflubenzuron (DU
112307). Dietary levels of 0, 10, 20, 40, and 160 ppm
diflubenzuron were fed for 104 weeks. All rats were examined
daily for signs of ill health, toxicity, and behavioral
changes. Food and water consumption were recorded including
utilization of the food.
All rats were examined macroscopically to
determine the cause of death. Urine and blood were examined
frequently. At termination, all surviving rats were killed by
COp asphyxiation. The microscopic examination was routinely
performed on seven tissues (adrenals, thyroid, ovaries, liver,
spleen, lymph' nodes, and pituitary gland) and all macroscopically
observed lesions suggestive of neoplasia. Blood smears were
-40-
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Conclusions on the Mouse Study
Because the 'mouse study suffers from several
severe deficiencies which make it insensitive for purposes of
detecting an oncogenic response, it cannot, according to any
interpretation of its results be considered valid evidence
of a negative oncogenic response.
The study did provide suggestive evidence
of a carcinogenic response. Most of the pathologists who
reviewed the lymphoreticular slides from the female mice
found a statistically significant increase in lymphoreticular
tumors in the 16 ppm treatment group compared to controls by
Fisher's exact test. If CAG had used the practice now
common at NCI in multiple-dose experiments, of using the
Bonferroni upper bound as a significant level for a single
dose comparison, only the Kirsten panel diagnoses would have
provided statistically significant results. The Bonferroni
upper bound is the normal significance level divided by the
number of dosage levels. However, CAG has not followed the
approach of using the Bonferroni procedure with Fisher's
exact test since this procedure tends to mask weak carcinogenic
responses. Furthermore, the Agency concludes that the more
conservative approach of not using the Bonferroni correction
in evaluating an insensitive and poorly conducted study such
as this one is especially justified.
-39-
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also routinely made. Abnormalities detected on the blood smear
were confirmed by examination of bone marrow sections.
(i) Results
No significant difference was found in the
control versus experimental groups for any type of tumor.
(ii) Quality of the Study
As was the case with the mouse study, the
rat study suffered from several severe deficiencies which
made it incapable of detecting a carcinogenic response. The
discussion of these deficiencies, from the CAG Report, is
summarized as follows:
1. There is no indication that the maximum
tolerated dose (MTD) was used in this study. The definition
of the MTD, the importance of using the MTD to maximize the
ability to detect a carcinogenic response, and the appropriate
method of determinining the MTD have already been discussed.
In the subchronic study to determine the MTD, the highest
dose of diflubenzuron in the diet was only 200 ppm.
Based on the results of preliminary acute toxicity studies,
doses possibly as high as 50,000 ppm diflubenzuron in the
diet should have been used. If much higher doses had been
used in the subchronic study, it is possible that the MTD
would have been determined to be much higher than 160 ppm,
the highest dose used in the chronic study.
-41--
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It appears that Huntingdon Laboratory
selected 160 ppm as the MTD for the chronic test because it
observed "piecemeal" necrosis of the hepatocytes in rats of
both sexes administered 50 and 200 ppm diflubenzurbn in
the subchronic study (Phillips-Duphar, B.V., 1973b). However,
independent evaluations of liver slides from this study by
Drs. A.J. Newman and C.A. van der Heyden (Phillips-Duphar)
did not confirm these findings. Moreover, no liver necrosis
was reported among any of the experimental groups in the 104-
week chronic study.
The registrant has suggested that the
presence of methemoglobinemia in rats treated with 160 ppm
diflubenzuron in the chronic study is evidence that the MTD
was used in that study. However, the level of methemoglo-
binemia found in the 160 ppm group was not significantly
different from the level found in the controls. Furthermore,
even if it had been significantly different, this fact could
not have been used as a basis for determining the MTD since
a life-shortening toxic effect must be found in the subchronic
study. The methemoglobinemia was found only in the chronic
study and was not established to shorter life.
Two Thompson-Hayward consultants, Robert A.
Squire and Jack I. Radomski, have questioned whether the
MTD was used in this study (Appendices II-l and II-2).
-42-
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Conclusions on the Rat Study
This study is'not valid in view of the
defects discussed above. Thus, the Agency is precluded from
using the results of this study as evidence of the ojncogenic
potential of diflubenzuron.
c. 4-Chloroaniline - (Oral study in rats and
mice) (NCll
A bioassay testing for the possible carcino-
genicity of 4-chloroaniline was conducted by the NCI bioassay
program using Fischer 3^ rats and B6C3F1 mice. The NCI
camera-ready report of this bioassay was reviewed by CAG
and the summary of the report was accepted by CAG as an
accurate interpretation of the results (NCI, unpublished).
The NCI summary is presented in its entirety below:
P-Chloroaniline was administered in the
feed, at either of two concentrations, to groups
of 50 male and 50 female animals of each species.
Twenty animals of each sex and species were
placed on test as controls. The high and low
dietary concentrations of p-chloroaniline were,
respectively, 500 and 250 ppm for rats and 5000
and 2500 ppm for mice. The compound was
administered in the diet for 78 weeks, followed
by an observation period of 24 weeks for rats
and 13 weeks for mice.
There were no significant positive associa-
tions between the dietary concentrations of
p-chloroaniline administered and mortality in
female rats or in mice of either sex; however,
there was a significant positive association
between concentration and mortality in male
rats. Adequate numbers of animals in all groups
survived sufficiently long to be at risk from
-44-
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2. Another severe deficiency in this study
is that only seven tissues wer'e routinely examined microsco-
.pically in-spite of the fact that the NCI guidelines specify
over 30 tissues and organs which should be so examined.
As a consequence, many small tumors could have been missed
in the other tissues and organs, which were examined only
macroscopically.
3. The strain of rats used was not suitable
for this experiment for two reasons. First, the female
control rats had an unusually high incidence of tumors
(91-98J). Second, the survival rate for all groups of rats,
including the controls, was very low. Terminal percent
survival (e.g. percentage of animals living through the term
of the experiment) for male and female rats ranged from only
1%% to 36% and was only 21% and 36$ in male and female
controls, respectively.
Both of these factors (high spontaneous tumor
rate and lower terminal survival) make it very difficult to
detect an oncogenic response.
4. The report of the results of the chronic
rat studies did not indicate that the doses of diflubenzuron
were verified by chemical analysis of the diet of the treated
rats during the course of the experiment.
-43-
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late-developing tumors^ Mean body weight
depression, in relation to controls, was observed
in high dose female rats and dosed mice of both
sexes, indicating that the concentrations of
p-chloroaniline administered to these animals
may have approximated the maximum tolerated '
concentrations. Although splenic lesions were
observed in male rats, no mean body weight"
depression relative to controls was associated
with administration of p-chloroaniline to
the animals. Therefore, it is possible that
these animals may have been able to tolerate a
higher dietary concentration of the compound.
The only neoplastic lesions found that
might be related to administration of the
compound were mesenchymal tumors in the spleens
of male rats and hemangiomatous tumors in mice.
In male rats, there was significant positive
association between compound administration and
the incidences of fibroma or fibrosarcoma of the
spleen. The incidences of these tumors were
not significantly elevated when compared to
those in control rats, but the rarity of these
tumors in male Fischer 344 rats (0/360 in
historical male control rats in this laboratory)
strongly suggests a chemically related effect.
In adddition, three sarcomas of other types were
found in high dose male rats. In mice of both
sexes, hemangiomas and hemangiosarcomas were
found at elevated incidences, when compared to
control mice, in the spleen, liver, kidney, and
multiple body sites. The increased incidences
in dosed mice were statiscally related to dose
but were not statistically significant when
compared directly to matched control animals.
In comparison to historical control data, the
incidences of hemangiomatous tumors in the dosed
mice were elevated, but not greatly. The
evidence was considered insufficient to conclu-
sively relate the hemangiomatous tumors in mice
to compound administration. Nonneoplastic
proliferative and chronic inflammatory lesions
were also found in the spleens of dosed rats and
mice.
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and sarcomas in the spleens of male rats was
considered strongly suggestive of carcinogenicity
because of the rarity of these tumors in the
spleens of control rats. Hemangiomatous tumors
in dosed mice may also have been associated with
administration of p-chloroaniline. However, it
is concluded that, under the conditions of this
bioassay, sufficient evidence was not found to
establish the carcinogenicity of p-chloroaniline
for Fischer 3^4 rats or B6C3F1 mice.
d. Overall Conclusion on the Carcinogenic
Risk of Diflubenzuron
The rat study suffered such severe
deficiencies that the data cannot be used to determine
whether or not diflubenzuron is an oncogen. Because of the
invalidity of this study and the deficiencies of the mouse
study, the Agency is not able to fully assess the oncogenic
potential of diflubenzuron". However, the Agency has
determined that the increase of lymphoreticular tumors in
female mice in the 16 ppm dosage group was suggestive of a
positive effect. These results were used to estimate the
risk resulting from diflubenzuron use on cotton that is
developed in the following section.
In addition, the NCI study provides
strongly suggestive evidence of the oncogenicity of 4-
chloroaniline, a metabolite of diflubenzuron, that has been
identified in mammalian systems, plants, soil, and water.
