Esfenvalerate is a synthetic pyrethroid insecticide which is used on a wide range of pests such as moths, flies, beetles, and other insects. It is used on vegetable crops, tree fruit, and nut crops. It may be mixed with a wide variety of other types of pesticides such as carbamate compounds or organophosphates. Esfenvalerate has replaced the naturally occurring compound fenvalerate (to which it is almost identical) for use in the U.S. Much of the data for fenvalerate is applicable to the pesticide esfenvalerate because the two compounds contain the same components. The only differences in the two products are the relative proportions of the four separate constituents (isomers). Esfenvalerate has become the preferred compound because it requires lower applications rates than fenvalerate, is less chronically toxic, and is a more powerful insecticide. The compound contains a much higher percentage of the one insecticidally active isomer (84% for esfenvalerate and 22% for fenvalerate). A pyrethroid is a synthetic chemical compound similar to the natural chemical pyrethrins produced by the flowers of pyrethrums (Chrysanthemum cinerariaefolium and C. coccineum). Pyrethroids are common in commercial products such as household insecticides and insect repellents. In the concentrations used in such products, they are generally harmless to human beings but can harm sensitive individuals. They are usually broken apart by sunlight and the atmosphere in one or two days, and do not significantly affect groundwater quality except for being toxic to fish. (4, 7, 8)
belongs to the class of organic compounds known as pyrethroids. These are organic compounds similar to the pyrethrins. Some pyrethroids containing a chrysanthemic acid esterified with a cyclopentenone (pyrethrins), or with a phenoxybenzyl group.
Both type I and type II pyrethroids exert their effect by prolonging the open phase of the sodium channel gates when a nerve cell is excited. They appear to bind to the membrane lipid phase in the immediate vicinity of the sodium channel, thus modifying the channel kinetics. This blocks the closing of the sodium gates in the nerves, and thus prolongs the return of the membrane potential to its resting state. The repetitive (sensory, motor) neuronal discharge and a prolonged negative afterpotential produces effects quite similar to those produced by DDT, leading to hyperactivity of the nervous system which can result in paralysis and/or death. Other mechanisms of action of pyrethroids include antagonism of gamma-aminobutyric acid (GABA)-mediated inhibition, modulation of nicotinic cholinergic transmission, enhancement of noradrenaline release, and actions on calcium ions. They also inhibit calium channels and Ca2+, Mg2+-ATPase. (9, 10, 5)
Metabolism
Esfenvalerate is readily absorbed by the oral route, but less so dermally; absorbed deltamethrin is readily metabolized and excreted. The main urinary metabolites from the acid moiety are CPIA glucuronide, 3-hydroxy-CPIA (free and lactone), 2,3-hydroxy-CPIA glucuronide and 2-(4-chlorophenyl)-cis-2-butenedioic acid anhydride. The main urinary metabolite from the alcohol moiety is 3-(4'-hydroxyphenoxy)benzoic acid sulfate (16-24% of the administered radioactivity). Other metabolites included 3-phenoxybenzoic acid (free and glycine and glucuronide conjugates), 3-(4'-hydroxyphenoxy)benzoic acid (free and glucuronide) and 3-(2'-hydroxyphenoxy)benzoic acid (free and sulfate). (2)
At high doses, signs of poisoning attributable to esfenvalerate include profuse salivation and pulmonary edema, clonic seizures, opisthotonos (i.e., the spine is bent forward such that a supine body rests on its head and heels), coma, and death. At lower doses, commonly observed effects include paresthesia and erythema. (6)
Symptoms
Following dermal exposure to esfenvalerate, feelings of numbness, itching, burning, stinging, tingling, or warmth may occur, that could last for a few hours. Dizziness, headache, nausea, muscle twitching, reduced energy, and changes in awareness can result from inhalation or ingestion of large amounts of esfenvalerate. Paralysis can occur after exposure. (5)
Treatment
Following oral exposure, the treatment is symptomatic and supportive and includes monitoring for the development of hypersensitivity reactions with respiratory distress. Provide adequate airway management when needed. Gastric decontamination is usually not required unless the pyrethrin product is combined with a hydrocarbon. Following inhalation exposure, move patient to fresh air. monitor for respiratory distress. If cough or difficulty breathing develops, evaluate for respiratory tract irritation, bronchitis, or pneumonitis. Administer oxygen and assist ventilation as required. Treat bronchospasm with inhaled beta2 agonist and oral or parenteral corticosteroids. In case of eye exposure, irrigate exposed eyes with copious amounts of room temperature water for at least 15 minutes. If irritation, pain, swelling, lacrimation, or photophobia persist, the patient should be seen in a health care facility. If the contamination occurs through dermal exposure, Remove contaminated clothing and wash exposed area thoroughly with soap and water. A physician may need to examine the area if irritation or pain persists. Vitamin E topical application is highly effective in relieving parenthesis. (3)
