Chlorpyrifos

Description

Chlorpyrifos is a chlorinated organophosphorus (OP) ester manufactured as an insecticide, acaricide, and miticide. Like the other OP insecticides, the most prominent toxicity of chlorpyrifos is associated with binding and inhibition of the enzyme acetylcholinesterase (AChE) in insects and mammals. Chlorpyrifos requires metabolic activation to chlorpyrifos oxon to yield anticholinesterase activity.
First sold in 1965, chlorpyrifos is used globally to control agricultural and structural pests and mosquitos. In the 1990s, chlorpyrifos ranked as one of the top selling pesticides in the world, for the most part, replacing the persistent organochlorine insecticides. Over the last decade, concerns regarding toxicity to the developing nervous system have limited its use. By 2001, residential uses and uses in schools and parks were prohibited, and many agricultural uses were restricted and the US Residential use limitations were also imposed in Canada, Australia, and the European Union (EU). It continues to be used in large quantities to control crop damage worldwide. In the developing countries, excessive agricultural application and lack of protective devices result in hundreds of thousands of deaths yearly.

Description

Chlorpyrifos is a thiophosphate insecticide and acaricide sold under such names as Lorsban and Dursban. Dow Chemical first marketed it in 1965 as a household pesticide. Because chlorpyrifos is associated with several health problems, in 2001 FDA severely restricted its use , but it is still widely used in some countries. More recently,?researchers found that it affects several regions of the brain.

Description

Chlorpyrifos is an organophosphate insecticide. It is lethal to A. melinus, G. ashmeadi, E. eremicus, and E. formosa adults (LC₅₀s = 0.8, 6, 12, and 17 ng/ml, respectively). Chlorpyrifos induces mortality in O. insidiosus adults when applied to corn, sorghum, and alfalfa plants. It is toxic to mice (LD₅₀ = 155 mg/kg). Postnatal day 11 to 14 exposure to chlorpyrifos (3 mg/kg) decreases nest building and defense behaviors in adult female mice. Formulations containing chlorpyrifos have been used in the control of insects in agriculture.

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

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.

The Uses of Chlorpyrifos

Chlorpyrifos belongs to a class of insecticides known as organophosphates. Technical chlorpyrifos is amber to white crystalline solid with a mild sulphur odour. Formulations of chlorpyrifos include emulsifiable 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 in animal houses. The U.S. EPA classified chlorpyrifos as GUP.

The Uses of Chlorpyrifos

Chlorpyrifos is an organophosphorus insecticide used to control insects on a wide variety of crops including fruits, vegetables, ornamentals and forestry

The Uses of Chlorpyrifos

Chlorpyrifos is used to control many types of insect pests in a wide range of crops and ornamentals. It is also used to control household pests, including termites.

What are the applications of Application

Chlorpyrifos is An organothiophosphate cholinesterase inhibitor that is used as an insecticide

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.

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.

Reactivity Profile

Chlorpyrifos is sensitive to heat and is decomposed by moisture. Chlorpyrifos 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.

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

Cholinesterase inhibitor; heavy exposurecan produce acute, delayed, and chroniceffect; exhibits low to moderate toxicity inexperimental animals when administered byoral and dermal routes; however, severity ofeffects varies with species; highly toxic tobirds; ingestion of 1.5–2 g would probablyresult in onset of cholinergic effects in adulthumans.
LD50 oral (rat): ～150 mg/kg
LD50 oral (rabbit): 1000 mg/kg
LD50 oral (wild bird): 5 mg/kg
LD50 oral (chicken): 25 mg/kg
LD50 skin (rat): ～200 mg/kg
LD50 skin (rabbit): 2000 mg/kg.

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.

Flammability and Explosibility

Not classified

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®

Safety Profile

Poison by ingestion, intraperitoneal, skin contact, and inhalation routes. Human systemic effects by ingestion: paresthesia, muscle weakness, coma. Experimental reproductive effects: developmental toxicity. Mutation data reported. When heated to decomposition it emits very toxic fumes of Cl-, NOx POx and SOx

Potential Exposure

A potential danger to those involved in the manufacture, formulation, and application of this insecticide.

First aid

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Speed in removing material from skinis of extreme importance. Shampoo hair promptly if contaminated. Seek medical attention immediately. If thischemical has been inhaled, remove from exposure, beginrescue breathing (using universal precautions, includingresuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit.Medical observation is recommended.

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.

storage

Color Code—Blue: Health Hazard/Poison: Storein a secure poison location. Prior to working with chlorpyrifos you should be trained on its proper handling and storage. Chlorpyrifos must be stored to avoid contact withstrong bases, or acids, or acid fumes since violent reactionsoccur. Store in tightly closed containers in a cool, well-ventilated area away from sources of heat.

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.

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 S_N2 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.

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.

Precautions

Occupational workers should be careful during handling and use of chlorpyrifos. The workplace should have adequate washing facilities at all times and close to the site of handling and use. Eating, drinking, and smoking should be prohibited during handling and before washing after handling. Containers should be kept away from foodstuffs, animal feed and their containers, and out of reach of children.