-46-
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2- Methemoglobinemia and Sulfhemoglobinemia
»
Methemoglobinemia and Sulfhemoglobinemia
are impairments of the oxygen transport capability of
the blood. The formation of methemoglobin is reversible
in adults, but is not known to be reversible in children.
The formation of sulfhemoglobin is not known to be
reversible in either adults or children. Therefore,
methemoglobinemia in children and Sulfhemoglobinemia
will persist until the affected red blood cells are
replaced by red blood cells subsequently manufactured
by the body.
Methemoglobinemia has been demonstrated
after inhalation, oral, and dermal exposure to difluben-
zuron in rats, mice, rabbits, and sheep. Sulfhemoglo-
binemia was demonstrated only after oral exposure of
diflubenzuron to rabbits and rats. A study using
beagle dogs was negative for both methemoglobinemia and
Sulfhemoglobinemia.
Table II-4 summarizes the results of these
studies. Methemoglobinemia and Sulfhemoglobinemia were
detected in rabbits orally administratered 19.2 mg/kg
diflubenzuron. A no-observed-effect level (NOEL) was not
demonstrated in the rabbit. In rats, methemoglo-
binemia was detected at a dietary dosage level of 40
-47-
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Table II-4. Methemoglobinemia Formation
Test Aminal
Sex Report No.
Dosage
Result
Oral Exposure
Mice
Rabbit
Rabbit
Sheep
Rats
Rats
Beagle Dog
Rat
Rabbit
Rabbit
M 5bb45
M 56645/2/77
M 56645/13/77
M/F 229/77226
M 56645/15/77
M/F 243/77208
M/F 169/74157
M/F 197/741013
M/F 200/74b5
M/F 146/73845
10,000 mg/kg
(Gastric Intubation)
19.2 mg/kg
(Dietary;
4640 mg/kg
(Gastric)
20 mg/kg
100 mg/kg
400 mg/kg
(Dietary)
5000 mg/kg
(Gastric Intubation)
40 mg/kg
200 mg/kg
1000 mg/kg
" 5000 mg/kg
(Dietary)
0.41 mg/kg
0.84 mg/kg
1.64 mg/kg
6.24 mg/kg
(Dietary)
Inhalation Exposure
0.1 mg/L
0.8 mg/L
I.b5 mg/L
Dermal Exposure
69 mg/Kg
150 mg/kg
320 mg/kg
170 mg/kg
425 mg/kg
Me Hb detected
Su Hb detected
Me Hb
Me Hb detected
Me Hb detected
100 mg/kg
Me Hb and
Su Hb
Me Hb detected
in Male all
levels Me Hb
detected in
female at 200 mg/kg
level or higher
No Me Hb
detected
Me Hb all
levels
Me Hb detected
all levels
both sexes
Me Hb detected
all levels both
sexes
-48-
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mg/kg, the lowest level tested. A response was not
demonstrated at dietary dose levels from 0.41 to 6.24
mg/kg in the beagle dog. Thus, an NOEL was not shown in
either the dermal or inhalation tests in rats and rabbits.
As a matter of policy, the Agency bases its risk assessments
on the most sensitive species tested, which in this case
appears to be the rabbit.
The causative agent for methemoglobinemia
and sulfhemoglobinemia is believed to be 4-chlorophenyl-
hydroxylamine, a metabolite of diflubenzuron. Identifi-
cation of 4-chlorophenylhydroxylamine was made in Phillips-
Duphar study 56654/8/77 (Phillips-Duphur BV, 1977).
In this study rats developed methemoglobinemia after dietary
exposure to diflubenzuron. Analysis of the urine revealed
4-chloroaniline and its N-oxidation product 4-chlorophenyl-
hydroxylamine. N-Hydroxylamines are known to be potent
agents for induction of methemoglobinemia.
A similar mechanism is believed to
be responsible for the induction of sulfhemoglobinemia.
The major difference between methemoglobinemia and
sulfhemoglobinemia is that in sulfhemoglobinemia a
permanent change in the chemical structure results.
In summary, while studies are available to
demonstrate that diflubenzuron induces methemoglobinemia
-49-
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and sulfhemoglobinemia in test animals, the studies did
not demonstrate NOEL's. The A'gency must have studies
conducted in the most sensitive species and with a
demonstrated NOEL in order to fully evaluate the effect
of methemoglobinemia and sulfhemoglobinemia.
3. Mutagenicity
a. Ames Test
This test is the best validated test
for the correlation between mutagenicity and carcinoge-
nicity. Diflubenzuron and its metabolites have been
tested in a full or partial Ames battery of Salmonella
typhimurium strains by a number of different laboratories
with varying protocols and-results. Seuferer (December
1977 thesis) reported 2,6-diflurobenzoic acid as a base-pair
and frame-shift mutagen in all strains. This is in conflict
with the results of Litton and Borough (1977). Several other
diflubenzuron metabolites including 4-ehloroaniline were
considered slightly mutagenic.
Litton Bionetics [proprietary data, Thompson
HaywardJ performed an Ames test with negative results on
diflubenzuron. However, 4-chloroaniline was found to
be mutagenic.
Dorough (1977) [proprietary data, Thompson-
Hayward], used the TA-1537 and TA-98 strains of bacteria.
-50-
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He did not find activity with diflubenzuron but did obtain
positive dose-response results for 4-chloroaniline in Strain
TA-98 with metabolic activation. Subsequently, he tested
diflubenzuron more extensively in the entire Ames tester set
using the spot test. It also included a Salmonella
typhimurium bacteria repair test with strain TA-1978. These
were also negative. Other metabolites tested were negative
(MacGregor et al., 1979).
b. Other Studies
Negative results in mutagenicity studies
on diflubenzuron were obtained in the following: yeast
(Saccharomyces), a mouse micronucleous test, unscheduled
DNA synthesis in mammalian cells, and the dominant-lethal
test [proprietary data, Thompson-Hayward].
In summary, diflubenzuron is not mutagenic
in the Ames test. This result was confirmed in a number of
laboratories. Other mutagenicity tests performed do not
meet the multi-test criteria. Diflubenzuron is a halogenated
compound. This class of compound correlates poorly in terms
of mutagenicity/carcinogenicity test results. A metabolite,
4-chloroaniline, is mutagenic in the Ames test. However,
this one positive finding is not sufficient to declare that
the metabolite poses a mutagenic potential.
-51-
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4. Hormonal Effects
t>
The Agency has reviewed several papers and
summary"reports dealing with the effect of diflubenzuron
on testosterone levels in avians and animals. Most of this
work (two reported studies) was done at the USDA's Veterinary
and Toxicological Entomology Research Laboratory in College
Station, Texas. One additional study was conducted by
the USDA at the Poultry Research Laboratory, Beltsville,
Maryland.
The Texas studies were judged invalid by
the USDA investigator for technical reasons. An EPA team
of scientists reviewing these studies agreed with the
assessment of the USDA investigator (Chitlik and Biscardi,
1979). The Beltsville study shows a trend of decreasing
testosterone levels with diflubenzuron treatment. This
result was not statistically significant.
EPA has recently completed a study to determine
the effect of diflubenzuron on testosterone levels in the
rat. Preliminary results have been received, but until a
validation of the entire study can be completed, no con-
clusions can be made.
-52-
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B. Nontarget Effects
.1. Aquatic Invertebrates
X
Effects to nontarget organisms constitute a
major concern of the Agency. The projected use patterns and
registered use patterns of diflubenzuron could impact
significantly on the life-cycles of nontarget organisms
which come in contact with diflubenzuron through the use of
habitats common to areas of diflubenzuron use or difluben-
zuron runoff. The Agency reviewed the area of potential
significant adverse effects for nontarget exposure to
aquatic invertebrates including estuarine crustaceans.
Data available to EPA indicated that difluben-
zuron has acute and chronic effects on several aquatic
invertebrates. The effects on specific organisms are listed
in Table II-5. These data clearly indicate that difluben-
zuron, in laboratory situations, is toxic at extremely low
levels to aquatic invertebrates. The aquatic species at
risk are located primarily in estuaries and other areas in
the coastal zone.
Tables II-6 and II-7 compare the levels of
diflubenzuron exposure resulting in toxic effects in various
aquatic species with the levels of diflubenzuron predicted
by the Athens Environmental Research Laboratory model to
occur at the mouths of certain rivers. These tables
-53-
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Table II-5
Effects of Diflubenzuron Upon Aquatic Invertebrates
Acute Effects
Organism Effect Level
Daphnia (water flea) 1.5 ppb LCc0
Gammarus (sand flea) 30-45 ppb LCc0
Eulimnadia (clam shrimp) 0.15 ppb LC50
Triops (tadpole shrimp) >0.75 ppb LC5Q
Mysidopsis (mysid shrimp) 2.0 ppb LCc0
Artemia (brine shrimp) - 10 ppb LC^Q
SubAcute or Chronic Reproductive Effects
Test Duration Effect Level
Mysid shrimp 27 days 0.2 - 0.6 ppb
Grass shrimp 35 days 0.45 ppb
Blue Crab 6-18 days 0,50 ppb
Daphnia 42 days 0.61 ppb
March Crab 20-30 days 1.0 ppb
Brine Shrimp BO days 2.0 ppb
-54-
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Table II-6. Mean Summer Concentrations of Diflubenzuron at the Mouth of Selected Rivers From Applications
To Cotton* And the Nontarget Aquatic Invertebrates Likely to Be Exposed
Basin
Mississippi
.
