Offfe* *t
A*mnr ' Wih^toQ.OC 20460
&EPA Pesticide
Fact Sheet
Name of Chemical: METHYL PARATHION
t
Reason for Issuance: ISSUANCE OF GUIDANCE DOCUMENT
Date Issued: 0^3,^ 1986
Fact Sheet Number:117
1. DESCRIPTION OF CHEMICAL
Generic Name: 0,0-dimethyl-0-4-nitrophenyl phosphorothioate
Common Name: Methyl Parathion
Trade Names
and other
names: 0,0-dimethyl 0-(4-nitrophenyl) phosphorothioate;
0,0-dimethyl O-(p-nitrophenyl) phosphorothioate;
parathion-methyl; metaphos; Cekumethion;
Devithion; dimethyl parathion; E601; Folidol M;
Fosferno M50; Parataf; Paratox; Partron M;
Penncap M; Tekwaisa; Wofatox; Metacide; Bladan M;
Metron; Dalf; Nitrox 80.
EPA Shaughnessy Code: 053501
Chemical Abstracts Service (CAS) Number: 298-00-0
Year of Initial Registration: 1954
Pesticide Type: Insecticide
Chemical Family: Organophosphate
U.S. and Foreign Producers: Monsanto in the U.S., and
Bayer, AG in West Germany, Chemiekombinat Bitterfield VEB in
East Germany, and A/S Cheminova in Denmark.
2. USE PATTERNS AND FORMULATIONS
Application Sites: Field, vegetable, tree fruit and nut
crops, tobacco and ornamentals, forestry, aquatic food
crops, mosquito abatement districts, terrestrial and
non-crop sites.
Pests controlled: A wide variety of insects and mites as well
as tadpole shrimp.
Types and methods of application: Usual appication is foliar.
May be applied by aircraft or ground equipment.
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Types of Formulations: Dusts, wettable powders, micro-
encapsulated, emulsifiable concentrates,
and ready-to-use liquid.
Rates: 0.1 to 6.0 lbs. a.i. per acre
Usual Carriers: petroleum solvents, clay carriers
3. SCIENCE FINDINGS
Summary Science Statement:
Methyl parathion is a Toxicity Category I organophosphate
compound which is highly toxic to laboratory mammals, humans,
aquatic invertebrates, and birds. There is some evidence that
methyl parathion may effect reproductive success in birds.
Methyl parathion poses a hazard to many endangered species.
In laboratory rats of the Wistar strain, oncogenicity could not
be determined as the data were insufficient; the Agency is
requiring additional information on this study as well as a
repeat of the mouse study. Chronic toxicity data indicate that
methyl parathion causes retinal and sciatic nerve damage in
rats at high dose levels (50 ppm in diet). Because data are
not available, the Agency is unable to determine a no observed
effect level (NOEL) for sciatic nerve damage.
Chemical characteristics:
Little information is available. 3 echnica1 methyl para-
thion has a vapor pressure of 0.14 mg/rn at 20 C, and an
octanol/water parition coefficient of 3300. Methyl parathion
is soluble in most organic solvents and is slightly soluble
in aliphatic hydrocarbons. This compound is practically in-
soluble in water.
Toxicology Characteristics:
Acute Toxicity:
Methyl parathion causes cholinesterase inhibition. It is
highly toxic to rnamlnal3 y all routes of exposure and is classi-
fied In Toxicity Category I (LD 0 4.5 to 16 mg/kg).
Major Routes of Exposure:
The major route of exposure is acknowledged to be dermal
with inhalation, ocular, and oral exposure being much smaller.
Information from the California Department of Food and
Agriculture reported incidents of worker poisonings and
illnesses during mixing, loading and application of methyl
parathion. EPA is requiring additional Worker Safety Rules,
including protective clothing, to reduce exposure.
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Delayed Neurotoxicity:
Methyl parathion is not believed to cause delayed neurotox-
city.
Chronic feeding/Oncogenicity studies:
The Agency has two 2 year chi onic feeding/oncogenicity
studies in the rat, one in the mouse and a one-year dog study.
