E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Assessment Program.
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Pesticide
Information
Profile
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Terbufos
Publication Date: 3/94
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TRADE OR OTHER NAMES
Trade names include Contraven and Counter.
INTRODUCTION
Terbufos is an organophosphate insecticide and nematicide used on corn,
sugar beets and grain sorghum. Primarily formulated as granules, it is
applied at planting in a band or directly to the seed furrow. Terbufos
controls wireworms, seedcorn maggots, white grubs, corn rootworm larvae and
other pests.
Products containing 15% or more terbufos are classified as Restricted Use
Pesticides (RUP). Restricted Use Pesticides may be purchased and used only by
certified applicators.
TOXICOLOGICAL EFFECTS
ACUTE TOXICITY
Terbufos products are labeled with a DANGER signal word, and are
extremely toxic. Symptoms of acute toxicity often include nausea, abdominal
cramps, vomiting salivation, excessive sweating and diarrhea within 45 minutes
of ingestion. Absorption into the bloodstream may cause inhibition of
cholinesterase, an enzyme essential for normal functioning of the nervous
system. This, in turn, can lead to chest tightness, wheezing, blurred vision,
fatigue, headache, slurred speech and confusion. Symptoms from skin
absorption, such as localized sweating, may be delayed up to 12 hours. At
high enough doses, death may result from respiratory arrest, respiratory
muscle paralysis and/or constriction of the lungs.
No neurotoxic effects were observed in chickens given a single dose of 40
mg/kg, the highest dose tested (8).
The oral LD50 of terbufos is from 1.3 to 1.57 mg/kg in female rats, and
from 1.6 to 1.74 mg/kg in male rats (7). The oral LD50 for technical terbufos
in male mice is 3.5 mg/kg, 9.2 mg/kg in female mice, 4.5 mg/kg in male dogs,
and 6.3 mg/kg in female dogs (12). Rabbits given a single dose of 0.1 mg to
the eyes died within 2 to 24 hours after dosing (8).
The dermal LD50 for rabbits is 1.1 mg/kg for 24 hours (2, 5).
CHRONIC TOXICITY
Slow thinking, memory loss, irritability, delayed reaction times and
anxiety have been noted in workers chronically exposed to organophosphates
like terbufos.
When rats were fed approximately 0, 0.01, 0.02, 0.046 or 0.09 mg/kg/day
for 90 days, the NOEL was 0.02 mg/kg/day. Cholinesterase inhibition occurred
at higher doses (12). Similar results were obtained in a 1-year study with
rats. The NOEL was 0.025 mg/kg/day, with cholinesterase inhibition occurring
at 0.05 mg/kg/day, the highest dose tested (12).
EPA has established a Lifetime Health Advisory (LHA) of 0.001 mg/l of
terbufos in drinking water. This means that EPA believes that water
containing terbufos at or below this concentration is acceptable for drinking
every day over the course of one's lifetime, and does not pose any health
concerns. Consumption of terbufos at high levels well above the LHA level
over a long period of time has caused damage to the eye and stomach,
disturbances in fetal development and cholinesterase inhibition in animals
(13).
Reproductive Effects
In a long-term study in rats, no chronic reproductive effects were
observed after daily exposure to low doses of terbufos (7).
When rats were fed 0, 0.0125 or 0.05 mg/kg/day for 6 months, there was an
increase in the number of litters with dead offspring at the highest dose
tested. The reproductive NOEL for this study was 0.0125 mg/kg/day (12).
Rabbits were given doses of 0, 0.1, 0.2 or 0.4 mg/kg/day on days 7 to 19
of pregnancy. Cesarean sections were performed on day 29. No adverse effects
on the offspring were seen at any dose. Toxic effects on the mothers occurred
at the highest dose tested (12).
Terbufos appears unlikely to cause reproductive effects in humans.
Teratogenic Effects
Terbufos does not cause birth defects in animals, except in extreme
situations, and similar effects are not anticipated in humans. There were no
birth defects in the offspring of rats given 0.05, 0.1 or 0.2 mg/kg/day on
days 6 to 15 of pregnancy (12).
In a similar study on rabbits, no birth defects were observed in the off-
spring of rabbits given 0.25 mg/kg/day, the highest dose tested. The mothers
exhibited reduced body weight gain at this dose (8).
