Benomyl
Position Document 2/3
Special Pesticide Review Division
Office of Pesticide Programs
U.S. Environmental Protection Agency
August 22, 1979
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Benomyl: Position Document 2/3
CONTENTS
I. Introduction
A. Background
1. The Statute
2. The "RPAR" Process
3. Organization of this Position Document 2/3
B. Basis of the Rebuttable Presumption
1. Acute Toxicity:Hazard to Wildlife, Aquatic
Species
2. Mutagenic Effects in Multitest Systems
3. Other Chronic or Delayed Toxic Effects
a. Teratogenic Effects
b. Reduction in Spermatogenic Activity
4. Population Reductions in Nontarget Organisms
II. Risk Analysis and Assessment
A. Rebuttal Analysis
1. Rebuttals Relating to the Presumption of Acute
Toxicity: Hazard to Wildlife, Aquatic Species
a. Lack of Exposure Following Application
on Rice
b. Lack of Significant Adverse Effects
c. Lack of Fish Kills When Label Directions
Followed
d. Concentrations Less than 1/2 of the LC _
for Representative Organisms
e. Lack of Movement Downstream
2. Rebuttals Relating tp the Presumption of
Mutagenic Effects
a. Status of Mutagenicity Testing
b. Agency Perspective on Risk of Heritable
Genetic Effects
c. Chromosomal Effects: [Styles and Garner
(1974]
(i) Source and Composition of Test
Compound
(ii) Incorrect Cell Line Tested
(iii) Misinterpretation of Study
(iv) Insufficient Data
d. Chromosomal Effects: [DeBrander et al. (1976)]
e. Chromosomal Effects: [Seiler (1976)]
f. Chromosomal Effects: [Plants]
g. Chromosomal Effects: [Negative Studies
Cited in Rebuttal]
(i) Dassenoy and Meyer, 1973
(ii) Sherman et al., 1975
(iii) Hoffman and Peh, 1974
(iv) Mollet (1976)
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(v)
(vi)
(vii)
h.
i
j-
k.
Point
(i)
(ii)
Point
Point
Point
than
(1)
(ii)
(iii)
Siebert, Zimmerman and Lemperle (1970)
Seller (1977)
Conclusions Concerning Negative Studies
Cited by DuPont
Mutations: [Dassenoy and Meyer (1973)]
Inappropriate Test System
Inadequate Study
Mutations: [Seller (1972)]
Mutations: [Kappas (1976)]
Mutations: [Rebuttals Relating to More
One Study]
Repair Deficient Strain Used
Solvent Properties
Lack of Evidence for Incorporation into
DMA
1. Point Mutations: [Additional Studies Submitted
in Rebuttal]
(i) Haskell Laboratories (1977, 1978)
(ii) Shirashu, Mariya and Kato (1978)
(iii) Lamb and Lilly (abstract, 1973)
(iv) Conclusions Concerning Additional Studies
Submitted by duPont
Rebuttals Relating to the Presumption of
Teratogenicity
a. Negative Studies
b. Method of Administration
c. Validity of Test
d. Exposure
Rebuttals Relating to the Presumption of Reduction
in Spermatogenic Activity
a. New Test Available
b. Exposure
Rebuttals Relating to the
Reductions of Populations
Presumption Concerning
on Nontarget Organisms
Populations Occurs only
a. Reduction of Earthworm Populations Occurs only in
Certain Orchard Uses
b. Lack of Evidence of a "Significant" Local Population
Reduction
B. Information Submitted on Other Adverse Effects
C. Exposure Analysis
1. Dietary Exposure
2. Applicator Exposure
D. Risk Assessment
1. Aquatic Risk
2. Human Risk
a. Mutagenicity
(i) Point Mutations
(ii) Chromosome Breakage
(iii) Spindle Inhibition
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(a) Animal Studies (in vivo)
(b) Animal Studies (in vitro)
(c) Polymerization Studies (in vitro)
(d) Plant Studies
(e) Hazard Assessment
b. Teratogenicity
c. Spermatogenic Effects
III. Benefit Analysis
A. Introduction
B. Rice
1. Use Analysis
2. Economic Analysis
C. Other Uses
1. Soybeans
2. Fruit
3. Sugar Beets
i|. Citrus
5. Peanuts
6. Vegetables
7. Home Garden Use
IV. Risk - Benefit Analysis of Alternative Courses of Action
A. Basis for the Development of Options
B. Possible Alternate Courses of Action
1. Option 1: Continue Registration of the Use
2. Option 2: Continue the Registration of Benorayl
for the Use and Amend the Terms and Conditions
of Registration
a. Discussion of Proposal to Require Reduction of
Application Rates for Rice
b. Discussion of Proposed Requirement for
Additional Studies
(i) Additional Monitoring Study for Rice Use
(ii) Additional Gene Mutation Studies
c.. Discussion of Proposed Restrictions to Reduce
Applicator Exposure
(i) Require the Use of Protective Clothing
(ii) Require Water Soluble Packaging for
Packages 5 pounds and Larger
(iii) Require that Certain Uses be Classified for
Restricted Use
(iv) Require Label Warnings
3. Option 3: Cancel the Registrations
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Recommend Regulatory Action
A. All Uses
1. Require Label Warnings
2. Additional Mutagenicity Testing
B. Aerial Application
1, Water-soluble Packaging
2. Protective Clothing
C. Rice Use
1. Reduce Rate of Application
2. Monitoring Studies
D. Conclusions
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Acknowledgements
Writing Staff
Karen Flagstad, Writer/Editor, SPRD
Paul Parsons, Writer/Editor, SPRD
Esther Saito, Project Manager, SPRD, OPP
EPA Project Support Team
Cara Jablon, OGC
Chris Chaisson, HED, OPP
Harry Day, HED, OPP
John Leitzke, HED, OPP
George Beusch, HED
Harry Gaede, BFSD, OPP
Bernard Smale, BFSD, OPP
EPA Pesticide Chemical Review Committee (PCRC)
Marcia Williams, Chairperson, SPRD, OPP
Elizabeth L. Anderson, CAG, ORD
Richard N. Hill, OTS
Allen L. Jennings, 3RD, 0PM
Donna R. Kuroda, OHEE, ORD
John J. Neylan, PED, OE
David Menotti, OGC
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Benomyl Position Document 2/3
I. Introduction
Benomyl belongs to the benzimidazole class of fungicides.
It is a broad-spectrum systemic fungicide used mainly as a 50
percent wettable powder which is mixed with water for applica-
tion. Approximately 3 million pounds are currently used on 43
food crops and 41 ornamentals annually. Additional background
information was presented in the Rebuttable Presumption Against
Registration and Continued Registration of Pesticide Products
Containing Benomyl (EPA, 1977).
A. Background
1. The Statute
The Federal Insecticide, Fungicide, and Rodenti-
cide Act, as amended (FIFRA)(7 U.S.C. 136 et seq.) regulates
all pesticide products. Section 3(a) of FIFRA requires all
pesticide products to be registered by the Administrator
before they may be sold or distributed. Before the Adminis-
trator may register a pesticide, however, he must determine
that its use will not result in "unreasonable adverse
effects on the environment" [Section 3(c)(5)(D)], which is
defined by section 2(bb) of FIFRA to mean "any unreasonable
adverse effects to man or the environment, taking into
account the economic, social and environmental costs and
benefits of the use of any pesticide." In other words, any
registration decision must take into account both the risks
and the benefits from the use of the pesticide.
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Section 6(b) of FIFRA authorizes the Administrator
to issue a notice of intent to cancel the registration of a
pesticide or to change its classification if it appears to him
that the pesticide or its labeling "does not comply with the
provisions of [FIFRA] or, when used in accordance with wide-
spread and commonly recognized practice, generally causes
unreasonable adverse effects on the environment." Thus the
Administrator must cancel the registration of a pesticide when-
ever he determines that it no longer satisfies the statutory
standard for registration which requires, among other things,
that the pesticide not cause "unreasonable adverse effects on
the environment" [Section 3(c)(5)j. He may also cancel the
registration of a pesticide if its labeling does not comply
with the inisbranding provisions of FIFRA which require the
labeling to contain language "adequate to protect health and
the environment"[FIFRA 2(q)].
2. The "RPAR" Process
The Agency has designed a public process to gather
risk and benefit information about a suspect pesticide so that
the Administrator may make a balanced decision concerning it.
This process is known as the Rebuttable Presumption Against
Registration (RPAR) process; it is set out in the Code of
Federal Regulation (CFR) Title UO Section 162.11.
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In broad summary, these regulations describe
the various criteria for the determination of unreasonable
adverse effects, and provide that a RPAR shall arise if the
Agency determines that any of these criteria have been met.
Once the Agency issues such a rebuttable presumption, the
regulations provide an opportunity for registrants, appli-
cants, and interested persons to submit evidence to rebut
the presumption. These persons may also submit evidence
relating to the economic, social, and environmental benefits
of any use of the pesticide. If the presumptions of risk
are not rebutted, the evidence on the benefits of the
pesticide is then evaluated and considered along with the
information on the risks from the pesticide. The Agency
then analyzes various methods of reducing the amount of risk
from the pesticide together with their costs and determines
whether it can regulate the pesticide in such a manner so as
to strike the balance between risks and benefits. Striking
the balance may necessitate cancelling certain uses of the
pesticide.
3. Organization of Position Document 2/3
This Position Document contains five parts.
Part I is the introductory section. Part II contains an
evaluation of the risks associated with benomyl. It includes
the Agency's original RPAR decision, descriptions of relevant
experiments and field observations, Agency responses to RPAR
rebuttal comments, and the Agency's assessment of those
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risks in light of the comments received. Part III describes
the process which the Agency employed to gather and to
analyze use-specific information about the economic benefits
associated with benomyl. Part IV delineates the range of
regulatory options available to the Agency for the reduction
of unreasonable adverse effects, and explains the basis of
the Agency's selection of alternative courses of action for
each registered use of benomyl. Part V sets forth the
Agency's evaluation of the risks and benefits associated
with each use of benomyl and the Agency's evaluation of each
available regulatory option. The beneficial and adverse
impacts for each alternative course of action are evaluated,
and the rationale for the decision on each use is set
forth.
B. Basis of the Rebuttable Presumption
1. Acute Toxicity: Hazard to Wildlife, Aquatic
Species
40 CFR Section 162.11 (a)(3)(i)(B)(3) provides
that a rebuttable presumption shall arise if use of a
pesticide results in a maximum calculated concentration
after direct application to a 6-inch layer of water which is
more that one-half the acute LC™ for aquatic organisms
representative of the organisms likely to be exposed as
measured on test animals specified in the Registration
Guidelines.
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The calculated concentration of ben'omyl in water
(0.731* ppro) after its direct application to rice according
to label directions is greater than one-half the LC_0 for
bluegill, channel catfish, and Daphnia magna-. Accordingly,
the Agency issued a presumption against all registrations
and applications for registration of pesticide products
containing benomyl which are for direct application to water
(EPA, 1977).
2. Mutagenic Effects in Multitest Systems
40 CFR Section 162.11 (a)(3)(ii)(A) provides-
that a rebuttable presumption shall arise if a pesticide's
ingredients, metabolites, or degradation products induce
mutagenic effects, as determined by multitest evidence.
In Position Document 1, the Agency cited studies which
show that benorayl and its metabolite, MBC, produce somatic
chromosomal abnormalities, spindle-effects, and point (gene)
mutations in microbial and mammalian test systems and
studies which show that these compounds cause mutagenic
effects in plants. The Agency concluded that benomyl and
MBC are mutagenic and issued a RPAB against all pesticide
products containing benomyl (EPA, 1977).
3- Other Chronic or Delayed Toxic Effects
40 CFR Section 162.11 (a)(3)(ii)(B) provides
that a rebuttable- presumption shall arise if a pesticide
causes any other chronic or delayed toxic effect in test
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animals at a dosage that is substantially higher than that
to which humans can reasonably be anticipated to be exposed
when ample margins of safety are taken into account (EPA,
1977).
a. Teratogenic Effects
In Position Document 1, the Agency cited a study
by Schentenberg and Torchinski (1972), which reported
teratogenic effects when benomyl was orally administered (in
vegetable oil) to Wistar rats in doses up to 125 ng/kg/day
from day 1 to 20 or from day 7 to 15 of gestation. Torchinski
(1973) later induced teratogenic effects in Wistar rats by
administering benomyl (1^5 mg/kg) by gavage on day 12 of
gestation. The Agency did not presume against benomyl on
the basis of teratogenicity from dietary exposure because
the anticipated exposure from food intake alone is suffi-
ciently low that an adequate margin of safety exists for the
teratogenic effects observed in the Schentenberg and Torchinski
study.
However, the Agency concluded that the
amount of benorayl to which .women of childbearing age might
be' exposed is too high relative to the dose which has
produced teratogenic effects in animals. This conclusion
was based on the Agency's finding that- the amount of benomyl
absorbed dermally during home garden use would not provide
an adequate margin of safety relative to the no-observable-
effect level observed in the Schentenberg and Torchinski
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study. The Agency also noted that a. person might be exposed
to additional amounts of benomyl through inhalation or
ingestion. Therefore, the Agency concluded that all home
use pesticide products containing benornyl resulted in an
unacceptable risk of teratogenic effects and the Agency
issued a presumption against registration for all home
use products (EPA, 1977).
b. Reduction in Spermatogenic Activity
In Position Document 1, the Agency cited
acute and subacute oral studies which identify the testes as
a primary, target of benomyl. It also cited inhalation
toxicity studies which showed a reduction in the sperma-
togenic activity of rats and dogs which are exposed to
concentrations of benomyl of 33 mg/kg and 82 rag/kg, respec-
tively. In these studies no effects were observed at
concentrations of 7.5 mg/kg in rats and 32 tng/kg in dogs.
In Position Document 1, the Agency concluded that current
uses of benomyl would not result in residues of benomyl
on food crops which would pose an unreasonable risk of
reduction in spermatogenic activity. However,' applicators
would be exposed to much higher concentrations of benotayi
than the general public. The Agency concluded that there was
not an adequate margin of safety 'between the concentration
of benomyl which an applicator might inhale during 4 hours
of spraying and the dose which had produced a decrease
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in spennatogenic activity in animals. Accordingly, the
Agency issued a RPAR against all pesticide products con-
taining benornyl (EPA, 1977)
4. Population Reductions in Nontarget Organisms
40 CFR section 162.11 (a)(3)(ii)(C) provides
that a rebuttable presumption shall arise if a pesticide
can reasonably be anticipated to significantly reduce local,
regional, or national populations of nontarget organisms.
In Position Document 1 the Agency evaluated
several studies which indicate that benomyl is highly toxic
to earthworms. In studies by Stringer and Wright (1973)
earthworm populations were "virtually eliminated" in apple
orchard plots sprayed with benomyl. Stringer and Lyons
(1974) reported that the spraying of benomyl in orchards
reduced not only the number and biomass of all earthworm
species combined, but also those of each individual species.
Tomlin and Gore (1974) applied benomyl to pastures and
reduced earthworm populations by over 90 percent. Black and
Neely (1975) found that injection of benomyl into the
P
soil at a rate of 36 g/m reduced the populations of
earthworms by 80 percent. The Agency concluded that the use
of benomyl according to current label directions can rea-
sonably be expected to result in significant reductions in
local populations of earthworms. Accordingly, the Agency
issued a RPAR against pesticide products containing benomyl
which are registered for outdoor use (EPA, 1977).
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II. Risk Analysis and Assessment
A. Rebuttal Analysis
The Agency has received comments concerning the
effects which were the basis for the RPAR, namely, (1) acute
toxicity to aquatic organisms, (2) mutagenic effects, (3)
reproductive effects, and (4) reduction of earthworm popula-
tions. The Agency has reviewed the available studies again in
light of the rebuttal comments and has concluded that
comments addressing the acute toxicity to aquatic organisms
fail to rebut the presumptions and that benomyl continues to
exceed the risk criteria outlined in 40 CFR Section 162.11
for this effect. The rebuttal comments on mutagenic
effects support the Agency's position that benomyl or its
metabolite, MBC, is a spindle poison which interferes with
proper chromosome segregation during mitosis resulting in
non-disjunction. Although benomyl has been shewn to function
as a weak point mutagen in bacterial systems, there is
insufficient evidence currently available to sustain the
presumption that benomyl is a point mutagen in mammalian
systems. On the basis of additional information submitted
in rebuttal, the Agency has revised the estimation of human
exposure and has concluded that the presumption based on
reduction in spermatogenic activity has been rebutted for
all uses except aerial application. Rebuttal comments
questioned the adequacy of the teratology study on
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which the presumption was based. The Agency concluded that
sufficient doubt was raised about the study to require an
attempt at - replication. Preliminary results from the new
teratology study identify benomyl as a teratogen but do not
establish a no-observable-effect level (NOEL) (Kavlock, 1978).
The rebuttal comments provide evidence that significant
local reductions in populations of earthworms would not
occur from the use of benomyl. The Agency has concluded
that the non-target organism presumption has been rebutted.
1. Rebuttals Relating to the Presumption of
Acute Toxicity; Hazard to Wildlife, Aquatic
Species
The Agency calculated that application of
benomyl at a rate of up to 2 Ib/acre according to the label
directions for use against rice blast and stem rot results
in a concentration of 73^ ppb in a 6-inch layer of water.
This concentration is greater than one-half the acute LC
for bluegill, channel catfish, and Daphnia magna (Table II-l)
(EPA, 1977).
The Agency received comments on the presumption
that benomyl presents a hazard of acute toxicity to aquatic
organisms. The Agency has evaluated the rebuttal comments
and the additional information submitted and has concluded
that these rebuttals do not successfully rebut the presump-
tion that benomyl presents a hazard of acute toxicity to
aquatic species.
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Table II-1
The 96-hour LCc0 for Bluegill Sunfish and
Channel Catfish and the 48-hourd LC5Q for
Daphnia magna
Organism
LC
50
Source
Bluegill sunfish
Bluegill sunfish
.Bluegill sunfish
Bluegill sunfish
Channel catfish
Yolk sac
6-Day-old fry
12-Day-old fry
Daphnia magna
1.2 pra
2.6 ppm
0.2 ppm
0.4-0.5
8-10 ppb
.12 ppb
10 ppb
0.64 ppm *
McCann (1973)
Knott (1968)
McCann (1977)
McCann (1977)
Finley (1977)
Finley (1977)
Finley (1977)
Canton (1976)
e 48-hour LC5Q value
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a. Lack of Exposure Following Application on
Rice
DuPont [30000/23:1296] contended that the
Agency's presumption does not conform to the provisions of
40 CFR because benomyl is not registered for any uses
involving its direct application to water. They further
stated that no aquatic organisms are exposed to benomyl
after its application on rice.
The Agency rejects this rebuttal. The Agency
has issued a registration for the application of benomyl on
rice while the rice is growing in a permanent flood of about
4 to 6 inches of water. In monitoring studies of rice
fields, residues of benomyl of up to 3800 ppb in mud and 90
ppb in the water were found. Therefore, the benomyl applied
to rice plants must have reached the water in the rice
field. DuPont does not supply any evidence in the rebuttal
to support their contention that no aquatic organisms are
exposed to benomyl following its application on rice.