The Agency is unable to definitively evaluate oncogen-
icity at this time; additional information is required in
the Wistar rat strain and another mouse study is required.
Chronic effects noted; retinal and sciatic nerve damage at
high dose levels(50 ppm) was observed in the rat.
Subchronic Studies:
Subchronic feeding studies show cholinesterase as the
primary target for the toxic action of methyl parathion.
A NOEL was establiched in the rat at 2.5 ppm or 0.25 mg I
kg/day. The NOEL in the dog was 0.3 mg/kg/day (this NOEL
was used to establish the current PADI). However, additional
subchronic studies in both the rat and dog are required to
determine the NOEL for retinal and sciatic nerve damage in
the rat and retinal damage in the dog.
Metabolism:
Data gap; additional data are required.
Teratogenicity:
Some evidence of embryotoxicity and fetotoxicity at
1.0 mg/kg in rats. However, maternal toxicity was not
established. Additional data are required. No signs of
developmental toxicity were noted in the rabbit.
Reproduction:
No reproductive effects were observed in rats at dietary
levels up to 25 ppm. No additional information is required.
Mutagenicity:
The Agency has evaluated the reports of a number of
assays which address the three major categories of alterations,
I e , ])gene mutation, 2), structural chromosomal aberrations,
and 3) other mechanisms of genotoxicity. Although results
of several of the individual tests are negative, other tests
in each of these major categories provide limited evidence
that methyl parathion is genotoxic. No additional information
is required.
Physiological and Biochemical Characteristics:
Methyl parathion acts by causing irreversible inhibition
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of cholinesterase enzyme, allowing accumulation of acetyicholine
at cholinergic neuroeffector junctions and autonomic ganglia.
Poisoning symptoms include headaches, nausea, vomiting,
cramps, weakness, blurred vision, pinpoint pupils, tightness
in the chest, drooling or frothingtof mouth and nose, muscle
spasms, coma, and death. The mechanism of pesticidal action
is not known.
Environmental Fate and Exposure:
Insufficient information is available for the analysis of
the environmental fate and the exposure of humans and nontarget
organisms to methyl parathion. Additional data are required.
Methyl parathion, it is believed, does not bioaccumulate.
Dermal, ocular, and inhalation exposure can occur during
mixing, loading, and application, cleaning and repair of equip-
ment, and during early reentry. EPA is requiring additional
Worker Safety Rules, including protective clothing, to reduce
exposure.
Methyl Parathion, it is believed, has little or no potential
to contaminate ground water. This chemical was not included
on the list of potential ground water contaminators.
Ecological Characteristics:
Avian Oral Toxicity: 6.6 mg/kg for mallard duck and 7.6 mg/kg
for bobwhite quail.
Avian Dietary Toxicity: 336 ppm for mallard duck and 90 ppm
for bobwhite quail.
Small Mammal Oral Toxicity: 57 to 379 mg/kg for microtine
rodents
Avian Reproduction: Laboratory studies showed no direct
reproductive impairment; however,
significant depression of brain cholines-
terase activity was observed (These
studies were conducted with the Penncap
II formulation.) Field studies
indicate the possibility of repro-
ductive impairment. Effects on the
survival of nestlings were also noted.
Freshwater Fish Acute Toxicity: 3.7 ppm for rainbow trout
and 4.4 ppm for bluegill.
Aquatic Invertebrate Acute Toxicity: Da hnia ma na 0.14 ppb
Marine and Estuarine Toxicity: Mysid shrimp 0.98 ppb
Sheepshead minnow 12,000 ppb
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Endangered Species:
Previous consultations with the Office of Endangered
Species have resulted in jeopardy opinions and labeling for
crops (alfalfa, apples, barley, corn, cotton, pears, peanuts,
sorghum, soybeans, and wheat), rangeland and pastureland,
silvacultural sites, aquatic sites, and noncropland use.
Labeling is required in an effort to reduce the risk to en-
dangered species.
