Description
DEF is a cholinesterase-inhibiting organophosphorus pesticide
compound used as a cotton defoliant that was registered
in 1960.DEF is a colorless to pale-yellow transparent liquid
with a skunk-like odor.It is completely miscible with
n-hexane, dichloromethane, toluene, and 2-propanol and has
an octanol–water partition coefficient of 3.31×10
5 at 25°C.
DEF toxicity is primarily attributed to inhibition of various
esterases, including acetylcholinesterase (AChE), butyrylcholinesterase
(BuChE), neuropathic target esterase (NTE),
and carboxylesterase, resulting in increased accumulation of
endogenous acetylcholine (ACh) in cholinergic nerve terminals
and related effector organs.
Chemical Properties
Tribufos is a colorless to yellow liquid. Tribufos is relatively
stable to acids and heat and is hydrolyzed slowly under
alkaline conditions. Tribufos has a mercaptan or skunk-like odor. Tribufos has a mercaptan or skunk-like odor.
Practically insoluble in water (2.3×10
-4 g/
100 mL); completely miscible in
dichloromethane, n-hexane, 2-propanol,
toluene.
Uses
DEF is an organophosphate chemical used as a cotton defoliant
to facilitate mechanical harvesting. Recommended
application rate is ～1–2.5 pints per acre per year applied as
a diluted spray. Two products containing DEF as their active
ingredient include DEF 6, manufactured by Bayer Corporation,
and Folex 6 DC, manufactured by Amvac Chemical Co.
Used for pest control in industrial agriculture (tends to be
more toxic agents), organophosphates of low to intermediate
toxicity are used to control ectoparasites on farm and
companion animals and humans (head lice), and for home
and garden pest control.
Uses
1,2,4-Tributylphosphorotrithioate is a defoliant for cotton.
Definition
ChEBI: Tribufos is an organic thiophosphate. It has a role as a defoliant.
General Description
Colorless to pale yellow liquid with mercaptan-like odor. Insoluble in water; soluble in aliphatic, aromatic, and chlorinated hydrocarbons.. Used as a growth regulator.
Air & Water Reactions
Insoluble in water. Hydrolyzed slowly by alkaline conditions.
Reactivity Profile
An organophosphate derivative. Organophosphates are susceptible to formation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides.
Hazard
Cholinesterase inhibitor.
Agricultural Uses
Defoliants are substances that induce premature
shedding of leaves and facilitate harvesting. Defoliants
and desiccants are both harvesting aids, and are used as
herbicides, as many are toxic in nature. They may be
organic or inorganic.
Tribufos is a very effective defoliant for cotton and
one of the many harvesting aids in use, for various kinds
of crops.
Agricultural Uses
Herbicide, Defoliant, Plant growth regulator: Tribufos is an organophosphate defoliant used for
cotton crops. It is specifically used to defoliate cotton in
preparation for machine harvesting. It was first registered
in the United States in 1961. Not approved for use in EU
countries
. Registered for use in the U.S.
Trade name
B-1776®; BUTIFOS®; BUTIPHOS®[C];
CHEMAGRO® 1776; CHEMAGRO® B-1776; DE-
GREEN®; DEF®; DEF DEFOLIANT®; DELEAFDEFOLIANT®; EASY OFF®-D; E-Z-OFF® D; FOLEX®
6EC FOS-FALL® A; ORTHO® phosphate defoliant
Safety Profile
A poison by ingestion,
skin contact, and intraperitoneal routes.
Experimental reproductive effects. Animal
experiments show an anti-cholinesterase
effect. When heated to decomposition it
emits toxic fumes of PO, and SO,. See also
PARATHION, PHOSPHATES, ESTERS,
and SULFATES.
Carcinogenicity
No carcinogenic effects occurred when rats were given diets with 0, 4, 40, or 320 ppm
tribufos (equivalent to 0.0, 0.2, 1.8, and 16.8 mg/kg/day in
males and 0.0, 0.2, 2.3, and 21.1 mg/kg/day in females,
respectively) for 2 years .