Ataohafalaya
Tomblgbee
i
Brazos
Colorado
Nueces
Year
1971
1972
1973
1974
1975
1971
1972
1973
1971
1972
1973
1974
1975
1973
1974
1975
1971
1972
1973
1974
1975
1973
1974
1975
Mean Diflu-
benzuron Cone.
For Cotton
Application (ppb)
0.40
0.17
0.22
0.12
0.09
0.57
0.26
0.23
0.07
0.09
0.09
0.03
0.02
0.98
1.43
0.57
2.93
2.63
0.83
0.40
0.17
2.55
1.65
2.40
Nontarget Aauatice Effects (Lowest Effect Level)
Mysid
Shrimp
>0.2 ppb
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Grass
Shrimp
>0.45 ppb
X
i
X
X
X
X
X
X
X
X
X
Blue Marsh Brine
Crab Crab Shrimp
>0.5 ppb >1.0 ppb >2.0 ppb
f
X
V
X
X X
X
XXX
XXX
X
X X ' X
X X
XXX
Total amount applied to cotton is 12 oz. AI/A/season(Note that operational use would call for 6 applications
at 2 oz./application but the EPA model used 4 applications at 3 oz./application for predicting concentrations
in water).
-55-
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Table II?-7. Mean Summer Concentrations of Diflubenzuron at the Mouth of Selected Rivers From Applications
To Cotton* And the Nontarget Aquatic Invertebrates Likely to Be Exposed
Basin
Mississippi
•
Atachafalaya
Torabigbee
Brazos
Colorado
Nueces
Year
1971
1972
1973
1974
1975
1971
1972
1973
1971
1972
1973
1974
1975
1973
1974
1975
1971
1972
1973
1974
1975
1973
1974
1975
Mean
Diflubenzuron Cone.
For Cotton 4 Soybean
Application (ppb)
0.20
0.09
0.11
0.06
0.045
0.28
0.13
0.11
0.035
0.045
0.045
0.015
0.01
0.49
0.71
0.29
1.46
1.31
0.41
0.20
0.08
1.28
0.82
1.20
Nontarget
Mysid
Shrimp
>0.2 ppb
X
X
X
X
X
X
X
X
X
X
X
X
Aquatice Effects (Lowest Effect Level)
Grass Blue Marsh Brine
Shrimp Crab Crab Shrimp
>0.45 ppb >0.5 ppb >1.0 ppb >2.0 ppb
•
X
X X
XXX
XXX
X X X '
X X
XXX
•Total amount applied to cotton is 6 oz. ai/A/season (Note that the operational use of Dimilin would call for
6 applications at 1 oz. ai/A but the EPA model used 4 applications at 1.5 oz./application for predicting
concentrations in water).
-56-
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indicate that diflubenzuron runoff may affect several
important species at the maximum use rates on the proposed
label for cotton (e.g., a maximum of 12 oz. per season for
cotton).
At a lower use rate of 6 oz. per season for
cotton, the potential for reproductive and acute effects is
reduced. The data indicate that the effluent in the south-
eastern rivers has a lower hazard potential to aquatic
invertebrates than the effluent in the southwestern rivers.
The data also indicate that among the threatened species are
economically important crustaceans and aquatic invertebrates
which are environmentally important as indicator organisms.
However, there is little-field data available to confirm
or deny the results predicted in the model.
2. Avian Reproductive Effects
A study performed on bobwhite quail by Cannon
Laboratories was submitted by Thompson-Hayward. An initial
review by the Agency indicated that at dietary levels of 10
ppm and 40 ppm lowered fertility and decreased egg production
and hatchability resulted.
This study was again reviewed by the Agency
after referral to SPRD. The Agency scientists who conducted
this review concluded that the adverse effects observed
were artifacts of the improper methodology of the study.
-57-
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Flaws included improper male:female ratios and lighting
which invalidated the data generated. The registrant has
subsequently submitted other studies on bobwhite quail which
did not demonstrate adverse reproductive effects at feeding
levels up to 250 ppm. They also submitted reports of field
studies of diflubenzuron treatments which did not show any
adverse effects on wild avians (Tucker and Rabert, 1978).
C. Exposure
1. Dietary Exposure
In developing the exposure profiles, a "worst
case" situation was assumed in which residues on cottonseed,
meat, milk, poultry, and eggs were projected to approach
levels as high as the minimum sensitivity of the analytical
enforcement method (0.05 ppm), or the tolerance level. It
was also assumed that all cottonseed products were derived
from diflubenzuron-treated crops. The typical human diet
contains about 0.15% cottonseed products according to the
Lehman food factor (Table II-8). On the basis of these
assumptions, it was estimated that the direct consumption of
cottonseed products will result in a worst case dietary
intake of diflubenzuron of 0.00000186 mg/kg/day.
Under worst case exposure of cattle to cotton-
seed from treated crops, the levels of diflubenzuron expected
in milk and edible tissues are predicted to be in the
-58-
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Table II-B. Human Dietary Intake of Diflubenzuron Residues9-
Human Food Source
Cottonseed
Meats, red -'
Milk and dairy
products
Poultry
Eggs
Proposed
Tolerance %
(ppm)
0.2
0.05
0.05
0.05
0.05
Percentage
of a
Diet
0.15
10.81
2B.62
2.91
2.77
Projected maximum
residue present (tug/kg)
0.05
0.00001
O.OOOOOB
0.001
0.001
Specific commodity
Intake (kg food/
160 kg person^-
0.00225
0.16215
0.1293
0.0111
t
0.01155
Total
Maximum difl.
Intake (mg dlf/
60 kg person/day
0.00011250
0.00000162
0.000003«0
0.00001110
0.00001155
0.00020317
Maximum difl
intake (mg/dif/kg
body weight/day)
0. 00000 1BO
0.00000003
0.00000006
0.00000071
0.00000069
0.00000310
aEstimates from Lehman, (1962).
Average "residue for edible tissues of red meat producing animals
°Based on 1.5 kg food intake/day/bo kg person.
-59-
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subparts per billion range. Data generated in studies
performed by Smith and Merricks using radio-labeled diflu-
benzuron projected that residues of diflubenzuron and its
metabolites were in the 8 x 10"7 ppm range for milk and
—4
8.6 x 10~ ppm range for liver. A study by Miller using
unlabeled diflubenzuron gave values of 2 x 10~7 ppm for
milk and 7.5 x 10~7 ppm for the liver.
The maximum calculated residue in the eggs and
edible tissue of poultry fed cottonseed from treated crops
falls within the M.5 x 10"^ ppm range for eggs and 3 x
10 to 6 x 10" ppm range for the edible tissues.
The likelihood of fish accumulating significant
residues of diflubenzuron is thought to be quite low.
It is possible that, through runoff, drift, or a combination
thereof, water concentrations of diflubenzuron as high as
0.001 ppm might, on occasion, be sustained over a period of
at least a few days. If such were the case, residues in fish
meat might reach levels approaching 0.05 ppm, assuming
a biomagnification of 50 times (Aperson et al., 1978; Booth
et al., 1976; Schaefer et al., 1978). Although fish are
capable of limited biomagnification of diflubenzuron from
water, appreciable water contamination from the cotton use
should be infrequent, since diflubenzuron is not highly
persistent in water (Schaefer and Dupras, 1976). Fish are
-60-
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also capable of rapidly depleting residues of diflubenzuron
from the body once exposure^ to the compound is terminated
(Booth et al., 1976; Schaefer et al., 1978). Thus, the
potential for significant human dietary exposure to
diflubenzuron via residues in fish would appear to be
slight.
Using the proposed tolerance values for cotton,
the "worst case" of the total dietary exposure to difluben-
zuron is estimated to be 3.^0 x 10 mg/kg body weight for
a 60-kg person. The contributions of the individual food
items are listed in Table II-8.
These dietary exposure levels reflect the
normal human adult average daily diet.
2. Mixer-Loader, Applicator, and Bystander Exposure
The exposure levels projected for mixer-loaders
for ground spray applications, mixer-loaders for aerial
applications, pilots, boom-spray drivers and bystanders
are reported in Table II-9 for the cotton use. The key
assumptions utilized in calculating exposure are listed
below.
1) Mixer-loaders will receive their primary
exposure by contact with dust.
2) No flagman will be utilized in the spray
operations.