On the contrary, field monitoring studies performed by duPont
demonstrated that water containing toxic levels of benomyl
(20 to 50 ppb} is drained from rice fields into natural
bodies of water which contain aquatic organisms (Leitzke,
1978a).
b. Lack of Significant Adverse Effects
DuPont [30000/23:1296] contended that the
anticipated exposure to local, regional, or national popu-
lations of nontarget organisms to benomyl is not likely
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to result in any significant adverse effects on these
organisms when it is used according to the directions and
restrictions on the label.
The Agency rejects this rebuttal contention
because the available evidence indicates that adverse
effects on aquatic species have resulted. For example,
the rebuttor noted in a letter from Glen Whitney, a plant
pathologist [30000/23:1296] that water from the fields where
users have sprayed benomyl can and does kill catfish. The
rebuttor also conceded that there are five reports in their
own complaint files which associate the use of benomyl with
adverse effects on fish, Two of these reports involved
catfish kills which allegedly occurred when water from a
rice field treated with benomyl drained into an adjacent
catfish pond (Leitzke, 1978a).
c. Lack of Fish Kills When Label Directions
Followed
DuPont [30000/23:1296] contended that
their files and those of EPA show that no fish kills
have resulted from the use of benomyl when users followed
the directions on the label.
The Agency rejects this rebuttal contention
because it fails to take into account the fact that docu-
mented fish kills have occurred as a result of draining water
from rice fields into catfish farms. 40 CFR 162.11 (a)(6)(ii)
provides additional grounds for cancellation for any pesticide
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which does not meet or exceed the 162.11(a) risk criteria if
the Administrator determines that "when used in accordance
with widespread and commonly recognized practice the pesticide
generally causes unreasonable adverse effects on the envi-
ronment." Thus, the Agency is justified in taking action to
prevent fish kills from the common practice of draining
benomyl-containing water from rice fields into catfish
farms.
d. Concentrations Less Than One-Half of the
LC5Q for Representative Organisms
DuPont [30000/23:1296] contended that
a field monitoring study shows that since users do not
apply benomyl directly to water, the actual concentration of
benomyl in the water of the rice fields is considerably
lower than the theoretical concentration calculated by EPA
and does not exceed one-half of the LC for the represen-
tative organisms bluegill and Daphnia.
The Agency rejects this rebuttal argument
because the regulations state that the risk criteria are
exceeded by a maximum calculated concentration based on the
highest level of application allowed by the label. The one
study cited by duPont, "Monitoring Study: Benomyl applied to
flooded rice fields", entailed the application of benomyl at
0.5 Ib/acre with two applications at a rate half the maximum
allowed by the label. In the duPont studies, the highest
concentration of benomyl measured in the water of the rice
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fields was 90 ppb. After the water was drained from the
rice fields into natural bodies of water, the concentration
reached 50 ppb. These concentrations are greater than
one-half the LC5Q for catfish (4 to 6 ppb). This study
did not include any fields on which growers applied benorayl
at the maximum rates specified on the label, but only fields
where growers applied benorayl at the minimum rates on the
label. If it is assumed that the application of benomyl at
the maximum rate would result in concentrations of benomyl
residues twice those actually measured, then the maximum
calculated concentration would be .greater than one-half the
LC5Q for the bluegill, but not for Daphnia (Leitzke,
1978a).
e. Lack of Movement Downstream
DuPont [30000/23;1296] argued that the
field study mentioned above also shows that no significant
amount of benomyl moves from the rice fields into bodies of
water downstream.
The Agency rejects this argument since in
duPont's study samples of water discharged from rice fields
showed concentrations of benomyl up to 50 ppb. In duPont's
study, samples of water taken 16 to 30 days after the last
application of benomyl contained residues in concentrations
up to 40 ppb in main drainage ditches and in a canal 1.14
miles from a rice field in Louisiana (Leitzke, 1978a).
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2. Rebuttal Relating to the Presumption
of Mutagenic Effects
The Agency received comments on the Agency's
presumption that benomyl or its metabolite MBC present a
mutagenic hazard to man as both a point (gene) inutagen and a
non-disjunctive agent. The Agency has evaluated the rebut-
tals and the additional information submitted concerning
these effects and has determined that as of this date the
evidence is insufficient to conclude that either benomyl or
MBC reacts directly with DNA to cause point mutations or
chromosomal aberrations in mammalian systems. However, the
evidence cited by the Agency in Position Document 1 and
additional material submitted during rebuttal support the
presumption that benomyl or its metabolite MBC is a spindle
poison capable of inducing non-disjunction. Spindle
inhibition could result in aneuploidy or polyploidy; both
are chromosomal aberrations of concern.
In the following sections the Agency addresses
the arguments submitted in rebuttal. The first two sections
present general arguments concerning mutagenicity and the
Agency's response to these arguments. Additional sections
present studies cited as evidence to support the presumption,
rebuttal arguments on the Agency's evaluations of these
studies, the Agency's response to these arguments, and
additional studies submitted in rebuttal.
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a. The Status of Hutagenicity Testing
DuPont [30000/23:1296] questioned whether
EPA has the authority to regulate a mutagen and asserted
that the status of mutagenicity testing is too uncertain to
allow EPA to analyze the risk of a compound classified as a
mutagen. In support of this position, duPont contended that
the only published draft Guidelines (Federal Register, June
25, 1975) specify that the mutagenicity of a compound
shall be tested in live mammals. DuPont also claimed that
the Agency, in its assessment of the risk of mutagenicity,
has not considered the amount of exposure humans might
receive from benomyl.
The Agency does not accept this rebuttal
attempt. The Federal Insecticide, Fungicide, and Rodenticide
Act (FIFRA) confers authority on the Environmental Protection
Agency to regulate pesticides to assure that these substances
do not cause unreasonable adverse effects on the environment.
FIFRA does not limit the types of adverse effects which are
of concern. In exercising its authority, the Agency may
take regulatory action on the basis of any available test
data or other information which adequately delineates that
risk.
The Agency is not bound by a rigid defini-
tion of what constitutes adequate test data or what constitutes
an adequate risk analysis. There is nothing in FIFRA or in
the Agency's regulations which require a quantitative risk
assessment.
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The regulations do not require that a
detailed exposure analysis be made when an RPAR notice is
issued on the basis of mutagenicity. Since exposure can
occur from dermal and/or respiratory routes through the
application of the product in both home and agricultural
uses, as well as from residues in food, a connection has
been established between the use of the pesticide and the
resulting exposure to humans. The risk assessment in this
document will consider the levels of exposure for each use
in determining the resultant hazard.
b. Agency Perspective on Risk of Heritable
Genetic Effects
DuPont [30000/23:1296] argued that
studies cited by the Agency in Position Document 1 do not
demonstrate mutagenic action. Specifically they contended
that spindle inhibition, mitotic delay and metaphase arrest
are not chromosomal effects, that the bone marrow-micronucleus
test does not demonstrate heritable effects and that neither
micronucleus formation nor lagging chromosomes or bridges
are necessarily evidence of chromosome effects.
The Agency rejects this rebuttal argument.
The' Agency considers data from somatic and/or germinal test
systems in order to assess the potential of heritable
changes in the human genome. Several biochemical mechanisms
could result in such a heritable change in the genetic
material of germ cells. Studies are cited which indicate
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that benomyl, or its metabolite MBC, has the capacity to
inhibit cell division. Total inhibition of cell division
could result in polyploidy, and incomplete inhibition
may yield aneuploidy. In humans polyploid conceptuses are
lost as spontaneous abortions. Aneuploid conceptuses are
also greatly selected against during the fetal period, but
some can survive into postnatal life. Within this context
the Agency considers a mitotic poison to be a potential
mutagen.
c. Chromosomal Effects: [Styles and Garner
11974)3
Styles and Garner reported on tests
conducted in rats and in cultures of human, mouse, and
hamster cell lines. In these studies, benomyl and MBC
caused mitotic delay, a low incidence of chromosomal
breakage, and multi-nucleation in mammalian cells in cul-
ture. Metaphase arrest and micronuclei formation occurred in
bone marrow cells of rats treated with MBC; in addition
there was a low frequency of chromosomal breakage and
formation of anaphase bridges. Benomyl caused similar
abnormal arrangements when injected intraperitoneally but
not-'when given orally (EPA, 1977).
(i) Source and Composition of Test
Compound
The rebutter (duPont [30000/23:1296])
pointed out that the source of the ben-omyl used in the
Styles and Garner study was not duPont and that an analysis
of purity was not provided.
-18-
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The Agency rejects this rebuttal attempt.
The authors state that the source of the test material was
Plant Protection Ltd., Jealotts Hill Research Station,
Bracknell, Berkshire, Great Britain. Although no analysis of
purity was given, there is no evidence that the compound
tested is different from the benoiayl used in the U.S.
(Chaisson, 1978a).
(ii) Incorrect Cell Line Tested
DuPont [30000/23:1296] asserted that the
chromosomal breaks noted in Chang liver cells were actually
seen in Hela cells, and that the results were therefore
invalid because tumor cells do not exhibit normal microtubule-
membrane-spindle interactions.
The Agency rejects the rebutter's claim
that the results are invalid because the observations were
made with Hela cells. First of all, the Agency notes that
the report by the American Type Culture Collection (Catalogue
of Strains 11, 1975) indicates a high incidence of Hela cell
contamination in many cell lines including Chang liver
cells. Although identifying enzymatic electrophoretic
profiles were not provided to help discount the possibility
of such contamination with the cells in this study, the
results remain useful in assessing the mitotic interaction
potential. Transformed cells, as well as non-transformed
cells, contain a mitotic apparatus and are dependent upon
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spindle formation and function for cell division. The
spindle effects observed in the study indicat that benoniyl
and/or its metabolite MBC is capable of interfering with
the mitotic apparatus of a dividing cell. Thus, the results
with Hela cells in this study provide one piece of
evidence which indicates that benomyl and/or its metabolite
MBC are capable of adversely affecting the spindle mechanism
(Chaisson, 1978a).
(iii) Misinterpretation of Study
DuPont ([30000/23:1296]) asserted that
"the purpose of the study was to assess cytotoxicity, not
mutagenicity."
The Agency rejects this rebuttal attempt.
The Agency interprets this study as evidence of the oiitotic
effects of benomyl and related compounds. The nomenclature
applied to the investigation does not diminish the impact of
the evidence establishing that benomyl and/or its metabolite
interfere with the mitotic apparatus (Chaisson, 19?8a).
(iv) Insufficient Data
DuPont [30000/23:1296] claimed that there
are no data in the Styles and Garner study to support the
claim of chromosomal breakage or anaphase bridges.
The Agency accepts this rebuttal argument,
Insufficient data were presented by the authors in order
to judge the validity of the claim of chromosome breakage
-20-
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and anaphase bridges. Although Styles and Garner noted
a low incidence of these effects, there was no evidence
presented regarding their statistical significance (Chaisson,
1978a).
d. Chromosomal Effects: [DeBrander et al.
(1976)]
In Position Document 1, the Agency
cited a study by deBrander which demonstrated that benoniyl
and MBC induced multinucleation in mouse cells (EPA, 1977).
DuPont [30000/23:1296] claimed that the
Agency misinterpreted this study because the actual event
which occurred was "multimicronucleation", a phenomenon
which is very different from "multinucleation".
The Agency rejects the rebuttal conten-
tion that this study does not show an adverse effect
attributable to benomyl. The Agency agrees that the effect
observed by deBrander is more correctly identified as
"multimicronucleation", a response induced by anti-tubulins.
The deBrander test was designed to test for mitotic spindle
inhibition alone rather than both chromosomal damage and
non-disjunction, which are measured in the classical
micronucleus test. Spindle-effects are considered by the
Agency to be mutagenic effects, [refer to part (b) of this
section (Chaisson, 1978a)].
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e. Chromosomal Effects: [Seller (1976)]
Seller found that both benorayl and MBC
produced dose-related mutagenic effects in the micronucleus
test in mice. In addition, lagging chromosomes, anaphase
bridges, unequally distributed chromosomes, and tripolar
anaphases appeared in mitotic bone marrow cells of treated
animals, whereas none of these effects was noted in control
cells. The author concluded that the main action of benomyl
was the inhibition of the raitotic spindle, which may predis-
pose the chromosomes to nondisjunctional errors (EPA, 1977).
DuPont [30000/23:1296] asserted that
Seiler (1976) reported that micronuclei were produced in
mouse bone marrow only when benomyl or MBC was administered
orally in gum arabic, a solvent known to produce cytogenetic
abnormalities, but not when administered intraperitoneally in
DMSO. DuPont submitted a report entitled "Study of the
Mutagenic Effects of Gum Arabic" (Stanford, 1972) which does
show some adverse effects on metaphase chromosomes when rats
are fed 5'.0 g/kg and 2.5 g/kg gum arabic.
The Agency rejects this rebuttal con-
tention because there is no evidence that the amount of gum
arabic used as a carrier would account for all of the
results noted by Seller. The absence of inicronuclear
effects after intraperitoneal administration can be explained
by the lack of solubility of MBC at pH7, which prevented
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efficient uptake of the test compound from the peritoneum.
The results and conclusions of the Seller paper remain
relevant and the Agency considers this study evidence of
benornyl's potential to cause non-disjun.ction (Chaisson,
1978a).
f. Chromosomal Effects: [Plants]
In Position Document 1, the Agency cited
two studies in which chromosomal aberrations were induced in
higher plants as evidence that benomyl and MBC are mutagens.
DuPont attempted to rebut the presumption
on the basis that "none of EPA's published or draft Guidelines
include any reference to mutagenicity assay using plants."
The Agency rejects this rebuttal attempt.
The purpose of the Guidelines is to provide guidance regarding
the test requirements necessary to achieve registration
of pesticides. As duPont noted, the Guidelines do not limit
the tests, that can be used either for registration or RPAR
purposes. Addendum III to the Proposed Guidelines published
August 22, 1978 states that positive results in test systems
not included in the battery of tests should not be rejected
as evidence of mutagenicity (Chaisson:1978a).
-23-
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g. Chromosomal Effects [Negative Studies
Cited in Rebuttal]
DuPont [_JOOO/23:1296 cited the following
studies as evidence that benomyl or MBC does not cause
chromosomal effects. Three of these studies were cited by the
Agency in Position Document 1; the other three were submitted
by DuPont in rebuttal.
(i) Dassenoy and Meyer, 1973
In the Dassenoy and Meyer study, cited in
Position Document 1, the authors found that benomyl gave a
negative response with Allium cepa. The Agency accepts this
as a valid negative study.
(ii) Sherman et al., 1975
The Sherman et al. (1975) dominant lethal
study in rats was cited in the RPAR position document. The
Agency accepts this as a valid negative study.
(iii) Hoffman and Pen, 1974
A review of the dominant lethal study by
Hoffman and Pen (1974) was contained within the WHO Pesticide
Residues Series as cited in the RPAR position document. The
Agency does not accept the negative conclusions of this
study because the data were not submitted for evaluation.
The Agency notes, however, that the results of this study
are consistent with those of Sherman.
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(iv) Mollett 1976
Mortality, somatic recombination and
induced mutations were measured in Drosophila rnelanogaster
larvae fed at sub-toxic levels (0.5 to 26 mM of MBC in a
live yeast suspension). The results showed no significant
increase in male mosaic and spot frequency when compared
with the corresponding control level. No somatic recom-
bination and mutation were detected. The Agency considers
this study valid supporting evidence that direct genetic
alteration in higher organisms via recombination is not
evident. The Agency notes that this author did not exclude
the possibility of an effect on somatic cells of the larvae.
(v) Siebert, Zimmerman, and Lemperle, 1970
P
Benomyl, as Benlate , was tested in Strain
D4 of Saccharomyces cerevisias for induction of gene conver-
sion at concentrations as high as 1000 ppm. Benomyl showed
no activity in this system. The Agency accepts this study
as valid and considers it to be supporting evidence that
benoiayl's mechanism of action is not via direct chromosomal
damage. This test system is sensitive for a recombination
mechanism in which breaks and genetic transfer to the
homologous chromosome occur. The Agency does not accept
duPont's interpretation that the results of this study imply
that no chromosomal effect (including aneuploidy) can occur.
Aneuplcidy would be caused by a mitotic interference.
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(vi) Seller, 1977
Thi \ dominant lethal study in rodents with
MBC is cited in the Seiler study. However, no details
or data were published or submitted to the Agency for
evaluation. The Agency does not accept this citation as
evidence of a negative result until an evaluation is possible.
(vii) Conclusions Concerning Negative Studies
Cited by duPont
In summary, the negative studies in Drosophila,
Saccharomyces, and Allium support the hypothesis that benomyl
does not produce direct chromosomal damage. The Agency
does not accept these studies as evidence that chromosomal
effects such as aneuploidy could not result from other mecha-
nisms such as spindle interference.
The negative dominant lethal studies discussed
above support the conclusion that benomyl does not cause
direct chromosomal damage. This evidence is not sufficient
to dismiss the possibility that genetic effects can be
produced in mammalian cells via another mechanism such as
mitotic interruption and spindle interference (Chaisson,
1978a).
h. Point Mutations: [Dassenoy and Meyer (1973)3
In Position Document 1, the Agency cited
as evidence of point mutation a study by Dassenoy and Meyer
in which auxotrophic mutants were isolated at rates signifi-
cantly greater than the control rate when conidia of Fusarium
oxysporum were treated with benomyl (EPA, 1977).
-26-
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(i) Inappropriate Test System
DuPont:[30000/23:1296] contended that
mutagenicity assays for fungicides should not be run in
fungi since biocidal compounds should not be evaluated with
respect to human safety in the organisms that they are
selected to control.
The Agency rejects this rebuttal attempt.
The results in Fusarium are not the only factor being con-
sidered in the evaluation of human risk. Fungi are useful
as test species because of their sensitivity. Although fungi
and higher eucaryotic forms display differences in the
mitotic process, tests on fungal species give relevant
evidence of the mechanism of action of a test compound such
as benomyl (Chaisson, 1978a).
(ii) Inadequate Study
The rebutters (duPont:[30000/23:1296] and
Sisler:[30000/23:1716]) contended that point mutational
activity was net demonstrated in the Dassenoy and Meyer
study. They cited the probability of selection of pre-existing
benomyl resistant mutants or non-disjunction events as
possible alternative explanations of the effects observed.
In addition, duPont [30000/23:1296] cited the genetic
instability of Fusarium, the lack of identification of the
carrier solvent, and the absence of back mutations as
reasons for disqualifying this study.
-27-
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The Agency accepts the rebuttal argument
that poin' mutational activity was not demonstrated unequiv-
ocally in this study. Although the control rate of 0/100,000
spontaneous revertants suggests a minimal probability of
genetic instability, tolerant strain selection is possible.
Therefore, the Agency has concluded that the evidence could
be interpreted as either selection of background mutants or
a non-disjunction event (Chaisson, 1978a).
i. Point Mutations: [Seiler (1972)]
In Position Document 1, the Agency
cited a study by Seiler which demonstrated that MBC and
other benziinidazoles induce base-substitution mutations as
detected by the Ames test without metabolic activation.
