Chlorpyrifos applications, toxicity and effects

Jonah Lester

The clorpyrifos is a broad spectrum crystalline organophosphate pesticide used in agricultural, industrial and domestic levels. This insecticide was developed by the Dow Chemical Company in the mid-1960s under the trade names Lorsban® and Dursban®.

It is used to control cockroaches, fleas and termites in homes, it is also the active ingredient in various insecticides applied to domestic pets. At the livestock level it is used to eliminate ticks from livestock, and at the agricultural level it controls various pests in commercial crops.

Chlorpyrifos molecule. Source: Benjah-bmm27 [Public domain], from Wikimedia Commons

According to the IUPAC nomenclature, chlorpyrifos is known as O, O-diethyl O-3, 5,6-trichloropyridin-2-yl phosphorothioate. Its insecticidal effect is reflected in that it prevents the synthesis of acetylcholinesterase, altering the nervous system of insects..

This pesticide is marketed in the form of a white crystalline solid with a strong characteristic aroma. It is a hydrophobic product, so it needs to be mixed with emulsions to be applied on crops, animals and facilities..

At the agricultural level, it acts as a non-systemic contact and ingestion insecticide with a direct effect on the pest insect. It is applied by spraying when the pest is detected, it can also be applied in the form of microcapsules.

In relation to its toxicity, it is a moderately toxic product causing neurological alterations, developmental and autoimmune disorders when chronic exposure occurs. Recently, the legislation of various countries has suppressed its use in pets and in domestic and institutional spaces..

Article index

  • 1 Physical and chemical properties
  • 2 Applications
  • 3 Mode of action
  • 4 Toxicity
  • 5 How does chlorpyrifos poisoning occur?
  • 6 Health effects
  • 7 Behavior in the environment
  • 8 References

Physical and chemical properties

Chlorpyrifos. Source:
  • Chemical name of the active ingredient: O, O-diethyl O-3,5,6-trichloro-2-pyridy phosphorothioate
  • Name CAS: O, O-diethyl O- (3,5,6-trichloro-2-pyridy) phosphorothioate
  • Name ISO: CHLORPYFOS (eng.) or CHLORPYRIFOS (esp.)
  • Chemical Classification: Organophosphate.
  • Action: contact, ingestion and inhalation.
  • Chemical Formula: C9HelevenCl3NOT3$
  • Atomic mass: 350.6 g / mol.
  • Appearance: white crystalline product with strong pungent odor.
  • Formulation: Emulsifiable concentrate
  • Melting point: 41º - 43º C
  • Relative density of the liquid (water = 1 g / ml): 1,398 to 43.5 ° C
  • Solubility in water: 0.39 mg / L (19.5º C) and 2 mg / L (25º C)
  • Photostability in water (T½): 39.9 days
  • Octanol / water partition coefficient: log Koa 5,0 - 24,5º C
  • Vapor pressure (Pa at 25º C): 0.0025
  • Use: insecticide
  • Toxicological band: II- Yellow
  • Dangers: Due to thermal decomposition (temperatures greater than 15º C) it generates toxic gases: COx, SWx, POx, NOTx and chlorine derivatives.
  • LDfifty: 82 - 270 Moderately Toxic (Class II).


Chlorpyrifos-based insecticides are used mainly to control pests in horticultural, fruit, cereal and ornamental crops. It is even used to control ants and termites in wood products in domestic and industrial areas..

On the other hand, controlled applications on domestic animals allow the control and eradication of fleas, ticks and lice. As well as the control of flies and mosquitoes in closed environments or schools, and for the control of insects in gardens, parks and golf courses.

The residential use of chlorpyrifos has recently been restricted in different countries, approving its use only in rural areas. Additionally, the production, importation and marketing of household products containing no more than 0.5% of the active ingredient of chlorpyrifos has been prohibited..

At the agricultural level, it is an insecticide used to control sucking and chewing insects. It does not represent toxicity problems in crops when applied at the recommended dose, being compatible in foliar applications with other pesticides.

Action mode

Chlorpyrifos does not have systemic effects, but acts by ingestion, contact and inhalation. Because it belongs to the group of organophosphates, it inhibits the action of acetylcholinesterase through recombination with this enzyme.

In fact, acetylcholine cannot be released from the receptor site, the nerve impulse does not stop, and it maintains a continuous flow. Indeed, the transmission of nerve impulses is increased, causing paralysis of the insect and later death.

