Chemical Properties
Chlorpyrifos belongs to the class of insecticides known as organophosphates. Technical
chlorpyrifos is an amber to white crystalline solid with a mild sulfur odor. It is insoluble in
water, but soluble in benzene, acetone, chloroform, carbon disulfi de, diethyl ether, xylene,
methylene chloride, and methanol. Formulations of chlorpyrifos include emulsifi able concentrate, dust, granular wettable powder, microcapsule, pellet, and sprays. Chlorpyrifos
is widely used as an active ingredient in many commercial insecticides, such as Dursban
and Lorsban, to control household pests, mosquitoes, and pests. Formulations of chlorpyrifos include emulsifi able concentrates, granules, wettable powders, dust, microcapsules,
pellets, and sprays. The US EPA has classifi ed chlorpyrifos as a GUP
General Description
CHLORPYRIFOS(2921-88-2) is a white crystalline or irregularly flaked solid. CHLORPYRIFOS(2921-88-2) has a very faint mercaptan-type odor. CHLORPYRIFOS(2921-88-2) is not soluble in water. CHLORPYRIFOS(2921-88-2) can cause slight irritation to the eye and skin.
Reactivity Profile
CHLORPYRIFOS is sensitive to heat and is decomposed by moisture. This chemical is hydrolyzed by strong alkalis. CHLORPYRIFOS is corrosive to copper and brass. CHLORPYRIFOS is also corrosive to copper alloys. CHLORPYRIFOS reacts with water and most reactive hydrogen compounds. The rate of hydrolysis in water increases with pH, with temperature and with the presence of copper and possibly other metals that can form chelates.
Air & Water Reactions
Insoluble in water. CHLORPYRIFOS reacts with water and most reactive hydrogen compounds. The rate of hydrolysis in water increases with pH, with temperature and with the presence of copper and possibly other metals that can form chelates.
Health Hazard
Exposures to chlorpyrifos cause adverse health effects and poisoning. The symptoms
include, but are not limited to, headache, dizziness, respiratory problems, muscular and
joint pains, numbness, tingling sensations, incoordination, tremor, nausea, abdominal
cramps, vomiting, sweating, blurred vision, respiratory depression, slow heart beat, nervousness, weakness, cramps, diarrhea, chest pain, pin-point pupils, tearing, salivation,
clear nasal discharge and sputum, muscle twitching, and in severe poisonings convulsions, coma, and death. Exposures to chlorpyrifos cause adverse effects to the nervous
system. The effects include phosphorylation of the active site, disturbance in the activity of the acetylcholinesterase (AChE) enzyme (inactivity). AChE enzyme is necessary to stop
the transmission of the chemical neurotransmitter.
In occupational workers, high concentrations of chlorpyrifos cause poisoning with
symptoms of unconsciousness, convulsions and/or fatal injury. Persons with respiratory ailments and disturbed liver function are known to be at increased health risk.
Also, repeated exposures to chlorpyrifos have been reported to cause disturbances in
the process of brain development.
Health Hazard
Symptoms of organophosphate insecticide poisoning: cholinesterase inhibition, headache, fatiguedizziness, blurred vision, weakness, nausea, cramps, diarrhea, chest discomfort, sweating, miosis, tearing, salivation, vomiting, cyanosis, papilledema, and muscle twitching. In advanced cases convulsions, coma, loss of reflexes, and loss of sphincter control may occur. EYES: Can produce mild to moderate eye irritation and transient corneal injury. SKIN: Undiluted liquid products can cause skin irritation. Prolonged or repeated exposure may cause superficial burns.
Potential Exposure
A potential danger to those involved in the manufacture, formulation, and application of this insecticide.
Fire Hazard
Combustible material: may burn but does not ignite readily. Containers may explode when heated. Runoff may pollute waterways. Substance may be transported in a molten form.
First aid
If this chemical gets into the eyes, remove any contact lenses at once and irrigate immediately for at least 15 minutes, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts the skin, remove contaminated clothing and wash immediately with soap and water. Speed in removing material from skin is of extreme importance. Shampoo hair promptly if contaminated. Seek medical attention immediately. If this chemical has been inhaled, remove from exposure, begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR if heart action has stopped. Transfer promptly to a medical facility. When this chemical has been swallowed, get medical attention. Give large quantities of water and induce vomiting. Do not make an unconscious person vomit. Medical observation is recommended.
Shipping
UN2783 Organo phosphorus pesticides, solid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials. UN3018 Organophosphorus pesticides, liquid, toxic, Hazard Class: 6.1; Labels: 6.1-Poisonous materials.
