Phosmet - Chemical Fact Sheet 10/86
CHEMICAL FACT SHEET FOR:
FACT SHEET NUMBER: 101
DATE ISSUED: OCTOBER 1, 1986
1. DESCRIPTION OF CHEMICAL
- Generic Name: N-(mercaptomethyl) phthalimide S-(O,O-dimethyl
- Common Name: Phosmet
- Trade Names: Phthalofos, PMP, Appa, Imidan, Kemplate, Prolate, R-1504
- EPA Shaughnessy Code: 059201
- Chemical Abstract Service (CAS) Number: 732-11-6
- Year of Initial Registration: 1966
- Pesticide Type: Insecticide-acaricide
- Chemical family: Organophosphate
- U.S. Producer: Stauffer Chemical Company
2. USE PATTERNS AND FORMULATIONS
- Application sites: Terrestrial food crops (field, vegetable and
orchard crops such as alfalfa, apples, almonds, apricots, blueberries,
citrus, corn, cotton, grapes, nectarines, pears, peaches, pecans,
plums, and potatoes). Terrestrial non-food crops (nursery and
ornamental crops) domestic outdoor and indoor.
- Types of formulations: Dust (1% and 5% active ingredient (A.I.),
wettable powders (7.5%, 12%, 12.5%, 50%, and 70% A.I.): impregnated
resins (15% A.I.) and emulsifiable concentrates [1 pound (lb.) per
gallon (gal.), 3 lb/gal, and 12.5% A.I.]
- Methods of Application: Foliar applications, aerial applications,
animal treatments, stored commodity treatments, and impregnated
3. SCIENCE FINDINGS
Chemical Characteristics: Information listed below references the
technical grade active ingredient unless specified as the pure active
- Physical state: Crystalline solid
- Color: White to greyish-white
- Odor: Typical phosphorodithioate
- Boiling Point: Not applicable - the technical is a solid at room
- Flash point: Not available in Agency files
- Melting point: 72.0 - 72.7 degrees C (PAI)
- Specific gravity: 1.03 at 20 degrees C
- Solubility: At 20 degrees C, in water, 25 ppm; acetone, >/- 1,000
grams/liter(g/l); kerosene, 10 g/l; xylene, 200 g/l.
- Stability: Not available in Agency files.
- Acute toxicity. Phosmet has moderate to low acute oral, dermal, and
eye/skin irritation. Phosmet, like other organophosphate chemicals,
can be absorbed by inhalation and skin penetration.
- Acute oral (rat): 113-304 mg/kg.
- Acute dermal (rabbit): >3,160 mg/kg
- Primary eye irritation: Produced mild redness when instilled in
the unwashed eyes of 3 rabbits at 24 hours after exposure.
Phosmet also produced corneal opacity, redness, chemosis, and
discharge in 1 of 3 rabbits. Eyes were normal within 7 days.
- Chronic Toxicity
- Oncogenicity: Phosmet has been classified as a "tentative"
Category C carcinogen. This conclusion was reached after review
of two (a 2-year mouse and a 2-year rat) oncogenicity studies.
Phosmet was associated with a significantly elevated incidence of
liver tumors (adenomas, and adenomas plus carcinomas combined) in
male B6C3F1 mice at the highest dose tested. These incidences
were associated with liver hyperplastic changes and a decrease in
the time to tumor occurrence. In female B6C3F1 mice, the chemical
was associated only with positive dose-related trends for liver
adenomas and carcinomas. A 2-year rat oncogenicity study was
considered inadequate (the number of animals sacrificed at the end
of the study were too small to fully evaluate tumor responses).
The chemical was essentially non-mutagenic (only one positive
result occurred in a limited and inadequate battery of tests) and
no positive correlation with respect to oncogenicity and
mutagenicity could be made with known structural analogs. After a
2-year rat oncogenicity study and additional mutagenicity studies
are submitted and evaluated, the Agency will reassess the
oncogenicity issue and determine if dietary and worker risk
assessments are necessary.
