United States Office of Pesticide? end Toxic Substances
Environmental Protection Office of Pesticide Programs (TS-766C)
Agency Washington. DC 20460
540/FS-89-019
v>EPA Pesticide
Fact Shi
Name of Chemical: phorate
Reason for Issuance: Registration Standard
Date ISSUed: December 1988
Fact Sheet Number: 34.2
DESCRIPTION OF CHEMICAL
Generic name: 0,0-diethyl S-[(ethylthio)methyl]
phosphorodithioate
Common name: Phorate
Trade Names: Thimet, AAstar and Rampart
Other Chemical
Nomenclature: 0,0-diethyl-S-(ethylthio)
methyl phosphorodithioate
and 0,0-diethyl S-
[(ethylthio)methyl] ester
EPA Pesticide Chemical (Shaughnessy) Number: 057201
Chemical Abstracts Service (CAS) number: 298-02-2
Year of initial registration: 1959
Pesticide type: Insecticide
Chemical family: Systemic Organophosphate
U.S. Registrants: American Cyanamid Company, Uniroyal
Chemical Company Inc., Aceto Chemical
Company Inc., Wilbur Ellis Co.,
Riverside Terra Corp., Farm Bureau
Cooperative, and Platte Chemical Co.
USE PATTERNS AND FORMULATIONS
Application sites: Terrestrial food crop use on beans,
corn (field and sweet), cotton,
hops, peanuts, potatoes, sorghum,
soybeans, sugar beets, sugarcane,
barley and wheat.
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Terrestrial non-food crop use on
lilies (bulb production).
Formulations: Granular
Pests Controlled: Various leaf-feeding insects, mites,
and soil insects
Methods of application: Soil and foliar applications
(band, broadcast, in-furrow and
drilling) using conventional
ground and aerial equipment
3. SCIENCE FINDINGS
Summary Science Statement
Technical phorate is in Toxicity Category I by the oral,
dermal and inhalation routes. The acute oral administration of
phorate to hens did not cause a delayed neurotoxic effect.
Based on results of acceptable subchronic and chronic feeding
studies with rats and dogs, cholinesterase (plasma, blood or
brain) is the primary target for phorate. Phorate does not
produce oncogenic effects, based on results of acceptable
chronic studies in rats or dogs. Phorate does not induce
teratogenic effects, based on results of acceptable teratology
and reproduction studies. Phorate did not cause a mutagenic
response in several in vitro (microbial and mammalian cells)
studies or in an in vivo dominant lethal study. Results of an
acceptable metabolism study using male rats indicated that a
large proportion of phorate labeled metabolites were excreted in
urine and feces within 24 hours of dosing. The total
radioactivity levels in tissues was low. The oxidative,
phosphorylated products (metabolites of phorate which may be more
potent anticholinesterase compounds through oxidative
desulfuration and/or sulfide oxidation) represented a minor
proportion of the phorate metabolites measured.
Based on acceptable laboratory data, technical phorate is
characterized as very highly toxic to birds on an acute oral
basis; highly toxic to birds on a dietary basis; very highly
toxic to mammals on a dietary basis and very highly toxic to
freshwater fish and aquatic invertebrates and estuarine and
marine organisms on an acute toxicity basis. Results of the
terrestrial field studies (Level 1) showed mortalities to avian
and mammalian species. An aquatic field study (required in the
1984 Standard) is still in progress and is due in 1991.
Many of the tolerances for phorate are still not adequately
supported. Additional data (residue studies, residue analytical
methods, processing and cooking studies, poultry metabolism study
and storage stability data) are needed before the Agency can
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determine the adequacy of current tolerance levels and perform a
tolerance reassessment. Based on the NOEL for brain
cholinesterase in a one year dog study (0.05 mg/kg) and applying
an uncertainty factor of 100, the Agency has calculated the
Anticipated Residue Contribution (ARC) for the U.S. population
average to be 0.000491 mg/kg/day, corresponding to 98% of the
RfD. The ARC assumes residues are present at tolerance levels,
but takes into account percent of crop treated, where possible.
For children 1 to 6 years of age, the ARC occupies 235% of the
RfD, and for non-nursing infants, the ARC occupies 331% of the
RfD. The Agency is requiring processing and cooking studies to
assess anticipated residue levels in meat and milk. The Agency
expects that cooking and processing of meat and milk will reduce
residues of phorate to levels which will be of little or no
concern.
