UhHcd SUMS Qffiw of PMtUte «nd Toxic
CnnlrooiuMrtrf Protection CWk» of PortMd* PiBoraim (T8-766C)
Agency Wnlihgton. DC 2O460
540/FS-88-095
&EPA Pesticide
Fact Sheet
Name of Chemical: Fenthion
Reason for Issuance: Issuance of Registration standard
Date Issued: June so, 1988
Fact Sheet Number: 169
1. DESCRIPTION OF CHEMICAL
Generic Name: 0,0-d1methyl-0-L4-(methylth1o)-m-tolylJ phosphorotMoate
(Chemical)
Other Chemical
Names: 0,0-d1methyl-n-L3-methyl-4-(methylthio)pfienyl
phosphorothioate
n,D-dimethyl-0-4-methylthio-m-tolyl phosphorothioate
Common Name: Fenthlon (FDA), No American National Standards Institute
Common Name
Trade and Other Names: Baytex; Entex; Bayer 29493; Bayer S-1752;
Baycld; Lebaydd; Spotton; Tlguvon;
Mercaptophos
EPA Chemical Code: 053301
Chemical Abstracts Service (CAS) Number: 55-38-9
Year of Initial Registration: 1965
Pesticide Type: Insectlclde/Acarlclde, Avlclde. Mosqu1toc1de (adults and
1arvae)
Chemical Family: Organophosphate
U.S. and Foreign Producers: Mobay Chemical Corp. (United States); and
Bayer AG (Federal Republic of Germany)
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2. PHYSICAL AND CHEIIICAL CHARACTERISTICS
Chemical Characteristics of the Technical Material 1
Physical State: Liquid.
Color: Yellow-tan.
Odor: Slight garlic odor.
Molecular Weight and Formula: 278.3 - C 10 H 15 O 3 PS 2
Melting Point: <—25°C
Boiling Point: 105°C at 0.01 mm Hg.
Vapor Pressure: 3 x i0 mm Hg at 20°C.
Density: 1.250 at 20 0 C.
Solubility in various solvents: Practically insoluble in water (55 mg/i ),
soluble in methanol, ethanol, ether,
acetone, and many other organic solvents
(especially chlorinated hydrocarbons).
Physiological and Biochemical Characteristics
Mechanism of Pesticidal Action: Cholinesterase inhibition following
ingestion of fenthion or dermal
absorption from contact with treated
surfaces.
Metabolism and Persistence in Plants and Animals: The metabolism of
fenthion in plants and animals Is not
adequately understood. The available plant
metabolism data indicate that the following
metabolites were found in the leaves of
cotton plants treated with fenthion: fenthion
oxygen analog, fenthion oxygen analog
sulfoxide, fenthion oxygen analog sulfone,
dimethyl phosphorothtolc acid and dimethyl
phosphoric acid. Fenthion sulfoxide, fenthion
sulfone, fenthion oxygen analog sulfoxide, and
fenthion oxygen analog sulfone were the
metabolites detected in fenthion treated bean
plants. The available animal metabolism data
indicate that the metabolites fenthion
‘The physical/chemical properties of fenthion listed in this section were
obtained from Merck Index 10th Edition .
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sulfoxide and fenthion oxygen analog
identified as one entity, and fenthion
sulfone, fenthion oxygen analog sulfoxide, and
fenthion oxygen analog sulfone identified as
another single entity were tentatively
identif led In steak, liver, milk, urine, and
feces from cattle. Dimethyl phosphoric acid
and dimethyl thiolophosphoric acid were also
tentatively Identified In urine from cattle.
The metabolites fenthion sulfoxide, fenthion
sulfone, fenthion oxygen analog, fenthion
oxygen analog sulfoxide and fenthion oxygen
analog sulfone were Identified in muscle,
heart, fat, kidney, and liver from swine.
Swine liver was also found to contain the
additional metabolites fenthion sulfoxide
phenol and fenthion sulfone phenol while in
swine kidney the additional metabolites
detected in swine liver plus the metabolite
fenthion phenol. All of the metabolites found
in swine tissues were individually identified.