- Mutagenicity: Phosmet was evaluated in several mutagenicity
assays. The chemical was found to be positive only when tested in
S. typhimurium strain TA-100. No mutagenicity study of phosmet
was performed in mammalian cells in culture. Additional
mutagenicity studies are required.
- Teratogenicity: No teratogenic effects were reported for phosmet
in oral teratology studies in monkeys (NOEL = 8.0 mg/kg) and
rabbits (NOEL = 60 mg/kg).
- Reproductive effects: Phosmet had no adverse reproductive
performance effects in a 3-generation oral reproduction study in
rats. (NOEL = 80 ppm).
- Neurotoxicity: Delayed neurotoxic effects were not observed at
levels up to 2,050 mg/kg of phosmet. Body weight, food
consumption, and egg production were significantly decreased in
the 2,050 mg/kg test group.
- Metabolism: Data indicates that phosmet is rapidly eliminated
with 78% being eliminated in the urine and 19% in the feces within
72 hours after administration of a single oral dose in rats.
However, the major water soluble urinary metabolites have only
been "tentatively" identified. A general metabolism study will be
Physiological and Behavioral Characteristics
- Mechanism of Pesticide Action - organophosphate cholinesterase
Environmental Characteristics and Groundwater Concerns
- Few data are available on the environmental fate of phosmet. Phosmet
appears to be moderately mobile to immobile in soils ranging in
texture from sand to silty clay loam. Because of phosmet's physio-
chemical properties the potential exists for phosmet, and possibly its
degradates, to contaminate groundwater. To date the Agency is not
aware of incidents where phosmet has contaminated groundwater. To
fully assess and complete the environmental fate profile of phosmet,
the Agency is requiring hydrolysis, soil dissipation, anaerobic soil
metabolism, leaching, photodegradation, rotational crop and reentry
- Avian acute toxicity: Mallard duck - 2009 mg/kg
- Avian dietary toxicity: Bobwhite quail - 501 ppm; Japanese quail -
2000 ppm; Mallard duck - >5000 ppm
- Avian reproduction: Bobwhite quail - 69-150 ppm; Mallard duck - 25-60
- Fish: Rainbow trout - 230 ppb; Bluegill sunfish - 70 ppm
- Aquatic invertebrates: Daphnia magna - 5.6 ppb; Gamma fasciatus -
- Sufficient data are available to characterize technical phosmet as
very highly toxic to warmwater fish and highly toxic to coldwater
fish. The chemical is also very highly toxic to aquatic and estuarine
invertebrates. Monitoring data in runoff water following terrestrial
applications of phosmet is being required to complete the hazard
- Phosmet is practically non-toxic to slightly toxic to birds and
mammals. Phosmet may cause reproductive impairment in birds and
mammals due to a buildup of residues on avian food items. Residue
monitoring of avian and mammalian food items (apples, corn, cotton,
and alfalfa) will be required to complete an evaluation of the
- Phosmet is very highly toxic to honeybees and displays extended
- Endangered species: Use on apple and pear orchards, alfalfa, corn,
and cotton crops, could place endangered species in the vicinity of
treated areas at risk. Also two endangered insect species in the
vicinity of food crop uses in certain counties of California could be
threatened. Residue monitoring data will be required to aid in
completion of the assessment of hazards to endangered species.
- Tolerances have been established for residues of phosmet in raw
agricultural commodities, meat, fat and meat byproducts (40 CFR
180.26) and in processed food (21 CFR 193.279) for phosmet and its
oxygen analog at levels ranging from 0.1 to 40.0 ppm.
- The metabolism of phosmet in plants and animals is not adequately
understood. Additional residue data and metabolism data will be
required to reassess the adequacy of existing tolerances and to
issue new tolerances. Processing studies are also being required
for potatoes, apples, plums, peaches, grapes, field corn grain, and
- The acceptable daily intake (ADI) for humans was based on a 2-year
chronic feeding study in rats. The ADI in humans was calculated to
be 0.02 mg/kg/day and the maximum permitted intake (MPI) is equal to
1.2 mg/kg/day with a NOEL of 40 ppm and a safety factor of 100.