Chemical/Physical Characteristics of the Technical Material
Chemical/Physical
Characteristics: Color: pale straw to light brown
(TGAI, 2749-106); COlor-
less to very light yellow
(TGAI, 241-212 and 241-213)
Physical state: liquid
Odor: characteristic of mercaptan
containing compounds
Boiling Point: 118-120 °C, 0.8 mm Hg
Specific Gravity: 1.15 at 20 °C (TGAI,
2749-106); 1.17 at
25 °C (TGAI for 241-
212 and 241-213)
Solubility: 50 mg/1 in water;
miscible with carbon
tetrachloride, vege-
table oils (unspecified),
xylene, and unspecified
alcohols, ethers and
esters
pH: 5-7 (TGAI, 2749-106);
3.56-3.81 (TGAI, 241-212 and
241-213)
Viscosity: 80 cps at 21 °C
Corrosion: non-corrosive to steel,
aluminum, porcelain,
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fiberglass, and phenolic
resins
Toxicology Characteristics
Acute Oral:
Acute dermal:
Toxicity Category I (LD50 of 3.7 and 1.4 mg/kg
in male and female rats, respectively)
Toxicity Category I (LD50 of 9.3 and 3.9 mg/kg
in male and female rats, respectively)
Acute inhalation:
Toxicity Category I (LD50 of 60 and 11
mg/m3 for male and female
rats, respectively)
Primary dermal irritation:
None Available. Not required
since the toxicity of phorate
prohibits the administration of
appropriate dosage levels.
Primary eye irritation:
None Available. Not required since
the toxicity of phorate prohibits
the administration of appropriate
dosage levels.
Skin sensitization:
None available. Not required due to the
high acute toxicity of the chemical.
Delayed Neurotoxicity:
Did not induce delayed neurotoxicity in
an acceptable study in hens.
Subchronic non-rodent study:
None available. Not required
since acceptable chronic
data for the non-rodent are
available.
Subchronic rodent study:
A rat study is available. The LEL
in this study was 2.0 ppm (0.1
mg/kg/day); the NOEL was 0.66 ppm
(0.033 mg/kg/day).
Chronic toxicity:
Oncogenicity:
Dog study is available (NOEL and LEL for
systemic toxicity were 50 and 250
ug/kg/day, respectively). Mouse study is
available (NOEL and LEL were .45 and .9
ug/kg/day, respectively). Rat study is
available (LEL was 0.05 mg/kg/day, NOEL
was not determined)
The rat combined chronic toxicity and oncogenicity
study did not reveal any evidence that phorate
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Mutagenicity:
Teratogenic ity:
Reproduction:
was oncogenic under the condition of that
study. Based on a reevaluation of the mouse
study, the evidence does not show that an MTD was
attained. Confirmatory data are required.
Phorate was negative in all areas of
mutagenicity testing (gene mutation,
structural chromosome aberration and tests for
other genotoxic effects)
A rat study is available (LEL for
developmental toxicity, based on
embryotoxicity, and maternal
toxicity was 0.50 mg/kg and the
corresponding NOEL for each was 0.25 mg/kg).
A rabbit study is available (LOEL and NOEL
for maternal toxicity was 0.5 and 0.15
mg/kg, respectively. The NOEL for
developmental toxicity was 1.2
mg/kg, the highest dosage administered).
A mouse study is available (LEL was .45
mg/kg/day and the NOEL was .23 mg/kg/day).
Metabolism:
A study in male rats is available. Results
indicated that a large proportion of the
administered 14C was recovered in urine and
feces. Oxidative, phosphorylated products only
represented a minor proportion of the metabolites
measured.
Environmental Characteristics
Based on the results of an acceptable leaching study, 14C
phorate was reported to be very mobile to mobile in loamy sand,
sandy loam, silt loam, and loam soils. The 1984 Registration
Standard indicated that phorate has some potential to leach
through the soil and contaminate groundwater. Based on recently
submitted data, phorate does not appear to be a potential
leacher. However, its sulfone and sulfoxide degradates show
greater persistence and mobility in soil, and therefore may have
a greater leaching potential. Since data are still outstanding,
the Agency cannot fully assess phorate's potential for
contaminating groundwater.
Ecological Characteristics
Based on acceptable acute data, technical phorate is
characterized as very highly toxic to birds on an acute oral
basis, highly toxic to birds on a dietary basis, very highly
toxic to mammals on a dietary basis, and very highly toxic to
freshwater fish and aquatic invertebrates and estuarine and
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marine organisms on an acute toxicity basis.
- Acute LD50 (mallard):
0.62 mg/kg
- Acute LD50 (chukar):
12.8 mg/kg
- Dietary LC50
248 ppm (waterfowl)
441 ppm (upland gamebids)
28 ppm (small mammals)
- Freshwater invertebrates toxicity (96-hr LC50) for
amphipods: 0.68 ppb to 9 ppb
- Fish acute toxicity (96-hr LC50) for rainbow trout: 6
to 13 ppb
- Fish acute toxicity (96-hr LC50) for bluegill sunfish:
2 ppb; 5 ppb for bass
- Estuarine fish and invertebrates (LC50)
0.11 to 1.9 ppb for shrimp and 1.3 to 5.0 ppb for
spot and sheepshead minnow; for mollusks (900 ppb)
Tolerance Assessment
Tolerances for residues of phorate in or on food and feed
commodities are published in 40 CFR 180.206. A tolerance for
residues of phorate on the processed feed commodity, dried
sugarbeet pulp, is published in 21 CFR 180.590. Tolerances are
expressed in terms of phorate and its cholinesterase-inhibiting
metabolites.