3. USE PATTERNS AND FORMULATIONS
Application Sites: Mosquito and insect control on swamps, standing water,
recreation areas, alfalfa, pasture grass, forests,
barns, poultry houses, nonfood/feed areas of restau-
rants and commercial buildings, and homes; lice control
on cattle (beef and non—lactating dairy) and hogs;
control of ants, mites, leafhoppers, and aphids on
ornamentals and flowers; bird control; rice to control
mosquitoes (in the State of California only).
Types and ?lethods of Application: Ground application is used for all uses
of fenthion. Both ground and aerial
applications are used to control
mosquitoes with control measures being
directed to both the aquatic (larval!
pupal) stages and the free-flying adult
stage.
Types of Formulations: Dust, emulsifiable concentrates, soluble
concentrate/liquid, granular, and liquid-ready to
use.
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4. SCIEPJCE FINDIP GS
Suimnary_Science Statement
——Fenthion is moderately toxic (Toxicity Category II) by the oral,
dermal and inhalation routes of exposure.
——Fenthion is minimally Irritating (Toxicity Category IV) to the skin
and eyes.
——Fenthion is not teratogenic in rabbits, and does not denonstrate
mutagenic effects. Other subchrontc and chronic effects, such as
oncogenicity and reproductive effects, are not characterized at this
time because of lack of data.
—-There are insufficient data to fully assess the environmental fate of
fenthi on.
——Preliminary data indicate that fenthion degrades in soil rapidly,
having a half life of less than one day. Other environmental fate
characteristics are undefin i, Including fenthion’s ability to
contaminate ground water.
—-There are insufficient data to characterize the acceptable dietary
exposure to fenthion.
——Fenthion Is highly toxic to aquatic organisms, birds, and honey bees.
However, field kills of fish and birds have not been documented.
——Fenthion is likely to jeopardize endangered species when used as a
mosquito larvicide.
Toxicology Characteristics
——Except for r’vitagenlclty studies, acute oral, dermal, and inhalation
s .s dies, dcute dermal and eye irritation studies, and a ra )it
teratology study, the Ay ncy has no acceptable toxicology studies
for fenthion.
——The acute oral LD 50 for rats Is 25O mg/kg (males) and 295 mg/kg
(females).
——The acute dermal LD 50 for rats is 1680 mg/kg bw (males) and 2830
mg/kg bw (females).
—-The acute inhalation LC 50 for rats Is 1200 mg/rn 3 (males) and 800
mg/rn 3 (females).
—-Fenthion is moderately toxic (Toxicity Category II) by the oral,
dermal and Inhalation routes of exposure.
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——Fenthion Is minimally Irritating (Toxicity Category IV) to the skin
and eyes.
- i nt ilon Is not teratogen c In rabbits.
——The fetotoxic NOEL in the rabbit is 1 mg/kg/day.
——The maternal toxicity NOEL in the rabbit is 6 mg/kg/day.
——The teratogenic NOEL In the rabbit is >18 mg/kg/day.
——Fenthion is non-mutagenic In male mice up to 25 mg/kg bw (the highest
dose tested).
—-Fenthion’s systemic NOEL for mutagenictty Is 10 mg/kg bw.
Environmental Characteristics
——Available data are insufficient to fully assess the environmental
fate and transport of fenthion. (Data gaps exist for nearly all
applicable studies.)
—-The available data indicate that fenthion degrades fairly rapidly,
with a half—life of less than a day reported in nonsterile silt loam
soil in the dark at 75% moisture and room temperature.
—-Data also suggest that fenthion degrades to 53% under anaerobic
conditions after 60 days incubation.
——The major nonvolatile degradates reported were fenthion sulfoxide,
3-methyl -4(methyl sulfonyl) phenol, and 3-methyl -4(methyl sulfinyl)
phenol.
——Data currently available are insufficient to characterize fenthIon’s
leaching potential for contamination of ground water. (Data to
characterize the potential to contaminate groundwater are being
required.)
Ecological Characteristics
Avian acute toxicity: Acute toxicity values of 5.94 mg/kg in the mallard
duck, < 4.0 mg/kg in the bobwhite quail, and 2.50
mg/kg fii doves.
Avian dietary toxicity: Subacute dietary toxicity values ranged from 30
ppm In the bobwhite quail to 231 ppm in the
mallard duck. The potential for secondary toxicity
was demonstrated when kestrels died after being fed
house sparrows that had been killed by an oral dose
of 10 mg/kg fenthion.