Using these calculations the percent utilization of the ADI would be
09.29 percent. Since virtually all of the ADI has been used up by
the TMRC and the Agency is aware of a potential oncogenic response
to phosmet, new tolerances and/or new uses will not be issued if
they contribute significantly to the TMRC and/or result in a
significant increase in the dietary exposure.
- Established Phosmet Tolerances:
Commodity Parts Per Million
Almond, hulls 10.0
Cattle, fat 0.2
Cattle, meat 0.2
Cattle, mby 0.2
Citrus fruits 5.0
Corn, fresh (including
sweet K + 6 WHR) 0.5
Corn, fodder 10.0
Corn, forage 10.0
Corn, grain 0.5
Goats, fat 0.2
Goats, mbyp 0.2
Goats, meat 0.1
Hogs, fat 0.2
Hogs, mbyp 0.1
Hogs, meat -0.2
Horses, fat 0.2
Horses, mbyp 0.2
Horses, meat 0.2
Kiwi fruit 25.0
Peas, forage 10.0
Peas, hay 10.0
Plums (fresh prunes) 5.0
Sheep, fat 0.2
Sheep, mbyp 0.2
Sheep, meat 0.2
Sweet potatoes 10.0
Cottonseed oil 0.2
Reported Pesticide Incidents
- In the period from 1978 to 1979, 67 incidents involving a flea dip
formulation (Paramite) of phosmet were reported to the Agency. Of
these 67 incidents, 39 involved cats only, 16 involved dogs only, 2
involved cats and dogs, 8 involved human reactions, and 2 involved
dogs and human reactions. Reported mortalities from these incidents
were 20 cats (one leukemic) and 12 dogs. Additional incidents of
adverse animal reactions (primarily cats) involving the same
formulation have been reported up through 1985. The Agency is re-
evaluating the use of phosmet on pets.
Summary Science Statement
- Phosmet is a member of a chemical family known as the
organophosphates (OPs). OP pesticides act on the nervous system by
interfering with an enzyme acetylcholinesterase. This effect (known
as cholinesterase inhibition) is reversible once exposure stops.
There are antidotes for this type of poisoning (atropine and 2-pam).
Phosmet has a moderate to low acute oral, dermal, and eye/skin
irritation toxicity. It is moderately toxic (Toxicity Category II)
to humans by ingestion. Additional data (acute inhalation and
dermal sensitization) is required to complete the acute toxicity
profile for technical phosmet. Insufficient data exists to fully
assess the subchronic dermal, mutagenicity, oncogenicity, and general
metabolism of phosmet. Reentry data is necessary in order to
establish permanent worker reentry intervals.
- Phosmet has been classified as a tentative category C carcinogen.
This conclusion was reached after review of a 2-year mouse
oncogenicity study. Additional studies are being required to
complete the oncogenic assessment of the chemical. Currently
available data indicate that phosmet does not cause neurotoxic,
teratogenic, or reproductive effects.
- The environmental fate of phosmet is not well documented. A review
of preliminary data indicates phosmet is moderately mobile to
immobile in soil and hydrolyzes rapidly in soil. The physical-
chemical characteristics of the chemical indicate a potential for
phosmet and possibly its degrades to contaminate groundwater.
Hydrolysis, soil dissipation, anaerobic soil metabolism, leaching,
photodegradation, and rotational crop and reentry data are required
- Phosmet is practically non-toxic to slightly toxic to birds, and
mildly toxic to mammals. It is unlikely that phosmet would be
lethal to birds or mammals after a single application. Available
data indicates the possibility of reproductive effects in birds and
mammals due to the buildup of phosmet on avian and mammalian food
items (apples, corn, cotton, and alfalfa) from repeat applications.
Residue monitoring data on these food items is required to determine
the magnitude of exposure. Phosmet is highly toxic to honeybees,
fish, aquatic and estuarine invertebrates. Field monitoring studies
are being required to determine the magnitude of exposure from the
major crop uses. Additional fish and aquatic invertebrate studies
are being required to complete the evaluation of hazard.