Salmonella typhimurium strains his GU6 and TA1530 were used.
In addition, forward mutations were induced in Salmonella
strain LT-2 (EPA, 1977).
DuPont [30000/23:1296] cited several
omissions in the study such as the failure to explain the
protocol completely, the failure to define the number of
experiments, replicate dishes or variations, the failure to
describe the zone of activity in the spot test, and the
failure to show a dose response relationship.
The Agency accepts the rebuttal argument
that the Seiler study had certain shortcomings which limit
the utility of this study for determining the potential point
mutagenic risk attributed to benomyl (Chaisson, 1978a).
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j. Point Mutations: [Kappas (1976)1
In Position Document 1, the Agency
cited a study by Kappas which demonstrated that benomyl
induces base-substitution mutations without metabolic
activation in Salmonella typhimurium strain TA 1535.
Reverse mutations were induced in Escherichia coli strain
WP2 uvrA, which is excision-deficient but not in strain WP2
which is excision proficient. The authors concluded that
benomyl may be incorporated into DNA but that the abnormal
base is removed in repair-proficient strains but not in
repair-deficient strains (EPA, 1977).
DuPont [30000/23] argued that "this
result, lacking a dose response relationship, cannot stand
alone as evidence for point mutational activity and requires
confirmation in a thorough standard plant incorporation
assay."
The Agency accepts the rebuttal argument
that this study alone is inadequate to determine if benomyl
is a point mutagen and that the point mutational activity
needs confirmation through additional tests (Chaisson, 1978a)
k. Point Mutations: [Rebuttals Relating
to More Than One Study]
(i) Repair Deficient Strain Used
The rebutter (duPont [30000/23:1296])
objected to the use of results obtained in repair deficient
strains because human cells possess repair mechanisms.
-29-
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The Agency rejects this rebuttal argument.
Tests in repair deficient strains are acceptable models
for mutagen detection. The-absence of repair capacity
increases the sensitivity of the test system and maximizes
the opportunity to detect induced mutations. Such systems
are valuable tools in assessing the intrinsic mutagenic
capacity of the compound even though direct quantitative
extrapolation to repair competent cells is not possible
(Chaisson, 1978a).
(ii) Solvent Properties
DuPont [3000/23:1296] asserted that
the positive results obtained when DMSO was used as a
solvent must be regarded with suspicion. The unusual
solvent properties of DMSO (e.g. enhancement of chemical
reactions, alteration of biological molecules, and alteration
of cellular permeability) are sufficient grounds for question-
ing the validity of positive 'results.
The A-gency rejects this rebuttal argument.
Although DMSO can affect the in vitro culture conditions or
membrane integrity, the use of this dispersal agent does not
invalidate the results of the study. DMSO is a generally
recognized carrier, and in the absence of data to suggest a
biochemical problem which could influence the expression of
mutagenic potential, this vehicle is considered an appropriate
solvent.
-30-
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(iii) Lack Q£.Evidence for Incorporation
J.II w U L/ iM ri
DuPont [3000/23:1296] contended that
"there is no evidence that benomyl or MBC are incorporated
into DMA." They contended that the Seiler papers (1972, 1975)
cited by the Agency in Position Document 1 do not present an
unequivocal demonstration that benzimidazole is incorporated
into DNA.
The Agency accepts this rebuttal contention
The Agency cited the Seiler studies as supporting evidence
for the Kappas study. However, the Agency agrees that these
results with benzimidazole do not prove that similar activity
would be found with benomyl or MBC (Chaisson, 1978a).
1. Point Mutations: [Additional Studies Sub-
mitted in Rebuttal]
DuPont has submitted the following studies
as evidence that benomyl, MBC, or 5-HBC do not cause
point mutations. Some of these studies were also cited by
Sisler as evidence of lack of point mutation potential of
MBC.
(i) Haskell Laboratories, 1977,1978
Benomyl was tested in Salmonella typhi-
murium strains TA 1535, TA 100, TA 1537, TA 1538 and TA
98 with and without metabolic activation. The technical
grade was tested at doses of 200 to 10,000 ug/plate.
Positive results were found" in the frame-shift detection
-31-
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strain with metabolic activation. Benotnyl, analytical
grade, was retested twice in the same strains at concentra-
tions ranging from 1000 to 15,000 ug/plate. Weakly positive
results were shown in TA 1537, a frame-shift tester with
metabolic activation. In another retest, benomyl as Benlate
wettable powder gave negative results at 100 to 750 ug/plate
with activation and 100 to 1200 ug/plate without activation.
Benomyl, 99 percent pure, was tested in doses from 40 to 500
ug/plate, with only strain TA 1537 without activation
showing borderline positive results. The major animal
metabolite, 5 HBC, was tested in this system at doses of 200
to 20,000 ug/plate with negative results.
The Agency has validated these studies
and has concluded that the positive result obtained with the
technics! grade benomyl may have been due to a contaminant.
Since some trials were run at concentrations far below those
which are cytotoxic, these data are not accepted as proof
that benorayl cannot induce point mutations (Chaisson,
1978a).
(ii) Shirashu, Mariya, and Kato, 1978
Benorayl was tested in the recozabinant
assay with B^ subtilis strains M45 and H17. No inhibition
zones were noted. The Agency accepts this study as valid.
-32-
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Benorayl at a concentration of 5 to 1QOO
ug/plate was tested in Salmonella typhimurium TA 1535, TA
1537, TA 1538, TA 98, and TA 100 .and Escherichia coli WP2
with and without metabolic activation. Benorayl induced no
increase in mutation in any strain in any test condition.
The Agency has evaluated this study and considers the
results valid.
Benomyl was administered by gastric intu-
bation of two doses (200 or 1000 mg/kg) , and S. ^ghiraurium
G *J6 was inoculated intraperitoneally to male ICR mice. .
(Total doses were 400 or 2000 mg/kg). The results of this
host-mediated assay were negative. The Agency has evaluated
this study and considers the results valid (Chaisson, 19?8a),
(iii) Lamb and Lilly (Abstract) 1973
p
Benomyl, as Benlate , was fed to male
fruit flies (D. melanogaster) at a dosage of approximately
14 ug in a sex-linked recessive lethal test. No evidence of
mutagenic potential was presented, and. the Agency agrees
with the authors that this submission is not adequate to
support a conclusion of a negative result since the data
base was limited and incomplete (Chaisson, 1978a).
(iv) Conclusion Concerning Additional
Studies Submitted by duPont.
In summary, the Agency considers the
valid negative mutagenicity studies as supportive evidence
that the mechanism of action of benomyl is not via point
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mutations. However, these negative studies cannot be construed
as conclusive evidence of the inability of benornyl or its
metabolites to produce point mutations.
3. Rebuttals Relating to the Presumption of
Teratogenicity
In Position Document 1, the Agency cited
'three studies in which benomyl was subjected to terato-
genicity testing. Teratogenic effects were noted when
Schtenberg and Torchinski administered benomyl orally to
Wistar rats. Torchinski also induced teratogenic effects
in Wistar rats by administering benomyl by gavage.
However, Sherman _e_t a]L. did not observe any teratogenic
effects when Charles River-CD rats were administered
benomyl in their diet. The Agency concluded that the
anticipated dermal exposure to benomyl for women of child
'bearing age is high relative to the dose which produced
teratogenic effects in animals; it issued a RPAR for
pesticide products containing benomyl which are registered
for home use (EPA, 1977).
a. Negative Studies
DuPont [30000/23:1296] attempted to rebut
the presumption by citing animal studies which showed
evidence that neither benomyl nor MBC is a teratogen.
The Agency rejects this rebuttal attempt.
The negative teratogenic potential in Charles River-CD
strain of rats does not rebut the positive findings in the
-------
Wistar strain. As stated in Position Document 1, the Agency
used the more sensitive strain to determine the teratogenic
potential of benomyl. In addition, although duPont submitted
a negative teratogenic study for MBC, Delatour et al. have
reported positive results (Delatour, 1976).
b. Method of Administration
The rebuttor (duPont:[30000/23:1296])
claimed that the intubation method used by Schentenberg and
Torchinski is a questionable method of administration
because the metabolic capacity of the animal is overwhelmed
and acute effects are expressed.
The Agency rejects this rebuttal argument.
Based on accepted scientific principals expressed in the
Proposed Guidelines, intubation is an appropriate method of
administration and is probably the most common method used
in teratology testing (Burnam, 1978a).
c. Validity of Test
The rebuttor (duPont:[30000/23:1296])
questioned the validity of the Schentenberg and Torchinski
study claiming the design was inadequate, concurrent controls
were lacking, the number of fetuses examined was insuffient,
and details concerning the type or number of abnormalities per
fetuses were lacking.
The Agency rejects this rebuttal attempt.
Although the study was flawed in many of the aspects listed
by duPcnt, serious adverse fetal effects which were not
evident at 62.5 mg/kg/ day were noted, in a dose-dependent
manner, at 125, 250, and 500 mg/kg/day. The additional work
-35-
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by Torchinski (1973) provided confirmatory evidence that
benomyl has the potential to produce teratogenic or fetotoxic
effects. In view of the deficiencies in the Russian studies,
the Agency contracted for a teratology study in an attempt
to verify the results observed by Shentenberg and Torchinski
(Burnam, 19?8a).
d. Exposure
The rebuttor (duPont:30000/23:1296) claimed
that the assumptions used by the Agency to calculate possible
exposure were grossly in error. Experiment-derived exposure
data for home garden use was submitted.
The Agency has now reviewed exposure and
dermal absorption data and has revised its original estimates
The new estimates of exposure and risk will be discussed in
parts C and D of this Section.
4. Rebuttals Relating to the Presumption
of Reduction in Spermatogenic Activity
In Position Document 1, the Agency cited
studies which identify the testes as a primary target
of benomyl. These included acute and subacute oral studies
in which benomyl administered by intubation to rats
induced testicular damage. Inhalation toxicity studies
showed a reduction in spermatogenic activity in rats and
dogs (EPA, 1977).
-36-
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a. New Test Available
The rebutter (duPont:[30000/23:1296])
has not questioned the validity of the studies on which
the presumption was based. However, DuPont contends that
a more recent inhalation toxicity study submitted in
rebuttal, which showed a higher no-observable-effect
level in Charles River rats, should be used to determine the
no-observable-effect level.
The Agency rejects the duPont contention
that the most recent test data should be used to establish a
no-observable-effect level. No evidence was provided which
negates the results of the earlier inhalation toxicity
study in Charles River rats; therefore, the Agency will use
7.5 mg/kg as the no-observable-effect level (Burnain, 19?8b).
b. Exposure
The rebutter (duPont:30000/23:1296) claims
that the assumptions used by the Agency to calculate possible
exposure to applicators were grossly in error.
The Agency has now reviewed exposure and
dermal absorption data and has revised its original esti-
mates. The new estimates of exposure and risk will be
discussed in parts C and D of this Section.
5. Rebuttals Relating to the Presumptions Concerning
Reductions of Populations on Nontarget Organisms
In Position Document 1 , the Agency cited
studies which demonstrated that benomyl and MBC are toxic
to earthworms. The Agency concluded that under normal use
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benomyl can reasonably be expected to result in significant
reductions of local earthworm populations and issued an
RPAR against pesticide products containing benomyl which
are registered for outdoor use (EPA, 1977).
a. Jteducition of Earthworm Populations
Parallelism only in Certain Orchard Uses
DuPont [30000/23:1296] contended that
reductions in earthworm populations under actual conditions
of use have been observed only in certain orchard uses. They
also stated that there is no evidence that reduction in
earthworm populations occurs when benomyl is used on field or
row crops, and that there is no evidence that earthworms are
beneficial organisms.
The Agency rejects this rebuttal contention.
The levels of benomyl tested in non-orchard sites (Black,
1975 and Tomlin, 1974) were not greatly in excess of normal
field use rates. Although there is no data on the effect of
benomyl on earthworm populations in field or row crops,
studies by Stringer clearly demonstrate that benomyl is
toxic to Lumbricus terrestris (Leitzke, 1978a). Furthermore
the argument that earthworms are not beneficial is not
germane to the issue of population reduction by benomyl.
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b. Lack of Evidence gf a "Significant"
LiUua.1 FuuuJ-d.Lj.Oti Kcu.uCL.LOn
DuPont (30000/23:1296) argued that granted
the fact that benomyl is toxic to earthworms, "significant"
local, regional, or national population reductions of
earthworms will not occur.
The Agency accepts this rebuttal argument
that "significant" population reductions in earthworms would
not occur from the use of benomyl. The Agency has concluded,
in the light of all available information about this effect,
that concern is not warranted because (1) the toxic effects
are limited to the site of application because benomyl and
its metabolites are essentially immobile in soil and do not
leach or move significantly from the site of application;
(2) the impact of the loss of earthworms will not extend
into adjacent areas because earthworm movement during a year
is restricted to only a few meters; (3) the population of
the earthworms can rebound to normal a few years after the
termination of benomyl treatment since benomyl does not
completely eliminate the earthworm population; and (4) the
sites of application are reasonably limited, in that entire
regions or massive areas of the country are not involved in
a regimen of benomyl treatment.
B. Information Submitted on Other Adverse 'Effects
The Agency solicited further information bearing on
the likelihood and significance of potential reactions between
benomyl or its metabolites and nitrites to form N-nitroso com-
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pounds. This information was solicited because two papers
by Borzsonyi et al. suggested the possible formation of
N-nitroso compounds and induction of lymphosarcomas in Swiss
mice (EPA, 1977).
DuPont [30000/23:1296] submitted experimental data
on their attempt to synthesize a sample of the N-nitroso
derivative of MBC for use as an analytical standard.
Studies designed to investigate possible reaction of MBC
with nitrite under conditions simulating the mammalian
stomach were also submitted.
The Agency notes that based on a level of sensitivity
of 7000 ppm, the evidence seems to indicate that nitroso
formation did not occur; however, levels below this figure
could be present, since the N-nitroso derivative may act
as a neutral compound and be insoluble in dilute acid; hence
the extraction procedures may not recover the N-nitroso
compound if it is formed. Therefore, despite duPont's
extensive experimentation, the question of N-nitroso
formation remains open and unresolved (Day, 1978).
C. Exposure Analysis
DuPont [30000/23:1296] and the U.S. Department of
Agriculture (Walla, 1978) provided data on patterns of
benomyl use which the Agency has used both to identify the
populations exposed to benomyl and to estimate the extent of
the populations' exposure. In addition, duPont submitted
new dermal absorption studies [30,000/23:1296].
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1. Dietary Exposure
In Position Document 1, the Agency assumed
that the average person would consume 0.03 mg/kg of benomyl
or its benziniidazole metabolites per day. This amount
represents the maximum dietary exposure which would result
when residues of benomyl are present in individual foods
at tolerance levels and when all foods are assumed to be
treated. The Agency now believes that 0.02 ing/kg/day of
benomyl or its benzimidazole metabolites is a more realistic
estimate of dietary exposure (Johnson, 1979). This figure
was derived from consideration of the actual percentage of
crops treated with benomyl. MBC may also be present on
crops which have been treated with thiophanate-methyl;
however, 40 CFR section 180.3 (d)(10) prohibits the benzi- .
midazole moiety to exceed the highest established tolerance
for a pesticide having this metabolite.
2. Applicator Exposure
The Agency's major concern focuses on the
level of exposure of applicators to benomyl. The estimate
of exposure for benomyl application is based on the follow-
ing four studies. The Agency used the model developed
by Jegier (1964) to estimate the exposure of mixer/loaders
and the pilot for aerial application. The duPont data
submitted in rebuttal [30000/23:1296] were used to estimate
exposure from hand spraying during home use. Studies by
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Wolfe and Durham (1967) were used to estimate exposure for
other uses. The USDA/State/EPA Benomyl Assessment Team
report was used to estimate the daily and yearly exposures.
The values calculated from these models are summarized in
Table II-2 and Appendix I.
The applicators with the greatest potential
for exposure to benorayl are the mixer/loaders for aerial
application and the applicators using airblast equipment.
The total body dose of benomyl each of these applicators
would receive was calculated assuming complete uptake for
the oral and inhalation exposure and almost no exposure
through dermal absorption.
In Position Document 1 , because no data on dermal
absorption of benomyl were available, the Agency assumed
that 10 percent of benomyl that came in contact with the
skin would be absorbed. DuPont [30000/23:1296] submitted a
study on the effect of time and dose on the absorption of
benomyl through rat skin. This study was reviewed by the
Agency and was used to estimate the total total body dose of
benomyl from dermal exposure (Appendix II).
-42-
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Table 11-2. Use Patterns and Applicator Exposure
EXPOSURE KG/KG
TTSE
1.
2.
3.
4.
.5.
6.
7.
8.
9.
I/ 1/
PATTERN POPULATION HRS/DAY
Rice (aerial)
Pilots
Mixer/Loader
Flaggers
Soybeans (aerial)
Pilots
Mixer/Loader
Flaggers
Stone Fruits (aerial)
Pilots
Mixer/Leader
Flaggers
Stone Fruits (airblast)
Comrcercial
Private
Graoe's (aerial)
Pilots
Mixer/Loader
Flaggers
Cranes (airblast)
Commercial
Private
Berries (aerial)
Pilot
Loaders/Flaggres
Berries (airblast)
Commercial
Berries (ground)
80
200
300
200
500
700
120
300
240
60
3000
20
40
50
60
40
15
20
-.28
3
6
6
3
6
6
3
6
6
7
8
3
8
8
3
4
3
5
3
2/
DERMAL/HR
0.02
1.8
0.19
0.02
1.8
0.19
0.02
1.8
0.19
0.5
0.05
0.02
1.8
0.19
0.5
0.5
0.02
1.8
0.5
2/
INHALATION/DAY
0.003
0.24
0.00024
0.003
0.24
0.00024
0.003
0.24
0.00024
0.005
0.006
0.003
0.32
0.00032
0.002
0.003
0.003
0.2
0.002
Private
210
0.05
0.003
-------
Table II-2. Use Patterns and Applicator Exposure (Continued)
/JSE
10.
LI.
L2
13.
W.
PATTERN POPULATION
Fruit Crops (aerial)
Pilots
Mixer/Loader
Flaggers
Fruit Croos (airblast)
Private 21
Citrus (airblast)
Applicators
Homeowner
Turf
Ornamentals 534
Vegetables
All Types
20
40
50
,000
714
75
,000
1515
HRS/DAY.
3
8
8
6
8
0.5
0.5
2
EXPOSURE MG/KG
2/ 2/
DERMAL/KR ' INHALATION/DAY
0.02 0.003
1.8 0.32
0.19 0.00032
0.5 0.004
0.5 0.006
0.04 0.0002
0.04 0.0002
0.04 0.0006
I/ ESTIMATED USDA/STATE/EPA BENOMYL ASSESSMENT TEAM REPORT
ll SEE APPENDIX I
-------
The greatest amount of dermal exposure would
occur during during the mixing and loading of the product
for aerial application; however, no more than 0.006 mg/kg
body weight would be absorbed during an 8 hour day at this
exposure level (refer to Appendix II). A proportion of this
maximum value depending on how many hours per day the
applicator worked was added to the mixer/loader total body
doses; for all other activities the amount absorbed is too
low to be mathematically significant and will be discounted.
