United States Office of Pesticides end Toxic Substances
Environmental Protection Office of Pesticide Programs (TS-766C)
Agency Washington, DC 20460
&EPA Pesticide
Fact Sheet
Name of Chemical: TERBUFOS
Reason for Issuance: REGISTRATION STANDARD AMENDMENT /
_ . . CLASSIFICA1TON FOR RESTRICTED USE
Date Issued: Feb. It 1985
Fact Sheet Number:
5.1
1. Description of Chemical
Generic name: S-[[(1,1-dimethyl-ethyl)thio]methyl] 0,0-
diethyl phosphorodithioate
Common name: Terbufos
Trade name: Counter
EPA Shaughnessy code: 105001
Chemical Abstracts Service (CAS) number: 13071-79-9
Year of initial registration: 1974
Pesticide type: insecticide-nematicide
Chemical family: organophosphate
U.S. and foreign producer: American Cyanamid Company
2. Use Patterns and Formulations
Application sites: Corn, sugar beets, and grain sorghum
Types of formulations: granular
Types and methods of application: soil incorporation
Application rates: vary according to formulation and crop
Usual carriers: Confidential Business Information
3. Science Findings
Summary science statement:
Terbufos is highly toxic to humans, fish and wildlife.
Due to a number of major data gaps, the Agency cannot
complete a full risk assessment until the data required
under this Standard have been submitted and reviewed.
Reassessment of established tolerances must await receipt
and evaluation of required toxicological studies. Available
chronic toxicity studies are only supplementary data, and
a "No Observable Effect Level" (NOEL) cannot be established
at this time, and a maximum permissible intake (MPI) cannot
be calculated.
Chemical characteristics;
Terbufos, an organophosphate, is a clear slightly brown
liquid. It is relatively stable in water under neutral
or slightly acidic conditions but is subject to hydrolysis
under alkaline conditions. It decomposed on prolonged
heating at temperatures greater than 120°C. The chemical
does not present any unusual handling hazards.
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Ter bu fo s
fact sheet 2
Toxicology characteristics :
Current available toxicology studies on terbufos are as
follows:
— Oral LD 50 in rats: from 1.3 to 1.57 mg/kg in females and
1.6 to 1.74 mg/kg in males (Tox category I)
— Dermal LD 50 in male rate: 1.0 mg/kg (Tox category I)
— Eye irritation: due to the high acute toxicity of the
chemical and the rapid death of animals, eye irritation
scores were not reported
— Dermal irritation: due to the high acute toxicity of the
chemical and the rapid death of animals, skin irritation
scores were not reported
Symptoms of acute cholinesterase inhibition were reported
in all acute studies.
— Multigeneration reproduction study in rats: NOEL of
0.25 ppm and LEL of 1.0 ppm based on noted increase in
the percentage of litters with offspring death in each
of the three generations as compared to the controls.
— Chronic feeding/oncogenicity in rats: both the ChE NOEL
and the systemic NOEL appear to be lower than 0.25 ppm
(LDT). The oncogenic potential of terbufos could not
be assessed because too few animals of each group were
histologically examined. Exophthalmus was noted in
treated females in a dose—related fashion during the
first year. This effect appeared to subside during the
second year of the study.
— 6—month chronic feeding in dogs: a ChE of 0.0025 mg/kg!
day for both plasma and red blood cells cholinesterase
inhibition. However, it is not clear how the dosage
was mixed with the feed and how homogeneous the distri-
bution of the test substance was in the diet. Also,
the raw data were not available. A one—year study is
now required.
— 18—month oncogenicity in mice: the oncogenic potential
of terbufos could not be determined because too few
animals were histologically examined. Dose—related
exophthalmia was noted in treated males during the
first year. This effect subsided in the second year.
— Two 90—day subchronic feeding studies in rats: both
studies reflected a ChE NOEL of 0.25 ppm; one study
reflected a systemic NOEL of 0.25 ppm. A systemic
NOEL could not be determined for the other study be-
cause histological data were not reported.
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Terbufo s
fact s et
— 28—day feeding study in dogs: only one dose (0.05
mg/kg) was tested at 6 and 7 days/week exposure.
Both groups of animals showed similar levels of
ChE activities with plasma ChE being significantly
inhibited (79% inhibition) while no inhibitiOn was
observed in RBCChE activity.
— 30—day dermal study in rabbits: systemic NOEL was
determined to be 0.02 mg/k for the technical material.
— Acute delayed neurotoxicity in hens: terbufos did not
produce signs of neurotoxicitY after the second 21—
day dosing period using the technical material at
40 mg/kg (the L1 0 dosage).
— MutagefliCity the Ames test on bacterial system was
performed with and without microsomal activation —
with negative results.
Additional data are needed to fully assess the toxicity of
terbufos.
Environmental characteristics :
Based Ofl available data, terbufos is not expected to
leach into ground water. However, additional data are
needed to fully assess the environmental fate of terbufos.
Ecological characteriStic :
The following data are available:
— Avian oral LDS0: 28.6 mg/kg (highly toxic)
— Avian dietary LC5O: 143 ppm (highly toxic)
— Fish LC5O: 0.77—3.8 ppb (bluegill sunfish);
9.4—20.0 ppb (trout)
— Aquatic invertebrate LC 5 O: 0.31 ppb for
Daphnia magna (very highly toxic)
The Agency S requiring further monitoring of water,
sediment, and fish; in ponds adjacent tO treated fields,
to fully assess the potential hazard to nontarget
aquatic species. Avian and mammalian field testing are
required to assess the potential hazard tO terrestrial
organisms.
