Monocrotophos - Chemical Fact Sheet 9/85
CHEMICAL FACT SHEET FOR:
FACT SHEET NUMBER: 72
DATE ISSUED: SEPTEMBER 30, 1985
1. DESCRIPTION OF CHEMICAL
- Generic Name: dimethyl phosphate of 3-hydroxy-N-methyl-cis-
- Common Name: monocrotophos
- Trade Names: Azodrin, Apodrin, Bilobron, Crisodrin, Glore Phos 36,
Hozodrin, Monocil 40, Monocron, Nuracron, Pillardrin, Plantdrin,
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 Company (U.S.A.)
2. USE PATTERNS AND FORMULATIONS
- Application sites: Terrestrial, non-domestic food uses on cotton,
peanuts, and sugarcane; terrestrial, non-domestic non-food 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
- Usual carriers: Confidential Business Information
3. SCIENCE FINDINGS
- Technical monocrotophos is a reddish-brown solid with a melting point
of 25-30 degrees 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 simple
alcohols and glycols at room temperature; and relatively stable in
sunlight. It is nonvolatile at 100 degrees F and decomposes at 310-
320 degrees F. At 20 degrees C, hydrolysis is quite slow. Its half-
life in solution (2 parts per million) at pH 7 and 38 degrees C is 23
- Current available toxicological studies on monocrotophos are as
- Acute oral toxicity: rat, LD50 = 23 mg/kg for males and 18 mg/kg
for females. Toxicity Category I.
- Acute dermal toxicity: rat. LD50 r 354 mg/kg. Toxicity
- Primary eye irritation: rabbit, slight to moderate irritation and
corneal opacity reversible by day 14. Toxicity Category II.
- Primary dermal irritation: rabbit, PIS = 0.6 to 1.0, slightly
irritating. Toxicity 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.
- 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. Systemic LEL = 9.0 ppm
(body weight decrease in males, decreased survival in females).
This study 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).
- Dog chronic feeding: NOEL - ChE I = 1.6 ppm. LEL - ChE I =
16.0 ppm. Systemic NOEL = 16.0 ppm. Systemic LEL = 100 ppm
(salivation and tremors).
- 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 mg/kg/day).
- Rat reproduction: Generated a reproductive (and offspring) NOEL
of 2.7 ppm and an LEL of 9.0 ppm (as evidenced by 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 studies assessing DNA damage/repair and
sister chromatid exchange.
Physiological and Biochemical Behavioral Characteristics
- 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).
- Metabolism and persistence in plants and animals: The metabolism
of monocrotophos in animals 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
- Monocrotophos hydrolyzes rapidly (half-life of 14-21 days at pH
9 and 25 degrees 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 bioaccumulation in catfish and
are depurated fairly rapidly.
- Monocrotophos is mobile 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 groundwater contamination.
- 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 0.188 mg/kg for the golden eagle (very highly
- Avian dietary toxicity: Dietary studies on the ring-necked
pheasant and mallard duck resulted in dietary toxicity values of
3.1 and 9.6 ppm, respectively (very highly toxic).
- Fish acute toxicity: Test results for warmwater acute fish
toxicity range from 12.1 ppm for bluegill sunfish to >50 ppm for
fathead minnows (moderately toxic).
- Freshwater invertebrate acute toxicity: Test results for acute
toxicity to Daphnia magna were 0.034 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 (nontoxic
to reproduction). Typical reproductive 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
feed a toxic dose to their brood.
- Honeybee acute toxicity: 0.350 micrograms per bee (highly 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 monitoring 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
- Established tolerances for monocrotophos are published in 40 CFR
180.296 and 21 CFR 193.151. They are:
Commodity Parts per million
Tomatoes 0 5
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 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 systemic effects at 0.9 ppm), generating an ADI of
0.00015 mg/kg/day (systemically, 0.0045 mg/kg/day), which results in
the TMRC for previously published tolerances occupying 397% 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 since submitted an application with revised labels, removing both
tomatoes and potatoes from their Section 3 product labels. The
elimination of the use of monocrotophos on tomatoes and potatoes
lowers the TMRC to 66% of the ADI. Nevertheless, the Agency 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 a tolerance reassessment can be
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.
4. 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 (Section
162.11 (a)) have 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 reassessment is made, and a well-designed
field test in birds has been evaluated.
- Because of the high acute toxicity of monocrotophos to humans:
- All end-use products containing monocrotophos shall continue to be
classified for restricted use.
- The Agency is requiring applicators with a high exposure to
monocrotophos, mixers, and loaders to wear protective clothing.
The use of backpack or knapsack sprayers for application of
monocrotophos is being prohibited.
- The Agency will continue to require the reentry interval of 48
hours established under 40 CFR 170 for all outdoor uses of
monocrotophos in order to minimize exposure to 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
sensitive 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 trimethyl phosphate (TMP) contaminant
persist 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 characteristics.
- 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
- Toxicology: Studies on acute and 21-day inhalation, dermal sensiti-
zation, general metabolism, and rabbit teratogenicity; and additional
information on the mouse oncogenicity study.
- 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 reentry protection and spray drift.
6. CONTACT PERSON AT EPA
William H. Miller
Product Manager 16
Registration Division (TS-767)
Environmental Protection Agency
401 M Street S.W.
Washington, DC 20460
DISCLAIMER: THE INFORMATION PRESENTED IN THIS CHEMICAL INFORMATION FACT
SHEET IS FOR INFORMATIONAL PURPOSES ONLY AND NOT TO BE USED TO FULFILL
DATA REQUIREMENTS FOR PESTICIDE REGISTRATION AND REREGISTRATION.