The total body doses calculated for benomyl are contained in
Table II-3.
D. Risk Assessment
The RPAR criteria for risk reflect a concern with
a pesticide's potential to produce adverse effects on man
and the environment. The frequency and severity of the
anticipated adverse effects vary with the extent of exposure
to the pesticide, and the anticipated exposure is dependent
on the pesticide's mode of use.
1. Aquatic Risk
As a result of its use on rice, benomyl poses
a significant hazard to natural, local populations of channel
catfish and other Ictalurids; it can also cause a decrease in
fish-food organisms from chronic exposure to its longer-lived
metabolite MBC, thus posing an indirect hazard to other fish
as well. As a result of possible drift from multiple aerial
-U3-
-------
Table II.-3- Total Body Dose Calculations
USE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
I/
POPULATION HRS/Day
Rice (aerial)
Pilots
M/L
Fl.
Soybeans (aerial)
Pilots
M/L
Fl.
80
200
300
200
500
700
3
6
6
3
6
6
2/
DERMAL
0
0.004
0
0
0.004
0
TOTAL BODY
DOSF MG/KG/DAY
3/ 4/
INHALATION TOTAL
0.003
0.24
0.00024
0.003
0.24
0.00024
0.023
0.264
0.020
0.023
0.264
0.020
Stone Fruits (aerial)
Pilots
M/L
Fl.
Stone Fruits (air
Comnercial
Private
Grapes (aerial)
Pilots
M/L
Fl.
Grapes (air blast)
Commercial
Private
Berries (aerial)
Pilots
M/L
Berries
120
300
240
blast)
60
3000
20
40
50
60
40
15
20
3
6
6
7
8
3
8
8
3
4
3
5
0
0.004
,0
0
0
0
0.006
0
0
0
0
0.004
0.003
0.24
0.00024
0.005
0.006
0.003
0.32
0.00032
0.002
0.003
0.003
0.2
0.023
0.264
0.020
0.025
0.026
0.023
0.346
0.020
0.022
0.023
0.023
0.224
Commercial
28
0.002
0.022
-------
Table II-3. Tbtal Body Dose Calculations (Continued)
USE
11. Berries (ground)
Private
12. Fruit Crops (air
Pilots
M/L
Fl.
13. Fruit Crops (air
Private
V
POPULATION
210
blast)
20
40
50
blast)
21,000
V
HRS/Day
3
3
8
8
6
TOTAL BODY DOSE MG/KG/D^
2/
DERMAL
0
0
0.006
0
0
3/
INHALATION
0.0003
0.003
0.32
0.00032
0.004
4/
TOTAL
0.020
0.023
0.346
0.020
0.024
14. Wheat (E) (aerial)
Pilots
M/L
Fl.
15. Homeowner
10
10
10
75
3
7
7
0.05
0
0.005
0
0
0.003
0.28
0.0003
0.0002
0.023
0.305
0.020
0.020
I/ ESTIMATED USDA/STATE/EPA BENOMYL ASSESSMENT TEAM REPORT.
2/ SEE APPENDIX I.
3/ ASSUMES 100% OF RESPIRED BENOMYL.
4/ TOTAL REPRESENTS THE SUM OF THE DERMAL AND INHALATION PLUS THE ASSUMED ORAL DOSE (BACKGH
RESIDUE OF BENOMYL AT TOLERANCE LEVELS =0.02 MG/KG/DAY). TOTAL BODY DOSE ASSUMES COMPLETE
UPTAKE FOR ORAL AND INHALATION EXPOSURE AND LIMITED DERMAL ABSORPTION AS OUTLINED IN APPEN-
DIX II.
-------
applications on berries and orchards, benomyl also poses a
potential threat to sensitive aquatic species (Leitzke,
1978b). On the basis of currently available information,
the Agency is unable to quantify this risk; however, actual
evidence of fish kills exists only when the product was
misused.
2. Human Risk
The risk assessment for benomyl is based on
the premise chat a pesticide product which has been shown
to induce teratogenic, spermatogenic, or mutagenic effects in
test species will present a hazard to man— which will vary
depending on the extent of exposure.
I/ The Agency has not yet developed a standard procedure
for defining mutagenic risk in quantitative terms. At the
present time, much attention is being focused on developing
a battery of test systems and other data that are predictive
of mutagenic risk in humans. Until such time as more
quantitative methods and procedures for risk estimation
are developed for each mutagenic endpoint of concern, the
Agency will evaluate each mutagenic chemical on a case by
case basis, taking into account all available test data.
The approach taken by the Agency will of necessity be
conservative in order to assure that man and the environment
are protected from the risk of "unreasonable adverse effects"
through the action of mutagenic agents. The evolving nature
of methodology in the field of mutageniclty testing dictates
that the Agency will revise its risk estimation procedure
for future chemicals under evaluation as superior risk
predictive models and other relevant information become
available. As well, the Agency will revise its risk estimates
for chemicals which have previously been subjected to risk
assessments if additional more relevant test data and other
predictive information are developed.
-------
a. Mutagenicity
(i) Point Mutations
The Agency presumed that benomyl or its
metabolite MBC presents a mutagenic hazard to humans by
producing point (gene) mutations. The data sources
used in the original Position Document for point mutations
are summarized in Table II-4. Work by Sailer (1973, 1975)
suggests that benzimidazoles can be incorporated into the
DNA of J5. coli. The similarity of the chemical structures
of MBC and benomyl to the purines suggested to Sailer that
these compounds may act as base analogues.
Further support for the hypothesis that
benomyl and/or MBC can cause point mutations is
provided by the demonstration that these compounds induced
forward mutations in Fusariuin (Dassenoy) as well as by
positive test results in several strains of bacteria.
However, test results in the microbial systems were con-
flicting or not completely reproducible and did not show
dose response. Specific rebuttals on these tests are
discussed in the Rebuttal Analysis section of this document
Fahrig and Seiler (1979) have also demon-
strated coat color changes in mice treated in utero with
MBC. Their findings are less than definitive, but are
consistent with a point mutation mechanism. The utility of
the mouse spot test is still being investigated by experts
in the field of mutagenicity.
-45-
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Table II-'I. Studies Cited for Evidence of Point Mutations
Test Model
Compound
Citation
Fusarium oxysporum
auxotrophic mutants
Salmonella typhimurium
his GH6, TA1530, TA1534, Lt-2
TA1531, TA1532, his D3052
(without ativation)
E.Coli WP2, WP2 (uvrA),
CM61 (uvrAlexA)
S. typhiinurium TA1534, TA1538
incorporation studies with E. Coli
incorporation studies with E. Coli
S. typhimurium spot test, host mediated.
his G46 and TA1530, TA1950
(no mutations for benorayl
doubtful for MBC)
*Mouse cytogenetic spot test
benorayl, MBC
MBC, benzimidazolea
benomyl
benzimidazoles
benzimidazoles
benomyl, MBC
MBC
Dassenoy and Meyerj
1973
Seiler, J.P., 1972
Kappas, Green,
Bridges et al., 1976
Seiler, J.P., 1972
Seiler, J.P., 1973
Ficsor, G. and Bordas,
1978
Fahrig, R. and
Seilerr, J. P.
unpublished
*Not cited in Position Document 1.
-------
The available information on the point
mutagenesis of benomyl and MBC does not clearly demonstrate
a risk of point mutations to humans, and hence the presump-
tion that benomyl and/or its metabolites meet or exceed the
criteria for point mutation has been successfully rebutted.
However, various studies suggest that benomyl may cause
point mutagenesis and the Agency is not assured of the
safety of benomyl with regard to this mechanism, particularly
in light of the fact that test data are available from only
a selected number of the available test systems designed to
detect point mutational events. Due to the limited data
base and the equivocal results achieved in the test systems
which were studied, the Agency will be requesting that
additional studies be performed to assess the point rnutagenic
potential of benomyl and metabolites should registration be
continued.
(ii) Chromosome Breakage
The Agency's presumption of mutagenic
risk from chromosomal effects was summarized in the PD 1 on
benomyl. Reports of chromosome-breaking activity were
cited in references on higher plants (Zutshi and Kaul,
1975) and on mammalian cells in culture and in vivo (Styles
and Garner, 1974). Other studies were unable to confirm
these observations. Thus the status of the ability of
benomyl or its-metabolites to break eukaryotic chromosomes
has not been adequately resolved.
-46-
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(iii) Spindle Inhibition
The other chromosomal mutational effect
which has been observed with benorayl or its metabolite MBC
deals with the inhibition of the nuclear division spindle.
There is substantial evidence that benoinyl and/or its
metabolite MBC are spindle inhibitors capable of inducing
the failure of chromosomes to separate properly at anaphase.
This type of effect may- lead to numerical chromosomal
mutations such as aneuploidy, which occurs when one or a few
chromosomes are gained or lost during cell division, or
polyploidy, which occurs when the whole spindle is inhibited
and there is a failure of nuclear division. Both aneuploidy
and polyploidy have been produced in plant and animal
cells by physical and chemical agents which block the
spindle (Brachet, 1957; Burnhara, 1962).
The consistency of effects observed in a
variety of test systems, namely in vivo mammalian studies
(Styles and Garner, 1974; Seiler, 1976), mammalian cells in
culture (Styles and Garner,1974; deBrander et al., 1976),
biochemical studies on fungi (Hammerschlag and Sisler, 1973;
Richmond and Phillips, 1975, Kappas et al., 1974; Davidse,
1973; Bignaini et al. 1977), rat tubulin in vitro (Seiler,
1977; deBrander et al., 1976), and plant cytological and
genetic studies (Zutshi and Kaul, 1975; Boyle, 1973) support
the mechanism of spindle inhibition for benomyl and/or
MBC.
-47-
-------
Recent studies (Wilson et al., 197^; Davidse and
Flack, 1977) have provided information concerning the process of
inhibition of the nuclear division spindle fibers at the molecular
level. The nuclear division spindle fibers are composed of
raicrotubules, which are protein fibers within cells that are
essential for many structural and functional activities. Micro-
tubules consist of polymerized protein subunits called tubulin.
Various drugs which block cells in raetaphase appear to act by
binding to tubulin monomers and preventing their polymerization
into microtubules. MBC, colchicine, and several other chemicals
appear to bind at the same specific site on tubulin.
(a) Animal Studies (in vivo)
Styles and Garner (197*0 demonstrated that
benomyl and MBC (1000 rag/kg, intraperitoneally) and MBC (1000
mg/kg, perorally) produced metaphase arrest in rat bone marrow
cells. As well, in studies designed to measure micronucleus
production and blood levels following peroral administration of
two daily doses of 50, 100, 500 and 1000 rng/kg MBC to mice,
Seller (1976) found that 100, 500, and 1000 mg/kg doses of MBC
produced dose-dependent increases in the number of cells contain-
ing micronuclei. At a dose level of 50 mg/kg, the fraction of
cells containing micronuclei remained at background level. The
blood values of MBC following 100 and 500 mg/kg peroral admini-
stration reached peak values of 12 and 22 ug/ml, respectively.
The administration of 100 and 500 mg/kg doses of MBC intraperi-
-------
toneally did not result in increased micronucleus production and
gave similar blood levels of MBC (8ug/ml).
Seiler (1976) made other observations to
elucidate the mechanism of micronucleus formation in MBC-
treated animals. Many micronuclei in erythrocyte precursors
were rather large, suggesting the presence of whole rather
than broken chromosomes. Seiler noted that other investigators
had observed similar phenomena with anti-mitotics such as
colchicine and vinblastine.
Also, configurations suggesting spindle
inhibition were noted in nucleated bone marrow cells from
rats treated orally with MBC; these included increased
metaphase frequency, lagging chromosomal material, unequal
distribution of chromatin during division, and multipolar
mitoses.
Lastly, Seiler treated Chinese hamsters
with MBC (two daily doses of 1000 mg/kg administered orally)
and analyzed bone marrow cells arrested in metaphase for
chromosome aberrations; no evidence of chromosome breakage
was found.
(b) Animal studies (in vitro)
Culture metaphase arrest was found in Chang
liver cells exposed to 2 ug/ml MBC, but not in cells exposed
to 0.02 mg/ml (Styles and Gardner, 1974). In addition
benomyl and MBC produced micronucleation in the MO mouse
cell line used by DeBrabander at 10 ug/ml but not at 1
ug/ml.
-49-
-------
(c) Polymerization Studies (in vitro)
In vitro studies on the inhibition of
tubulin polymerization support the hypothesis that benorayl
and/or MBC function as a spindle poison. Seller (1977)
demonstrated that polymerization of rat neurotubulin was
not inhibited by about 2 ug/ml MBC,— but 25 and 100 percent
inhibition occurred at about 10 and 20 ug/ail respectively.
Consistent with these observations, Davidse (cited by
Seiler, 1977) did not observe any inhibition of mammalian
tubulin polymerization at about 2 ug/ml. Likewise, DeBrander
et al. (1976) found that polymerization of rat neurotubulin
was inhibited about 20 percent by 5 ug/ml MBC.
(d) Plant Studies
Numerous cytological studies show that
benomyl or its metabolites inhibit the nuclear spindle
in fungal cells, and a similar interpretation has been
given to the sectoring phenomenon produced in heterozygous
fungal clones by these chemicals. Cytological studies
in higher plants have produced less substantive information,
but certain observations are consistent with the spindle
inhibition; these observations include increased mitotic
2J Molar concentrations in the papers have been roughly
converted to ug/ml using the following approximation
5 X 10~5 M MBC = 10 ug/ml.
-50-
-------
index, shortening of metaphase chromosomes, some dispersion
of metaphase chromosomes instead of organization into a
spindle, and lagging chromosomal material during anaphase.
Also, c-mitoses (colchicine-like metaphase arrest) have
(R^
been observed in higher plant cells after Benlatevn;
administration; this action is similar to the observations
in mammalian cells. Davidse and Flack (1977) demonstrated
that polymerization of fungal tubulin could be inhibited by MBC
and that it was more susceptible to inhibition of polymeri-
zation by MBC than was mammalian tubulin.
(e) Hazard Assessment
We have strong evidence in many test
systems across several phyla (both kingdoms) pointing to the
ability of benomyl or its metabolites to interfere with the
cell division spindle. Furthermore, there are two lines of
evidence which indicate that these chemical metabolites may
reach the mammalian gonad. The first demonstrates that MBC,
and benomyl to a lesser degree, may damage testicular
structure in rats (Styles and Garner, 197U) . Further
evidence is provided by studies by Gardiner (1974), who
demonstrated that radioactive benomyl reaches the testes of
rats and dogs. Thus, there is an adequate basis for a
qualitative presumption against benomyl for initiating
potentially heritable spindle effects.
-51-
-------
Lacking at this point is definitive evidence
that benomyl induces these effects in germ cells. However,
some preliminary results from a promising new test system
indicate that MBC may produce effects which may lead to
chromosomal nondisjunction in germ cells (Tates, 1978). On
the basis of all the above information humans exposed to high
levels of benomyl may be at risk from the induction of
spindle effects. At the present time the Agency does not
have the means to estimate the degree of risk from such
exposures. However, the existing data are not adequate to
demonstrate the existence of a significant risk from these
effects at current exposure levels. At such time that the
Agency does have the means it may elect to reevaluate this
assessment.
b. Teratogenicity
The teratology presumption was based on a study
by Schentenberg and Torchinski in which benomyl was embryo-
cidal and teratogenic at doses of 125 mg/kg/day and greater
but not at 62.5 ing/kg/day in Wistar rats. The Agency
concluded that the Schentenberg study should be confirmed
under more controlled circumstances and sponsored a study to
replicate the protocol of the Schentenberg study. The
results from the EPA sponsored study showed that benomyl was
teratogenic at 62.5 mg/kg/day, the lowest dose tested.
Therefore, the Agency does not have a no-observable-effect-
-52-
-------
level (NOEL) with which to conduct a teratology risk assess-
ment. Both EPA and duPont are conducting studies
designed to establish a NOEL and to examine the relationship
between methods of administration in producing teratogenic
effects. These studies are scheduled for completion
by November 1979; at that time the Agency will reevaluate
the teratogenic risk of benomyl to humans. Until the Agency
obtains the information from these studies, the assumption
will be made that the NOEL for teratogenic effects would
not be less than the NOEL for spermatogenic effects, the
most sensitive effect level for benomyl, and will use
7.5 mg/kg/day to calculate a preliminary margin of safety
for teratogenicity. These margins of safety range from
21 for mixer/loaders to 380 the background level from
dietary exposure. The teratogenic risk of benomyl will be
reevaluated if necessary between the proposed decision and
the final decision if the studies indicate significant
changes in the NOEL.
c. Spermatogenic Effects
The Agency has no epidemiologic evidence indi-
cating that exposure to benomyl might result in depressed
sperm counts. Therefore, the Agency has utilized 7.5 rag/kg,
the NOEL observed in rats, which are the most sensitive
species tested, to determine the margin of safety for
spermatogenic effects. The calculated margins of safety
range from 21 for mixer/loaders to 380 the background level
from dietary exposure.
-53-
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III. Benefit Analysis
A. Introduction
This section of the position document was derived
from An Analysis of Current Benomyl Uses; Their Benefit, the
Role of Alternatives, and Importance to Agriculture from
Changes in Benomyl Use Patterns, Part II, which was prepared
by the USDA/State/SPA Benomyl Assessment Team. After
completing the risk analysis, the Agency determined that
it was possible to reduce the risk to humans could be
reduced to an acceptable level by methods short of cancellation
The human risk analyses indicated that the use of benomyl
does not pose significant risks to the general population
through dietary exposure, and applicators are at risk only
as the result of inhalation during mixing and loading
operation.
The Agency determined that the additional restric-
tions necessary to reduce risk would cause inconsequential
changes in the use patterns or benefits. A quantitative
economic analysis was not performed because it was assumed
that the use of the chemical demonstrated its benefits. A
general discussion of benorayl uses compriseded in this
section. A more detailed discussion of the uses listed in
Table III-l is presented in the Assessment team report.
The Agency determined that the hazard to aquatic
organisms could not be reduced to an acceptable level short
-54-
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Table III-l. Eencmyl Fungicide Use in the United States - 1977—^
Crop . Total Lbs A.I. Used
Soybeans 761,000
Stone Fruits 344,000
Rice 299,250
Citrus 259,694
Bananas 200,000
Grapes 173,692
Peanuts 158,500
Vegetables 151,500
Turf 150,000
Ornamentals 125,000
Pecans 100,000
Apples 96,184
Berries (Strawberries, Blueberries, Raspberries) 71,911
Almonds • 63,800
Sugarcane 26,COO
Sugar-Beets 13,500
Wheat^' 11,150
Mushrooms 11,034
Pears 10,928
Elm 7,010
Mangoes 6,000
Avocados 1,628
Pineapples 1,506
Macadaniia Nuts 100
I/ Total use based on actual surveys conducted by the Senomyl Assessment
Team.
2/ Benomyl use data based on 1976 season due to the extreme drought in
1977.
-------
Table III-2. Rice Acreage by State and Total U.S. (1975,
1976, 1977, and 1978)
State
Arkansas
California
Louisiana
Mississippi
Missouri
Texas
Total U.S.