-61-
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Table II-9. Lifetime Exposure and Cancer Risk to Various Groups Exposed to Dirtubenzuron from Use on Cotton
Worker Group Number
Exposed
1) Mixer Loader 110
(Aerial)
Dermal
Inhalation
Total
2) Mixer Loader 1510
(Tractor Boom Spray)
Dermal
Inhalation
Total
3) Pilots 110
Dermal
Inhalation
*
Total
1) Tractor Drawn 1510
Boom Applicators
Dermal
Inhalation
Total
5) Area Residents
(Distance from Sprayed Area)
0-25 meters . 6875
26-M5 meters 6875
16-96 meters 6875
Levels
Total Risk from Application
Aerial Applicators
Total Risk including
Days/year Dose
Exposed mg/day
12
26.5
.31
26.81
10
26.5
•31
26.81
12
.08
.005
.085
10
5.6
.03
5.63
9 .61
9 .33
9 .15
2.01 x 10"2
6.35 x 10-5
2.01 x 10"5
Ground
5.82 x 10"3
2,6 x 10-6
Dose
mg/kg/year
18.55
.217
18.77
1.12
5.17 x 10~2
1.17
.056
.001
.060
.933
.005
.938
.096
.050
.023
Lifetime Avg. Lifetime Probability of
Dose (ppm) Tumors Due to
in Diet Diflubenzuron
1.16
1.1 x
1.17
.277
3.21 x
.280
3.5 x
2.5 x
3.75 x
.058
.0003
.0583
1.05 x
5.18 x
2.52 x
1.99 x 10~2
-2 -1
10 2.11 x 10
2.01 x 10~2
1.76 x 10~3
10~3 5.57 xlO ~5
1.82 x 10
10~3 6.01 x 10~5
-1 -6
10 3.11 x 10
-3 -5
1- J 6.35 x 10
-1
9.96 x 10
5.15 x 10"b
1.00 x 10~3
10~2 1.80 x 10"M
-3 -5
10 9.11 x 10
-3 -5
10 1.33 x 10
Expected Timor
per Year Due to •
Diflubenzuron
.125
.002
.127
.105
1.23 x 10~3
106
3.8 x 10 ~"
-5
2. 16 x 10 '
-1
1.02 x 10
.022
1.13 x 10""
2.21 x 10~2
1.77 x 10~2
-3
9.21 x 10
_3
1.26 x 10
' Levels -
Total Risk from Application M.B2 x 10~3
Ground Applicators 1.00 x 10-3
Aerial
2.01 x 10"2
2.6 x 10-6
5.b2 x 10~3
By-standers
1.80 x lO"*1
2.6 x 10-6
5.82 x 10
~3
2.01 x 10
"2
1.82
-62-
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3) All spray areas will be posted to
minimize exposure to bystanders.
4) Exposure via ground application will
be similar to that described by Wolfe
(1961) for dinoseb.
D. Risk Calculations
1. Qnoogenioity
The Interim Cancer Guidelines state that when a
chemical is judged to be a potential human carcinogen, the
Agency will estimate its possible impact on public
health at anticipated levels of exposure. These guidelines
also recognize that the available techniques for assessing
the magnitude of cancer risk to human populations based on
animal data are at best very crude. This is due, among other
causes, to uncertainties in the extrapolation of dose-response
data to very low dose levels and to differences in levels of
susceptibility of animals and humans. Accordingly, the risk
estimates are neither scientific certainties nor absolute
upper limits, but are used by the Agency only as rough
approximations of potential health risks.
a. Dietary
The risk levels were predicted from the
one-hit model using the proportion of tumors in the controls
-63-
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and that in the 16 ppm dose group. This equation is
expressed below.
B = logn [(1-PX) - (i-po)]!)!7.
B = logn [(1-15M3)/(1-7M9)]/16
= 1.718 x 10"2
The slope of the one-hit model, (B, or 1.718 x
_2
10 ), is used to calculate lifetime probability (P) of a
tumor caused by diflubenzuron. This is shown below:
P = Bx
(1.718 x 10"2)x
where x is the average equivalent exposure of difluben-
2 /
zuron in the diet.—
1/ B = slope
logn = natural logaritham
Po = mice with tumors in the control group
Px = mice with tumors in the treated group
D = dose
2/ Another method of conducting a conservative extrapolation
is to follow the approach suggested by Ian Nesbit in the
Clement Associates submission. He fitted a linear model to
all the data points and obtained a slope of .11 with an
estimated 99$ confidence bound on the slope equal to .6.
However, it appears that a numerical error was made in the
estimation of the confidence limit. The correct estimate
for the confidence interval of the slope would be .85.
Using this value, the risk would be about one-half that found
by the CAG for all exposure situations.
-64-
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The dietary risks were determined from the
dietary exposure after adjusting mg/kg to ppm in the
diet. The calculated values are shown in Table 11-10.
Lifetime dietary exposure was assumed in making these
calculations. The risk resulting from consumption of diflu-
benzuron-treated cottonseed, meat, milk, poultry, and eggs
exceeds 2.6 x 10" . This represents roughly 2.6 tumors
per million people exposed to diflubenzuron for a lifetime.
b. Applicators and Bystanders
The oncogenic risk for these groups was
calculated from the exposure levels projected in Table II-9.
The risk estimates are also provided in Table II-9. Conversion
from mg/kg/year to equivalent ppm in the diet is expressed
in the equation below:
x r (60 kg) u3/ (40 years)
(365 days) (70 years)(1.5 kg)
= 6.26 x 10"6 u
= per lifetime diflubenzuron
mg kg food eaten per lifetime
where x is the ppm in the diet and u is the mg/kg/year.
The 40 years refers to work history and 70 years is the
lifespan. This equation assumes a 40-year exposure for
workers. For bystanders, a 70-year exposure is assumed.
3/ U = mg/kg/year
-65-
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The oncogenic risk to applicators from the
mixing and loading of diflubenzuron and the oncogenic risk
to bystanders for cotton programs are shown in Table II-9.
For the use on cotton the oncogenic risk to the mixer-loader
in aerial applications and ground applications is 2.01 x
10"2 and H.82 x 10~3, respectively. This means that,
assuming a MO-year occupational exposure, the number of
tumors produced from exposure to diflubenzuron in the
respective groups is two per 100 for aerial application
personnel and five per 1,000 for ground application personnel,
The pilots and tractor drivers would have risk levels of
6.35 x 10 and 9«96 x 10~ or roughly six tumors per
100,000 pilots and one per 1,000 tractor drivers for a
40-year exposure. If any of these personnel perform both
functions (e.g., mixing-loading and applying the pesticide),
the risks produced from each increment would be additive. In
all cases the applicator risk is additive to the dietary
risk.
The highest projected risk is to mixer-loaders,
with the majority of the risk coming from dermal exposure.
The risk from inhalation is approximately one or two orders
of magnitude below the risk from dermal exposure.
Bystanders in the cotton areas are assumed
to include workers in other fields as well as people living
-66-
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nearby. It was assumed that they would not be protected in
any special manner other titan by wearing standard clothing
common to field workers and farm families. It was also
assumed that they would be exposed for a lifetime of 70
years.
2. Methemoglobinemia and Sulfhemoglobinemia
No-observed-effect levels (NOEL's) for methemo-
globenemia and Sulfhemoglobinemia have not been established
for certain species of animals including the rabbit. However,
the lowest daily doses causing observed effects in all of
these species were considerably greater than the anticipated
exposure to humans from the diet or pesticide application.
In studies on other animals, such as beagle dogs, where
NOEL's were demonstrated, these levels were also greater
than the theoretical exposure to humans.
The Agency has concluded that these studies
do not raise significant concern about the potential for
adverse effects on humans exposed to diflubenzuron. However,
further study of the relationship between diflubenzuron
exposure and methemoglobinemia and Sulfhemoglobinemia is
necessary before the risk to humans can be fully evaluated.
3. Hormonal Effect
The studies performed with avians at VTERL
were not valid. The Beltsville study data showed a trend of
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decreased testosterone levels, but this trend was not
»
statistically significant. The study in rats done by EPA
cannot be used as a measure of effects until the entire
report is reviewed and validated. Thus, the data on
hormonal effects which have been reviewed do not raise
significant concerns about the potential for adverse effects
on humans exposed to diflubenzuron.
4. Non-Target Effects
The risks to nontarget organisms posed through
use of diflubenzuron on cotton are qualitatively addressed
in Tables II-6 and II-7. These risks impact several species
of aquatic invertebrates. However, since the exposure
levels used in determining risks are based on a model which
has not been validated by field studies, there is no certainty
as to the actual levels of diflubenzuron to which nontarget
organisms may be exposed. In the model, there was a signi-
ficant trend towards reduction of hazard with reduction of
diflubenzuron usage. The data indicate that the use
of 12 oz. of diflubenzuron (A.I.) per season per acre
results in a linear increase over the use of 6 oz. in the
number of species subjected to hazardous levels of the
compound and in the frequency of adverse effects occurring
over a 5-year span. The use of diflubenzuron, if limited to
6 oz. per acre per season, may well represent a tolerable
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risk. A small number of aquatic species may be significantly
affected even at this application rate. However, the Agency
does not have sufficient data on the extent to which
diflubenzuron runoff into bodies of water occurs to make any
definite risk assessments.
III. Benefits
This section discusses the benefits of the proposed
use of diflubenzuron to control bollweevils on cotton.