Efficacy review results :
None required.
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Terbufos 4
fact sheet
Tolerance assessments :
Tolerances have been established, under 40 CFR 180.352,
for combined residues of terbufos and its cholinesterase—
inhibiting metabolites in or on the following raw agri-
cultural commodities:
Commodity PPM
Beets, sugar; roots 0.05 negligible
residues (N)
Beets, sugar; tops 0.1
Corn, field; fodder, 0.5
forage
Corn, pop; fodder, forage 0.5
Corn, grain 0.05(N)
Corn, sweet (kernel + cob 0.05(N)
with husk removed)
Corn, sweet; fodder, forage 0.5
Sorghum; fodder, forage 0.5
Sorghum; grain 0.05
There are currently no food or feed addivitve tolerances
and it has been determined that none are required for
food and/or feed byproducts of these commodities.
There are no tolerances for meat, milk, poultry and eggs,
nor are any required since there is no reasonable
expectation of finite residues occuring in these foods
from feed use of the raw agricultural commodity including
their processing byproducts. Request for new livestock
feed crops, however, may require tolerances for meat,
milk, poultry and eggs.
The established tolerances for terbufos are presently
expressed in terms of terbufos and its cholinesterase—
inhibiting metabolites without specifying the latter as
phosphorylated metabolites. The Agency will proceed to-
wards revising 40 CFR 180.352 by changing the wording to
read “.....terbufos ..... and its phosphorylated (cholin—
esterase inhibiting) metabolitesR.
Reassessment of the established terbufos tolerances
must await receipt and evaluation of pertinent toxi-
cological studies. Available chronic toxicity studies
are only supplementary data and thus may not be used
as a basis for tolerance assessment. Consequently,
a “No Observable Effect Level” (NOEL) cannot be estab-
lished at this time, hence a maximun permissible intake
(MPI) cannot be calculated.
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Terbufos Fact Sheet
Pg. 5 revised 2-85,
see also new Pg. 5a
Terbufos 2—85.
1 fact sheet
The Pesticide Incident Monitoring System (PIt4S) reports
through June, 1981, include 31 reports involving terbufos,
of which 19 involved terbufos alone. Of these 19 incidents,
9 involved humans, 8 involved domestic livestock and 2 in-
volved wildlife. No human fatalities resulted. In those
human exposure incidents which were reported with some
detail, it appears that carelessness or negligence were
important factors. In two of these incidents, the granular
pesticide was reported to have been handled with bare hands
during loading and application procedures.
In those instances involving livestock, one resulted in the
death of about 600 cattle, another in the death of 127 cattle.
The accidental contamination of livestock feed was reported as
the cause in these incidents.
The two wildlife instances involved fish kills which were
reportedly due to runoff from treated fields. Only one
included analysis of the water samples. Though the samp-
ling agnecy was unable to test for terbufos, no evidence of
organophosphorus compounds was found in the sampled water.
Careless and/or negligence appear to have been important
factors in most incidents. Strict adherence to proper
storage and application techniques as prescribed in the
label directions and precautions will minimize the risk
of potential adverse effects to humans and domestic animals.
4. Summary of Regulatory Position and Rationale :
Use classification: Based on the acute oral and dermal
toxicity, granular end—use products containing 15% or
more terbufos are classified for “Restricted Use”. All
such products released for shipment on September 1, 1985,
or thereafter, must be labeled for restricted use.
Similarly, all such products which are in channels of
trade on or after September 1, 1986 must bear restricted
use labeling.
Restrictions: end—use products formulated from manufacturing-
use products under the standard must be granular formulations
for ground incorporated application only.
Unique warning statements:
— Labeling of manufacturing—use products must contain the
following statements:
“Wear protective clothing, rubber gloves and goggles.”
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TerbufoS Fact Sheet
Pg. 5a, new 2/85
Terbufos
fact sheet —6—
“Wear a pesticide respirator jointly approved by the
Mining Enforcement and Safety Administration (formerly
the U.S. Bureau of Mines) and by the National Institute
for Occupational Safety and Health under the provision
of 30 CFR Part 11 for organic phosphate protection.”
— Labeling of end—use products must contain the statements:
“Restricted Use”
“Wear protective clothing, gloves and goggles.”
“Not for use or storage in or around the home.”
5. Summary of major data gaps :
Toxicology: inhalation LC 50 , 2 chronic feeding studies,
2 oncogenicity studies, 2 teratogenicity studies, and
additional mutagenicity studies. These studies must be
submitted no later than June, 1986.
Wildlife and Aquatic Organisms: avian reproduction,
simulated and actual field testing — mammals and birds,
fish early life stage and aquatic invertebrate life—cycle;
and acute LC 50 for estuarine and marine organisms. These
studies must be submitted no later than June, 1986.
Environmental Fate: photodegradation in water, lab volatitily
study, rotational crop field study, and monitoring studies
(soil and water, sediment and fish). These studies must
be submitted no later than June, 1986.
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
DISCLAIMER: The information presented in this Chemical Information
Fact Sheet is for informational purposed only and may not be used
to fulfill data requirements for pesticide registration and
reregistration.
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