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Freshwater fish acute toxicity: 96—hour acute toxicity values ranged from
3.20 ppm for fathead minnows to 1.58 ppm
for cutthroat trout.
Marine fish acute toxicity: LC 50 value of 1.6 ppb for striped mullet.
Freshwater invertebrate toxicity: The acute toxicity values ranged from
0.62 ppb for Simocephalus (Daphnld) to
0.80 ppb for Daphnla pulex .
Marine Invertebrate toxicity: EC 50 value of 340 ppb for mollusks; 96-hour
LC 50 value of 0.11 ppb for pink shrimp.
These data show that technical fenthion is very highly toxic to birds on an
acute oral and dietary basis; moderately to highly toxic to both warrnwater
and coidwater fish species; very highly toxic to aquatic invertebrates;
very highly toxic to pink shrimp; moderately toxic to striped mullet; and
highly toxic to mollusks.
TOLERANCE REASSF.SSFIEWT
Tolerances have been established for residues of fenthion and its
cholinesterase Inhibiting metabolites in a variety of raw agricultural
comii odities (40 CFR 180.214). The Agency has evaluated the residue and
toxicology data supporting these tolerances and has determined that it does
not have sufficient data to support the currently established tolerances for
residues of fenthion. Because of the extensive residue chemistry and
toxicology data gaps, no significant new tolerances or new food uses will be
granted until the Agency has received data sufficient to evaluate the
dietary exposure to fenthion.
In addition to United States tolerances, there are also Canadian tolerances,
Mexican tolerances, and Codex riaximum Residue Limits (flRLs) established for
fenthion. However, some incompatibility exists between some of the
permanent Codex MRLs and the U.S. tolerances. The issue of incompatibility
will be addressed when residue data are submitted and evaluated.
The available toxicity data are insufficient for the Agency to calculate an
Acceptable Daily Intake (ADI) for fenthion and therefore the Maximum
Permissible Intake (IIPI) for a 60 kg human has not been determined.
5. REQUIRED UNIQUE LABELING SUMIIARY
Personal protective equipment and work safety statements must appear on the
label of all registered end use products containing fenthion.
All end-use products containing fenthion as an active Ingredient with
directions for use on agricultural crops, ornamental plants and forest
trees, uncul ti vated agricultural and non-agri cul tural outdoor areas, aquatic
sites, livestock and bird roosting areas must bear the following restricted
use labeling statements:
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RESTRICTED USE PESTICIDE
Due to Very High Acute Toxicity to Birds, Fish and Aquatic Invertebrates
For retail sale to and use only by certified applicators or persons
under their direct supervision and only for those uses covered by the
certified applicator’s certification. Certified applicators must also
ensure that all persons Involved In these activities are Informed of
the precautionary statements.
Environmental hazard statements and a bee precautionary statement must
appear on the label of all end—use fenthion products.
The following reentry Interval statement and protective clothing for early
reentry statement must appear on the labeling of all fenthion products
labeled for use on ornamentals:
“Reentry into treated area Is prohibited for 24 hours (1 day) after the
end of application, unless the protective clothing specified on this
label for early reentry Is worn.
FOR EARLY REENTRY INTO TREATED AREAS BEFORE SPRAYS HAVE DRIED [ OR DUST
HAS SETTLED, as applicable] wear all protective clothing specified on
this label for an applicator.
FOR EARLY REENTRY INTO TREATED AREAS AFTER SPRAYS HAVE DRIED [ OR DUST
HAS SETTLED, as applicable] wear protective suit of one or two pieces
covering all parts of the body except head, hands, and feet; chemical-
resistant gloves; chemical—resistant shoes (or chemical—resistant shoe
covers or chemical—resistant boots).
6. REGULATORY POSITION SUMMARY
The Agency will not grant any tolerances for significant new food uses 2
until sufficient data (residue chemistry and toxicology) are submitted f or
the Agency to calculate an Acceptable Daily Intake (ADI) for fenthion.
The Agency Is classifying all fenthion end—use products with directions for
use on agricultural crops, ornamental plants and forest trees, uncultivated
agricultural and non—agricultural outdoor areas, aquatic sites, livestock
and bird roosting areas as Restricted Use pesticides, based on avian, fish
and aquatic Invertebrate toxicity.
The Agency Is establishing an interIm 24—hour reentry interval for the use
of fenthion on ornamentals until adequate data have been submitted and
evaluated.