4. SUMMARY OF REGULATORY POSITIONS AND RATIONALES
- No referral to Special Review is being made at this time. A repeat
rat oncogenicity study and additional mutagenicity studies must be
submitted. The Agency will reassess the oncogenicity issue and
determine if dietary and worker carcinogenicity risk assessments are
necessary. The available data also indicate that phosmet is highly
toxic to fish. Terrestrial residue analysis and aquatic runoff
modeling indicate that certain use patterns could result in exposure
of certain aquatic organisms to hazardous levels of the pesticide.
Additional data are needed before the Agency can complete a full
assessment of this hazard potential.
- The Agency will reassess the adequacy of the existing tolerances after
required metabolism data and residue data are submitted.
- New tolerances and uses will be issued on a case-by-case basis.
amended by depleting the reference to "cholinesterase-inhibiting"
- The Agency has determined that endangered species label restrictions
are necessary in order to prevent unreasonable adverse effects on the
- In the absence of reports of fish kills following phosmet application
and actual field monitoring data, the Agency will not restrict certain
uses of phosmet to certified applicators, but has determined, based on
the high toxicity of phosmet to aquatic organisms, that precautionary
labeling will be required. The restricted use classification may be
required if additional studies indicate that phosmet use poses risks
to aquatic organisms that could be mitigated by increased controls in
- The Agency is imposing a 24-hour reentry interval. Foliar dissipation
data are required on crops whose propagation requires human tasks that
involve substantial, prolonged human contact.
- Protective clothing is required for mixers/loaders and applicators.
- The Agency will analyze the safety and efficacy data of a phosmet flea
dip formulation (Paramite) to determine if further regulatory action
is warranted. A warning statement indicating that improper dilution
of the product could cause serious injury to pets is being required.
- The Agency has determined that the tolerance for cranberries should be
revoked because there are no registered uses for phosmet on
- The Agency is requiring processing data for the following agricultural
commodities: Potatoes, apples, plums, peaches, grapes, field corn
grain, and cottonseed.
- The Agency is not requiring a rotational crop restriction. If
required data demonstrate that follow-up crops take up phosmet
residues from soil, rotational crop restrictions or tolerances in
those crops may be necessary.
- The Agency is not imposing a ground water advisory statement on
phosmet labeling at this time, but is requiring data to fully
characterize the potential of this chemical to reach ground water.
- While data gaps are being filled, currently registered end-use
products containing phosmet as the sole active ingredient may be sold,
distributed, and used, subject to the terms and conditions specified
in the Registration Standard.
5. SUMMARY OF MAJOR DATA GAPS
- Product Chemistry
- Product Chemistry Feb. 1987
- Residue Chemistry
- Plant/Livestock metabolism Feb. 1988
- Plant/Animal Residues Feb. 1988
- Storage Stability Feb. 1988
- Environmental Fate
- Hydrolysis/Photodegradation July 1987
- Mobility Studies Sep. 1987
- Accumulation (Rotational) Crops Dec. 1989
- Glove Permeability Mar. 1987 - protocol
Nov. 1987 - final report
- Anaerobic Soil Metabolism Dec. 1988
- Soil Dissipation Dec. 1988
- Acute Inhalation Toxicity (rat) July 1987
- Dermal Sensitization July 1987
- 21-Day Dermal (rabbit) Sep. 1987
- Oncogenicity (rat) Nov. 1990
- Gene Mutation July 1987
- Structural Chromosome Aberration Sep. 1987
- Other Genotoxic Effects Sep. 1987
- General Metabolism Sep. 1988
- Ecological Effects
- Acute Toxicity to Freshwater
Invertebrates July 1987
- Acute Toxicity to Estuarine and
Marine Organisms Sep. 1987
- Fish Early Life Stage and Aquatic
Invertebrate Life Cycle Dec. 1987
- Field Monitoring (avian, aquatic,
and mammalian) Feb. 1988
6. CONTACT PERSON AT EPA
George T. LaRocca
Product Manager Number 15
U.S. Environmental Protection Agency
401 M. Street S.W.
Washington, 0. C. 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.