This insecticide is used on sorghum and corn to control various root pests of the crop, such as the pinworm (Diabrotica spp). Also the blind hen (Phyllophaga sp.), wireworm (Ischidiontus sp., Megapentes sp., Melanotus sp., Agriotes lineatus) and colaspis larvae (Colaspis sp.).

Pinworm (Diabrotica spp). Source:


The mean lethal dose (LDfifty) acute oral is 135 - 165 mg / kg. It is an insecticide belonging to category II - moderately toxic. The DLfifty is the classification of pesticides proposed by the WHO based on their degree of danger.

How does chlorpyrifos poisoning occur?

Chlorpyrifos poisoning can occur through ingestion, inhalation, or direct contact. In case of ingestion, it passes easily from the intestine to the bloodstream, rapidly distributing throughout all the body systems.

Application of Insecticides. Source:

In case of inhalation, either by inhalation of controlled sprays or dust with particles of the active ingredient, it manages to enter the lungs and is rapidly distributed through the blood.

By contact, the product can enter through the skin, however, the toxic effects by this route are less than by ingestion and inhalation. Contact poisoning, in general, is more dangerous for children and babies who become intoxicated when walking through places fumigated with this pesticide..

Children's skin is more sensitive to the toxic effect, if babies crawl or play on places sprayed with this element, they expose their body to this type of contamination. In addition, in recently fumigated areas they are exposed to inhaling the fumigant vapors.

Health effects

Exposure to organophosphate pesticide products, such as chlorpyrifos, can affect the central nervous system, the cardiovascular system, and the respiratory system. Likewise, it can cause irritation in the soft parts of the skin, mucous cavities and eyes..

The ingestion of pesticides is lethal to health. Source:

In the short term (acute toxicity) it can cause numbness of the extremities, tingling sensations, disorientation, vertigo, imbalance, followed by headache, tremors, nausea, abdominal cramps, sweating, blurred vision, abnormal breathing rate, tachycardia and bradycardia.

In case of a very high and prolonged dose, it can cause seizures, loss of consciousness and death. In low doses, the first symptoms are detected within 15 to 30 days, depending on the patient's condition, obvious symptoms may or may not be present.

In the long term (chronic toxicity), symptoms similar to those seen in acute exposure, including symptoms manifest late effects. Chronic toxicity includes neurological damage, headache, difficulty communicating, disorientation, nausea, loss of appetite, and drowsiness..

As the insecticide makes contact with the person, the product is absorbed through the skin, the lungs or the gastrointestinal tract. In the body it acts on the hormonal system, affecting the functioning of female hormones or estrogen.

Chlorpyrifos exposures during pregnancy influence the development of the hypothalamus neuroendocrine mechanism that controls social activities. Individuals who have experienced this phenomenon tend to lose memory and suffer frequent changes in behavior, in fact they can develop disorders such as autism.

Similarly, contamination with chlorpyrifos can alter the metabolism of insulin and fats, causing pathologies similar to those presented by patients with symptoms similar to diabetes and arteriosclerosis..

Behavior in the environment

Chlorpyrifos is incorporated into the environment through direct spraying on crops, gardens, domestic animals, homes, schools and work spaces. In the same way, it can be incorporated into the environment through the washing of waste and application material, and by dollarization of product remains..

When the ingredient is incorporated into the soil, it adheres firmly to the clay particles while remaining in the area of ​​application. In fact, chlorpyrifos particles are unlikely to be released from the soil, due to their low solubility in water..

In the event that the active ingredient reaches tributaries of natural waters, it will be in minimal quantities, remaining on the surface of the water. Over time it will evaporate easily due to its hydrophobic nature.

Once incorporated into the soil, water or air, chlorpyrifos deteriorates due to the effect of chemical processes in the soil, sunlight or bacterial action. However, the volatilization process is the primary way in which this pesticide diffuses after its application..


  1. Chlorpyrifos (1997) Agency for Toxic Substances and Disease Registry - CDC. Recovered at:
  2. Chlorpyrifos (2017) Central American Pesticides Manual. Recovered in:
  3. Cocca, C., Ventura, C., Núñez, M., Randi, A., & Venturino, A. (2015). Chlorpyrifos organophosphate as an estrogen disruptor and risk factor for breast cancer. Acta toxicológica argentina, 23 (3), 142-152.
  4. Lorsban 5G Datasheet (2018) Dow Agro Science. Recovered at:
  5. Information Clorpirifós- Dursban (2016) Fertitienda. Recovered in:
  6. Morales, C. A., & Rodríguez, N. (2004). Chlorpyrifos: Possible endocrine disruptor in dairy cattle. Colombian Journal of Livestock Sciences, 17 (3), 255-266.

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