This analysis is based on the "Preliminary Biological and
Economic Assessment of Diflubenzuron" which was prepared by
an Assessment Team composed of scientists and economists
from EPA, the U.S. Department of Agriculture, and cooperating
State agencies and land-grant universities. In order to
assess the benefits of the proposed use of diflubenzuron on
cotton, the Assessment Team had to estimate the range of
diflubenzuron use, the frequencies and rates of application,
the restrictions that might be placed on its use, and the
cost. Most assumptions are based on expert opinion and
reflect the best information available.
A. Biological Assessment
The boll weevil (Anthonomus grandis) infests
two-thirds of the cotton belt, i.e., the eastern two-thirds
of the Southwest region, the Delta region, and the Southeast
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region. The Southwest region includes Texas and Oklahoma;
the Delta region consists of Missouri, Arkansas, Tennessee,
Mississippi, Louisiana, and Kentucky; and the Southeast
region is comprised of Virginia, North Carolina, South
Carolina, Georgia, Florida, and Alabama.
The boll weevil is an insect causing extensive
damage to cotton in the areas listed above. A total of 7.3
million acres of cotton are infested with boll weevils. These
insects lay their eggs in cotton squares, which become food
sources for the immature weevil. Under favorable weather
conditions, weevil populations can increase 2.5 times a week.
Dry weather may drastically reduce this rate of increase.
The bollworm-budworm complex (Heliothis zea
and E. virescens) also causes very extensive damage to cotton
in the area defined. Other pests include thrips, aphids, cut-
worms, plant bugs, fleahoppers, and spider mites.
Cotton is currently treated at frequent
intervals from early spring to late summer to control both
boll weevils and the bollworm-budworm complex. The insecti-
cides used for control are predominantly organophosphorous
compounds.
Diflubenzuron does not kill adult boll
weevils but inhibits egg hatching and interferes with the
growth of the weevil larvae by inhibiting enzymes necessary
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for the synthesis of chitin. Unlike currently used insecti-
cides, diflubenzuron controls boll weevils without signifi-
cantly reducing the populations of most of the natural
v
parasites and predators of cotton pests. The boll weevil
appears early in the season at the pinhead-square stage of
development of the cotton. Therefore, in order to control
the boll weevil, pesticide application must begin early in
the season. On the other hand, use of pesticides to control
the bollworm-budworm complex does not begin until mid-season,
when these pests first become a problem. Diflubenzuron
which does not kill the bollworm-budworm complex, assists in
its control because it does not kill its natural predators
and parasites. In contrast, the organophosphate pesticide
regime currently used for cotton insect control destroys the
predators and parasites which attack the bollworm-budworm
complex. Therefore, greater quantities of pesticides are
required to control the bollworm-budworm complex when
alternative pesticides are used to control the boll weevil
than when diflubenzuron is used.
Predators and parasites of cotton pests
include big-eyed bugs (Geocoris spp.), lady beetles
(Hippodamia spp.), damsel bugs (Nubis spp.), and green
lacewings (Chrysopa spp.). Under natural conditions, these
insects frequently hold bollworm-budworm populations below
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economic loss thresholds early in the season. Thus, if
populations of these beneficial species can be preserved,
initial treatments of conventional insecticides for control
of the bollworm-budworm complex can be delayed. However, the
data available from field trials with diflubenzuron do not
conclusively show that predators and parasites will keep
bollworm-budworm populations below economic thresholds.
B. Economic Assessment
This economic analysis compares two insecticide
regimes: that which is currently used, and a combination of
diflubenzuron and currently-used insecticides. This analysis
is separated into a discussion of the benefits of the use of
diflubenzuron by individual farmers in boll weevil control,
and the impact of its use in the APHIS program to eradicate
boll weevils. The savings in control costs realized when
diflubenzuron is used represents the measure of the benefit
of the compound.
1. Boll Weevil Control
Because diflubenzuron is not currently
registered for use on cotton, several assumptions had to be
made to perform this analysis. These assumptions follow:
- Six 1-oz. applications of diflubenzuron
would be applied at 5- to 7-day intervals
beginnning when pinhead squares appear
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on the plant and terminating no later than
when the. bolls opened.
- Diflubenzuron will cost $3.00 per ounce.
- The Farm Enterprise Data Systems (FEDS)-X
budgets represent the cost of controlling
all cotton pests with currently-used insec-
ticides.
Because alternative pesticides are
less expensive and approximately as efficacious as diflu-
benzuron, economists estimated that diflubenzuron could
probably be used only where fields are infested by both boll
weevils and the bollworm-budworm complex and where current
control costs are high, i.e., $M5 or more per acre according
to the FEDS data. The extent of the acreage where these
conditions exist is given in Table III-1, Column 3- The
average cost for control of all insects is listed in Column
4 by FEDS area. These figures were obtained by increasing
the 1975 costs, the most recent available, by a composite
inflation factor derived from fourteen leading economic
indicators. This average cost includes the price of control-
ling spider mites, thrips, leafhoppers, and other cotton
pests, as well as boll weevils and the bollworm-budworm
complex.
17FEDS is a system of budgets and cost-estimating procedures
operated by the Economic Research Service of USDA in coopera-
tion with Oklahoma State University. It provides production
cost estimates and projections.
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Table III-1. Representative Boll Weevil and Heliothls Control Costs for the Currently-Used Insecticide Regime and the Dlflubenzuron Regime
Acreage
Region and State FEDS Area in Area
(1,000)
Acres)
(1) (2) (3)
Control Costs With
Currently Used Insecticides
All . , Boll Weevils^
Insects^' Weevil
and
: Heliothiac/
(1) (5) (6)
Value of
Heliothis^ Natural f/
Preda torsi
(7) (B)
Cost of
Hellothis
Control in
the Diflih
benzuron™
Regime
(9)
Cost of
Weevil and Savings from Use of
Heliothis Diflubenzuron Regjune'
Control in Per,
Difluben- acre—
zuron
Regirae
uo; (it)
Feasible Aggregate
Acreage ($1,000)
(1,000
acres)
(12) (13)
; Southeast
•: Alabama
Georgia
North Carolina
; South Carolina
1
Total
100-200
500
MOO
500
All
100
200
50.81
18.21
92.2M
80.89
85.71
51.73
101.97
11.91
39.80
90.12
79.03
61.71
19.80
92.79
18
18
30
30
21
18
21
23-91
21.80
60.12
19.03
10.00
28.80
71.79.
7.66
6.98
18.01
11.71
8.00
1.15
2.87
16.28
11.82
12.08
31.32
32.00
27.65
68.92
12.68
11.22
71.18
63-72
61.10
51.65
95.95
0
0
18.61
15.31
0.32
0
0
75.7
57.3
56.0
0
0
1,111.0
877.3
17.9
0
0
2,306.2
Delta
Lousiana
Mississippi
Total
Southwest
Texas
Total
TOTAL
100
100
600
600
289.0
712.5
1,001.5
55.5
55.9
111.1
1,513.1
65.00
68.29
16.62
53.16
58.18
62.11
11.96
53-16
15
15
21
21
13.18
17.11
17.96
29.16
16.11
22.16
10.78
17.68
26.77
21.98
7.18
11.78
51.67
51.38
38.08
38.78
3.51
7.76
3-88
11.68
289.0
712.5
1,001.5
55.5
55.9
111.
1,301.9
1,011.1
5.529.0
6,513-1
215.3
820.6
9,885.5
a/_ USDA, ERS, Firm Enterprise Data System, prepared in cooperation with Oklahoma State University, Stillwater, Oklahoma, 1975. All costs have been
inflated to 1977 price levels,
b/ Includes spidermites, thrips, leaf hoppers, etc. in addition to boll weevils and the bollwonn-budworm complex.
c7 Cost of currently used insecticides regime. Calculated by subtracting control costs for all Insects except boll weevils and the bollworm-budworm
complex from Column 1. The cost of controlling the other insects was obtained from the Assessment Team survey.
d/ Costs of insecticide, oil carrier, and application.
e/ Column 5 minus boll weevil control costs.
£/ Data from the Assessment Team Survey.
g/ Column 7 minus Column 8
h/ Column 9 plus the cost of diflubenzuron to control boll weevils.
I/ Column 5 minus Column 10.
Source: USDA/EPA/State Assessment Report
-------
The occurcence of insects other than
the boll weevil and the bollworm-budworm complex would make
the use of diflubenzuron impractical since organophosphates
would be needed to control these insects.
The Assessment Team conducted a survey
to determine the number of acres in which the simultaneous
infestation of boll weevils and insects other than the
bollworm-budworm complex would occur. Column 5 shows the
current cost of controlling cotton pests when these acres
are eliminated from consideration.
Applying organophosphates to control
the boll weevil costs $3.00 per treatment. This cost was
multiplied by the number of applications the survey showed
was needed in each region to generate the cost of controlling
boll weevils (Column 6). This figure was subtracted from
the cost of controlling boll weevils and the bollworm-budworm
complex (Column 5) to give the cost of controlling the
bollworm-budworm complex with the current insecticide regime
(Column 7).
