| Chemical Abstract Number (CAS #) |
13071799
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| Synonyms | Terbufos |
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Phosphorodithioic acid, O,O-diethyl-S-[(1,1-dimethylethyl)thio]methyl ester | Counter | Phosphorodithioic acid, S-[(tert-butylthio)methyl] O,O-diethyl ester |
| Analytical Method |
EPA Method 8141A |
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| Molecular Formula | C9H21O2PS3 |
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| Use | Soil insecticide
Control of nematodes in beet, maize, cotton, sorghum, onions, cabbage, and bananas
Effective initial and residual activity against soil dwelling arthropods. Soil application of
granules controls Diabrotica species larvae on maize, Tetanops myopaeformis on sugar beet,
Delia brassicae on cabbages, millipedes, onion maggots, symphylids, wireworms and other soil
dwelling arthropods. Various above ground pests also are controlled on plants grown in terbufos
treated soil. It has nematicidal activity.
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| Apparent Color | Yellowish liquid
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| Boiling Point | 69 deg C at 0.01 mm Hg
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| Melting Point | -29.2 deg C
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| Molecular Weight | 288.41
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| Density | 1.105 at 24 deg C
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| Environmental Impact | Terbufos is released to the environment through its use as an insecticide. If released to
soil, terbufos is expected to be slightly mobile and, therefore, very little leaching in soil is
expected. Terbufos should undergo rapid primary biodegradation if released to soil. Terbufos is
expected to degrade in the ambient atmosphere by reaction with photochemically produced
hydroxyl radicals with a half-life of 0.004 day. If released to water, volatilization is not expected
to be a dominant fate process. In aqueous media, terbufos predominately undergoes chemical
degradation rather than microbial degradation. Bioconcentration in aquatic organisms and
absorption to sediments of terbufos are expected to be important fate processes. Exposure of
terbufos to the general population is possible by inhalation of air contaminated by release during
its use as an insecticide. In occupational settings, exposure to terbufos may occur through
inhalation of vapors and through eye and skin contact.
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| Environmental Fate | TERRESTRIAL FATE: Oxidative and hyrolytic degradation occurs in soil. No
accumulation.
TERRESTRIAL FATE: Based on a measured log Kow of 3.68 , an estimated Koc of 2400
can be calculated suggesting terbufos is slightly mobile in soil . Numerous aerobic degradation
and field studies in soil have been conducted on terbufos(5-12). Results from these studies
indicate the rapid degradation of terbufos in soil to its oxidation products terbufos sulfoxide and
terbufos sulfone(5-12). A typical half-life for the degradation of terbufos in soil is reported to be 5
days .
AQUATIC FATE: Based on a measured water solubility of 5.07 ppm at 25 deg C and a
reported vapor pressure of 3.2X10-4 mm Hg at 25 deg C , a Henry's Law constant for terbufos
can be estimated to be 2.4X10-5 atm-cu m/mole. Based on this Henry's Law constant
terbufos is not expected to readily volatilize from water. The volatilization half-life from a
model river (1 m deep flowing 1 m/sec with a wind velocity of 3 m/sec) and a model
environmental pond can be estimated from this Henry's Law constant to be approximately 14.9
and 169 days, respectively(3-4,SRC). Aerobic persistence studies of terbufos degradation in
distilled, natural, and sterile water produced half-lives of 3.3, 3.2, and 3.5 days, respectively .
The reported half-lives indicate that chemical degradation, not microbial degradation, is the
predominate route of terbufos degradation in aqueous media . Based on a measured log Kow of
3.68(6), an estimated Koc of 2400 and an estimated BCF of 369 can be calculated, which
indicate that adsorption to suspended solids and sediment is expected to be an important fate
process, but bioconcentration in aquatic organisms will be minimal(3,SRC)
ATMOSPHERIC FATE: Based on a reported vapor pressure of 3.2X10-4 mm Hg at 25 deg
C , terbufos is expected to exist in both the vapor and particulate phases in the ambient
atmosphere . Vapor phase terbufos is degraded rapidly in the ambient atmosphere by reaction
with photochemically formed hydroxyl radicals. The half-life for this reaction in typical air can be
estimated to be about 0.044 day(3,SRC).
The degradation of eptam, carbofuran and terbufos in soils was studied and was related to the
rate and frequency of their application, the cropping system, presence of other pesticides applied
either simultaneously or sequentially, and the physicochemical properties of the soils. Frequent,
repeated applications of these pesticides resulted in accelerated rates of biodegradation.
Pesticides, such as eptam or carbofuran, may act as inducers of microbial enzymes which degrade
other pesticides.
When terbufos at 1.9 g/10 m row was applied to a silt loam soil at seeding for cabbage maggot
control, its effectiveness was comparable to or better than that of the registered chemicals
fensulfothion, chlorfenvinphos, and diazinon. Terbufos oxidized to its sulfoxide and sulfone in
soil. The calculated half lives of terbufos and total residues were 15 and 22 days, respectively. The
total residues in soil were <1.0 ppm after 106 days. Terbufos translocated from soil into broccoli.
The plant residues consisted mostly of terbufos sulfoxide, terbufos oxon sulfoxide, and terbufos
sulfone, but the parent cmpd accounted for only 5% of the total. After 57 days there were 0.43
ppm total residues in the plant but only traces (<0.01 ppm, fresh wt) in the marketable heads of
broccoli harvested 90 days after seeding. In marketable cabbage and cauliflower grown and
treated and harvested in the same way, total residues ranged from nondetectable to trace.
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| Drinking Water Impact | Waters from 21 wells and 2 springs located in a typically farmed, mostly agricultural PA
watershed (the Mahantango Creek Watershed) were analyzed for 11 pesticides, including
terbufos. Pesticides were selected according to a farm use survey, and samplings were made
during Dec 1985, Aug 1986, and Mar/Apr 1987. Terbufos was applied in 1985 but not in 1986.
No terbufos was found in any sampling (< 3 ng/l).
SURFACE WATER: Terbufos was qualitatively identified in water samples taken from Lake
Erie . Terbufos was found at concentrations ranging from 0.005-0.011 ppm and 0.011 ppm in
samples taken from Lake Michigan's Black River and Clinton River, respectively .
GROUNDWATER: Terbufos was detected in 1 out of 1438 well water samples taken from
various locations in Nebraska .
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