United State* Office of Pesticides and Toxic Substances
Environmental Protection Office of Pesticide Programs (TS-766C)
Agency Washington. DC 20460
v>EPA Pesticide
Fact Sheet
Name of Chemical:
Reason for Issuance: REGISTRATION STANDARD
Date Issued:
3Q/ 1985
Fact Sheet Number: 72
1. Description of Chemical
Generic Name: Dimethyl phosphate of 3-hydroxy-N-methyl-
cls-crotonamide
Cannon Name: Monocrotophos
Trade Names: Azodrln; Apodrin; Bllobron; Crlsodrln;
Glore Phos 36; Hozodrln; Monocll 40;
Monocron; Nuracron; Pillardrin; Plantdrln;
Susrin; and Ulvair.
EPA Shaughnessy Code: 058901
Chemical Abstracts Service (CAS) Number: 6923-22-4
Year of Initial Registration: 1965
Pesticide Type: Insecticide/acaracide
Chemical Family: Organophosphate
U.S. and Foreign Producers: Shell Chemical Co. (U.S.A.)
2. Use Patterns and Formulations
Application Sites: Terrestrial, nondomestic food uses on
cotton, peanuts and sugarcane.
Terrestrial, nondcraestlc nonfood uses on
tobacco, ornamental conifers (nursery
stock), ornamental flowering plants
(nursery stock), ornamental woody shrubs
(nursery stock), and ornamental deciduous
trees (nursery stock).
Types of Formulations: Soluble concentrate liquid
Types and Methods of Application: Aerial and ground application.
Application Rates: 0.125 - 1 pound per acre (Ib/a)
Usual Carriers: CONFIDENTIAL BUSINESS INFORMATION
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3. Science Findings
Summary Science Statement :
Toxicology, environmental fate, ecological effects, product
chemistry and residue chemistry data gaps preclude the Agency
from making a complete assessment for monocrotophos. However,
based on available data, monocrotophos can be characterized
as having very high acute oral toxicity to both humans and
birds. Monocrotophos is a potent cholinesterase inhibitor
(NOEL = 0.03 ppm in rats). Monocrotophos is also fetotoxic
(NOEL = 1.0 ppm) but not teratogenic at the highest dose
tested (2 mg/kg), decreases fertility at 9.0 ppm (NOEL = 2.7 ppm)
and is weakly mutagenic in vitro.
Chemical Characteristics :
Technical monocrotophos is a reddish brown solid with a
melting point of 25 to 30 °C. Its odor is characteristic of a
mild ester. Monocrotophos is soluble in water, acetone, and
alcohol. It is stable when stored in glass or polyethylene
containers; stable in simile alcohols and glycols at room
temperature; relatively stable in sunlight and nonvolatile
at 100 °F; decomposes at 310 to 320 °F. At 20 °C, hydrolysis
is quite slow. Its half—life in solution (2 parts per million
(ppm)) at pH 7 and 38 °C is 23 days.
Toxicology Characteristics :
Current available toxicological studies on monocrotophos
are as follows:
o Acute oral toxicity: rat, L 5 o = 23 mg/kg (males)
and 18 mg/kg (females), (Tox Category I).
o Acute dermal toxicity: rat, LD 50 = 3514 milligrams
per kilogram (mg/kg) (Tox Category II).
o Primary eye irritation: rabbit, slight to moderate
irritation and corneal opacity reversible by
day 1 4 (Tox Category II).
o Primary Dermal irritation: rabbit, PIS = 0.6 to
1.0, slightly irritating (Tox Category IV).
Major routes of exposure: Application by ground and aerial
equipment increases the potential for exposure of humans,
livestock and wildlife due to spray drift. Human exposure to
monocrotophos from handling, application and reentry operations
is minimized by the use of approved respirators and other
protective clothing.
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Chronic toxicity results:
° Rat chronic feeding and oncogenicity:
Not carcinogenic at the highest dose tested
(HDT) 9 ppm.
No Observable Effect Level (NOEL)
- ChE I = 0.03 ppm.
Lowest Effect Level (LEL) — ChE I = 0.09 ppm.
Systemic NOEL = 0.9 ppm.
S stem1c LEL = 9.0 ppm (body weight decrease
in males; decreased survival in females).
This stud, Indicates that the rat is the
most sensitive species for measuring
cholinesterase Inhibition (NOEL = 0.03 ppm)
compared to the dog (NOEL = 1.6 ppm).
o Dog chronic feeding:
NOEL - ChE I = 1.6 ppm.
LEL - ChE I = 16.0 ppm.
Systemic NOEL = 16.0 ppm.