Incompatibilities
Above 130°C this chemical may undergo violent exothermic decomposition. The substance decomposes on heating at approximately 160°C and on burning, producing toxic and corrosive fumes including hydrogen chloride, nitrogen oxides; phosphorous oxides, sulfur oxides. Reacts with strong acids; strong bases; causing hydrolysis. Attacks copper and brass. Contact with oxidizers may cause the release of phosphorous oxides. Contact with strong reducing agents, such as hydrides, may cause the formation of flammable and toxic phosphine gas.
Waste Disposal
This compound is 50% hydrolyzed in aqueous MeOH solution at pH 6 in 1930 days; and in 7.2 days at pH 9.96. Spray mixtures of <1% concentration are destroyed with an excess of 5.25% sodium hypochlorite in <30 minutes @ 100°C; and in 24 hours @ 30°C. Concentrated (61.5%) mixtures are essentially destroyed by treatment with 100:1 volumes of the above sodium hypochlorite solution and steam in 10 minutes. In accordance with 40CFR165, follow recommendations for the disposal of pesticides and pesticide containers. Must be disposed properly by following package label directions or by contacting your local or federal environmental control agency, or by contacting your regional EPA office.
Physical properties
Chlorpyrifos is a white crystalline or irregularly flaked solid. Chlorpyrifos has a very faint mercaptan-type odor. Chlorpyrifos is not soluble in water. Chlorpyrifos can cause slight irritation to the eye and skin.
Definition
ChEBI: An organic thiophosphate that is O,O-diethyl hydrogen phosphorothioate in which the hydrogen of the hydroxy group has been replaced by a 3,5,6-trichloropyridin-2-yl group.
Flammability and Explosibility
Notclassified
Agricultural Uses
Insecticide, Nematicide: A U.S. EPA restricted Use Pesticide (RUP).
Chlorpyrifos is one of the most widely used insecticides
in the U.S., both around the home and in agriculture. A
broad-spectrum insecticide, originally used primarily
to kill mosquitoes but no longer registered for that use.
Chlorpyrifos is effective in controlling cutworms, corn
rootworms, cockroaches, grubs, flea beetles, flies, termites,
fire ants, and lice. It is used as an insecticide on grain,
cotton, field, fruit, nut and vegetable crops, as well as on
lawns and ornamental plants. It is also registered for direct use on sheep and turkeys, for horse site treatment, dog
kennels, domestic dwellings, farm buildings, storage bins,
and commercial establishments. Chlorpyrifos acts on pests
primarily as a contact poison, with some action as a stomach poison. It is available as granules, wettable powder, dustable powder and emulsifiable concentrate. Top crop uses
in California include cotton, alfalfa, almonds, and oranges.
Trade name
(Note: EPA Office of Pesticide Programs
lists 2135 products, both active and past-registered)
ALUDOR®; BAR 500 EC®; BRODAN®; CHLORBAN®;
CHLORPIRIFOS 480 CE MILENIA®; CHOIR®;
COROBAN®; CURIGNA®; CYREN®; DETMOL U. A. ®;
DORSAN®; DORSAN®-C; DOWCO® 179; DURSBAN®;
EF 121®; EMPIRE®; ERADEX®; GLOBAL CRAWLING
INSECT BAIT®; KENSBAN®; LORSBAN®; MURPHY
SUPER ROOT GUARD®; PAQEANT®; PILOT®;
PYRINEX®); SCOUT®; SPANNIT®; STIPEND;
TALON®; TAFABAN®; TERIAL®; TWINSPAN®
Carcinogenicity
Some recent studies have
reported associations between chlorpyrifos exposure and
increased risk for cancer for farm workers participating in
the Agricultural Health Study. Specifically, increased risk for
glioma and rectal cancer has been associated with chlorpyrifos
exposure . Chlorpyrifos was also one pesticide
associated with trends toward higher incidence of lung
cancer through 2001 . For all cancers though, follow-
up periods are short and exposures are based on recall so
results may be unreliable.
Environmental Fate
Biological. From the first-order biotic and abiotic rate constants of chlorpyrifos in
estuarine water and sediment/water systems, the estimated biodegradation half-lives were
3.5–41 and 11.9–51.4 days, respectively (Walker et al., 1988)
Soil. Hydrolyzes in soil to 3,5,6-trichloro-2-pyridinol (Somasundaram et al., 1991).
