A general introduction to pyrethroids
Pyrethroids are synthetic pyrethroids that are synthetic insecticides and are synthetic esters derived from the chemical structure of natural pyrethrins. Natural pyrethrin is an ancient plant pesticides, the active ingredient is natural Juju, is an effective component of pyrethrum, the chemical structure to the 20th century, the study was determined in the 1940s, after which began the synthesis of similar substances. Because of its broad spectrum insecticide, good effect, low residue, no accumulation of the advantages of the past 30 years, more and more common. In addition to the prevention and control of agricultural pests, and in the prevention of vegetables, fruit trees and other pests to achieve better results; of mosquitoes, cockroaches, head lice and other pests, there are quite satisfied with the killing effect of its use of large, wide range of applications, Large, contact with the crowd, so poisoning cases occur frequently.
Pyrethroid insecticides are more toxic to insects than to mammals, with contact and stomach kill. Mainly used to kill cotton, vegetables, fruit trees, tea and other crops on the pests, is a spectrum of highly efficient pesticides.
Main varieties of Pyrethroids
Cypermethrin, deltamethrin, cypermethrin, beta-cypermethrin, cypermethrin, fenvalerate, fenvalerate, cyanate ester, cypermethrin, flufenvalerate, Cypermethrin, fenvalerate, cyfluthrin, fenvalerate, cyhalothrin, fenpropathrin, resmethrin, dextrin.
Biochemical effects of Pyrethroids
This pesticide is not soluble in water or insoluble in water, soluble in a variety of organic solvents, light and heat and acid stability, alkali (pH> 8) easily decomposed. Can be the digestive tract, respiratory and skin mucosa into the body. But because of its small fat-soluble, so difficult to absorb through the skin, not completely absorbed in the gastrointestinal tract. Poison into the blood, the legislature even p distributed in the body. Especially the nervous system and liver and kidney and other organs of higher concentrations, but the level of concentration and poisoning performance is not necessarily parallel. Toxic substances in the body, in the liver microsomal mixed function oxidase (MFO) and pyrethroid esterase under the action of oxidation and hydrolysis reaction to produce acid (such as free acid, glucuronic acid or glycine binding form), alcohol ( Methyl-carboxylate) of water-soluble metabolites and conjugates and excreted. Mainly by renal excretion, a few with the stool. Within 24 hours of discharge more than 50%, 8 days, almost all of the discharge, only trace residues in the fat by the liver. A large number of animal experiments show that pyrethroids have no carcinogenic, teratogenic and mutagenic effects. Some people (Bhunya) that deltamethrin has mutagenic effect.
The main characteristics of pyrethroids
Pyrethroids are a kind of broad-spectrum insecticides that can control many kinds of pests. Their insecticidal toxicity is 10 ~ 100 times higher than that of the old insecticides such as organochlorine, organophosphorus and carbamate. Pyrethroid insects have a strong role in the contact, and some species of both stomach poisoning or fumigation, but there is no systemic effect. Its mechanism of action is to disturb the normal physiological nerve insects, so that by the excitement, cramps and paralysis and death. Pyrethroids because of the small amount, the use of low concentrations, so the human and animal safety, environmental pollution is very small. Its shortcomings are mainly toxic to fish, for some beneficial insects are also hurt, long-term re-use can lead to insecticide resistance.
Toxicity mechanism of pyrethroids
Pyrethroid pesticide poisoning mechanism, has not yet fully elucidated. Neuronal membrane gate theory that pyrethroids can selectively slow down the nerve cell membrane sodium ion "M" channel gate closure, so that sodium ion channels remain open, depolarization period prolonged, peripheral nerve repetitive action potential , So that the sensorial transmission of the sensory nerve to the heart impulse, leading to sustained muscle contraction. Due to the permeability of the cell membrane is disturbed, nerve conduction is further inhibited, can also cause other than the nervous system cells, tissue lesions. In addition, the pyrethroids, but also directly on the nerve endings and adrenal medulla, so that blood glucose, lactate, epinephrine and norepinephrine levels increased, leading to vasoconstriction, arrhythmia.
Rat acute deltamethrin poisoning can cause dance-like limbs Xu Xu mechanism is not clear, there have been observed in rat poisoning tremor and ataxia, the cerebellum of the cyclic phosphorous guanosine levels increased significantly, the use of glucose The rate also increases. This type of insecticides on the body have a significant local stimulation.
Toxicity symptoms of pyrethroids
Productive poisoning mainly through the respiratory tract and skin absorption, poisoning after 2-6h onset, oral poisoning, the incidence of rapid, can occur within 10-30min symptoms of poisoning.
1, mild poisoning with headache, dizziness, fatigue, blurred vision, nausea, vomiting, salivation, sweating, loss of appetite and miosis.
2, moderate poisoning In addition to the above symptoms, there are muscle fibrillation.
3, severe poisoning may have coma, pulmonary edema, respiratory failure, myocardial damage and liver and kidney damage, a contact with carbamate pesticide poisoning, blood cholinesterase activity in 15min more than the lowest level of decline, 30- 40min can be restored to 50% -60%, 60-120min after the cholinesterase returned to normal, with the recovery of cholinesterase activity, the clinical symptoms gradually improved and disappeared, repeated contact with carbamate insecticides , Blood cholinesterase can be inhibited to 50%, while the clinical symptoms can be no poisoning.
Diagnostic examination of pyrethroids
Combined with contact history, clinical manifestations and reduced blood cholinesterase activity, the diagnosis is not difficult, carbaryl in the main hydrolysis of 1-neonol, increased urinary excretion of naphthol contribute to the diagnosis. Differential diagnosis needs and organic phosphorus pesticide poisoning, heat stroke, encephalitis B and acute gastroenteritis identification.
Treatment of pyrethroids
1, remove toxic skin pollution with soap and water thoroughly washed, gastric lavage with 2% sodium bicarbonate solution.
2, atropine mild poisoning 1-2mg, moderate poisoning 5mg, severe poisoning 10mg, and repeated injections, but to prevent excessive. Cholinesterase resurrection of carbamate insecticide-induced inhibition of cholinesterase no resurgence, and there may be side effects, disabled.