1975
Acres
898
525
658
171
18
548
2,818 2
1976
Harvested (
847
399
568.
144
14
508
,480 2,
1977
1,000
837
308
475
111
17
501
249
1978
acres)
1,170
499
587
215
30
558
3,059
-------
of cancellation. Thus a complete economic analysis was
conducted in order that the Agency might make a decision on
the "unreasonable adverse effect" of this use.
B.. Rice
1. Use Analysis
There has been considerable variation in
the acreage of rice harvested in the United States in recent
years (Table III-2). Rice is planted mainly in the southern
states of Arkansas, Mississippi, Texas, and Louisiana with
small acreages found in Missouri. Significant rice acreage
is also planted in California. Benomyl is used on rice in
the Grand Prairie of Arkansas, northeast Arkansas, the
Mississippi River Delta (including Missouri), southwest
Louisiana, and the Gulf Coast of Texas. The other major
rice producing areas, the Sacramento and San Joaquin
Valleys of California, do not use benomyl. About 19 percent
of the U.S. rice acreage planted in 1977, or approximately
422,000 acres, were treated with benomyl.
Benomyl is registered and used to control
rice blast and stem rot for all states except California.
In addition, a special local needs label which permits the
use of benomyl to control sheath rot, brown leaf spot,
sheath blight, and leaf smut in Texas was granted. There
are no other chemicals registered for control of these rice
diseases.
-55-
-------
In 1975, benomyl was first registered for
foliar application on rice to control rice blast, which is
one of the most serious diseases of rice in the United
States. Benomyl also controls stem rot, the other major
fungal disease of rice. These two diseases cause an esti-
mated 12 to 15 percent loss in rice production annually (Walla,
1978).
Cultural practices are not effective in
reducing or controlling stem rot or rice blast . Although
the severity of rice blast can be reduced by early planting,
the large acreage of many rice farms would not enable the
farmers to plant all of the acres early enough in the
season. The occurrence of frequent showers during the
planting season is also a serious constraint on early
planting. Crop rotation was used to reduce the severity of
stern rot in the past, but given the existing demand for
rice, crop rotation is no longer economically sound. In
addition, the pressure of urbanization has reduced land
available for rice production, further affecting the feasi-
bility of crop rotation. At present there are no rice
varieties that are resistant to the prevalent strains of
blast and stem rot. In some cases, using less nitrogen
fertilizer will reduce the effect of these diseases; however,
the yields will also be drastically reduced. Nor is water
management is not effective in controlling rice blast.
-56-
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2. Economic Analysis
The economic analysis of the use of benomyl on
rice was based on the following assumptions:
a. The price of rice was assumed to be $7.00
per hundredweight, the mid-point of the $6.50 to $7.50 per
hundredweight price range forecast by USDA for the 1978
season. This price is low relative to prices that have
ranged from $8.35 to $13-80 per hundredweight from 1973
to 1977 and does not include an allowance of deficiency
payments for prices below $8.53 per hundredweight on national
allotment acres. In 1978 deficiency payments were made
for 58 percent of the 3-1 million harvested acres.
b. There will be an increase in yield of 500
pounds per acre on the acres which have been treated with
benomyl.
c. Benomyl was used to treat the same percen-
tage of the rice crop in 1978 as was treated in 1977.
d. Rice yields, as shown in crop production
budgets, were assumed to be produced in the absence of
diseases and therefore to be representative of the benomyl
treated acreage.
e. The price of benomyl is $16.32 per pound
active ingredient (a.i.) ($8.16 per pound of BenlateR 50 WP)
as indicated in the Texas Gulf Coast rice production budgets.
f. The first application of benomyl by custom
aerial applicators will cost $2.00 per acre. For the second
-57-
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application, a per acre charge of $1.50 was used because
about 25 percent of the time the second application includes
an insecticide.
g. Improved grain quality (reduction of
"peck") will result in a milling premium of 30 cents per
hundredweight to rice growers who use benomyl in Texas and
southwest Louisiana.
h. Yield increases of 500 pounds would be
attained at the seasonal application rates of either 0.5 or
1.0 pounds (a.i.) per acre. Application rates, to achieve
disease control, vary directly with the degree of infestation.
It is estimated that using benomyl through-
out the five-state area would increase average rice yields
500 pounds per impacted acre for a total increased value of
approximately $17.8 million (Table III-3). Furthermore,
benomyl reduces "peck", a discoloration of the rice kernel;
this reduction results in an increase of the milling quality
of Southwest Louisiana and Texas Gulf Coast rice by approxi-
mately 30 cents per hundred weight or $5.0 million. After
the cost of benomyl treatments ($6.0 million for material
and $1.8 million for application) are deducted, an annual
net economic benefit of about $15 million is realized.
Texas is estimated to accrue about $10.2
million, or 68 percent, of the total economic benefits of benomyl
use on rice. Increases in net returns per impacted acre in
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Table III-3-
State, 1978
Treatment Costs and Value of Production Changes for Benomyl Use on Rice by
Treatment Costs a/
State
Arkansas
Louisiana
Mississippi
Missouri
Texas
Total
Material
Cost
1.97
1.42
0.10
0.01
2.53
6.03
Appli-
cation
Cost
0.45
0.33
0.02
d/
0.98
1.78
Total
Cost
_ _ —mi 1
2.42
1.75
0.13
0.01
3.51
7.82
Production Changes b/
Value of
Yield
Increase
4.50
3.29
0.22
0.02
9.76
17.79
Value of
Quality
Increase
1.04
—
__
3.93
4.97
Total Value
of Produc-
tion Changes
4.50
4.33
0.22
0.02
13.69
22.76
Economi*
Impact
c/
2.08
2.58
0.09
0.01
10.18
14.94
a/ USDA/EPA. 1979. Economic Analysis of Benomyl and Thiophanate-methyl. Appendix Table 2,
t>/ Ibid. Appendix Table 3.
c:/ Total value of production changes minus total treatment costs,
d/ Less than $5,000.
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different states varied from $23 to $38. These increases are
significant to impacted ice producers, who typically have
high production costs and low profit margins (Table III-4).
The economic impact of a benomyl cancellation
on rice would be insignificant in terms of the total value
of U.S. rice production and the total U.S. economy; therefore
it should have little, if any, impact on prices, consumption
and U.S. rice exports. However, the economic impact would
be significant to the rice producers of Texas, Louisana and
Arkansas.
C. Other Uses
Benomyl is a broad spectrum fungicide which
controls a wide range of diseases at a low rate of applica-
tion (2 to 16 ounces of active ingredient per acre).
Benomyl was the first major systemic fungicide developed.
In addition to preventing fungal disease, benomyl can
control fungal infections that are already established; this
allows more flexibility in the timing of applications. Also,
the systemic activity prevents excessive loss of the fungicide
during heavy rainfall. Since benomyl is applied at 14 to 21
day intervals rather than 7 to 14 day intervals, as are
alternative fungicides, growers can apply the compound less
frequently. This should decrease both labor and application
costs.
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Table III-4. Per Acre Returns over Direct- Production Costs on Rice Acreage Treated
with Benomyl and Untreated, by Regions, 1978 a/
Region
Northeast Arkansas
Grand Prairie Arkansas
Mississippi Delta
Southwest Louisiana
Texas Gulf Coast
Upper Counties
Lower Counties
Benomyl
0.50 Ib.
per acre
25.86
18.811
-16.53
30.18
-6. -7 5
-19.79
Treatment
a.i.
b/
c\ n 1 1 ri i^ Q
— .
Per Season
1.0 Ib. a.i.
per acre c/
17-70
10.68
-24.69
22.02
-14.91
-27.95
Untreated
d/
2.52
-4.50
-39.87
-4.29
-43.74
-57.62
deficiency payments.
b/ USDA/EPA. 1979. Economic Analysis of Benorayl and Thiophanate-methyl. Appendix
Table 4.
c/ Ibid. Appendix Table 5.
d/ Ibid. .Appendix Table 6.
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1. Soybeans
Benomyl is used in the Southeast plus the
Louisiana and Texas soybean-producing areas. Warm tempera-
tures and high humidity prevail in these areas and are
conducive to the development of plant pathogens that
cause serious disease losses. Yield data obtained with the
use of benomyl show an average increase of 5.5 bushels per
acre. The quality of the soybean also improves when benomyl
is applied (USDA[30000/23:1795l).
2. Fruit
The use of benomyl has resulted in a substan-
tial improvement in the level of disease control on several
fruit crops. The dramatic reduction in brown rot of stone
fruits and the significant reduction in losses due to scab
and powdery mildew on grapes and to Botrytis fruit rot of
strawberries are particularly important. Benomyl is more
efficient against a larger group of pathogens which attack
fruit crops than any other fungicide. Although captan and
mancozeb have been widely used since the early 1950's, they
lack the high anti-sporulation action which benomyl displays
against many fungi. Therefore, the loss of benomyl for use
in orchards could soon result in increased inoculum levels
of several pathogens and could require an increase in
fungicide usage. The development of b.enomyl resistant
strains of pathogens is of major concern to orchard growers
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Consequently, California stone fruit growers use benomyl
only in combination with other ungicides. Pacific Northwest
apple and pear growers use benorayl only for post-harvest
disease control to reduce the possibility of developing
tolerant strains (USDA [30000/23:795]).
3. Sugar Beets
Benomyl is used extensively on sugar beets in
the irrigated areas where Cercospora. leaf spot is a problem.
Although benomyl is labeled only for control of Cercospora
sp., it also controls the secondary diseases powdery Eildew
and Rhizoctonia root rot. Alternate materials registered
for use on sugar beets do not control these secondary
diseases. In addition, these alternative pesticides are
not cleared for beet residues fed to livestock, whereas
benomyl is (USDA [30000/23:1795]).
4. Citrus
Citrus producers in Florida are dependent on
benomyl for the control of greasy spot and scab. If not
controlled, greasy spot can cause serious premature defolia-
tion, tree deterioration, and yield reduction. Scab is a
fungal disease of economic importance on several citrus
varieties grown for fresh market. Scab also presents a
problem in citrus nurseries since certain root-stocks are
susceptible to scab (USDA : [30000/23:1795]).
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5. Peanuts
One of the most destructi diseases of
peanuts is Cercospora leaf spot. This foliage disease occurs
wherever peanuts are planted and- must be controlled for
peanuts to be grown economically in the U.S. Many fungi-
cides are available that provide a certain degree of control
of Cercospora leaf spot fungi. In 1973 an estimated 49
percent of all peanuts produced in the U.S. were treated
with benomyl. When strains of Cercospora resistant to
benomyl were found in 1973, the amount of benomyl used in
Georgia, Florida, and Alabama declined drastically. In 1977
benorayl was used on an estimated 22 percent of the peanut
acreage. Since the Cercospora fungus has developed resistance
to benomyl, a combination of benomyl and either Manzate or
Dithane is recommended (USDA [30000/23:1795]).
6. Vegetables
Benomyl is used on the vegetables listed in
Table III-5. The percentage of the crop treated ranges from
100 percent for cabbage seeds to 18.4 percent for tomatoes
(USDA..[30000/23: 1795]).
7. Home Garden Use
Benorayl is used by homeowners for control
of tar spot, anthracnose, powdery mildew, leaf spot, apple
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scab, and flower blight on shade trees and for control
of powdery mildew and black spot on roses. Over three
hundred letters, representing thirty-eight states and
written by individuals and various associations, were
submitted in rebuttal which described their previous
use of products containing benomyl and its effectiveness.
Alternatives are generally less effective, and more expensive
than benomyl resulting from the fact that the alternatives
are nonsystematic and thus more treatments may be required
for the same result.
-62a-
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TABLE III-5. USE PATTERN OF BENOMYL ON VEGETABLES-'
APPLICATION
SITE
CUCUMBER
CANTALOUPES
WATERMELONS
SQUASH
TOMATOES
CELERY
SNAP BEANS
DRY BEANS
CABBAGE SEED
TOTAL POUNDS AI
USED IN 1977
8,700
9,700
21 ,000
5,100
42,000
15,000
13,300
34,200
1,500
ACRES
TREATED
81,235
65,362
171,620
22,683
90,694
30,280
139,064
386,920
2,240
% OF TOTAL
CROP
43.9
79.5
66.7
90.0
18.4
87.5
37.3
24.2
100.0
1/ USDA/STATS/EPA BENOMYL ASSESSMENT REPORT
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IV. Risk/Benefit Analysis of Alternative Courses
of Actfon
This section of the Position Document discusses the basis
for the Agency's development of regulatory options, evaluates
methods of risk reduction, and identifies the options selected
for consideration.
A. Basis for the Development of Options
FIFRA provides that the Administrator may cancel
the registration of a pesticide whenever he determines that
it no longer satisfies the statutory standard for registra-
tion which requires (among other things) that the pesticide
performs its intended function without "unreasonable adverse
effects on the environment" [FIFRA Section 3(c)(5); 7 USC
Section 136a(c)(5)]. "Unreasonable adverse effects on the
environment" means "any unreasonable risk to man or the
environment, taking into account the economic, social and
environmental costs and benefits of the use of any pesticide"
[FIFRA Section 2(bb); 7 USC Section 136(bb)]. In taking any
final action under section 6(b), the Administrator is
required by statute to "consider restricting a pesticide's
use or uses as an alternative to cancellation and shall
include among those factors to be taken into account the
impact of such final action on production and prices of
agricultural commodities, retail food prices, and otherwise
on the agricultural economy..." [Section 6(b)].
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In effect, FIFRA requires the Administrator to
weigh the risks and benefits associated with each use of a
pesticide. If he determines for any particular use that
the risks exceed the benefits, he must then determine
whether those risks can be sufficiently reduced (so that
they are outweighed by the benefits) by the imposition of
restrictionss upon use through modifications to the terms
and conditions of registration (reflected by changes
in the labeling) and/or by the classification of the use for
restricted use. If he determines that adequate risk reduc-
tion cannot be achieved by such regulatory measures, the
registration of the pesticide for that use must be fully
cancelled.
Under the Rebuttal Presumption Against Registration
Process detailed in 40 CFR 162.11, the registrant or applicant
may rebut a presumption that a pesticide meets or exceeds
the risk criteria by sustaining the burden of proving (1)
that "when considered with ... proposed restrictions on and
directions for use and widespread and commonly recognized
practices of use, the anticipated exposure to an applicator
or user and to local, regional or national populations of
nontarget organisms is not likely to result in any significant
acute adverse effects"; or (2) that "when considered with
proposed restrictions on use and widespread and commonly
recognized practices of use, the pesticide will not concentrate, persist,
-64-
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or accrue to levels in man or the environment likely to
result in any significant chronic adverse effects"; or (3)
"that the determination by the Agency that the pesticide
meets or exceeds any of the criteria for risk was in error."
In effect, the presumption can be rebutted by showing that
the risks are far lower than indicated by the Agency's
initial determination; that there is not sufficient exposure
to warrant the Agency's concern about the potential risk of
the pesticide; or that modifications to the terms and conditions
f
of registration will reduce any potential risk below the
level of concern. Where modifications to the terms and
conditions of registration which will adequately reduce
risks can be achieved without significant impacts on the
benefits of the affected use, it is not necessary to undertake
a detailed analysis or quantification of benefits. Rather,
the in-depth consideration of benefits comes into play only
when the risks cannot be reduced by such modifications to
the terms and conditions of registration, or where such
reduction in risk can only be achieved at a cost which has a
substantial impact on benefits.
Concerning benomyl - except as it is used on rice -
the Agency has determined that proposed modifications to the
terms and conditins of registration will adequately reduce
risks, and that such risk reduction can be achieved with
only an insignificant impact on the benefits. Concerning
-65-
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the use of benomyl on rice, the Agency has determined that
risk can not be adequately reduced by any method short of
cancellation. A detailed analysis, or quantification of the
benefits of the use of benomyl on rice was therefore necessary
in order to make determination of unreasonable adverse risk,
and that analysis is discussed at some length in Section
III.
B. Possible Alternate Courses of Action
Evaluation of the risk and benefit data suggests these
principal regulatory options:
1. Continue registration of the use;
2. Continue registration of the use; amend the
terms and conditions of registration;
3. Cancel the use.
1. Option 1: Continue Registration of the Use
Option 1 would indicate that the Agency concludes
that the benefits associated with each use of benomyl
outweigh the respective risks, and that therefore, the use
in question will not cause unreasonable adverse effects.
This option would not reduce the risk of adverse reproductive
effects to applicators during the mixing/loading and flagging
operations for aerial application or during the airblast
operation. Under this option the risks associated with
mutagenic, spermatogenic, and teratogenic effects would remain
at the present level. Likewise, the risk associated with the
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use of benomyl on rice would remain at the same level. Field
tests show that residues of benomyl in water drained from rice
fields which were treated at minimum label rates are greater
than the LC,-0 for channel catfish. If maximum label rates
are applied, residues of benomyl greater than one-half the LCj-o
for bluegill can be expected as well. This option would not
result in any adverse economic impacts and would retain the
usefulness of benomyl as an economical, effective tool for
the control for fungi. The choice of this option would indi-
cate that the Agency is willing to tolerate the highest risk
in return for the highest possible benefits.
2. Option 2; Continue the Registration of Benomyl
for All Uses and Amend the Terms and Conditions
of Registration
The adoption of option 2 would indicate that
the Agency concludes that the benefits of benomyl's continued
use will outweigh the risks after certain terms and conditions
of registration are amended. The terms and conditions which
have been considered in conjunction with this option are
enumerated below.
a. Discussion of Proposal to Require Reduction
of Application Rates for Rice
This option is designed to reduce the residues
of benomyl to which aquatic organisms are exposed when
water is drained from rice fields after application of
benomyl by amending the label rate to include an application
rate of 1/4 pound active ingredient per acre. Benomyl is
registered to control rice blast and stem rot in all states
except California when applied twice at 1/2 to 1 pound
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active ingredient per acre. A special local needs registration
was granted by Texas which permits the use of benomyl at 1/4
to 1/2 pound active ingredient twice a year. The application
of benomyl at the lower rate should reduce the levels of
benomyl which aquatic organisms are exposed to by a factor
of two. This reduction would result if the concentration of
benomyl in water is in a linear relationship to the application
rate. However, application at this lower rate can result in
concentrations greater than the LC-Q for most of the
tested lifestages of the channel catfish. No information
currently available indicates whether this option would
actually reduce the risk to aquatic organisms.
b. Discussion of Proposed Requirement for
Additional Studies
(i) Additional Monitoring Study for Rice Use
This option is designed to provide additional
data with which the Agency can more adequately evaluate the
risk to aquatic organisms. The Agency has no data on the
equilibrium between the adsorption of benomyl to the soil
and the water concentration in rice fields. The Agency
assumed a linear relation between application rates and
water concentration in determining risk. To perform a more
precise risk determination, the Agency would require a field
monitoring study which involves: (1) replicated fields
treated twice at 1/4, 1/2 and 1 pound active ingredient per
acre; and (2) residue sampling before and after both applica-
tion and drainage in the rice fields, the main drainage
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ditches, and the nearest body of water at the point of entry
and several places downstream . Thus, although this option
would not reduce the hazard to aquatic organisms, it would
provide information the Agency requires to make a determination
of risk to aquatic organisms.