The Assessment Team used this survey to
estimate where natural predators surviving diflubenzuron
treatments would be able to control bollworm-budworm popula-
tions. The "Value of Natural Predators" (Column 8) shows the
savings in the cost of organophosphate insecticides used to
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control the bollworm-budworm complex that would accrue when
diflubenzuron is used for boll weevil control. Values in
t
Column 8 were subtracted from the cost of bollworm-budworm
complex control using conventional insecticides (Column 7)
to give the cost of bollworm-budworm complex control in the
diflubenzuron regime (Column 9).
The cost of six diflubenzuron applications
was added to the cost of controlling the bollworm-budworm
complex, found in Column 9, to give the total cost of treating
cotton with insecticides when diflubenzuron is used (Column
10). When the diflubenzuron regime was more expensive than
currently used insecticides, a zero was entered in the
column.
"Feasible Acreage" (Column 12) represents
those areas where diflubenzuron is less expensive than its
alternatives. The feasible acreage was multiplied by
the savings per acre to give the aggregate savings (Column 13).
Analysts identified 1.3 million acres where the diflubenzuron
regime for suppression of boll weevil populations and
control of the bollworm-budworm complex would be used
because it is more cost-efficient than the current insecticide
regime (Column 12). These 1.3 million acres are approximately
18? of the cotton fields that are infested with boll weevils,
or 18% of the Southeast, 27% of the Delta, and 2% of the
Southwest.
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The total decrease in insect control costs
for all regions is roughly estimated at $9.9 million. Most
of this savings ($6.5 milion) would go to growers in the
Delta, with smaller portions realized by growers in
the Southeast ($2.3 million) and in the Southwest ($1.0
million). The weighted average of the savings per acre was
$7.80. In areas where diflubenzuron is likely to be used,
the average savings per acre ranged from $0.32 in North
Carolina to $18.64 in Georgia.
The Assessment Team did not associate use
of diflubenzuron with changes in crop yield. A number of
entomologists from cooperating State agencies and land
grant universities, however, believe that cotton yields
would increase because a reduction in the amount of organo-
phosphate insecticide used would allow the crop to mature
earlier, and beneficial insects would provide greater
control of the resistant strain of tobacco budworm.
2. Boll Weevil Eradication (APHIS)
USDA's Animal and Plant Health Inspection
Service (APHIS) is investigating the technical and economic
feasibility of instituting a national boll weevil eradication
program (USDA/EPA/State, 1978). They are now conducting
a trial eradication program in North Carolina. If a complete
beltwide eradication program is initiated, it will begin in
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this eastern area and gradually extend to contiguous affected
areas.
The currently proposed eradication tech-
nology integrates chemical, biological, and agricultural
control measures. Specifically, it contains the following
elements: destruction of the source of food supply for
boll weevils by defoliation and stalk destruction, use of
pheromone traps, release of sterile boll weevils, and use
of determinant strains of cotton.
USDA has proposed the use of diflubenzuron
to augment the present eradication strategy. Diflubenzuron,
through its specific mode of action, augments the effects
from the release of sterile insects in the eradication
program; that is, it does not kill mature adults, but
rather, inhibits the synthesis of chitin, which disrupts
body wall formation and causes larval death. At the same
time, it helps minimize flair-up in the bollworm-budworm
problem because the natural enemies of the bollworm-budworm
complex are not eliminated as they are with the use of
conventional insecticides. It is predicted that there could
be substantial cost savings in the eradication program if
diflubenzuron is utilized as the primary element of control.
-------
IV* Risk/Benefit Analysis of Alternative Courses of Action
A. Introduction
The foregoing review analyzes and summarizes infor-
mation on the risks and benefits of the use of diflubenzuron
on cotton. This section presents the basis for the Agency's
development of regulatory options, identifies the options
selected for consideration, and discusses the risks and
benefits of each of these options.
B. Basis for the Development of Regulatory Options
The Administrator may register a pesticide only if
he has first determined that its use will not pose an unrea-
sonable risk to man or the environment. This determination
must be made for each proposed use of a pesticide and must
take into account the risks and benefits associated with each
use. Even if the Administrator determines that a pesticide
will pose an unreasonable risk if used as proposed, before
denying registration he must consider whether prescribing
any restrictions on the pesticide's use will sufficiently
reduce the risks to warrant registration.
It is therefore apparent that the Administrator
must consider a spectrum of regulatory options for each use
of a pesticide. Approval of registration with no added
restriction and denial of registration are the regulatory
options at opposite ends of this spectrum. Between these
end points are options the Administrator may consider which
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approve registration but with prescribed restrictions and
*
conditions designed to reduce risks. For example, the
Administrator may specify the permissible sites for use, the
directions for use, the labeling language, and may require
that the pesticide be used by certified applicators only.
Under special circumstances, the Administrator
may conditionally register a pesticide when the full comple-
ment of data required for full registration under Section
3(c)(5) has not been submitted. The conditional registration
provision of FIFRA which is applicable to diflubenzuron is
Section 3(c)(7)(B) of FIFRA as amended in 1978. Diflubenzuron
falls within the purview of Section 3(c)(7)(B) because it is
currently registered for use as a pesticide to control gypsy
moths. This Section provides that the Administrator may
conditionally register additional uses of a currently
registered pesticide if he determines: first, that the
applicant has submitted satisfactory data pertaining to the
proposed additional use, and second, that the conditional
registration of the additional use will not significantly
increase the risk of any unreasonable adverse effect on the
environment. The conditional registration of the new use is
not permitted if the Administrator has issued a notice
stating that the pesticide or any of its ingredients meets
or exceeds the risk criteria enumerated in MO CFR 162.11 for
human dietary exposure or if the additional use of the
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pesticide involves a major food or feed crop or a minor food
or feed crop where an effective alternative pesticide which
does not meet or exceed the risk criteria is available.
If the Administrator makes these determinations and
grants conditional registration, the registrant is required
to generate and submit data required for full registration
within the time required by Section 3(c)(7)(B), or if such
time requirements are inapplicable, in the time specified by
the Administrator. Furthermore, the Administrator may
impose other terms and conditions that he deems appropriate.
For example, the Administrator may provide for the automatic
termination of the conditional registration after passage of
a specific interval of time or if data generated after
conditional registration has been granted indicate that the
risks caused by the registration are significantly greater
than initially anticipated. In addition, restrictions on
the use and method of application of the pesticide may be
imposed.
If the Administrator determines that the registrant
has failed to take appropriate steps toward fulfilling any
condition imposed, or that a condition has not been met
within the period prescribed for satisfying such a condition,
the Administrator shall issue a notice of intent to cancel
the conditional registration.
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C. Alternative Pesticides
The weighing of regulatory options includes
a consideration of the risks and benefits of the alternative
pesticides that are available for use. Alternative pesticides
currently used on cotton are, in descending order of predomi-
nance of use, methyl parathion, a combination of toxaphene
and methyl parathion, azinphosmethyl (Guthiori), monocrotophos
(Azodrin), and EPN. Table IV-1 summarizes the toxicological
hazards and the ^environmental effects of these compounds.
Methyl parathion and the combination of toxaphene and methyl
parathion, the most prevalently used pesticides for the
control of cotton pests, have a very high acute toxicity for
humans and are very toxic to fish, birds, and bees. The
other pesticides currently in use also have a high acute
toxicity for humans and also pose extremely high hazards to
various nontarget species.
Toxaphene is currently under RPAR review for
oncogenicity. The administration of toxaphene to two mouse
strains resulted in a statistically significant increase in
the incidence of hepatocarcinomas in both male and female
animals. A study with rats provided suggestive evidence for
the increased incidence of thyroid tumors with toxaphene
treatment. In addition, toxaphene has been shown to be far
more toxic to aquatic species than diflubenzuron and is
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Table IV-1. Alternate Chemicals for Cotton
RPAR ADI
Pesticide Candidate mg/kg/day
Methyl Parathion No 0.001
Toxaphene Yes 0.001
(with Methyl
Parathion)
Azinphosmethyl No 0.0025
Monocrotophos No 0.0003
EPN Yes None
Malathion No 0.02
Diflubenzuron Yes None
Acute
Toxicity
Category
Highly
Toxic
Highly
Toxic
Highly
Toxic
Highly
Toxic
Highly
Toxic
Moderately
Toxic
Slightly
Toxic
Environmental
Effects
Very Toxic to
Fish, Birds, and
Bees
Very Toxic to
Fish, Birds, and
Aquatic Inverte-
brates
Very Toxic to
Fish and Aquatic
Invertebrates
Very Toxic to
Birds, Aquatic
Invertebrates,
and Bees
Very Toxic to
Fish and Aquatic
Invertebrates
Very Toxic to
Fish, Aquatic
Invertebrates,
and Bees
Very Toxic to
Aquatic Inver-
Chetnical
Class
Organo-
phosphate
Organo-
chlorine
Organc-
phosphate
Organo-
phosphate
Organo-
phosphate
Organo-
phosphate
Organo-
chlorine
Use
Rate
Frequency
1-2 Ibs. AI/A
4-5 days
3 Ibs. AI/A
Weekly
intervals
0.25 lb. AI/A
as needed
0.75 lb, ,AI/A
as needed
1 lb. AI/A
5 days
1 lb. AI/A
as needed
O.Ob lb. AI/A
5-7 days
tebrates
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apparently far more persistent than diflubenzuron. The only
other alternative chemical currently under review in the
RPAR process is EPN, which has been shown to cause delayed
neurotoxic effects.