Tolerance Assessment:
Present United States, Canadian, Mexican and Codex
tolerances for methyl parathion in or on raw agricultural
commodities are specified in Table 1. Established tolerances
for residues of methyl parathion are also listed in 40 CFR
Sections 180.121 (a) and (b). Because there are considerable
gaps in both residue chemistry and toxicology, a tolerance
assessment cannot be made at this time. The nature of the
residue in plants and animals is not adequately understood
because of inadequate metabolism data. When the required
data are submitted to the Agency, the following will be
evaluated: 1. the tolerance definition in plants; 2. the
need for and nature of tolerances in or on animal commodities.
Because data gaps prevent the formulation of an acceptable
daily intake, a provisional acceptable daily intake has been
established. The PADI for methyl parathion is 0.0015 mg/kg/day
with a safety factor of 200. This figure will be retained
until additional data are received. The theoretical maximum
residue contribution for methyl parathion is approximately
800% of the provisional acceptable daily intake.
Reported Pesticide Incidents:
Most of the pesticide incidents reported involve illnesses
during mixer/loading, application, and drift from target areas.
4. Summary of Regulatory Position and Rationale
A review of the data available indicates that risk
criteria listed in 40 CFR 154.7 have been met or exceeded for
methyl parathion.
The Agency is requiring avian reproduction and terrestrial
full field testing and simulated or full field aquatic testing
to better define the extent of exposure and hazard to wildlife.
B. No new tolerances or new food uses will be considered
until the Agency has received data sufficient to
assess existing tolerances for methyl parathion.
C. The Agency is concerned about the potential for human
poisonings (cholinesterase inhibition) from the use of
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methyl parathion. The Agency will continue to classify
for restricted use (due to very high acute toxicity).
The Certified applicator must b physically present
during mixing, loading, application, equipment repair ,
and equipment cleaning . Information from the California
Department of Food and Agriculture reported incidents of
worker poisonings and illnesses during mixing, loading,
and application. EPA is requiring more stringent Worker
Safety Rules, including protective clothing, to reduce
exposure.
D. A 48 hour re-entry interval, previously established
under 40 CFR 170.3 (b) (2) will remain in effect.
E. The Agency has concluded that data are not adequate to
determine the oncogenic potential of methyl parathion.
and is requiring another mouse study and additional
information on the Wistar rat.
F. The Agency is requiring glove permeability and drift
studies because of the high acute toxicity of methyl
parathion.
G. All manufacturing-use products and end-use products must
bear appropriate labeling as specified in 40 CFR 162.10.
Additionally, the following information must appear on
the labeling:
a. Labeling requirements have been imposed to protect fish
and wildlife (including endangered species).
b. Methyl parathion will continue to be classified
Restricted Use and the labeling must state the reason,
Due to very high acute toxicity. Certified applicator
must be physically present during mixing, loading,
application, repair and cleaning of equipment.
c. Effluent containing methyl parathion may not be dis-
charged into lakes, streams, ponds, estuaries, oceans
or public waters unless this product is specifically
identified in an NPDES permit. Discharge of effluent
containing this product is forbidden without prior
notice to the sewage treatment plant authority.
d. Protective clothing requirements are mandatory in
order to protect applicators, fieldworkers, mixer/loaders,
and persons who clean and repair application equipment.
e. During aerial application, human flaggers are strictly
prohibited.