(ii) Additional Gene Mutation Studies
This option is designed to provide addi-
tional data with which the Agency can more adequately
evaluate the risk of point mutagenic potential for man. The
evidence the Agency has available from the point mutation
studies on benomyl is inadequate to determine the point
mutagenic potential for man. The registrants of benomyl and
applicants for registration of pesticide products containing
benomyl will be required to submit additional tests to
detect gene mutations in the following test systems (1)
Drosophila, (2) mammalian somatic cells in culture, and (3)
an appropriate eukaryotic microorganism for benomyl and its
metabolite MBC.
c. Discussion of Proposed Restrictions to
Reduce Applicator Exposure.
(i) Require the Use of Protective Clothing
The population with one of the greatest potential
exposures to benorayl consists of persons who are directly
involved in the airblast application of benomyl and persons
who are involved in the mixing, loading, and transfer
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operations for aerial applications. Data from Table II-2
show the theoretical exposure range for these persons when
the Agency made the assumption that no protective clothing
was worn. The Agency assumed that 85 percent of the body is
normally clothed and that the hands, forearms, neck, face,
upper chest, and head are not covered. Data from Table II-3
show that the total body dose results from the oral background
and inhalation exposure with only an insignificant amount
from dermal exposure. Since these exposures could result in
a margin of safety as low as 20 for reduction in spermatogenic
activity and teratogenic effects (Table II-5), the Agency
believes that it is both necessary and prudent to explore
means for reducing respiratory contact with benomyl.
Respiratory protection could be attained by
requiring that a cloth mask be worn during mixing and
loading. Wearing a mask would reduce inhalation exposure to
zero. The margin of safety would then be 380, the margin
from background due to residues on food. The economic
impact of this regulation would be slight.
(ii) Require Water-Soluble Packaging for
Packages 5 Pounds and Larger
The projected levels of exposure are greatly
influenced by the degree of care exercised in mixing the
pesticide solution. In this method of packaging, water-soluble
bags containing benomyl would be added to the water, and the
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formulation would be released and mixed when the bag dissolved
There would be no dust generated from pouring the products.
The adoption of this option would essentially eliminate expo-
sure from mixing/loading operations (Day, 1979).
Adopting this option would not cause any
severe economic impact on the use or users of benomyl. The
primary economic impacts of this option would be the cost of
water-soluble packaging for containers of five of more
pounds of formulated wettable powder. Exposure rates to
individuals mixing amounts less than five pounds of formulated
product for a given application are consdered low enough not
to justify water-soluble packaging. The, requirement
of water soluble packaging is not completely beyond the
producer's current technology or marketing techniques.
DuPont is currently test marketing formulated benomyl in
water-soluble packages as a measuring/mixing convenience.
The estimated additional cost of benomyl to
the user, as related to the cost of water-soluble packaging
for five or more pounds of formulated product, ranges from
$.80 to 1.00 per pound active ingredient. The cost per acre
would be about $.60 for approximately 4.5 million acres
treated each year with benomyl. This amounts to $2.4 to
$3.0 million, based on annual benomyl usage of approximately
3.0 million pounds active ingredient and would not effect
the benefits of benomyl usage.
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This option is useful because it is a passive
protective measure. Applicators would not need to take any
stringent protective measures than they do at present. Also,
there would be no need for additional enforcement activities
in order to monitor compliance with this requirement.
(iii) Require that Certain Uses Be Classified for
Restricted Use
Under FIFRA, hazardous pesticides may be
classified for restricted use and thereby 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 they have proven themselves competent to
use restricted pesticides.
The Agency believes that the classification
of benomyl for restricted use would not be necessary for
every use pattern of the compound; however, use patterns
involving aerial application should be considered for
retricted use classification. Preventing untrained persons
from applying benomyl aerially should significantly reduce
the risks to man and the environment caused by misuse or
carelessness. Any marginal costs that might result from
restriction to certified applicators would be minimal, since
state programs to certify applicators are operational in all
states; there is little difficulty in obtaining applicator
certification and hence, there are many certified applicators.
Most aerial applicators are already certified and thus the
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adoption of this option would produce very little reduction
in risk.
(iv) Require Label Warnings
Under FIFRA, the Agency may require precaution-
ary and warning statements to appear on pesticide labeling.
The Agency has assessed the impact of additional cautionary
and warning statements with respect to the teratogenic and
mutagenic effects and spermatogenic depression caused by
benomyl. The warning on a five pound or larger bag would
state:
Warning to Workers
The United States Environmental Protection
Agency has determined that benomyl causes birth defects and
reduced sperm production in laboratory .animals. Exposure to
benomyl during pregnancy should be avoided. Exposure to
benomyl might cause a depressed sperm count. Workers must
be sure to wear a cloth mask while mixing benomyl for aerial
application. In case of accidental spills or other unusual
exposure, cease work immediately and follow directions for
contact*" with benomyl.
The Agency believes that some reduction in risk
will be achieved by the education of the user about the poten-
tial adverse reproductive effects of benomyl. The cost associ-
ated with these risk-reduction measures would be negligible.
3. Option 3: Cancel The Registrations
Adopting this option would indicate that the
Agency concludes that the risks associated with certain uses
of benomyl outweigh the respective benefits and hence that these
uses will result in unreasonable adverse effects. The choice
of this option would indicate that the Agency is unwilling to
tolsrate the level of risk associated with these uses. It
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would further indicate that the Agency believes the only
regulatory option by which an adequate reduction in risk can
be achieved without causing unacceptable economic consequences
is cancellation. This option would eliminate the risk
associated with the use of benomyl on rice, but at a cost to
individual growers of approximately $15 million per year.
There should be little, if any, impact on the price of rice
to the consumer (Gaede, 1979).
This option would not increase the use of
alternate chemicals at this time since there are no other
chemicals presently registered for the control of these rice
diseases.
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V. Recommended Regulatory Action
The analysis of the risks and benefits from the
continued uses of benomyl indicates that the primary areas
for Agency concern and regulatory action are: (1) inhalation
exposure and hence risk incurred by mixer/loaders during aerial
application, (2) the potential of benomyl as a gene mutagen,
and (3) the acute hazard to aquatic organisms which results
when benomyl is applied to rice.
The Agency recommends Option 2 as its regulatory
action:
Continue Registration of All Uses; Amend the Terms and
Conditions of Registration
This option contains several restrictions on the con-
ditions of use, each designed to reduce the risks associated
with exposure to benomyl without simultaneously creating the
the adverse economic, social, and environmental impacts asso-
ciated with cancellation (Table V-l).
A. All Uses
1. Require Label Warnings
This option will educate the user to the potential
adverse reproductive effects of benomyl. The Agency recommends
this option for all pesticide products containing benomyl
packaged in 5 pound or larger bags.
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Warning to Workers
The United States Environmental Protection
Agency has determined that benomyl causes birth defects and
reduced sperm production in laboratory animals. Exposure to
benomyl during pregnancy should be avoided. Exposure to
benomyl might cause a depressed sperm count. Workers must
be sure to wear a cloth mask while mixing benomyl for aerial
application. In case of accidental spills or other unusual
exposure, cease work immediately and follow directions for
contact with benomyl.
2. Additional Mutagenicity Testing
The evidence available to the Agency on the
gene mutational potential of benomyl is inadequate to allow
the Agency to conclude that there is no human risk attri-
butable to this effect; nor is there clear evidence that
such effect does pose a human risk. Additional gene mutation
studies will enable the Agency to determine if the use of
benomyl will cause unreasonable adverse effects to man or
the environment because of its potential to change point
mutations. The Agency will require additional tests in
this area. Specific requirements will be directed to the
manufacturers by the Order.
B. Aerial Application
Pesticide products containing benomyl with
directions for aerial application require the following
restrictions:
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1. Water-Soluble Packaging.
The greatest level of exposure to benomyl
from any of its uses is to the mixer/loader for aerial
application. This exposure mainly occurs during the process
of opening the bag containing the benomyl wettable powder
and mixing the solution. To lessen this exposure, this
option would require that all packages containing five or
more pounds be packaged in water-soluble bags as soon as
technically feasible.
2. Protective Clothing
The Agency believes that the risk to mixer/loaders
can be reduced to an acceptable level if protective clothing
is worn. A cloth mask of fine weave must be worn during mixing
and loading for aerial application of benomyl if the pesticide
is not in water soluble packages.
This reduction in risk can be accomplished with
little, if any, economic impact, since applicators are likely
to have a cloth mask of fine weave either at their disposal or
readily available to them. Therefore the Agency recommends
this option.
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C. Rice Use
1. Reduce Rate of Application
Application of benomyl on rice results in
residues in water that is drained from the rice fields
and that eventually reaches fish-bearing streams. These
residues present a hazard to aquatic organisms.
DuPont submitted information demonstrating that
the lower rate used in Texas would not be efficacious in the
other rice growing areas (du Pont, 1979). This option also
would not result in the elimination of the hazard to all
aquatic organisms and thus is not recommended.
2. Monitoring Studies
The evidence available to the Agency on the-poten-
tial hazard to aquatic organisms is inadequate to allow the
Agency 'to conclude that no risk attributable to this effect
exists. Additional monitoring studies will enable the Agency
to further quantify the potential hazard to aquatic organisms,
The Agency will require additional studies in this area.
Specific requirements will be directed to the manufacturers
by the Registration Division.
D. Conclusions
In summary, the Agency recommends continued registra-
tion for all uses of benomyl with the following terms and
conditions: (1) additional gene mutation studies will be
required for all uses; (2) when sold in five pound or larger
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packages with directions for aerial application, benomyl
should be packaged in water-soluble bags as soon as techni-
cally feasible, (3) a cloth mask will be required during
mixing and loading for aerial application if the product is
not packaged in water-soluble bags, (4) a monitoring study
on the fate of benomyl in the environment is required for
the continuation of the registration for the rice uses, and
(5) additional, precautionary labeling will be required. The
impacts of the recommended options appear in Table V-l.
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TABLE V-1 . Risks/Benefits Matrix
IMPACTS OF REGULATORY OPTIONS SELECTED
REGULATORY
OPTIONS
ENVIRONMENTAL
RISKS
HUMAN
RISK
ECONOMIC IMPACT
ISSUES
1. REGISTER ALL USES
AMEND CONDITIONS
FOR REGISTRATION
A. REQUIRE MONI- RISK LEVEL
TORING STUDY UNCHANGED
ON RICE USE
B. REQUIRE PROTEC- RISK LEVEL
TIVE CLOTHING UNCHANGED
FOR MIXER/
LOADERS (CLOTH
MASK)
REQUIRE WATER RISK LEVEL
SOLUBLE PACKING UNCHANGED
FOR 5 POUND AND
LARGER PACKAGES
OF BENOMYL
D. REQUIRE ADDI- RISK LEVEL
TIONAL GENE UNCHANGED
MUTATION TESTS
E. REQUIRE ADDI- RISK LEVEL
TIONAL UNCHANGED
PRECAUTIONARY
LABELING
RISK LEVEL
UNCHANGED
INHALATION
RISKS ARE
REDUCED
DERMAL RISKS
ARE REDUCED.
INHALATION
RISKS ARE
REDUCED.
RISK LEVEL
UNCHANGED
RISK LEVEL
REDUCED
COST TO MANU-
FACTURER FOR
MONITOR STUDY
PRODUCTION AND
QUALITY MAIN-
TAINED AT PRESENT
LEVELS FOR THESE
USES
PRODUCTION AND
QUALITY MAIN-
TAINED IMPACT
WOULD BE ABOUT
$0.60 PER ACRE
COST TO
MANUFACTURER
($9,000-13,000)
COST TO MANU-
FACTURER FOR
LABEL CHANGES
FATE OF BENOMYL
IN RICE FIELDS
UNKNOWN AT PRESENT
EXPOSURE TO
APPLICATORS CAN .
BE REDUCED
GROWERS WOULD
NOT MEED TO PURCHASE
NEW SAFETY EQUIPMENT
EXPOSURE DURING
MIXING CAN BE
REDUCED BY 9Q%
PASSIVE METHOD OF
REDUCING EXPOSURE.
TEST-MARKETING
ALREADY IN PROGRESS
TEST-NECESSARY
NECESSARY TO
DETERMINE RISKS
WARNS CONSUMER
OF RISKS
-------
Benomyl Bibliography
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Morpurgo, 1977. Mutagenic and recombinogenic action of
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Black, W. M. and D. Neely. 1975. Effect of soil-injected
benomyl on resident earthworm populations. Pest. Sci.
6:543-545.
Boyle, W. S., 1973. Cytogenetic effects of Benlate fungicide
on Allium cepa and Secale cereale. J. Hered. 64(1):49-50.
Brachet,J. 1957. Biochemical Cytology. Academic Press,
New York.
Burnham, C. R. 1962. Discussion in cytogenetic. Burgess,
Minneapolis.
Burnam, W. 1978a. Analysis of Rebuttals - Teratogenicity
for Benomyl [F.R. 30000/23] . Unpublished.
Burnam, W. and L. Bennett. 1978b. Analysis of Rebuttal -
Reduction in Spermatogenic Activity for Benomyl [F.R.
30000/231. Unpublished.
Canton, J. H. 1976. The toxicity of benomyl, thiophanate-
methyl, and BCM to four freshwater organisms. Bull. Environ.
Contain. Toxicol. 16(2) :2l4-2l8 .
Chaisson, C. F. 1978a. Analysis of Rebuttals - Mutagenicity
for Benomyl [F. R. 30000/23]. Unpublished.
Davidse, L. C. 1973- Antimitotic actvity of methyl benzimi-
dazol-2-yl carbamate (MBC) in Aspergillus nidulans. Pest.
Biochem. Physiol. 3:317-325.
Day, H. 1978. Benomyl. Memorandum to Esther Saito, Project
Manager, SPRD. 3pp.
Day, H. 1979- Memorandum to Esther Saito, Project Manager,
SPRD. p.
DeBrander, M., R. Van de Veire, F. Aerts, S. Geuns, and
J. Hoebeke. 1976. A new culture model facilitating rapid
quantitative testing of mitotic spindle inhibition in
mammalian cells. J. Nat. Cancer Inst. 56(2):357-363.
Delatour, P., and Richard. 1976. Embryototoxic and anti-
mitotic properties of benzimidazole compounds. Therapie
31:505-515.
Dassenoy, B. and J. A. Meyer. 1973. Mutagenic effect of
benomyl on Fusarium oxyhsporum. Mutat. Res. 21:119-120.
-------
Davidse, 0. C., and W. Flack. 1977. Differential binding
of methyl benzimidazol-2-yl carbamate to fungal tubulin as
a mechanism of resistance to this antimitotic agent in
mutent strains of Aspergillus nidulans J. Cell Biology
72:174-194.
E. I. duPont De Nemours and Co. (Inc.) March 23, 1978.
[30000/23:#1296].
Environmental Protection Agency, December 6, 1977. Rebut-
table Presumption Against Registration and Continued
Registration and Continued Registration of Pesticide
Products Containing Benomyl. Federal Register, Part II.
42(234) :61788-61801.
Environmental Protection Agency, August 22, 1978. Proposed
Guidelines for Registering Pesticides in the U.S.; Hazard
Evaluation: Humans and Domestic Animals. Federal Register,
Part II. 43(163) :37336-37403.
Fahrig, R. and J P. Seller, 1979. Dose and effect of
methyl-2-benzimidazolylcarbamate in the "mammalian spot
test", an in vivo method for the detection of genetic
alterations in somatic cells of mice. Chem. Biol. Inter-
actions 26:115-120.
Finley, M. T. August 1, 1977. Letter to Esther Saito,
Project Manager, SPRD with attachments. 27 pp.
Gaede, H. 1979. Economic Impact Analysis of Benomyl and
Thiophanate-methyl. Memorandum to Esther Saito, Project
Manager, SPRD. With Attachments. 26 pp.
Gardiner, J. A., J. J. Kirkland, H. L. Klopping, and H.
Sherman. 1974. Fate of benomyl in animals. J. Agr. Food
CHem 22(3) :4l9-427.
Hammerschlag, R. S. and H. D. Sisler. 1972. Differential
action of benomyl and methyl-2-benzimidazole-carbamate (MBC)
in Saccharomyces cerevesiae. Pest. Biochem. Physiol.
2:123-131.
Hammerschlag, R. S. and H. D. Sisler. 1973. Benomyl and
methyl-2-benziznidazolecarbamate (MBC): Biochemical, cyto-
logical, and chemical aspects of toxicity to Ustilago maydis
and Saccharomyces cerevesiae. Pest. Biochem. Physiol.
Haskell Laboratory - Ames Test. 1977. Tab 11 of Vol. 2.
E. I.. duPont de Nemours and Co. (Inc.), March 23, 1973
C30000/23:#1296].
Hoffman and Peh, 1974 cited by E. I. duPont de Nemours and
Co. (Inc.) March 23, 1978 [30000/23 :#1296] .
-------
Jeiger, Z. 1964. Health hazards in insecticide spraying of
crops. Arch. Environ. Health. 8:670.
Johnson, D. 1979. Exposure Analysis. Human Dietary Aspect.
Benomyl. Memorandum to Esther Saito, Project Manager, SPRD.
17 pp.
Kappas, A., S. G. Georgopoulos, and A. C. Hastie. 1974.
On the genetic activity of benzimidazole and thiophanate
fungicides on diploid Aspergillus nidulans. Mutat. Res.
26(l):17-27.
Kappas, A., M. H. L. Green, B. A. Bridges, A. M. Rogers and
W. J. Muriel. 1976. Benomyl - a novel type of base analogue
mutagen? Mutat. Res. 40:379-382.
Knott, B. S. and C. D. Johnston. August 5, 1968. Fungicide
1991 safety evaluation of bluegill sunfish. Woodard Research
Corporation. Submitted to EPA by E. I. duPont de Nemours
and Company on October 30, 1969. EPA Accession No. 091561.
Kavlock, R. 1979. Report on the Status of Teratogenicity
Studies with Benomyl. 6pp.
Lamb, M. J. and L. J. Lilly. 1973. Research Notes.
Drosophila; Information Service (University of Oregan)
Eugene. 50:82.
Leitzke, J. S. 1978a. Analysis of Adequacy of Benomyl and
Thiophanate-Methyl Rebuttal. Memorandum to Esther Saito,
Project Manager, SPRD. 17 pp.
Leitzke, J. S. 1978b. Benomyl Risk Analysis. Memorandum to
Esther Saito, Project Manager, SPRD. 58 pp.
McCann, J. 1973. Fish Toxicity Laboratory Report No. 355.
Animal Biology Laboratory, EPA. Beltsville, Md.
McCann, J. A. June 24, 1977. Request for information on
Benlate fungicide. Memorandum to Esther Saito, Project
Manager, SPRD. With Attachments. 6pp.
Mollet, P. 1976. Lack of proof if induction of somatic
recombination and mutation in drosphila by methyl-2-benzi-
midazole carbamate, dimethyl sulfoxide and acetic acid.
Mutat. Res. 40:383-388.
Richmond, D. V. and A. Phillips. 1975. The effect of
benomyl and carbendazim on mitosis in hyphae of Botrytis
cinerea Pers. ex Fr. and roots of Allium cepa L Pest.