The half-lives in a silt loam and clay loam were 12 and 4 weeks, respectively (Getzin,
1981). In another study, Getzin (1981a) reported the hydrolysis half-lives
Leoni et al. (1981) reported that the major degradation product of chlorpyrifos in soil
is 3,5,6-trichloro-2-pyridinol. The major factors affecting the rate of degradation include
chemical hydrolysis in moist soils, clay-catalyzed hydrolysis on dry soil s
Plant. The half-life of chlorpyrifos in Bermuda grasses was 2.9 days (Leuck et al.,
1975). The concentration and the formulation of application of chlorpyrifos will determine
the rate of evaporation from leaf surfaces. Reported foliar half-lives on tomato, orange and
cotton leaves were 15–139, 1.4–96 and 5.5–57 hours, respectively (Veierov et al., 1988).
Dislodgable residues of chlorpyrifos on cotton leaf 0, 24, 48, 72 and 96 hours after
application (1.1 kg/ha) were 3.64, 0.13, 0.071, 0.055 and 0.034 μg/m2, respectively (Buck
et al., 1980)
Surface Water. In an estuary, the half-life of chlorpyrifos was 24 days (Schimmel et
al., 1983).
Metabolic pathway
The metaboic fate of chlorpyrifos in soil, plants and animals is similar,
with oxidative dealkylation or hydrolysis to diethyl phosphorothioate
and 3,5,6-trichloro-2-pyridinol being the major route of detoxification.
The latter metabolite is conjugated as the glycosides or glucuronides in
plants and animals. De-ethylation is not a major route of detoxification in
mammals. Activation by desulfuration to the active acetylcholinesterase
inhibitor, chlorpyrifos oxon, occurs in both animals and plants but the
compound is often not detected owing to its rapid rate of hydrolysis.
Dechlorination of the chloropyridine ring also occurs in the environment,
principally by photolysis.
Degradation
Chlorpyrifos is hydrolysed in acid, neutral and alkaline solution (PM).
In neutral solution (approximately pH 7 and 25 °C) the DT50 for decomposition
was variously reported as between 29 and 72 days. DT50s in
buffered solutions at pH 4.7,6.9 and 8.1 were reported as being 62.7,35.3
and 22.9 days respectively (Racke, 1993). Hydrolysis is much faster
in alkaline solutions and the DT50 at pH 11 was reported as 0.5 day
(Macalady and Wolfe, 1983). The mechanisms of hydrolysis and nature of
the products are pH-dependent. As has been found with many organophosphates,
O-dealkylation predominates at acid and neutral pH values
and in alkaline solution the main mechanism is cleavage of the P-O-aryl
bond. Macalady and Wolfe (1983) showed that in buffered aqueous polar
solvent mixtures at pH 9.7 to 12.9 the only products were 3,5,6-trichloro-
2-pyridinol(2) and diethyl phosphorothioate (3). In near neutral solution
(pH 7.68) the main products were desethylchlorpyrifos (4) and ethanol
with lesser amounts of 2 and 3. The mechanism for base-catalysed
hydrolysis is via SN2 hydroxide attack on phosphorus, whereas under
acid and neutral conditions the nucleophile is water and the rate is pH-independent
with a half-life of 72.1 days and 72.9 days being reported at
pH 5 and 7 respectively. Chlorpyrifos oxon (10, Scheme 2) was much
more easily hydrolysed (Kenaga, 1971). Pathways for the hydrolytic
degradation of chlorpyrifos in acid and base solution are shown in
Scheme 1.
Toxicity evaluation
Chlorpyrifos undergoes abiotic hydrolysis, photodegradation,
and biotic degradation in soil and water. Depending on
the soil type and climate, its soil persistence varies from 2 weeks
to over 1 year. Microbial degradation is indicated by the shorter
half-lives in natural soils than sterile soils. Chemical hydrolysis
produces O-ethyl-O-3,5,6-trichloro-2-pyridyl phosphorothioate
or 3,5,6-trichloro-2-pyridinol (TCP) and phosphorthioic acid
at alkaline conditions. Half-lives in river and well waters vary
from 4.8 to 38 days, with the rate of hydrolysis increasing
with temperature and alkalinity. The estimated Log Koc of
3.73 predicts strong adsorption to soil and resist leaching
to groundwater. Chlorpyrifos can persist indoors for several
months.
Oxidation of chlorpyrifos to its more toxic metabolite chlorpyrifos
oxon could occur through photolysis, aerobic metabolism,
and chlorination. Water chlorination is the major route
of chlorpyrifos oxon formation. It is subsequently rapidly hydrolyzed toTCP.TCP and its glucuronide conjugates have been
detected in fish tissues. The measured Kow of 4.8 indicates
a potential for bioaccumulation in aquatic and terrestrial food
chains.
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