As shown in Table IV-1, the application rates for
the most predominantly used chemicals, i.e., methyl parathion
and the combination of toxaphene and methyl parathion, are
much higher than those for diflubenzuron. The remaining
alternative chemicals have application rates ranging from
1/4 pound/acre for azinphosmethyl to 1 pound/acre for EPN.
There is no restriction on the number of applications per
season for these six alternatives; a minimum of six applications
per season is generally required to obtain control.
The proposed application rate for diflubenzuron is
1 oz./aere with a maximum of six applications per season to
control boll weevils on cotton. Thus, the use of difluben-
zuron to replace methyl parathion, the combination of methyl
parathion and toxaphene, and the other alternatives which
have higher application rates, will achieve a signifi-
cant reduction in the total poundage of pesticides used in
cotton pest control. Most significantly, the use of difluben-
zuron to replace toxaphene will substantially diminish the
oncogenic hazard attributed to toxaphene for the human
population at risk.
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D. Regulatory Options Selected
From the range of possible conditions of registra-
tion, the Agency has formulated three regulatory options for
consideration in making the decision regarding registration.
In order of increasing restrictiveness, the options selected
are:
1) Conditionally register diflubenzuron until
January 1, 1984, under the condition that required studies
are submitted by January 1, 1983.
2) Conditionally register diflubenzuron until
January 1, 1984, with the data requirements set forth in
Option 1 and restrictions on use.
3) Deny the application for the registration of
diflubenzuron on cotton.
Granting full ("unconditional") registration of
diflubenzuron on cotton was not selected as an option
because some of the data supporting the petition for registration
are not sufficient to meet the Agency's requirements for
full registration under Section 3(c)(5) and therefore do not
warrant a balancing of the risks and benefits resulting from
long-term use. Specifically, the chronic feeding studies
submitted by the registrant suffer from severe deficiencies
in design which preclude a long-term risk assessment. The
Agency has also concluded that insufficient data exist for
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determining the long-term hazard to humans from methemoglobinemia
and sulfhemoglobinemia and ,the long-term hazard to aquatic
species that might result from runoff of diflubenzuron into
streams, rivers, estuaries, and other water bodies. Finally,
the Agency has determined that field studies substantiating
the efficacy and benefits of diflubenzuron are necessary
before a long-term risk/benefit analysis can be performed.
Under both options of conditional registration,
the Agency would require that more studies be submitted
by January 1, 1983. These include additional chronic
feeding studies in rats and mice, studies establishing
NOEL's for methemoglobinemia and sulfhemoglobinemia in an
appropriate species, monitoring data on the runoff of
diflubenzuron and its breakdown products, and field studies
on the benefits of diflubenzuron. Such field studies should
confirm the measurable benefit of diflubenzuron from an
increase in crop yield or a decrease in the costs of
controlling Heliothis spp. In addition, the registrant
would be required to develop a method for formulating the
pesticide that would reduce exposure to applicators.
Finally, the Agency may require the generation and submission
of any other data it determines are necessary to meet the
requirements for full registration.
Under Option 2 the following restrictions would
be imposed.
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1) Diflubenzuron Vould be classified for restricted
use by certified applicators only.
2) Applicators would be required to wear protective
clothing and respirators while mixing, loading, and applying
diflubenzuron.
3) Application of diflubenzuron would be prohibited
in the coastal zone of the Gulf States.
4) Application of diflubenzuron near any person or
dwelling would be prohibited. Use of flagmen in the field
would be prohibited.
5) Workers would be prohibited from entering
treated fields until the-day following application and the
spray deposit has dried.
6) Use of diflubenzuron would be limited to six
1-oz. applications/acre per season.
Under Option 2, the Agency could impose any other
restrictions on use which it determines are necessary to
prevent a significant increase in the risk of any unreasonable
adverse effects during the period of conditional registration.
E* Impact of Regulatory Options
1. Option 1. Conditionally register diflubenzuron for
use on cotton until January 1, 1964, under the
condition that required studies are submitted.
Choosing Option 1 would indicate that the Agency
had reached the following conclusions: first, the data
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pertaining to the use of diflubenzuron on cotton is satis-
factory for purposes of assessing the risks and benefits
resulting from this use over a period of four growing
seasons; second, conditional registration for this period
would not significantly increase the risk of unreasonable
adverse effects on humans or the environment; and third,
granting conditional registration of diflubenzuron would be
in the public interest.
There is considerable uncertainty as to whether
diflubenzuron is an oncogen. Section II of this document
contains a "worst case" risk assessment of the oncogenicity
of diflubenzuron that is based on the available data. This
assessment shows that the risks to the general population
from a lifetime exposure (70 years) to the compound would be
slight. The risk from using diflubenzuron for four growing
seasons would be decreased proportionately.
There is also uncertainty concerning the risks of
methemoglobinemia and sulfhemoglobinemia. Although an NOEL
for this effect has not been established for some of the
species of laboratory animals tested, the NOEL's available
and the lowest daily doses causing observed effects in all
species studied were considerably greater than the anticipated
exposure to humans. Thus, the Agency has concluded that the
available studies on methemoglobinemia and sulfhemoglobinemia
do not raise significant concern about the potential for
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adverse effects to humans exposed to diflubenzuron. However,
further study of these effects is necessary before the risks
to humans can be fully evaluated.
V
Conditionally registering diflubenzuron "for use
on cotton will result in some hazard to certain aquatic
invertebrates from diflubenzuron runoff. Monitoring studies
on the runoff of diflubenzuron and its metabolites, particularly
in areas of high usage and the Gulf States, are necessary
before the Agency can complete its assessment of risk.
Although use of diflubenzuron on cotton would
pose some risks, conditionally registering it would reduce
the overall risks posed by pesticides used on cotton.
Specifically, diflubenzuron would replace other pesticides
used to control boll weevils such as the organophosphates
and toxaphene, which appear to pose substantially greater
risks to man and the environment. Organophosphates are much
more acutely toxic to man and substantially more toxic to
aquatic species than diflubenzuron. NCI and CAG have
determined that toxpahene is a carcinogen. It is much
more toxic to aquatic species and more persistent in the
environment. Furthermore, the risks, as stated above, are
compounded by the fact that the application rates of the
alternates are much higher than the diflubenzuron application
i
rate. It is anticipated that the overall risks would be
reduced by the fact that diflubenzuron's use for boll
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weevil control will leave the populations of the beneficial
»
insects intact, thereby reducing the amount of organophosphate
pesticides required to control the bollworm-budworm complex.
Choosing Option 1 may also result in substantial
economic benefits. As noted previously, diflubenzuron does
not kill the natural predators of the bollworm-budworm
complex. Therefore, use of diflubenzuron for boll weevil
control instead of other pesticides that do kill natural
predators would reduce the amount of pesticides used to
control the bollworm-budworm complex. This reduction in pesticide
use could result in an overall saving of up to $10 million a
year for cotton growers.
Additional significant economic benefits may be
realized if diflubenzuron is used in the boll weevil era-
dication program.
2. Option 2. Conditionally register diflubenzuron
until January 1, 198M, with the same data requirements
set forth in Option 1 and restrictions on use.
Choosing this option would indicate that the
Agency had reached the conclusions described under Option 1
regarding the adequacy of the data, the level of risk, and
the serving of the public interest, providing that the
specified restrictions were imposed.
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The risks and benefits of this option are the same as
»
those for Option 1 except as modified by restrictions. These
restrictions and their impacts are described below.
a) Classify diflubenzuron as a restricted use
pesticide requiring certified applicators.
Under FIFRA, hazardous pesticides may be
classified for restricted use and may be limited to use only
by or under the direct supervision of certified applicators.
Certification programs are administered primarily by the
States. These programs use various methods to certify
applicators, after a determination that these applicators
are competent to use restricted .pesticides.
The Agency believes that the classification of
diflubenzuron for restricted use would ensure that the
material would be available only to competent persons.
Preventing untrained persons from using the pesticide would
significantly reduce the risk of human exposure due to
misuse or carelessness. Any marginal costs that might result
from restriction to certified applicators would be minimal
since programs to certify applicators are operational
in all States, there are many certified applicators,
and cotton pesticides are usually applied by certified
applicators.
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b) Require the use of protective clothing during
the mixing, loading, and application of diflu-
benzuron. Require respirators during mixing,
loading, and ground application of diflubenzuron.
Dermal exposure to diflubenzuron is of considerable
concern to the Agency. This exposure may arise from mixing and
loading, spills, maintenance of application equipment, ground spray
application, and aerial spray application (including wind drift).