2 New useu is defined in 40 CFR 152.3(p). In the case of a new food or feed
use, the Agency will generally consider as significant an Increase in the
Theoretical Maximum Residue Contribution (ThRC) of greater than 1%.
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The Agency is requiring special studies, In rodent and nonrodent species, on
the effects of fenthion on the eye.
The U.S. Fish and Wildlife Service (FWS) has determined that certain uses of
fenthion may jeopardize the continued existence of endangered species or
critical habitat of certain endangered species. EPA is developing a program
to reduce or eliminate exposure to these species to a point where use does
not result in jeopardy, and will issue notice of any necessary labeling
revisions when the program is developed. No additional endangered species
labeling is being required at this time.
A feed additive tolerance must be proposed for residues of fenthion and its
choli nesterase-i nhi biting metabol I tes in rice hulls.
While data gaps are being filled, currently registered manufacturing use
products and end use products containing fenthion may be sold, distributed,
formulated, and used, subject to the terms and conditions specified in the
Registration Standard for Fenthion. Registrants must provide or agree to
develop additional data in order to maintain existing registrations.
7. Sumary of tajor Data Gaps
Toxicology
Dermal Sensitization
Acute Delayed Neurotoxicity
Subchronic 90-Day Feeding, two species (rodent and nonrodent)
Chronic Toxicity, two species (rodent and nonrodent)
Oncogenicity, two species
Teratogenicity (rat)
Rep roductl on
Envi ronmental Fate/Exposure
Hydrolysis
Photodegradati on, water
Photodegradation, soil
Photodegradation, air
Anaerobic Aquatic Metabolism
Aerobic Aquatic Metabolism
Leaching and Adsorptton/Desorptlon
Volatility, laboratory
Volatility, field (based on results of the laboratory volatility study)
Terrestrial Field Dissipation
Aquatic Field Dissipation
Forestry Dissipation
Soil Dissipation, long term (based on the results of the Terrestrial,
Forestry and Aquatic Field Dissipation studies)
Confined Accumulation, rotational crops
Field Accumulation, rotational crops (may be required depending on results
of acceptable confined rotational crop accumulation data)
Accumulation, irrigated crops
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Fish Accumulation, laboratory (registrant should first submit an Octanol/
water Partition Coefficient)
Field Accumulation, aquatic nontarget organisms (may be required depending
on the results of laboratory accumulation study)
Follar Dissipation
Droplet Size Spectrum
Drift Field Evaluation
Ecological effects
Avian Acute Oral (for Degradates)
Avian Subacute Dietary (for Degradates) (upland game bird and waterfowl
Wild Mamal Toxicity (for Technical Grade and Degradates)
Avian Reproduction (upland game bird and waterfowl)
Simulated and Actual Field Testing for mamals and birds
Freshwater Fish IC 50 (for Degradates) (warmwater and coidwater species)
Freshwater Invertebrate LC 50 (typical end-use product)
Estuarine and Marine Organisms LC 50 (Technical Grade and typical end-use
product)
Aquatic Organism Accumulation
Simulated or Actual Field Testing (Aquatic organisms)
Honeybee - Toxicity of Residues on Foliage
Special Tests —
—(Residue Monitoring in Water and on Animals)
—(Bivalve Toxicity)
—(Reptile and Amphibian Toxicity)
Residue Chemistry
Nature of Residues (Metabolism IP lants, and Livestock])
Residue Analytical Methods
Residue Storage Stability
Magnitude of Residues In Plants
Product Chemistry
All Product Chemistry Studies
8. CONTACT PERSON AT EPA
George T. LaRocca
Product Manager (15)
Insecticide-Rodenticide Branch
Registration Division (TS—767C)
Office of Pesticide Programs
Environmental Protection Agency
401 11 Street, S. W.
Washington, D. C. 20460
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Office location and telephone number:
Room 204, Crystal Mall #2
1921 Jefferson Davis Highway
Arlington, VA 22202
(703) 557—2400
DISCLAIMER: The information in this Pesticide Fact Sheet Is a sumary only and
niay not be used to fulfill data requirements for pesticide registration and
reregistration. The complete Registration Standard for the pesticide is
available from the National Technical Information Service. Contact the Product
Manager listed above for further information.
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