Mutagenic Effects
Several tests have shown that terbufos is not mutagenic. These include a
dominant lethal study in rats, an Ames test, a DNA repair chromosomal
aberration test, and a test for DNA repair in rat liver cells (8, 12).
Carcinogenic Effects
No tumors were found in mice given 1.8 mg/kg/day, the highest dose
tested, for 18 months. The same results occurred in a 2-year study with rats
given up to 0.40 mg/kg/day, the highest dose tested (8, 12). EPA has stated
that terbufos does not increase the risk of cancer in humans (13).
Organ Toxicity
Because terbufos inhibits cholinesterase, this pesticide can affect the
eyes, lungs, skin, and central nervous system, depending on the route of
exposure, and the concentration.
Fate in Humans and Animals
In rats given a single oral dose of terbufos, 10% remained in the liver
six hours after dosing. Breakdown products were found in the kidney 12 hours
after dosing. Of the original dose administered, 83% was excreted in the
urine within seven days after dosing, and 3.5% was found in the feces.
Terbufos and its metabolites did not accumulate in tissues (7, 12).
No detectable residues have been found in the eggs, milk or body tissues
of animals (hens and cows) fed very high dietary doses of terbufos and its
cholinesterase inhibiting metabolites (7).
ECOLOGICAL EFFECTS
Effects on Birds
Terbufos is extremely toxic to birds. Its acute LD50 in bobwhite quail
is 28.6 mg/kg. Its dietary LC50 in bobwhites is 143 to 157 ppm (7).
There were no effects on bird reproduction from chronic exposure to
terbufos (7, 11).
Effects on Aquatic Organisms
Terbufos is extremely toxic to fish, and aquatic invertebrates (7). The
acute LC50 for terbufos in freshwater fish species is 0.77 to 20 ppb (7). The
LC50 for terbufos in Daphnia magna, a small freshwater invertebrate, is 0.31
ppb (7).
Effects on Other Animals (Nontarget species)
Terbufos is extremely toxic to mammals, and reptiles (7). It is not
toxic to bees when used properly.
ENVIRONMENTAL FATE
Breakdown of Chemical in Soil and Groundwater
Terbufos is moderately persistent in the soil. It is rapidly converted
to its metabolites which tend to persist in the soil and may be detected at
harvest time (1). Terbufos and its metabolites quickly degrade during the
first 15-30 days after application, then gradually stabilize. Only 3% of the
original application stayed in field-study soils after one month, with 1.5% of
the chemical present after 60 days (4).
In a study on silty clay loam soil in South Dakota, the half-life of
terbufos was about two weeks. The half-life for the metabolite, terboxon
sulfone, was two to three times longer (1).
When applied to a silt loam soil, the half-life for terbufos was
calculated at 15 days, while the total residue half-life was 22 days. After
106 days, the total residues were less than 1.0 ppm (6).
Terbufos dissipation is generally faster in soils with very low organic
carbon, while binding increases with increasing organic carbon content. Sandy
soils lose more of this chemical than do soils with clay over the same time
period (4).
Terbufos is generally immobile and is therefore unlikely to leach or
contaminate groundwater (4, 12). Much of the chemical can be recovered near
the site of application. In one study, over 90% of the applied terbufos was
recovered in the top four inches of a soil profile despite heavy rainfall and
thorough incorporation down to two-and-one-half inches (4).
Soil moisture does not appear to affect the degradation of terbufos.
This chemical will breakdown at about the same rate in soils regardless of the
level of wetness (4). As temperature increases, terbufos degrades more
quickly.
Being of low water solubility, terbufos is not often found in
groundwater. Terbufos has been found in a few groundwater samples collected
from locations across the United States. The concentration found was
approximately 11 ug/l (10).
Breakdown of Chemical in Surface Water
Terbufos hydrolyzes rapidly. At a concentration of 4.6 ppm, its
hydrolysis half-lives were 4.5, 5.5 and 8.5 days at pH 5, 7, and 9
respectively (7, 12). In another study, terbufos hydrolyzed with a half-life
of 2.2 weeks at pH 5, 7 and 9. Formaldehyde was the major degradate detected
(7).
