A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.
Deltamethrin is a synthetic insecticide based structurally on natural pyrethrins, which rapidly paralyze the insect nervous system giving a quick knockdown effect (13). Deltamethrin has a rapidly disabling effect on feeding insects and for this reason there is hope that it may be useful to control the vectors of "non-persistent" viruses (viruses that can be passed on by the vector within a few minutes of starting to feed on the plant) (3). Deltamethrin's mode of action is thought to be mainly central in action, or at least originate in higher nerve centers of the brain. Death of insects seems to be due to irreversible damage to the nervous system occurring when poisoning lasts more than a few hours (11). Deltamethrin poisoning occurs through cuticular penetration or oral uptake. The susceptibility of insects is dependent on a variety of factors and can vary, as with many insecticides, according to the environmental conditions. Flies are most susceptible to pyrethroid poisoning shortly before dawn. The LD50 drops by the factor of 2 as compared to full daylight activity (13, 20).
Many pyrethroids are not very active against cattle ticks, but some alpha cyano compounds (of which deltamethrin is one) have higher activity than organophosphates or amidines, the former standard compounds for this purpose (13). Deltamethrin has very good residual activity for outdoor uses (field crops, cattle dip, tsetse) and for indoor uses (mosquitoes, stable flies, horsefiles, fleas, cockroaches, stored product insects) (9, 20). Deltamethrin has very broad spectrum control. It is considered the most powerful of the synthetic pyrethroids. It is up to three orders more active than some pyrethroids (14, 20).
The signs of poisoning produced in rats by deltamethrin are not the same as those produced by other pyrethroids. Especially characteristic are rolling convulsions. The site of action is considered to be central with little or none of the peripheral component demonstrated for other pyrethroids. The sequence of signs is clearly defined, progressing from chewing, salivation, and pawing to rolling convulsions, tonic seizures, and death. Blood pressure begins to drop promptly, but slowly; it tends to normalize about the time choreoathetosis (abnormal movements of the body of a combined choreic and athetoid pattern) begins but falls precipitously prior to death. The early signs, including choreoathetosis, are reversible, but rats that exhibit a tonic seizure and shock almost always die promptly (18).
Acute exposure effects in humans include the following: ataxia, convulsions leading to muscle fibrillation and paralysis, dermatitis, edema, diarrhea, dyspnea, headache, hepatic microsomal enzyme induction, irritability, peripheral vascular collapse, rhinorrhea, serum alkaline phosphatase elevation, tinnitus, tremors, vomiting and death due to respiratory failure. Allergic reactions have included the following effects: anaphylaxis, bronchospasm, eosinophilia, fever, hypersensitivity pneumonia, pallor, pollinosis, sweating, sudden swelling of the face, eyelids, lips and mucous membranes, and tachycardia (17).
Studies have shown many cases of dermal deltamethrin poisoning after agricultural use with inadequate handling precautions, and many cases of accidental or suicidal poisoning by the oral route at doses estimated to be 2- 250 mg/kg. Oral ingestion caused epigastric pain, nausea, vomiting and coarse muscular fasciculations. With doses of 100-250 mg/kg, coma was caused within 15-20 minutes (16).
Suspected chronic exposure effects in humans include the following: choreoathetosis, hypotension, prenatal damage and shock (17). Workers exposed to deltamethrin during its manufacture over 7-8 years experienced transient cutaneous and mucous membrane irritation, which could be prevented by use of gloves and face masks. No other ill effects were seen (16).
In mammals, the point of death from deltamethrin poisoning is sharply defined by respiratory or cardiac failure (11). Rats and dogs given oral doses of 10 mg/kg/day for 13 weeks exhibited some motor symptoms but no fatalities or pathological changes. The dogs exhibited diarrhea and vomiting. In another study, rats given 15 daily oral doses of 10 mg/kg showed severe motor symptoms, but a full neuropathological examination of the central nervous system showed no pathological changes (16).
Physical signs of deltamethrin poisoning can include dermatitis after skin contact; exposure to sunlight can make it worse. Severe swelling of the face including lips and eyelids can occur. Symptoms and consequences of poisoning include: sweating, fever, anxiety and rapid heartbeat. If swallowed, symptoms are likely to include feeling sick, vomiting, diarrhea, twitching of arms and legs, and convulsions if poisoning is severe (12).
A health survey of 199 workers who repacked pyrethroid insecticides into boxes by hand indicated that about two-thirds of the workers had a burning sensation and tightness and numbness on the face, while one-third had sniffs and sneezes. Abnormal sensations in the face, dizziness, tiredness and red rashes on the skin were more common in summer than in winter. Workers did not wear protective gloves in summer because of the heat. The symptoms usually occurred thirty minutes after exposure to the pyrethroids and rarely lasted more than 24 hours (12).