Biochem. Physiol. 5:367-379.
-------
Schentenberc, A. I. and A. M Torchinsky, 1972. On the
interrelationship of general toxic, erabryotic, and tera-
togenic action of chemicals extraneous for the organism and
the possibilities for prognosticating their influence on the
antenatal period of ontogenesis. Vestinik Akad. Nauk SSR
3(27):39-46.
Seiler, J. P. 1972. The mutagenicity of benziraidazole and
benziraidazole derivatives I. Forward and reverse mutations
in Salmonella typhirauriurn caused by bezimidazole and some of
its derivatives. Mutat. Res. 15:273-276.
Seiler, J. P. 1973. The mutagenicity of benzimidazole and
binzimidazole derivatives. II. Incorporation of benzi-
midazole into the nucleic acids of Escheric'nia c c 1 i . Mutat.
Res. 17:21-25.
Seiler, J. P. 1975. The molecular mechanisms of benzimidazole
mutagenicity: In vitro studies on transcription and translation
biochem. Genet. 13(9/10): 635-641.
Seiler, J. P. 1976. The mutagenicity of benzimidazole and
benzimidazole derivatives. VI. Cytogenetic effects of
benzimidazole derivateves in the vone marrow of the mouse
and the Chinese hamster. Mutat. Res. 40:339-348.
Seiler, J. P. 1977. Apparent and real thresholds: A study
on two rautagens in progress in genetic toxicology, D. Scott,
B. A. Bridges and F. H. SObais. eds. Elsevier/North-Holland
Biomedical Press.
*
Sherman, H., R. Culik, and R. A. Jackson. 1975. Reproduction,
teratogenic, and mutagenic studies with benomyl. Toxicol.
Appl. Pharmacol. 32:305-315.
Shirasu, Y., M. Moriya and K. Kato, 1978. Tab 12 of Vol.
2. E. I. duPont de Nemours and Co. (Inc.), March 23, 1978.
[30000/23:#1296],
Siebert, D., F. K. Zimmerman, and.E. Lemperle. 1970.
Genetic effects of fungicides. Mutat. Res. 10:533-543.
Sisler, H. April 28, 1978. [30000/23:1716]
Stanford Research Institute. 1972. Study of mutagenic
effects of gum arabic (FDA No. 71-15). Distributed by:
National Technical Information Service, U. S. Department of
Commerce.
Stringer A., and M. A. Wright. 1973. The effects of
benornyl and some related compounds on Lumbricus terrestris
and other earthworms. Pest. Sci. 4:165-170.
Stringer, A. and C. K. Lyones. 1974. The effect of benomyl
and thiophanate-T.ethyl on earthworm populations in apple
orchards. Pest. Sci. 5:189-195.
-------
Styles, J. A. and R. Garner. 1974. Benzimidazole-carbamate
methyl ester-Evaluation of its effects in vivo and in vitro.
Mutat. Res. 26:177-187.
Tates, A. D. 1978. Microtus occononus (Rodentia) a useful
memo for study in nondisjuction induction in male germ cells.
NIEHS, workshop on systems to detect induction of aneuploidy
by environmental mutagens. Savana, Georgia, November 5-8.
Tomlin, A. D. and F. L. Gore. 1974. Effects of six insec-
ticides and a fungicides on the numbers and biomass of
earthworms in pasture. Bull. Environ. Contain. Toxicol.
12(4):487-492.
Torchinski, A. M. 1973- The role of diets with different
protein content in the manifestation of the teratogenous and
embryotoxic effect of some pesticides. Vapr. Pitan. 3:76-80.
United States Department of Agriculture. Undated. [30000/
23:1975].
Walla, W. J., Chairman. 1978. USDA/State/EPA. Benomyl
Assesment Team Report. Part II. An analysis of current
benomyl uses; their benefits, the role of alternatives, and
impacts to agriculture from changes in benomyl use patterns.
Unpublished.
Wilson, L., J. R. Bamburd, S. B. Mizeil, K. M. Grisham, and
K. M. Creswell. 1974. Interraction of drugs with microtubular
proteins. Federation Proceedings 33:158-166.
Wolfe, H. R. and W. F. Durham. 1967. Exposure of workers
to pesticides. Arch. Environ. Health. 14:622-633*
Zutshi, U. and B. L. Kaul. 1975. Studies on the cytogenetic
activity of some common fungicides in higher plants.
Cytobios 12:61-67.
-------
FINAL EXPOSURE ANALYSIS FOR BENOMYL
Prepared by: Harold R. Day
Environmental Fate Branch
Hazard Evaluation Division (TS-769)
November 28, 1978
-------
I. Introduction
Benomyl, methyl l-(T3Utylcarbamoyl)-2-benzimidazole carbamate, is a
fungicide marketed under the trade name BenlateR (EPA Registration
No. 352-354-AA). This systemic fungicide is used to control a
variety of pathogenic fungi on crops such as apples, roses, peaches,
soybeans, etc. (See label-Appendix A). Benlate is sold under only
one label as a 50% A.I. wettable powder with directions for spray
application on various crops. Benomyl rapidly converts to MBC "
(methyl 2-benzimidazolecarbamate) which is generally considered to
be the species which provides fungicidal activity (1) •
II. Use Practices
Benomyl is applied as a foliar spray on vegetables, fruits, etc.
by ground rig, air blast equipment, hand spraying, and aerially.
An agitated spray tank is needed to maintain a homogenous suspension.
It is also applied in combination with a spray oil to stone fruits,
and apples. Applications are made at various intervals (about
7-14 days) or as needed. Benomyl is added to a wax dip for fruit
to prevent fungal attack and as a dip for pineapple seed pieces.
Exposure from these dip residues are accounted for in food residues.
Specific use practices for benomyl are described in section V 9.
III. Recommended Mixing and Use Dilutions
-------
-2-
Aerial Application
Maximum Spray
Crop Product A.I. Ibs/acre
Almonds
Avacados
Beans
Cabbage
Cucurbits
Grapes
Peanuts
Pecans
Rice
Stone Fruits
Strawberries
Soybeans
Sugar Beets
Trees, Flowers,
etc.
Ground Spray
Almonds
Apples
Avacados
Beans
Celery
Citrus
0.5-0.75
0.5-1.0
0.75-1.0
1.0
0.25
0.5-0.75
0.18-0.25
0.5
0.5-1.0
0.375-0.75
0.5
0.25-0.5
0.18-0.25
0.25-0.5
0.5-0.75
0.125-0.18
0.4-1.0
0.75-1.0
0.125-0.25
0.75-1.5
Dilution (gal.)
10-20
10-20
10-20
5-10
.5-10
15-20
5-10
10-20
3-10
10-20
10-20
3-10
5-10
20
*
200-500
*
*
*
*
Concentration % v/w
0.9
1.2
1.2
2.4
0.6
0.6
0.6
0.6
4.0
0.6
0.6
2.0
0.6
0.3
*
0.0125
*
*
*
*
-------
-3-
Ground Application Continued
Maximum Spray
Crop Product A.I. Ibs/acre
Curcurbits
Grapes
Macademia Nuts
Mangoes
Mushrooms
Peanuts
Pears
Pecans
Rice
Soybeans
Stone Fruits
Strawberries
Sugar Beets
Tomatoes
Roses, Flower,
etc.
Bulbs (dip)
0.125-0.25
0.5-0.75
0.875
0.5-1.0
0.5
0.18-0.25
0.125-0.18
0.25-0.5
0.5-1.0
0.25-0.5
0.375-0.75
0.5
0.18-0. 25
0.25-0.5
0.25
0.83
Dilution (gal . )
*
*
*
*
100
*
*
*
*
*
*
*
*
100
100
100
Concentration \ w/w
*
*
*
*
0.
*
*
*
A
•ft
*
*
ft
0.
0.
0.
06
06 .
03
1
*Recommended dilution not provided
-------
-4-
IV. Assumptions
1. The spray concentrations listed in III are in common use.
2. An applicator weighs 60 kg.
3. Equipment used to apply benomyl and applicator protection
are comparable to examples used by Wolfe and Durham (3) in
their calculation of worker exposure to pesticides.
4. Label directions are followed.
V. Unit Exposure for Benomyl
The main volume of the approximately 3 million pounds of benornyl
used in 1977 was for control of fungi on the following crops (4):
Crop ; Total Ibs ai Used
Soybeans 761,000
Stone Fruits 344,000
Rice '. 299,000
Citrus 259,250
Bananas 200,000
Grapes 173,692
Peanuts 158,500
Vegetables 151,500
-------
-5-
Turf 150,000
Ornamentals -. 125,000
Pecans 100,000
Apples 96,184
Berries (Strawberries, Blueberries, Rasberries.... 71,911
Sugarcane 26,000
Sugar Beets 13,500
Wheat 11,150
Mushrooms 11,034
Pears 10,928
Elm 7,010
Mangoes 6,000
Avocados 1,628
Pineapples 1,506
Macadamia Nuts 10Q
Total 3,043,387
-------
-6-
This exposure analysis will provide an estimate of exposure related to
benomyl application on most of the above crops by air and by ground
spray equipment and include other minor uses.
1. Exposure to mixer/loaders
This group according to Jegier (5) receive relatively high
levels of exposure since they handle the concentrated product.
During this operation the product is transferred to a spray tank
or other container and water is added. During this time, dermal
and inhalation exposure can occur. Jegier found that while loading
25% Guthion WP, an applicator received a dermal exposure of 53 mg/hr
and 1.27 mg/hr inhalation exposure (mean values). To estimate ex-
posure for benomyl in an analogous case, a factor needs to be
considered to arrive at a comparable estimate.
Since benomyl is twice as concentrated, the exposures recorded
should multiplied by two:
Dermal exposure:
53 mg/hr X 2/60 kg = 1.8 mg/kg/hour.
Inhalation exposure:
1.27 mg/hr X 2/60 kg = 0.04 mg/kg/hr.
-------
-7-
2. Exposure Via Air Blast Spraying in Orchards_
Wolfe and Durham (2) found that applicators applying pesticide
spray in apple orchards with power spray equipment received
exposure in the range of 15-SO ir,g/hr dermal and 0.02-0.1 mg/hr
inhalation. They found that the mean values for this application
method were 30 mg/hr dermal and 0.04 mg/hr by inhalation.
Dermal exposure: 30 mg/hr/60 kg = 0.5 mg/kg/hr
Inhalation exposure: 0.04 mg/hr/60 leg = 0.0007 mg/
kg/hr
3. Exposure Via Hand Spraying on Vegetables
Wolfe and Durham (3) found that handspraying of vegetables can lead to
exposure. With an applicator applying 0.093 parathion, an exposure
of 9.1 mg/hr dermal and 0.29 mg/hr by inhalation was recorded. Since
-the parathion spray is about one-third more than the recommended
benomyl spray (0.06%), an estimate of exposure to benomyl can be
made by incorporating a factor of 0.66.
Dermal exposure: 9.1 mg/hr X 0.66 (factor)/60 kg = 0.1 mg/kg/hr
Inhalation exposure: 0.29 mg/hr X 0.66 (factor)/60 kg = 0.003 mg/kg/hr
-------
-8-
DuPont, in Vol. 2 (Appendix 20) of their rebuttal document
provided measurements of applicator exposure to bencmyl from
hand spraying vegetables. In the experiment, three different
applicators treated vegetables with recommended spray dilution.
The results (averaged) indicate an average of 2.2 mg/hr dermal
and 0.015 mg/hr inhalation exposure. This compares well with the
extrapolation from the measured parathion exposure (adjusted for
concentration difference) of 6.0 mg/hr dermal and 0.2 mg/hr. Since
DuPont's data is based on actual use of benomyl, their data will
be used to estimate exposure.
Dermal exposure:
2.2 mg/hr/60 kg = 0.04 mg/kg/hr
Inhalation exposure:
0.015 mg/hr/60 kg = 0.0003 mg/kg/hr
4. Ground Boom Spraying of Vegetables
According of Wolfe and Durham (2), exposure to workers applying 0.09%
parathion spray with a ground boom sprayer, received 4.7 mg/hr dermal
exposure and. 01 mg/hr inhalation exposure. Since benomyl, as used en
tomatoes at 0.06%, is applied at about two-thirds the parathion
rate, an estimated exposure to benomyl can be calculated.
Dermal exposure: 4.7 mg/hr X 0.66 (factor)/60 kg = 0.052 mg/kg/hr
Inhalation exposure: 0.01 mg/hr X 0.66 (factor)/60 kg = 0.0001 mg/kg/
hr.
5. Exposure to Pilot-Aerial Application
A typical application of benomyl to beans calls for one pound of
benomyl diluted to 10 gallons (1.2* w/w) applied over one acre.
-------
-9-
Jeiger (5) measured the exposure of a pilot during application
of 0.6 pounds endrin (A. I.) per gallon (7.11 w/w) to 27 acres or
one pound/ acre (same as benomyl) . By analysis of respirator
pads and collector pads on the pilot's skin, he found pilots
were exposed to 1.18 mg/hr dermally and 0.08 mg/hr by inhalation.
Dermal exposure: 1.18 mg/hr/ 60 kg = 0.02 mg/kg/hr
Inhalation exposure: 0.08 mg/hr/60 kg = 0.001
6. Exposure from Drift
In aerial application of endrin to cotton and wheat, drift exposure
to persons in the vicinity of application was estimated (5) . At
At 0.4 pounds /acre, measurements of dermal exposure were made
for persons at different distances from the application site.
By correcting for the difference in the amount of pesticide
applied per acre (one pound benomyl per acre) an analogous exposure
estimate can be made. Since one pound per acre is 2.5 times 0.4
pounds per acre, the exposure for endrin has been multiplied by
this factor to estimate exposure to benomyl. The results are listed
in Table I.
-------
-10-
Table I
Estimated Dermal Exposure to Benomyl
Distance Downwind
Feet Meters Dermal Exposure mg/kg/ spray incident
83 25 0.04
149 45 0.02
314 96 0.01
644 196 0.004
1304 398 0.002
In a related exposure case Caplan et al. (6) determined the dermal
exposure to person directly beneath a spray application. In this
case the application rate was 0.46 pounds malathion per acre. Since
this rate is lower, an estimate can be made for benomyl exposure
at 1.0 pounds per acre by multiplying the observed exposure of 3.6
mg by (1.0/.46) 2.17 to arrive at 7.8 mg/incident (no time period was
provided). Therefore, dermal exposure would be 7.8 mg/60 kg or 0.13
ing/kg.
7. Exposure to Flaggers
Flaggers are personnel used to direct the spray swaths of the aerial
applicators; as such, they are in close proximity to the spray.
Wolfe (2) measured dermal and respiratory exposure to flaggers
in orchards being sprayed with 9% parathion. He found an average
-------
-11-
exposure for these flaggers to be 84 mg/hr dermal and 0.02 mg/hr
by inhalation. As in example #5, benomyl is used at 1.2% spray.
To relate this rate to a 60 kg flagger, the following calculation
of exposure can be.made:
84 mg/hr x 1.2 = 0.19 mg/kg/hr
60 kg 9.0
0.02 mg/hr x 1.2 = 0.00004 mg/kg/hr
60 kg 9.0
*
8. Exposure Via Benomyl Residues in Food
To obtain an estimate of benomyl in the diet, the following assumptions
were made:
a. Residues of benomyl exist in foods at the allowed tolerance
level and include possible post harvest: dips.
b. A person consumes an average diet as listed in an EPA memo
giving amounts and kinds of food
* The Residue Chemistry Branch has prepared a more
comorehensive report on dietary exposure which will
be submitted separately.
-------
-12-
Benomyl Residues Consumed
Average consumption (7) ug benomyl
Food Item Tolerance mg/kg (8) grams of food/person/day consumed/ 'day
pineapple
apricots
nectarines
cherries
peaches
plums
grapes
mushrooms
berries
apples/pears
rice
strawberries
tomatoes
celery
beans
almonds
avocados
cucumber
melons
pumpkin/squash
peanuts
soybeans
diary/meat
25
15
15
15
15
15
10
10
7
7
5
5
5
2
2
1
1
1
1
1
.2
.2
.1
5.87
2.23
0.59
2.03
7.82
2.63
9.72
0.59
3.54
55.19
10.94
3.65
6.97
5.97
40.42
0.59
0.59
14.38
39.69
2.23
7.09
18.19
841
147
33
9
30
117
40
97
6
24
386
55
18
35
12
81
0.6
0.6
' 14
40
2
1
4
84
1236.2
Average daily intake is 1.2 ing/day or 1.2/60 kg =0.02 mg/kg body weight/day
-------
-13-
9. Use Patterns and Applicator Exposure
The pesticide benomyl has about 25 distinctive uses as identified
by the USDA assessment team (4). Using their estimates of workers and
hours involved, and estimating applicators/hours (when not given) by
pounds of benomyl used, an estimate can be made of the number of persons
exposed to benomyl, and using the exposure estimate generated in
Section V (unit exposure), an estimate of their yearly exposure can
be made. In some cases only incomplete data are available necessita-
ting assumptions. The follo\ving table is a compilation of these uses
along with estimated exposure.
It should be noted that data assumes the person involved in application
of benomyl does not wear protective clothing or a respirator. It is
assumed that an unprotected applicator wears a short-sleeved open shirt,
no hat or gloves, and the proportion of skin exposed to that if pro-
tective clothing is worn is about 5 to 1; therefore, dermal exposure
could be reduced by about 80% if such clothing was worn. A respirator
could reduce respiratory exposure to zero. The following data re-
presents a compilation of applicator use pattern (4) and estimates
of exposure in V 1-8. It should be noted that some numbers (marked
with an E) are estimates based on acreage treated/pounds of benomyl
used/typical application times and frequency as stated in the
USDA report (4).
-------
-14-
8. Use Patterns and Applicator Exposure
Use Pattern Exposed Group Number
1. Rice Pilots 80
(aerial) mix/loaders 200
flaggers 300
2. Soybeans
(aerial) pilots ZOO
mixer/loader 500
flnggcrs 700
3. Stone Fruits pilots 1ZO
(aerinl) mixer/loaders 300
flnp.gers 240
"1. Stone Pruits applicators 60
(alrblast) (coninerclal)
S. Stone Fniits applicators 3000
(alrblnsl) (private)
6. Grapes pilots 20
(aerial) mix/loaders 40
Daggers 50
7. Gropes npplicatovs 60
(alrblast) (conmercial).