Based on data submitted in response to the 1984 Standard,
the nature of the residue in plants is adequately understood.
The nature of the residue in animals not adequately understood.
A poultry metabolism study is required. The available data
support the established tolerances for the combined residues of
phorate and its cholinesterase-inhibiting metabolites in or on
potatoes, sugar beets, sugar beet tops, sugar beet pulp, and
soybeans. Additional data (residue studies, processing and
cooking studies, residue analytical methods, poultry metabolism
study and storage stability data) are needed before the Agency
can determine the adequacy of current tolerance levels and
perform a tolerance reassessment.
The Agency has performed a preliminary dietary exposure
analysis using tolerance level residues and percent of crop
treated where possible. The ARC for phorate for the U.S.
population average is 0.000491 mg/kg/day. For the U.S.
population average, the ARC occupies 98% of the ADI. For
children 1 to 6 years of age, the ARC occupies 235% of the ADI,
and for non-nursing infants, it occupies 331% of the ADI. The
ARC is based on current tolerance levels, and, where possible, on
percent of crop treated. Due to the significant contribution
made by milk to the diet of children and non-nursing infants,
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data regarding the reduction of residues through cooking and
processing are required.
4. SUMMARY OF REGULATORY POSITIONS AND RATIONALES
Based on a high acute toxicity of phorate to avian species
and the current registered uses of phorate, there exists a high
potential for adverse effects to avian species from exposure to
phorate granules at or near the soil surface. This potential for
exposure to phorate is demonstrated from results of Level I
studies and is confirmed by bird kill incidents. The Agency is
currently evaluating these data in the context of a comparative
risk assessment of granular pesticides which may pose a risk to
birds. Based on this assessment, regulatory action may be taken.
The Agency is not placing phorate into Special Review at
this time for hazards to aquatic organisms. Available field
reports and laboratory data indicate that the concentrations of
phorate in the aquatic environment resulting from the registered
uses of phorate might expose aquatic species to residue levels
exceeding risk criteria for Special Review. Upon receipt and
evaluation of the aquatic field study (due in 1991), a
determination will be made regarding further regulatory action.
- Unique warning statements required include revised and
updated fish and wildlife toxicity statements, reentry
statements, and protective clothing statements.
The Agency is requiring special acute and subchronic eye
studies to evaluate phorate's effect on the eye.
The Agency will not approve significant new uses for this
chemical since many of the tolerances are still not adequately
supported.
The Agency will continue to restrict the use of products
containing phorate. Phorate meets the risk criteria of 40 CFR
152.170 due to acute oral and dermal toxicity and bird toxicity.
- The Agency is still unable to fully assess phorate's
potential for contaminating groundwater. Upon receipt of a
terrestrial field dissipation study, and other requested
environmental fate data, the need for groundwater monitoring
will be determined.
SUMMARY OF OUTSTANDING DATA REQUIREMENTS
Toxicology Time Frame
Special Testing for Eye Effects 9-18 Months
Metabolism 24 "
Mouse Short-term Study 12 "
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Environmental Fate/Exposure
Hydrolysis
Photodegradation in Water
Photodegradation on Soil
Aerobic Soil Metabolism
Anaerobic Soil Metabolism
Lab Volatility
Soil Dissipation
Confined Rotational Crop
Accumulation in Fish
Foliar Dissipation
Soil Dissipation
Fish and Wildlife
Avian Reproduction
Estuarine/Marine Organism Testing (TEP)
Freshwater and Estuarine Fish Early Life
Stage Life-Cycle Study
Freshwater and Estuarine Invertebrate
Life-Cycle Study
Aquatic Organism Field Testing
Residue Chemistry
Residue data - Raw Agricultural Commodities
Processing Studies
Poultry Metabolism
Cooking Studies
Storage Stability
Residue Analytical Methods
Product Chemistry
Majority of Data
9 Months
9 Months
9 "
27 "
27 "
12 "
27 "
39 "
12 "
18 "
18 "
24 Months
12 "
15 "
15 "
January, 1991
18 Months
24 "
18 "
24 "
15 "
15 "
9 -15 Months
6. Contact Person at EPA
William H. Miller
Product Manager (16)
Insecticide-Rodenticide Branch
Registration Division (TS-767)
Environmental Protection Agency
Washington, DC 20460
Tel. No. (703) 557-2600
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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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