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Pyrethrins and Pyrethroids
About these commonly used poisons.

Excerpts from Steve Tvedten's book "The Best Control (2nd Edition)"
 

Natural pyrethrins (brand names include Blitz, Drione, etc.) are botanical pesticide poisons extracted from the daisy species, Chrysanthemum cinerariaefolium and/or C. coccineum which can bring on allergic reactions, asthma attacks, dermatitis and interfere with nervous system functions.  They are often combined with organophosphates to kill.  Inhalation of just pyrethrins per the Extension Toxicology Network, California Public Interest Research Group can cause asthmatic breathing, sneezing, stuffiness, headaches, tremors, convulsion, burning and itching.  They are especially toxic to fish and other aquatic organisms.  Synthetic pyrethroids are a diverse class of more than 1,000 powerful, broad-spectrum insecticide poisons.  Pyrethroid toxicity is highly dependent on stereochemistry, the three dimensional configuration of the molecule.  Each isomer (molecules consisting of the same atoms, but with a different stereochemistry) has its own toxicity.  Some pyrethroids have as many as 8 different isomers and there are several different types.  Acute toxicity of a mixture of 2 isomers depends on the ratio of the amounts of the two isomers in the formulation.  For example, the female rat’s acute oral LD50 of permethrin increases from 224 milligrams of the pyrethroid per kilogram of body weight (mg/kg) to 6,000 mg/kg as the proportion of trans isomer increases from 20% to 80%. The route of exposure is also critical in assessing the acute toxicity of a synthetic pyrethroid.  Like DDT and many other registered insecticides, naturally occurring pyrethrins and the synthetic pyrethroids are nerve poisons.  Synthetic pyrethroid’s principal mechanism of action is believed to be the disruption of the permeability of nerve membranes to sodium atoms.  Organophosphates and carbamates are also nerve poisons, but they do not attack our peripheral (In addition to our central) nervous system as do DDT and synthetic pyrethroids. The half life of pyrethroids in soils ranges from 1 day to 16 weeks.  (It is amazing that people apply them for termite control; even though permethrin is supposedly effective against termites in the very same soil for 1 - 5 years.)  Insect resistance has begun to be openly reported.  Read more about these poisons in Chapter 16.

Some synthetic pyrethroids are already suspected by the EPA as being carcinogenic.  Long-term or chronic exposure to pyrethrum causes liver damage especially when used with the synergists and Freon propellants; causes allergic reactions and is a neurotoxin.  Synthetic pyrethroids have a very complex chemistry, most are primarily termite repellents.  Dr. Nan-Yau Su, Professor of Entomology for the University of Florida, has observed termites tunneling through pyrethroid-treated soil by lining their tunnels with clean soil particles.  See: Permethrin. (The use of pyrethroids should not be used for longer than 3 - 4 months in a commercial kitchen area or you will quickly create chemical resistance in the pest population.) Persons with respiratory problems are more sensitive to pyrethrins. People with multiple sclerosis (MS) can be on medication that affects sodium and potassium ion diffusion through neuron axons, so avoid the use of pyrethroids.  Do you really believe anyone in the poison industry asks if anyone has MS before they start spraying their poisons?  Pyrethroids can modify behavior in a number of ways.

FenDeet® which contained the insect repellent Deet and fenvalerate for use in the veterinary arena had a large number of poisonings reported - small, young cats were most often effected.  It appears that Deet which is readily absorbed through the skin, enhanced the absorption rate of fenvalerate sufficiently to lead to the development of toxic levels systematically (J. Am. Vet. Med. Assn. 196, 100, 1990).

Pyrethrum or pyrethroids, e.g., permethrin, should not be used by persons sensitive to ragweed; should not be used near the eyes; should not be inhaled or swallowed; should not come in contact with mucous membranes, e.g., the eyes, nose or mouth.  The Journal of Pesticide Reform in Fall of 1990 noted:  There are several inerts in pyrethroid formulations used in the U. S. which are known or suspected carcinogens (e.g., silica, trimethyl benzenes and ethyl benzene) or are poisons which depress the central nervous system (e.g., xylenes). There are also hazardous contaminants, e.g., ethylene oxide, benzene and arsenic, in several pyrethroid formulations.

Demand® CS, e.g., contains the active ingredient Lamdacyhalothrin 9.7% (pyrethroid microencapsulated for gradual release).  It also contians 90.3% “inerts” or petroleum solvent with 1,2,4 trimethylbenzene; label reads, “At high concentrations, vapors or aerosols of the solvent can produce respiratory and and central nervous depression, headache, dizziness and nausea.”

Marcy Trice remembers the day her life changed forever.  She was a 35-year-old limited licensed psychologist working with chronically ill patients at Detroit Receiving Hospital. Early on that August day in 1989, an insecticide (poison) company sprayed her office because of a bug problem.  When Trice returned later, she got some of the chemical mist on her hands.  She started to fall asleep at her desk.  Her asthmatic condition, previously under control, dramatically worsened.  The insecticide was pyrethrin, made from powdered flowers of the chrysanthemum family.  Poison control told Trice to get tested and warned her she could develop symptoms months later.  She did: headaches, frequent falling, kidney problems, memory lapses, fatigue.  Unknown to Trice, another office where she worked in Bloomfield Hills was periodically sprayed.  Her illness grew worse, and she stopped working in 1994. Trice has been diagnosed with multiple chemical sensitivity (MCS), a chronic condition marked by heightened sensitivity to many different chemicals.  Jewish News, Detroit 2/6/98. WD40 causes an extremely dangerous synergism with pyrethrin.  See also Chapter 16.

NCAP’s Journal of Pesticide Reform, Spring 1999, Vol. 19, No. 1states:  “Pyrethroid Insecticides Mimic the Hormone Estrogen:  Endocrine disruption, the ability of pesticides and other chemicals to disrupt the normal funcitons of our homone systems, has recently received wide publicity. Yet another chapter was added to this story by new research showing that commonly-used insecticides mimic the hormone estrogen.

Researchers Vera Go, Joan Garey, Mary Wolff and Beatriz Pogo from the Mt. Sinai School of Medicine looked at four insecticides from the synthetic pyrethroid family: sumithrin (also called phenothrin), fenvalerate, allethrin and permethrin.  The study used cultures of human breast cancer cells.  First, researchers looked at the activity of a gene called pS2.  They chose this gene because its activity is directly promoted by estrogen.  Two of the insecticides studied (sumithrin and fenvalerate) promoted pS2 activity.  Next, researchers looked at cell proliferation, how much the insecticides caused the number of breast cancer cells to increase.  Proliferation is another characteristic of estrogen.  All four of the insecticides caused cell proliferation.

The new study is clearly a warning.  As the authors of the study concluded, ‘pyrethroids are widely used, are prevalent in the environment, and can alter estrogen homeostatis [normal balance and equilibrium].  Therefore, their effects on the endocrine system in both humans and wildlife is of concern.’—Caroline Cox”

 

 

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