Systemic LEL = 100 ppm (salvation and tremors).
o Rat teratogenicity:
Fetotoxic effects were found at 2 mg/kg. The
effects consisted of runting, reduced fetal
weight and length (NOEL = 1.0 mg/kg), and
maternal toxicity in the form of reduced
body weight gain at 1.0 mg/kg (NOEL = 0.3
mg/kg). No teratogenic effect was observed
at the HDT (2.0 rng/kg/aay).
o Rat Reproduction:
Generated a reproductive (and offspring) NOEL of
2.7 ppm and an LEL of 9.0 ppm (as evidenced b
decreased fertility, pup viability and weight,
partly attributed to depressed maternal lactation).
° Mutagenicity:
A total of 19 studies evaluating monocrotophos
for mutagenicity are available, but only 10 are
adequate (acceptable). Monocrotophos is weakly
mutagenic in vitro , as determined mainly
from stud1 I asse8sing DNA damage/repair and
sister chromatid exchange.
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Physiological and Biochemical Behavioral Characteristics
o Mechanism of Pesticidal Action:
Monocrotophos is a systemic and contact poison.
As an organophosphate, monocrotophos exerts
its toxic action by inhibiting certain important
enzymes of the nervous system (cholinesterase).
O Metabolism and Persistence in Plants and Animals:
The metabolism of monocrotophos in animal8 and plants
has not been adequately described. Metabolism studies
utilizing ruminants and poultry will be required to
fill the animal metabolism data gaps. Currently,
no tolerances for residues of monocrotophos in
animal products exist; however, monocrotophos and
some of its metabolites have been identified in the
milk, muscle, and liver of cows and in the milk of
goats following ingestion of this chemical.
Additional plant metabolism data are required,
including studies to reflect the potential for uptake
of soil metabolites following foliar applicati.ons.
Environmental Characteristics
Monocrotophos hydrolyzes rapidly (half-life of 14—21 days
at pH 9 and 25 ° C), with the rate decreasing at lower pH’s and
increasing at higher temperatures. Degradation on soil exposed
to natural sunlight is rapid (half-life less than 7 days) and
on dark control samples is slower (half—life approximately
30 days). Residues have a low potential for bioaccumulatiori
in catfish and are depurated fairly rap1dl ’.
Monocrotophos is mobil in soil and although it degrades
rapidly, it may possess potential for groundwater contamination.
Pertinent data (mobility, metabolism and dissipation) are
necessary to fully assess monocrotophos’s potential for ground
water contamination.
Ecological Characteristics :
Avian Oral Acute Toxicity: Test results showed that acute
oral toxicity for upland game birds ranges from 0.763 to 6.49
mg/kg; 1.58 to 4.76 mg/kg for waterfowl; 1.00 to 5.62 mg/kg for
passerines and for the golden eagle, the value is 0.188 mg/kg
(very highly toxic).
Avian Dietar,y Toxicity: Dietary studies on the ringed-
neck pheasant and mallard duck resulted in dietary toxicity
values of 3.1 and 9.6 ppm, respectively (very highly toxic).
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Fish Acute Toxicity: Test results for warm water acute
fish toxicity range from 12.1 ppm for bluegill sunfish to
greater than 50 ppm for fathead minnows (moderately toxic).
Freshwater Invertebrate Acute Toxicity: Test results
for acute toxicity to Daphnia magna were 0.03 4 ppm (very
highly toxic).
Avian Reproduction: Test results are sufficient to
characterize monocrotophos as not having an effect on the
overall reproductive success of birds at levels of 0.1 to 3.0
ppm in the diet (non-toxic to reproduction). Typical repro-
ductive effects in the field are unlikely from the use of’
monocrotophos. Rather more likely, breeding birds will be
exposed to a toxic dose themselves or will lead/feed a toxic
dose to their brood.
Honeybee Acute Toxicity: 0.350 micrograms per bee (highlj
toxic).
Monocrotophos is one of the most toxic pesticides to birds.
Monitoring and incident reports contain numerous observations
of avian mortality attributed to monocrotophos; thus, it has
the potential for causing significant impacts on populations of
avian wildlife. The field studies that have been submitted are
inadequately designed and contain mostly cursory monttoring
information; therefore, terrestrial field testing for effects
on avian wildlife is needed. Monocrotophos has been reviewed
under the cotton “cluster” for endangered species, and no
Jeopardy has been determined for endangered avian species.
The Agency will initiate a formal consultation with the U.S.
Fish and Wildlife Service Office of Endangered Species
concerning potential adverse effects of monocrotophos on
terrestrial species for the remaining uses.
