Wednesday, September 5, 2007


I wrote here about the malaria eradication campaign in our small country led by the Taiwanese. I noted that the insecticide, alphacypermethrin, used to spray the inside of houses is claimed to be ecologically safe.

However, today I was talking to the wife of a colleague who has developed an allergy to alphacypermethrin and is being treated by our workplace doctor. So I got to looking it up on the web and found this information from the US Environmental Protection Agency:

"These modern synthetic insecticides are similar chemically to natural pyrethrins, but modified to increase stability in the natural environment. They are now widely used in agriculture, in homes and gardens, and for treatment of
ectoparasitic disease.

Pyrethroids are formulated as emulsifiable concentrates, wettable powders,granules, and concentrates for ultra low volume application. They may be combined with additional pesticides (sometimes highly toxic) in the technical product or tank-mixed with other pesticides at the time of application. AASTAR (discontinued
1992), for instance, was a combination of flucythrinate and phorate. Phorate is a highly toxic organophosphate. Nix and Elimite are permethrincreams applied to control human ectoparasites.


Certain pyrethroids exhibit striking neurotoxicity in laboratory animals when administered by intravenous injection, and some are toxic by the oral route. However, systemic toxicity by inhalation and dermal absorption is low. Although limited absorption may account for the low toxicity of some pyrethroids, rapid biodegradation by mammalian liver enzymes (ester hydrolysis and oxidation) is probably the major factor responsible for this phenomenon. Most pyrethroid metabolites are promptly excreted, at least in part, by the kidney.

The most severe, although more uncommon, toxicity is to the central nervous system. Seizures have been reported in severe cases of pyrethroid intoxication. Of 573 cases reviewed in China, there were 51 cases with disturbed
consciousness and 34 cases with seizures. Of those, only 5 were from occupational exposure. Seizures are more common with exposure to the more toxic cyano-pyrethroids, which include fenvalerate, flucythrinate, cypermethrin,
deltapermethrin, and fluvalinate. There are no reports in the literature of seizures in humans from exposure to permethrin.

Apart from central nervous system toxicity, some pyrethroids do cause distressing paresthesias when liquid or volatilized materials contact human skin.Again, these symptoms are more common with exposure to the pyrethroids
whose structures include cyano-groups.Sensations are described as stinging, burning, itching, and tingling, progressing to numbness.The skin of the face seems to be most commonly affected, but the face, hands, forearms, and neck are sometimes involved. Sweating, exposure to sun or heat, and application of water enhance the disagreeable sensations. Sometimes the effect is noted within minutes of exposure, but a 1-2 hour delay in appearance of symptoms is more common. Sensations rarely persist more than 24 hours. Little or no inflammatory reaction is apparent where the paresthesia are reported; the effect is presumed to result from pyrethroid contact with sensory nerve endings in the skin. The paresthetic reaction is not allergic in nature, although sensitization and allergic responses have been reported as an independent phenomenon with pyrethroid exposure. Neither race, skin type, nor disposition to allergic disease affects the likelihood or severity of the reaction.

Persons treated with permethrin for lice or flea infestations sometimes experience itching and burning at the site of application, but this is chiefly an exacerbation of sensations caused by the parasites themselves, and is not typical
of the paresthetic reaction described above.

Other signs and symptoms of toxicity include abnormal facial sensation, dizziness, salivation, headache, fatigue, vomiting, diarrhea, and irritability to sound and touch. In more severe cases, pulmonary edema and muscle fasciculations can develop. Due to the inclusion of unique solvent ingredients, certain formulations of fluvalinate are corrosive to the eyes. Pyrethroids are not cholinesterase inhibitors. However, there have been some cases in which pyrethroid poisoning has been misdiagnosed as organophosphate poisoning, due to some of the similar presenting signs, and some patients have died from atropine toxicity."

I also discovered it is toxic to butterflies! Hence my suspicions expressed in the previous post have been confirmed - as I said before neither biodiversity impact assements nor epidemiological studies on adverse reactions are being undertaken. Additionally, it is being used in higher concentrations than normal in agricultural use.

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