The estimates of dermal and inhalation exposure
to mixers, loaders, and applicators set forth in Section II
were made with the assumption that 85* of the body would be
clothed and that respirators would not be worn. Accordingly,
it was assumed that the hands, forearms, neck, face, upper
chest, and hair would be exposed. Requiring protective
finely-woven overgarments, gloves, and a hat would leave
only 3.5% of the body exposed. Thus, these protective
measures would reduce the risk from dermal exposure by more
than 15%. Requiring a respirator designed to filter dust
particles and spray mists would reduce inhalation exposure
to very low levels. The Agency estimates that the economic
impact of these protective measures would be very small,
especially in light of the fact that certified applicators
ordinarily have protective clothing and respirators available.
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c) Prohibit application of diflubenzuron within
the coastal zone of the Gulf States.
k
The estuaries and waters of the Gulf Coast
contain-most of the aquatic species to which diflubenzuron
is very acutely toxic, including those aquatic species that
are most economically important. Therefore, the Agency
considers the risk to aquatic species from use of difluben-
zuron greatest in these waters. This zone includes: 1)
the area between the coastline and a parallel 3-mile line
from the coastline including any bays or estuaries that are
contiguous to the sea and 2) the area with 3 miles of
tidally-influenced waters including coastal salt marshes and
rivers. Prohibition of the application of diflubenzuron in
these areas is anticipated to reduce the amount of runoff
into waterways where aquatic species would be most at
risk.
d) Prohibit application of diflubenzuron near
persons and dwellings. Prohibit the use of
flagmen in the field.
Bystanders in the vicinity of the cotton fields
at the time of diflubenzuron application may be exposed to
levels of the chemical that could present a hazard to these
individuals. This option would require that the label
instructions state that the application of diflubenzuron
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near any person or dwellng is prohibited. The instructions
would also recommend that the product be applied at least
300 feet from dwellings when they are downwind. The use of
flagmen to mark the spray swath or pattern would be prohibited.
e) Prohibit workers from entering treated fields
until the day following application and the
spray deposit has dried.
Fieldworkers entering fields after application
may be dermally exposed to residues of diflubenzuron on the
surface of cotton leaves. Therefore, this option would
require that workers be prohibited from entering the fields
until the day following application and the spray deposit
has dried.
f) Limit use of diflubenzuron to six 1-oz. Al/acre
applications per season with 5- to 7-day intervals
between applications.
This option would require that the label
limit the use of diflubenzuron to a maximum of six 1-oz.
Al/acre applications per season with 5- to 7-day intervals
between applications. The label would also specify that
diflubenzuron may not be applied after the bolls have
opened.
Data available to the Agency indicate that
this regime will adequately control boll weevils. Diflu-
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benzuron applied to open bolls could contaminate the fiber,
seed, oil, and meal, rendering the crop unfit for use.
x ^
3. Option 3. Deny the application for the regis-
tration of diflubenzuron for use on cotton.
Choosing this option would mean that the Agency
has reached one or more of the following conclusions: 1)
data satisfactory for making a short-term risk/benefit
assessment have not been submitted, 2) conditional registration
of diflubenzuron on cotton for four growing seasons would
significantly increase the risk of unreasonable adverse
effects on humans or the environment even if the restrictions
in Option 2 were adopted, or 3) conditional registration is
not in the public interest.
Adopting this option would maintain the status
quo regarding pesticide use on this crop. Therefore the
option would eliminate the possibility of reducing the
overall risk from pesticide use on cotton. In addition,
this option would eliminate a potential benefit of $10
million per year for cotton growers and other possible
economic benefits resulting from the use of diflubenzuron in
a government-sponsored boll weevil eradication program.
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V. Recommended Option
The Agency has determined that Option 2 is the most
desirable course of action. It would allow conditional
registration of diflubenzuron's use on cotton for four
growing seasons. Diflubenzurbn would be classified for
restricted use and would be applied only by certified
applicators. These applicators would be required to wear
protective clothing and respirators. Reentry intervals and
protective measures for bystanders would be established. A
new method for formulating the pesticide, which would reduce
exposure to humans, would be required. The rate of applica-
tion would be limited to six l-oz./acre applications per
season. Application would be prohibited in the coastal zone
of the Gulf States.
This option also requires more studies including addi-
tional chronic feeding studies in rats and mice, monitoring
studies of diflubenzuron runoff, studies establishing the
NOEL's for methemoglobinemia and sulfhemoglobinemia in an
appropriate species, and field studies demonstrating the
benefits of diflubenzuron's use on cotton. The registrant
would also be required to develop a method for formulating
the pesticide that would reduce exposure to applicators.
These studies must be submitted by January 1, 1983, with
annual reports of progress. Additional restrictions and
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studies may be required before or during the period of
conditional registration if the Agency determines that they
are necessary.
Option 2 has been selected for several reasons. The data
submitted by the registrant are satisfactory for balancing
the risks and benefits resulting from the use of diflubenzuron
for four growing seasons. Although the chronic feeding
studies on mice and rats submitted by the registrant
suffer from severe deficiencies, the Agency believes that
they are sufficient for concluding that the use of difluben-
zuron for the term of the conditional registration will
pose very small risks to humans, particularly when the
specified restrictions on use are considered.
The Agency has determined that the conditional regis-
tration of diflubenzuron on cotton would not significantly
increase the risk of unreasonable adverse effects on man or
the environment. Diflubenzuron would replace pesticides
currently used for boll weevil control that appear to be
more toxic to humans and more harmful to the environment.
In addition, it would reduce the amount of pesticides
required to control both boll weevils and the bollworm-
budworm complex. As a consequence, conditional registration
of diflubenzuron for use on cotton would result in a reduction
of the overall risks posed by pesticides used on cotton.
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Moreover, use of diflubenzuron may result in economic
»
benefits to growers and potentially significant, although
unquantifiable, benefits in the proposed USDA eradication
program.
Finally, conditional registration of diflubenzuron
for four growing seasons is in the public interest because
its use is anticipated to result in an overall reduction in
the risks to humans and the environment from pesticide use
on cotton.
Option 1 was not chosen because the Agency anticipates
that the restrictions on use delineated in Option 2 will
significantly reduce the risks to humans and the environment
with only a minimal impact on the economic benefits. These
precautions are particularly appropriate in light of the
weaknesses of the risk data.
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APPENDIX-II-1
Thompson-Hayward's Consultant (Submission October 19, 1977)
Robert A. Squire, D.V.M., Statements
"Although the proportions of diflubenzuron absorbed
apparently do not increase proportionally with dosage,
greater amounts are nonetheless absorbed as dosage increases.
The case may be made that bioavailability and potential
toxicity will not increase proportionally with dose, and
since the compound is relatively non-toxic at all levels
tested, one may conclude that little toxicity could be
predicted at higher doses. However, it must be recognized
that the only way to confirm this assumption is to actually
test the compound at a maximum tolerated dose (MTD)."
Dr. Squire therefore, by this statement establishes
that the experiment was not done at the MTD.
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APPENDIX-II-2
STATEMENT OF Jack L. Radomski
(Thompson-Hayward1s Consultant)
(Submission of October 19, 197?)
Review of Chronic Toxicity Studies of
DU112307 (Diflubenzuron) and p-chloroniline
"I have the following comments in response to the
questions (1-7) asked:
1) It seems to me that both the rat and mouse study
were carried out at a dose well below the MTD. This
probably happened because of the erroneous judgement that
200 ppm had a toxic effect in the sub-acute feeding study.
2) I see no evidence that there was any significant
increase in tumor incidence due to the feeding of DU112307
to rats at dietary concentrations up to 160 ppm for 104
weeks.
3) Perhaps the focal liver necrosis observed was
fortuitous, since it did not show up in the chronic
experiment.
4) I see no evidences of a dose-dependent response or
an increased tumor incidence due to the feeding of DU112307
to mice in concentrations up to 50 ppm in the diet for 80
weeks. Statistical analyses were not performed.
5) In my opinion the absorption studies carried out
with DU112307 do not support the notion that there would be
no point to testing this substance at concentrations higher
than 50 to 200 ppm in the diet for the following reasons:
1) The studies were carried out in aqueous
suspension in gum tragacanth. I have been unable
to find out what the solubilities of this compound
are in organic solvents, but my experience has been
that gum tragacanth will tend to retard absorption
(being un-absorbed itself) particularly at the
larger doses. If the material is soluble in corn
oil, studies in corn oil solution may have given
quite different results. In addition, these aqueous
solutions are not analagous to the way the material
is fed in a diet. Usually the oil present in an
experimental diet tends to promote absorption of
oil soluble compounds.
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v
Apperson, C.S., C.H. Schaefer, and A.E. Colwell.. 1978.
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Bull, D.L. and G.W. Ivie. 1978. Fate of diflubenzuron
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Campt., D.D. 1977. Letter of November H, 1977, to Dr. C.
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Chitlik, L., and S. Biscardi. 1979. Memo of data validation.
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Dubin, I.N. (Medical College of Pennsylvania and Hospital).
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Huntingdon Research Center. April 24, 1974. DU112307 -
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Litton Bionetics, Inc. August 2, 1977a. Evaluation of
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-104-
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Philips-Duphar, B.V. March 1973. Acute toxicity studies
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environment.
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