Breakdown of Chemical in Vegetation
Terbufos moves from the soil into plants, where it is broken down
rapidly. Little of the parent compound is found in plants. Fifty-seven days
after seeding and application, the total residues in broccoli were very low,
while the marketable heads of broccoli harvested 90 days after seeding held
only traces (less than 0.01 ppm, fresh weight) of residues. Under the same
conditions, marketable cabbage and cauliflower had trace to nondetectable
levels of total residues (6). Field corn banded with 1.12 kg/ha had no
detectable residues 60 days after treatment. Sweet corn and popcorn grain
harvested at maturity also showed no residue even though the surrounding soil
contained 10-14 ppm (6).
PHYSICAL PROPERTIES AND GUIDELINES
Terbufos is a clear, slightly brownish-yellow liquid which is usually
formulated into granules for agricultural applications. Its molecular weight
is 288.41. It decomposes at temperatures .
Exposure Guidelines:
| NOEL (rat): | 0.00125 mg/kg/day |
| ADI: | 0.000125 mg/kg/day (8) |
| LHA: | 0.001 mg/l (13) |
| RfD: | 0.000125 mg/kg/day (12) |
Physical Properties:
| CAS #: | 13071-79-9 |
| Chemical name: | S-[[(1,1-dimethylethyl) thio] methyl]O,O-diethyl phosphorodithioate |
| Chemical class/use: | organophosphate insecticide |
| Density: | 1.105 at 24 degrees C (12) |
| Solubility in water: | 10-15 mg/L (9); 5.5 mg/L (liquid at 19 degrees C) (3) |
| Solubility in solvents: | acetone, aromatic hydrocarbons, chlorinated hydrocarbons, and alcohols. |
| Melting point: | minus 29.2 degrees C (9) |
| Boiling point: | 69 degrees C (9); 55 degrees C at 0.02 mm Hg (7) |
| Decomposition point: | greater than 120 degrees C (7) |
| Vapor pressure: | 34.6 mPa at 25 degrees C (12) |
| log P: | 595 (12) |
BASIC MANUFACTURER
American Cyanamid
One Cyanamid Plaza
Wayne, NJ 07470
Review by Basic Manufacturer:
Comments solicited: November, 1992
Comments received: December, 1992
REFERENCES
Ahmad, N., D.D. Walgenbach and G.R. Sutter. 1979. Bull. Environm.
Contamination Toxicol. 23, 423-429.
Meister, R.T. (ed.). 1986. Farm Chemicals Handbook. Meister
Publishing Co., Willoughby, OH.
Bowman, B.T. and W.K. Sans. 1979. J. Environ. Sci. Health. B14(6):
625-34.
Felsot, A., L. Wei and J. Wilson. 1982. Environmental chemodynamic
studies with terbufos ("Counter") insecticide in soil under laboratory and
field conditions. J. Environ. Sci. Health. B17(6): 649-673.
Occupational Health Services Inc. Material Safety Data Sheet for
Terbufos. 4/15/87. OHS: NY.
Szeto, S.Y., M.J. Brown, J.R. Mackenzie and R.S. Vernon. 1986.
Degradation of terbufos in soil and its translocation into cole crops. J.
Agric. Food Chem. 34: 876-879.
U.S. Environmental Protection Agency. Sept. 9, 1988. Pesticide Fact
Sheet: Terbufos, Fact sheet No. 5.2. Office of Pesticide Programs, US EPA,
Washington, DC.
U.S. Environmental Protection Agency. Aug. 30, 1989. Pesticide
Tolerance for Terbufos. Federal Register 54 (167): 35896-7.
Windholz, M. et al. (eds.). 1983. The Merck Index. 10th ed. Merck &
Co., Inc.
Williams, W.M, et.al. 1988. Pesticides in Groundwater Data Base:
1988 Interim Report. U.S. Environmental Protection Agency, Office of
Pesticide Programs, Washington, DC.
Walker, M.M. and L.H. Keith. 1992. EPA's Pesticide Fact Sheet
Database. Lewis Publishers. Chelsea, MI.
U.S. Environmental Protection Agency. Aug. 1988. Health Advisory:
Terbufos. Office of Drinking Water, US EPA, Washington, DC.
U.S. Environmental Protection Agency. Jan. 1989. Health Advisory
Summary: Terbufos. US EPA, Washington, DC.
Disclaimer: Please read
the pesticide label prior to use. The information contained at this web
site is not a substitute for a pesticide label. Trade names used herein
are for convenience only; no endorsement of products is intended, nor is
criticism of unnamed products implied. Most of this information is historical
in nature and may no longer be applicable.
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