Cold burning and numbness of the skin occurred to two-thirds of humans in a Chinese factory exposed to about 5-12 mg deltamethrin per cubic meter of air. The other third suffered from sneezing and eye-watering. In addition, headache, heartburn and skin spots were reported, and these symptoms were dependent on the time of the year (13).
A study was conducted of pesticide workers (one mixer, one bagger, and three spraymen) who applied 5% deltamethrin to the inside walls of houses at an active ingredient rate of 0.05 g/m2. The work lasted two days. Each man wore overalls (washed daily), shoes, and a hat. The mixer wore a cartridge- type respirator and rubber gloves. The bagger wore the same, plus an apron. The spraymen did not wear masks. All practiced good personal hygiene. No complaints were received from the workers and no effect of exposure was detected by clinical examination (18).
A second trial lasting about five weeks involved three baggers, two mixers, two helpers, and nine spraymen. Conditions, including protective equipment, were the same except that all spraymen wore disposable face masks. Six of the nine spraymen, all baggers, and one of two mixers complained of "heat around the eyes," "heat in the face," or "heat in the face and upper shoulders" plus "burning of the eyes" and tiredness. Complaints lasted until evening of each work day. There were no positive clinical signs of exposure to deltamethrin by any of the workers (18).
In laboratory trials, the LC50 for fish was 1-10 micrograms/l. Aquatic fauna, particularly crustacea, may be affected, but fish are not harmed under normal conditions of use (2).
Deltamethrin is considered toxic to bees (1). The 24 hour oral LD50 for technical deltamethrin fed to bees was 0.079 micrograms ai/bee; and the 24 hour oral LD50 for the EC formulation of deltamethrin was equal to or greater than 0.4 micrograms ai/bee (11). The reported contact LD50 for bees is 0.05 micrograms ai/bee, but with a field rate of only 12 g ai/ha, the hazard ratio is very low (240). A hazard ratio is defined as exposure (g ai/ha) divided by intrinsic toxicity (LD50 in micrograms ai/bee). The hazard ratio is a risk estimate, or an indicator of the level of mortality that is to be expected in the field. A ratio of greater than 50 indicates the chemical is not dangerous to bees. A ratio between 50 and 2,500 indicates a field test is needed, and over 2,500 indicates the compound is considered dangerous to bees. Although the intrinsic toxicity of deltamethrin is similar to that of organophosphates such as azinphos-methyl, the low rate of use of deltamethnn makes its hazard ratio considerably lower (the azinphos-methyl hazard ratio is 8937) (15).
Deltamethrin is very toxic over long periods to the predatory mite Typhodromum pyri. The parasitic wasp Encarsia formosa, released in greenhouses to combat whitefly, is too sensitive to allow a treatment with deltamethrin against excessive outbreaks of whiteflies (13). Deltamethrin had little or no effect on adults or cocoons of Apanteles plutellae, a parasite of the diamond back moth in India. Spiders were also indicated to be strongly affected in field investigations (3, 15).
Deltamethrin is a lipophilic compound of high molecular weight and consequent low volatility. It is not used for soil application in agricultural practice because it moves neither in the vapor nor water phase and has no systemic action (11, 20).
|ADI:||0.01 mg/kg (9)|
|Appearance:||colorless crystalline powder (9); white or slightly beige powder (16)|
|Molecular weight:||505.24 (9)|
|Molecular formula:||C22H19Br2NO3 (6, 9, 16)|
|CAS No.:||52918-63-5 (1)|
|Chemical names:||cyano(3-phenoxy-phenyl)methyl; 3-(2,2dibromoethenyl)-2,2-dimethylcyclopropanecarboxylate (CA); [partial diff]-cyano-m-phenoxybenzyl, (1R,3R)-3-(2,2-dibromovinyl)-2,2-dimethyl -cyclopropanl-carboxylate, (S)-[partial diff]-cyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dibromovinyl)-2,2-dimethylcyclopropane-carboxylate (IUPAC) (1)|
|Chemical Class/Use:||pyrethroid/contact and stomach poison insecticide (2)|
|Solubility in water:||less than 0.1 mg/l (1) Insoluble: < 1 ppm at room temperature (8). 0.002 mg/l at 20 degrees C (9). Almost insoluble (3)|
|Solubility in other solvents:||in kerosene and isoalkanes, less than 0.5, isopropanol 0.6, ethanol 1.5, xylene 25, methylene chloride 70 (all in g/100 g at 20 degrees C) (1). In acetone 500g/1, benzene 450 g/l, dimethyl sulfoxide 450 g/l, cyclohexanone 750 g/l, dioxane 900 g/l all at room temperature (9), toluene 250 g/l (18)|
|Melting point:||98-101 degrees C (1, 2, 4)|
|Boiling point:||Decomposes on distillation (1)|
|Vapor pressure:||2 x 10 to the minus 8 mbar at 25 degrees C (1). Non-volatile: <1 x 10 to the minus 7 mmHg (8). 1.5 x 10 to the minus 8 mmHg at 25 degrees C (14)|