In a carcinogenicity study, mice were fed diets containing
tribufos at doses of 0, 10, 50, or 250 ppm (equivalent to 0.0,
1.64, 8.28, or 48.02 mg/kg/day in males and 0.0, 2.08, 11.14,
or 63.4 mg/kg/day in females) for 90 weeks . Carcinogenic
effects were evident at 250 ppm (48.02 mg/kg/day in
males and 63.4 mg/kg/day in females). Males exhibited a statistically significant increase in hemangiosarcomas and
adenocarcinomas of the small intestines and females exhibited
a statistically significant increase in alveolar/bronchiolar
adenomas.
Environmental Fate
Soil. Hydrolyzes in soil to ethyl mercaptan, carbon dioxide and diisobutylamine (Hartley and Kidd, 1987). Butylate is probably subject to degradation of soil microorganisms.
It was reported that butylate may degrade via hydrolysis of the ester linkage forming the
corresponding mercaptan (ethyl mercaptan), alkylamine (diisobutylamine) and carbon
dioxide. Transthiolation and oxidation of the mercaptan forms the alcohol which may
further oxidize to afford a metabolic pool (Kaufman, 1967). Somasundaram and Coats
(1991) reported butylate in soils is oxidized to the corresponding sulfoxide. The reported
half-life in soil is approximately 1.5–10 weeks (Worthing and Hance, 1991). The reported
half-life of butylate in a loam soil at 21–27°C was 3 weeks (Humburg et al., 1989). Residual
activity in soil is limited to approximately 4 months (Hartley and Kidd, 1987).
Groundwater. According to the U.S. EPA (1986) butylate has a high potential to leach
to groundwater.
Plant. In plants, butylate is metabolized to carbon dioxide, diisobutylamine, fatty acids,
conjugates of amines and other compounds (Hartley and Kidd, 1987; Humburg et al.,
1989).
Toxicity evaluation
DEF is relatively stable in aqueous solutions (pH 5 and 7) up
to 32 days but slightly degraded at pH 9 with a half-life of
124 days. The hydrolytic breakdown product of DEF is known
as desbutylthio tribufos. DEF is stable up to 30 days in sandy
loam soil exposed to natural sunlight, but degrades in
aqueous solution upon exposure to natural sunlight for
30 days, with an estimated half-life of 44 days. The estimated
soil adsorption coefficient (K
d) for DEF ranges from 60.6 for
sandy loam soil to 106 for clay loam. The estimated soil
adsorption constant (K
oc) for DEF ranges from 4870 for silt
loam to 12 684 for sand. DEF is highly persistent in soil with
biodegradation half-lives of 745 and 389 days in sandy loam
soil under aerobic and anaerobic conditions. Based on water
solubility, high soil adsorption, hydrolysis, and aerobic soil
metabolism data, DEF is not identified as a potential
groundwater contaminant. However, DEF is likely to become
airborne following aerial application or ground spraying.
Also, while DEF itself is not significantly volatile, its degradation
product, n-butyl mercaptan (nBM), is volatile and
accounts for a skunk-like odor near areas where DEF has been
applied. DEF is also formed via release of the defoliant merphos,
which undergoes rapid oxidation under environmental
conditions to tribufos. DEF has a vapor pressure of
5.3×10
-6 mm Hg at 25°C, suggesting its occurrence in both
vapor and particulate phases in ambient atmosphere. Vaporphase
DEF degrades by interacting with photochemically
produced hydroxyl radicals; half-life for this reaction in air is
estimated to be 5 h. Particulate-phase DEF gets removed from
atmosphere by wet and dry deposition. Volatilization of DEF
from water surfaces is not an important fate process based on
its Henry’s Law constant of 2.9 107 atmm3 mol1 at 20°C.