Tolerance Assessment
Established tolerances for monocrotophos are published in
4O CFR 180.296 and 21 CFR 193.151 and are:
Commodity Part per Million
pOtatOe8 0.1
tomatoes 0.5
cottonseed 0.1
peanuts .05
sugarcane 0.1
concentrated tomato products 2.0
The Agency is unable to complete a full tolerance assessment
for the established tolerances because of residue chemistry data
gaps including plant and animal metabolism studies and residue
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data to determine whether food/feed additive tolerances must be
proposed for the processed products of all the registered crops.
The NOEL for cholinesterase inhibition (ChE)-has been set
at 0.03 ppm (and for sy8tefnlc effects at 0.9 ppm), generating
an ADI of 0.00015 mg/kg/day (systemically, 0.00145 mg/kg/daj),
which results in the TMRC for previously published tolerances
occupying 397 percent of the ADI (132% based on systemic
effects). Thus, on either basis (ChE or systemic), the
margin of safety has been exceeded for those tolerances
already published which precludes granting any new requests.
The Agency requested, and the registrant agreed, to
voluntarily delete the use of’ tomatoes from currently approved
labels. The registrant has 8lnce submitted an application
with revised labels removing both tomatoes and 1 otatoes from
their section 3 product labels. The elimination of the use
of monocrotophos on tomatoes and potatoes lowers the TMRC to
66 percent of the ADI. Nevertheless, the Agenc,y will not
allow any new uses to be established for monocrotophos until
the required residue chemistry data (including animal metabolism
studies) have been submitted and evaluated so that a tolerance
reassessment can be made.
14• Summary of Regulatory Position and Rationale
The Agency has determined that it should continue to allow
the registration of monocrotophos. None of the criteria for
unreasonable adverse effects listed in the regulations [ 162.11
(a)] has been met or exceeded. However, because of gaps in
the data base a full risk assessment cannot be completed.
The Agency will not allow any significant new uses to be
established for monocrotophos until the residue chemistry
data deficiencies have been satisfied, a tolerance reassess-
ment is made, and a well—designed field test in birds has been
evaluated.
Because of the high acute toxicity of monocrotophos to humans:
O All end-use products containing monocrotophos shall
continue to be classified for re8trlcted use.
o The Agency is requiring applicators with a high exposure
to monocrotophos, mixers, and loaders to wear protective
clothing. The use of backpack or knapsack 8prayers for
application of monocrotophos Is being prohibited.
O The Agency will continue to require the reentry interval
of’ 148 hours established under 140 CFR 170 for all outdoor
uses of monocrotophos in order to minimize exposure to
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workers entering treated areas, pending the receipt and
evaluation of reentry data to assess the potential for
exposure to workers coming in contact with monocrotophos.
Because of the high acute toxicity of monocrotophos to birds:
° The Agency is requiring a well—designed field test on
birds. The field sites will include a number of sites in
each growing area and will investigate monocrotophos
exposure to birds from diet and drinking water and the
effect on young fledglings using nest boxes. The
design of the field testing protocols, selection of
8ensitlve indicator species (including avian predators),
and the selection of the test sites must be submitted
to the Agency. This protocol must be approved by the
Agency prior to the initiation of the study. Until the
study is conducted and reviewed, label precautionary
statements are required.
The Agency is requiring all end—use products registered
for outdoor use to bear a restriction on rotating food or
feed crops to monocrotophos treated soils unless monocrotophos
is registered for use on the rotated crop. This restriction
will remain in effect until such time as data are submitted
and reviewed which allow the Agency to determine a time
interval at which rotated crops planted In treated soil will
be free of pesticide residues.
The Agency is not requiring additional residue data to
determine if any detectable residues of the trirnethyl phosphate
(TM?) contaminant persists in raw agricultural commodities
or processed foods unless the plant metabolism study being
required shows that TMP persists.
5. Summary of Major Data Gaps
Product Chemistry: Data on product Identity, ingredients,
impurities, and physical and chemical
characteristic8.
Residue Chemistry: Studies on plant and animal metabolism,
storage stability of samples, and
residue data to determine whether food!
feed additive tolerances are required
for processed products of all registered
crops.
Toxicology: Studies on acute and 21—day Inhalation,
dermal sensitization, general metabolism,
and rabbit teratogenicity; and additional infor-
mation on the mouse oncogenicity study.
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Wildlife and Aquatic Organisms: A field test on birds and
acute toxicity to estuarine and marine
organisms.
Environmental Fate: Soil metabolism, mobility, dissipation
and accumulation studies and data on
reentr , protection and spray drift.
6. Contact Person at EPA : William H. Miller
Product Manager (16)
Insecticide-Rodenticide Branch
Regi8tratlon Division (TS-767)
Environmental Protection Agency
Washington, DC 2O1 6O
Tel. (703) 557—2600
DISCLAIMER: The information presented in this Chemical
Information Fact Sheet is for informational purposes only
and may not be used to fulfill data requirements for pesticide
registration and reregistration.
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