8. Grapes oppllcntors 40
(nirblast) (private)
9. Berries pilot IS
(nerlal) loaders/Daggers 20
Exposurc-mg/kR
Dental
hrs/
day
3
6
6
3
G
6
3
G
6
7
8
3
8
8
3
4
3
5
days/ lirs/ )ir
yr
10
10
10
15
15
15
40
40
40
40
6
5
5
5
20
IS
22
2Z
<1ny
year
Inhalation
hr
day
ycnr
yr
30
60
60
45
90
90
120
240
240
280
48
.15
40
40
60
60
66
110
0
1
0
0
1
0
0
1
0
0
0
0
I
0
0
0
0
1
.02
.8
.19
.02
.8
.19
.02
.8
.19
.5
.075
.02
.8
.19
.5
.5
.02
.8
0.06
10.8
1.14
0.06
10.8
1.14
0.06
10.8
1..14
3.5
4.0
0.06
14.4
1.52
1.5
Z.O
0.06
9.0
0
ion
11
0
162
17
2
432
45
140
.6
.0
.40
.9
.0
.10
.4
.0
.60
.0
Z4'.0
0
72
7
30
30
1
198
.3
.0
.60
.0
.0
.32
.0
0
0
0
0
0
0
0
0
0
(I
0
0
0
0
0
0
0
0
.001
.01
.00004
.001
.04
.00004
.001
.04
.00004
.0007
.0007
.001
.04
.00004
.0007
.0007
.001
.04
0.003
0.24
0.00024
0.003
0.24
0.00024
0.003
0.24
0.00024
0.005
0.006
0.003
0.32
0.00032
0.002
0.003
0.003
0.2
0.03
2.4
0.0024
0.045
3.6
0.0036
0.12
9.6
0.0096
O.Z
0.031
0.01S
1.6
0.00016
0.04
0.04
O.OC6
4.4
-------
-15-
'•
Patterns and Applicator Exposure
Use Pattern
10. Gerries
(airblast)
11. Berries
(ground)
12. Fruit Crops
(aerial)
13. Fruit Crops
(airblast)
14. Fruit
(postliarvest
15. Citrus
(airblast)
16. Citrus
(post harvest)
17. Pineapples
Exposed Group
applicators
(canmercial)
applicators
(private)
pilots
mix/loaders
Daggers
applicators
(private)
Mmiber
2fl
210
20
40
50
21,000
F.xposure-mjj/kg
Dermal
irs/
lay_
3
3
3
8
8
days/
Lr
196
20
50
50
50
hrs/
588
60
ISO
400
400
hr
0.5
0.05
0.02
1.8
0.19
day
1.5
0.15
0.06
14.4
1.52
year
294
3.0
3.0
720.0
70.0
Inhalation
hr
.0007
0.0001
0.001
0.04
0.00004
o.oo;
0.001
0.00.
0.32
0.001
12
72
0.5
3.0 36.0
Insufficient Information in USDA report. Applicators well protected
according to report.
applicators
714
8
30
240
0.5
4.0 120.0
According to USDA report, benomyl is used in closed system; hence, no exposure
applicators 3 According to USI>A report, exposure is negligible
0.0007 0.004
year
0.4
0.006
0.15
10.0
0.016
0.05
0.0007 O.OOfi 0.18
-------
-16-
8. Use Patterns and Applicator Exposure
Use Pattern
Exposed Group
Number
hrs/ days/ hrs/
day yjr yr
hr
Exposuro-mg/kg
Dermal Inhalation
day year hr day year
18. Sugarcane According to USDA report, operation is mechanized; hence no exposure
19. Mushrooms E
20. Wheat E
(aerial)
Zl. Wheat E
(ground)
applicators
pilots
mix/loaders
flaggers
applicators
1200
10
10
10
15
4.5
3
7
7
20
20
20
8 15
18
00
140
140
120
0.04
0.02
1.8
0.19
0.05
0.18 0.72
0.06 1.2
12.6 252.0
1.33 2.660
0.4 6.0
22. Peanuts According to USDA, peanut disease fungi have developed resistance; hence, not used now
23. Turf E
(ground)
24. Turf E
(handspray)
25. Ornamental
applicator?
homeowner
200
75
6
O.S
4
4
24
2.5
0.05
0.04
0.3 1.2
0.02 0.08
0.0003 0.001 0.005
0.001
0.04
O.OOOOA
0.003
0.28
0.0003
0.06
5.6
0.006
.0001 0.0008 0.012
applicator
(commercial) Insufficient information, according to USDA report exposure is minimal
26. Ornamentals homeowner
27. Vegetables E all types
534,000
1515
0.5
2
5
5
10
10
0.04
0.04
0.02 0.1
0.08 0.4
0.001
0.0003
0.0003
0.0003
0.006
0.0002
0.0002
0.0006
0.024
0.0006
0.0008
0.003
-------
-17-
References
1. Funchs, A. et al. A comparison of Benomyl and Thiophanate
with Respect to Some Chemical and Systemic Fungitoxic
Characteristics, Pesticide Biochemistry and Physiology
2:191, 1972.
2. Rohm and Haas Company. Benlate Label.
3, Wolfe, H.R. and Durham, W.F. Exposure of-Workers to Pesti-
cides Arch. Environ. Health. Vol. 14, April, 1967.
4. USDA/State/EPA Benomyl Assessment Team. An Analysis of
Current Benomyl Uses: Their Benefit, the Role of Alternatives,
and Impacts to Agriculture from Changes in Benomyl Use Patterns.
U.S. Department of Agriculture July, 1978.
5. Jegier, Z. Health Hazards in Insecticide Spraying of Crops.
Arch. Environ. Health. 8:670, 1964.
6. Caplan, B.D. and Thielan, W. C. Human Exposure of Populated Areas
During Plane Application of• Malathion, AMA Arch. Ind. Health,
14:326, 1956.
7. Food Factors. EPA Memo from R.D. Schmitt to O.E. Paynter,
Dec. 1977.
8. Code of Federal Regulations Title 40 Protection of the Environment
Part 180.294, As Revised July 1, 1976.
-------
-18-
Prepared by:
Harold R. Day, Environmental Chemist
Date: Z/L^Ax JX
Reviewed and .-^J^f^ ^f J/ _^-
Approved by: x ^T£^ /A--^- ."^^/-z^^Zs-S _• -
iie£, Environmental Fate Branch (/
•>*:
Date:
-------
ft nps
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
_....
DATE: April 3, 1979
SUBJECT: Dermal Absorfation of Benomyl
FROM: Pharmacologist, Toxicology Branch
TO: Christine F. Chaisscn
Biochemist/ Toxicology Branch
I have reviewed the DuPont paper entitled 2~14C-Bencmyl (50% WP)
Adsorption Through Rat Skin Part II: Effect of Tire and Dose Applied bv C.J.
Belosco. From the data supplied by this paper one may conclude that it" is
impossible to obtain a cyto toxic level of 10 ug/ml bencmyl in the blood
through dermal absorbtion from Benlate® Fungicide 50% WP~either dry or in
water.
In this DuPont study [2~14C]-benomyl (Benlate© Fungicide) was apolied
to the shaven skin of rats (200-260 gms) at 0.2, 2.0, 20.0 and 200.0 mg per
—part, 20 rats per dose. Rats were placed in metabolism cages and all urine
and feces were collected. Four rats at each dose were sacrificed at 0,5,
1.0, 2.0, 4.0 and 10.0 hours of exposure. Blood samples were collected at
sacrifice. Blood concentrations and total urinary excretion of benomyl were
determined for each dose at each time of exposure. No attempt was made to
distinguish between bencmyl and its metabolites of which MBC'is the active
cytotoxin.
EPA is concerned with the relationship between dose of bencmyl applied to the
skin and the maximum blood concentration of benomyl-MBC which results
therefrom. Figure 1 of the DuPont paper presents this data plotted by dose
as hours after treatment against blood concentration of Eencmyl. Each point
represents the mean of four animals. For each dose a maxinum"blood
concentration of bencmyl is reached after four hours of exposure. The
highest mean concentration is .070 ppm (70 nanograms per ml) at a 200 rog dose
while the highest single rat.concentration is .098 ppm (98 nangrams per ml).
at the same dose and time. This represents approximately one 80th of the
dose considered inactive by EPA but. with the data as presented in Figure one
it is impossible to determine if the no-effect concentration of 8 ug/ml can
be reached by increasing the dermal dose.
CPA FORM 132O-A (REV. 3-78)
-------
In the second figure, I have plotted the same data by hours after treatment
as dose against blood concentration of benomyl. Again each point is the
mean of four, animals. In this figure, the doses are plotted on a logrithmic
scale in which the intervals are equal for each 10 fold increase of dose.
This is a standard procedure in "pharmacology for obtaining an S-shaped dose
r><».5 <"""•* response curve. The line for 0.5 hours indicates that a maximum blood con-
. ^> centration in the order at 35-40 "ppcj will be reached with increased dermal
' dose and that skin penatration is tire limited at this interval. The remain-
. ing lines represent only approximatly the first half of the dose-response
curve and it is impossible to determine their limits and whether they will be
tine or permability limited from the data of this study. However, one may
make certian extrapolations from these lines and determine whether it is phy-
sically possible to reach the no-effect level of 8 ug par ml in bleed. The
central portion of a dose-response curve plotted in this fashion is linear.
Based on the physical-chemical properties of benomyl and of the skin, one can
expect no further increase in rate of penetration of bencmyl once the linear
portion of the dose-response curve is reached as long.as we continue to uti-
lize the dry powder or its water form. Wa also know that a limit in penetra-
tion rate.will be reached as noted above for the 0.5 hours exposure. We are
thus justified in making a linear extrapolation of the dose-response curve
as shown by the dashed lines in order to show clearly that a practical limit
to benomyl application on the skin is reached far before the concentration of
8 ug/ial in the bleed can be reached.
At dose of 2000 ing we estimate an average concentration of 100 ng bencrayl in
the blood utilizing this extrapolation. Since this means applying 2 grains of
benomyl (4 grams Benolate®) to four square inches of rat skin it appears im-
practical. However/ essentially this blood concentration has reached by one
rat at a 200 mg dose (98 ng). Therefore, we will extended cur extrapolation
another unit (to a 20,000 mg dose) in our search for a limit. At a dose of
20,000 mg we estimate an average blood concentration of BO'ng/ml (point 2).
At this point we are dealing with an obviously impossible situation. Twenty
grams of benomyl (as 40 grams of Benolate®) placed en 4 square inches of a
rats back! Only a small portion of the dose is in direct contact with the
rats skin and is available for absorption. This is a physical limit bo
absorption such that the amount absorbed can no longer increase with
increased doses. Thus we can conclude that there is an absolute limit to
dermal absorption such that a blood concentration of 8 ug/ml cannot be
reached.
The possibility of saturation of metabolic and excratory processes appear to
be remote but is should be considered* Bencmyl is rapidly converted to MBC
(the biologically active metabolic) in the mammal. MBC is then inactivated
by enzymatic 5-hydroxylation and glucronide or sulfate conjugation in the
liver. These compounds are highly polar and are rapidly excreted by the
kidneys. These detoxification and excratory processes are of large capacity
in the
-------
mammal and one would rot expect them to be saturated or even approach
saturation by the small concentrations of Benonyl-vMBC demonstrated in the
blood by these experiments. This lack of saturation is clearly shown in
Figure 3 which plots the excretion of bencmyl (as 2~14C metabolites)
against dose for 10 hours of dermal exposure. There is no indication of a
full-off of excretion with increased dose and thus no possibility of
accumulation due to saturation of the metabolic and excratory processes.
As a final 'point, one irust consider the possibility of bioaccurrulation by
tissue storage in the mammal. Eased en the physical-chemical properties of
benorryl and its metabolites and their pattern of excretion, one would not
expect benomyl-i-EC to accumulate in tissue. The only studies available which
bear en this question have been performed and reported bv duPont. duPont has
reported the results of analytical studies, utilizing C1* benontyl, en the
blood and testes of rats which received benonyl (a) at a single dose of 1000
rag/kg PO or (b) 10 repeated oral doses of 200 rog/kg/day.
At the 1000 rag/kg dose, total C14 residues (calculated as benontyl) ranged
from 3 to 13 ug/ml in the blood and from 2 to 4 ug/gn in the testes. At the
200 mgAg/dose one hour after the last dose .there was 1.5 ug/ml in the bleed
and 0.3 ug/gn in the testes. Twenty-four hours after the last dose no
residue was detected (<0.1 ug/gn). These results give no indication of
tissue accumulation.
Finally we will consider the application of this information to man. It is
-generally agreed that human skin is less permeable (by a factor of about
five) than the skin of the albino rat. Considering the information presented
in the rat dermal absorption study, it is not necessary to consider such a
factor and we will simply assume that the human skin is no more parmable than
the rat skin. Thus we can conclude that exposure of 16% of an individuals
skin to a dose of 200 mg will result in a blood concentration of no more than
100 raanograras per milliliter.
We can further conclude that an absolute limit to human dermal absortion of
benccnyl exists such that the no-effect level of 8 ug/ml cannot be reached by
dermal abrosption.
Robert Zendzian, Ph.D.
-------
Blood Level ot •*'•C-DcnomyjL J^quivaxencu ay
Influenced bv Doso and Time
j- ; mcj - ^nenptj/nat
n j 20.6 mg' * ^SJ-Bpnlotc^/?,at
-------
•Figure 2. Ilonomyl normal Absorbti on Blood Concentrations of 2
Bcnomyl nnd Metabolites moan value of Four rats at each Point
-14
ISnSljjS
MMMMmfiW^w^
,,.. i •..* i.... .. j. i.... i. |.. i..... |.. j
lilllllllj plill
IIIiiiSiiiHl
-------
-14
Figure 3. Benornyl Excretion ns 2 G metabolites
2 ,
10 hours dermal exposure to A in of akin mean value
of Four rats at each point
3*
Microgramn
excreted J.O
in 10 Ii ft u T~ a
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-------
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BIOES
-------
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
DATE: May 25, 1979
SUBJECT: Dermal Absorbtion of Benomyl Following Human Field Exposure
FROMt
Pharmacologist, Toxicology Branch/HED (TS-769)
Christine F. Chaisson
Biochemist, Toxicology Branch/HED (TS-769)
The human dermal absorbtion of Eencmyl is calculated as not exceeding 6.23
ug/kg in a worst case dermal exposure of 1.8 ing/kg/hr for 8 hours by a
mixer/loader during field application. This estimate is based on 'dermal
absorbtion studies of benomyl performed en the rat by the research
laboratories of E.I. duPont de Nemours and Co. It is concluded that the
dermal absorbtion of benomyl is in and of itself an insignificant dose
during spraying operations and it need not be considered for purposes of
exposure calculation.
In a previous memo, (Dermal Absorption of Benomyl, April 3, 1979) I
reveiwed the duPont study on the dermal absorbtion of benomyl and concluded
that it is impossible to reach a cytototoxic concentration of 10 ug/ml or
the no effect concentration of 8 ug/ml of bencnryl in the blood following
dermal absorbtion. This memo extends that analysis to the estimation of
human dermal absorbtion of benomyl during field exposure. The document
entitled, Final Exposure Analysis for Benomyl, December 12, 1975 by EFB,
HED, OPP, EPA, provides data on dermal exposure to benomyl during various
patterns of field use and associated exposure. The \vorst case of dermal
exposure reported involves a mixer/loader who receives 1.8 mg/kg/hour for 8
hours. This exposure is 108 mg/60 kg man/hour on 16% (2602in) of his
surface area.
The data from the benomyl absorbtion study which will be' used here consists
of two parts 1) the quantity of benomyl excreted with time at various doses
and 2) the blood concentrations of benomyl at various doses and times after
dosing.
'Figure I is a log- log plot of the micrograms benomyl excreted against the
dermal dose in millograms applied to 42 inches of rat skin. Each line
represents a different duration -of exposure. This graph can be used to
determine the excreted portion of the total amount of benomyl absorbed by
four square inches of skin following various doses for various time
periods.
The human field exposure data indicates that the mixer/loader was exposed
for eight hours and received a 1.8 mg/kg dermal dose for each hour of
exposure. This accumulation of dose can be approximated by the line in
Figure 2 but this does not truly represent the field situation in which the
dosing occurs in bits and dabs nor does 'it alia-; use of the rat
experimental data in which the entire dose was applied at time zero.
EPA FORM 1120-S (REV. 3-76)
-------
In order to utilize the rat data, I have assumed that 1) the entire hourly
dose was applied at the beginning of each hour and 2) that the entire dose
remains on the skin for the total subsequent exposure period. This pattern
of dosing may be plotted as shown in Figure 3 and will allow use of the rat
experimental data to estimate human dermal absorbtion. It must be noted
that .these assumptions err in overestimating the dermal dose which
accumulates, during the duration of exposure and which cannot be expected
to stay on the skin for the entire duration of exposure. The calculations
involved and results obtained are shown in Table I. The human dose is
converted from mg/kg/hr to mg/4^ in/hr. This figure is used on the one
hour line of the graph of Figure I to obtain the ug/kg excreted which
represents part of the quality absorbed. The remainder of the quantity
absorbed is estimated by using a factor obtained from the blood
concentrations of bencmyl in the rat at one hour after dermal doses of 2
and 20 mg/42 inches of skin.
A 250 gram rat has a blood volume of 6.4% or 16.1 ml. At a dose of 2
mg/rat the average blood concentration of benonyl in four rats at one hour
was 9 ng/ml for a total of 147 ng/rat. The quantity excreted was 310 ng
for a total quantity absorbed of 457 ng of which the quantity excreted was
68%. At a dose of 20 mg/rat the blood. concentration was 28 ng/ml or 451
ng/rat. The quantity excreted was 670 ng/rat for a total quantity absorbed
of 1121 ng/rat of which the quantity excreted was 60%. Since the 2 mg aid
20 mg doses defined the portion of the excretion curve used to obtain the
value in Table I, column three., the mean value of 64% excreted v/ill be used
to correct for the quantity retained in the body. The correction gives the
values in column five of Table I which are maximum values.
The values in column five of Table I are the total quantity absorbed after
each hour of exposure assuming that the rat skin and the human skin are
equally permeable to externally applied substances. There is
experimentally derived reason to believe that the human skin has only
one-fifth the permeability of the rat skin. This skin permeability factor
is used to obtain the figures in column six of Table I which are minimum
values,
From these calculations it is concluded that a mixer/loader exposed
dermally to 1.8 mg/kg/hr of bencmyl for 8 hours will absorb no more than
6.23 ug and no less than. 1.25 ug of benomyl per kilogram. If the high cose
were injected into the blood stream of a 60 kilogram man, it would result
in a blood concentration of 1.6 x 10~3 ug/ml. This dose is
approximately one four thousandth of the no effect level of 8 ug/ml. Not
only is this an insignificant dose but, intravenous injection will result in
a much higher blood concentration then could occur with slow dermal
absorbtion of the same amount of bencmyl ever a period of eight hours.
-------
Hour
I
2
3
4
5
6
7
8
Exposure
mg/42 in
/hr.
1.66
3.32.
4.98
6.64
8.30
9.96
11.62
13.28
Absorption
ug/42 in
/hr.
0.28
0.36
0.42
0.46
0.50
0.52
0.56
0.60
ugAg
/hr.
0.30
0.39
0.45
0.50
0,54
0..56
0.60
0.65
ugAg
£ hr.
0.30
0.69
1.14
1.64
2.18
2.74
3.34
•3.99
4- Blood quantity
ug/'kg S. hr.
0.47
1.08
1.78
2.5.6
3.41
4.28
5.22
6.23
-r Human skin
permability
ugAg 51 hr.
0.09
0.22
0.36
0.51
0.68
0.86
1.04
•1.25
Table I. Dermal Absorbtioh of Benomyl Following Field Exposure: Mixer/loaders 1.8 mg/kg/hour.
-------
J
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