6. SUMMARY OF MAJOR DATA GAPS
Animal and plant metabolism studies
Magnitude of residue in almost all crops
Full battery of Environmental Fate data
Additional subchronic toxicity testing to determine a NOEL
for cholinesterase inhibition and other systemic effects
(retinal degeneration, sciatic nerve effects, abnormal gait)
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Additional oncogenicity and teratogenicitv information
Glove permeability and drift studies
Aquatic accumulation studies
Avian reproduction and terrestrial full field testing
Simulated or full field aquatic testing
Early life stage and fish life cycle studies
Reentry studies
Applicator Exposure Monitoring studies
7. CONTACT PERSON AT EPA
Dennis Edwards
Acting Product Manager (12)
InsecticideRodenticide Branch
Registration Division (TS-767C)
Office of Pesticide Programs
Environmental Protection Agency
401 M Street, SW
Washington, DC 20460
Office Location and telephone number:
Room 202, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA 22202
(703) 5572386
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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t1Efl1YL PARTHIa:
TABLE I
S r iiarv of Present Thieranoes
1b1e rances (ppn ) (MRL)
CaTrnodity United Statesd/ canadad/ Mexicod/ International (Qxtex)b /
Garden Beets 1.0
Carrots 1.0
*Parsnips 1.0 0.7
Potatoes 0.1 0.1
Radishes 1.0 1.0
*Rutabagas 1.0
Sugar Beets 0.1 0.5
Sweet Potatoes 0.1 0.1
Turnip 1.0
*Gar ljc 1.0 1.0
Onions 1.0 1.0
Celery 1.0 1.0
* 5 jve 1.0
Lettuce 1.0 1.0
*parsley 1.0
Spinach 1.0 1.0
*Swjss Chard 1.0
Broccoli 1.0 1.0 0.2
Brussels Sprouts 1.0 0.2
Cabbage 10 1.0 0.2
Cauliflower 1.0 0.2
Collards 1.0 0.2
Kale 1.0 0.2
Kohirabi 1.0 0.2
Mustard Greens 1.0 - - 0.2
Beans 1.0 1.0 0.2
* j r Beans 0.2 1.0
Peas 1.0 0.7 1.0 0.7
*Lentj ls 1.0 1.0
Soybeans 0.1 0.1
Eggplant 1.0 1.0
Peppers 1.0 1.0
Ttinatoes 1.0 1.0 0.2
Cucumbers 1.0 1.0 0.2
Melons 1.0 1.0 0.2
Pumpkins 1.0 1.0 0.2
Squash 1.0 1.0
Squash 1.0 1.0 0.2
*Cltrus Fruits 1.0 1.0 1.2
Apples 1.0 1.0
Pears 1.0 1.0
*Qujnce 1.0
Apricots 1.0 0.2
Cherries 1.0 0.2
Nectarines 1.0 0.2
Peaches 1.0 1.0 0.2
Ά luns 1 ,0 0.2
, 1ackberries 1.0
B1ueberries 1.0 0.2
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Z TdYL PA? AThIC
TABLE I
Siitu ary of Preser Tolerances (cont)
Ib1eraz ces (cm __________
mnodity United Statesa/ C3nadaW Mexico 7 International (Lo3ex) J
*Hoyse rrjes 1.0 0.2
*Cr r, jes 1.0 0.2
*C irrants 1.0
1.0 0.2
Gooseberries 1.0 0.2
Grapes 1.0 0.2
* ga rrjes 1.0 0.2
*Raspberrjes 1.0 0.2
Strawberries 1.0 1.0 0.2
*Yo berrjes 1.0 0.2
A.ri Drx s 0.1
t Fi1be ts 0.1
Pecans 0.1
*Wa lfluts 0.1
Barley 1.0
Corn 1.0 1.0
Oats 1.0
Rice 1.0 1.0
R ie 0.5
Sorghun 0.1 0.1
4ieat 1.0
Forage Grass 1.0
Alfalfa Forage 1.25 1.25
Alfalfa Hay 5.0 5.00
Clover Forage & Hay 1.0
*Trefoil 1.25
*Trefoil Hay 5.0
Vetch Forage & Hay 1.0
Miscellaneous Crops
Artichokes 1.0 1.0
Avocados 1.0 1.0 0.2
Cottonseed 0.75 0.75
* tes 1.0 0.2
*Fjgs 1.0 1.0 0.2
1.0 1.0 0.2
Hops 1.0 0.05
1.0 1.0 0.2
Mustard Seed 0.2
*OJ a 1.0 1.0
*O ljves 1.0 0.2
Peanuts 1.0 1.0
*pj app1e 1.0 1.0 0.2
* pe Seed 0.2
0.1 0.1
Sunf1 r Seed 0.2
a = The U.S., Canadian, and Mexican tolerances expressed in terms of residues
of methyl parathion Se. b = The Codex NaXiITIIII Residue Levels
expressed as residues of methyl parathion and its ox jen analog, methyl
paraoxon. * These cani dities have tolerances but no Federal Registrations.
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