Permethrin is associated with greatly increased risk of getting Parkinson's and a higher death rate from Parkinson's. According to the study accompanying the above charts:
Counties with elevated production of high-permethrin crops exhibited PD mortality rates of 11.4 deaths per 100,000...By contrast, control counties with similar population and life expectancy exhibited PD mortality rates of 6.3 deaths per 100,000 ... On average, counties with high agricultural permethrin exhibited PD mortality rates 79.6% higher (p < 0.05) than did control counties. Additionally, counties known for farming of high-permethrin crops exhibited a 116% higher (p < 0.05) occurrence of PD death than did counties known for farming similar volumes of non-permethrin crops such as oranges.
Note that the death rate is not the same as the prevalence. Death from Parkinson's only occurs in extremely advanced cases after many years. In order to have an increased death rate there must be a proportional increase in prevalence. Parkinson's prevalence:
the overall prevalence of PD among those aged ≥45 years to be 572 per 100,000
- which is about .6%. Double or quadruple that represents significant added risk.
This study was not published in a peer-reviewed journal, however the next study was. Workers - pesticide users, mostly farmers - who handled permethrin without protective gloves had quadruple the risk of Parkinson's as compared to workers who did use protective gloves:
Protective Glove Use And Hygiene Habits Modify The Associations Of Specific Pesticides With Parkinson's Disease
Pesticides have been associated with Parkinson's disease (Parkinson’s disease), … Protective glove use modified the associations of paraquat and permethrin with Parkinson’s disease: neither pesticide was associated with Parkinson’s disease among protective glove users, while both pesticides were associated with Parkinson’s disease among non-users … permethrin OR [Odds ratio] 4.3...interaction p = 0.05 [Emphases added]
This means that unprotected workers who handled permethrin were more than four times more likely to end up with Parkinson's compared to those who did wear proper gloves. It would be unethical to experiment on people to to prove a cause and effect relationship between Parkinson's and permethrin exposure. Here is the next best thing - proof using an animal model:
Early life exposure to permethrin: a progressive animal model of Parkinson's disease
Methods: The permethrin-treated group received 34mg/kg daily of permethrin from postnatal day 6 to 21, whereas the age-matched control group was administered with the vehicle only.
Results: At adolescent age, the permethrin-treated group showed decreased levels of dopamine in the striatum, loss of dopaminergic neurons in the substantia nigra pars compacta and cognitive impairments [characteristic signs of Parkinson’s]. Motor coordination defects appeared at adult age...
Spraying permethrin on one's clothing and sleeping gear represents the polar opposite to using protective gloves and other equipment to prevent contact. Yes, permethrin is sold as a spray for clothing and camping gear. Here is one example:
Unscented bug spray with Permethrin 0.5% should be applied directly to clothing, sleeping bags, gear, and tents... lasts up to 5 washings or 40 days of sun exposure ... Also safe for use on dogs and horses
Lest there be any question regarding absorption of permethrin via skin contact:
Permethrin exposure from fabric-treated military uniforms under different wear-time scenarios
...Those wearing permethrin-treated uniforms under the longer wear-time scenario (Study A) excreted significantly higher cumulative mean levels compared with those in Study B (3.29 times higher for 3PBA and 2.23 times higher for the sum of c/tDCCA (P≤0.001)). Findings suggest that wearing permethrin-treated clothing does increase absorbed, internal dose levels of permethrin above population levels and is significantly related to wear-time duration.
The foregoing study says that the measured exposure levels of permethrin were safe, and references this study as evidence — Health Effects of Permethrin-Impregnated Army Battle-Dress Uniforms. Chapter 6 of this study covered neurotoxicity. However, every study cited therein, but one, addressed acute neurotoxicity. One animal study looked at long-term neurotoxicity but did not look at loss of dopaminergic neurons in the substantia nigra, which is where the Parkinson's damage occurs. So the safety of the measured levels of permethrin, with regard to Parkinson's, is open to question.
Parkinson's is a very slow-moving disease. Most Parkinson's patients realize in retrospect that they were having symptoms years before diagnosis – minor complaints such muscle cramps, insomnia, etc. Therefore the nexus between cause and effect is rarely obvious. Studies of acute neurotoxicity are not evidence of permethrin safety with regard to Parkinson's. Given the foregoing evidence, affirmative evidence of a safe level of exposure, if there is one, is needed to justify use, in my opinion. With respect to Parkinson's, no safe level of long-term exposure to permethrin has been established, to the knowledge of this author.
Here is information supplied with a 10 percent concentrate:
SAFE: Permethrin is highly toxic to insects but not to animals or humans ... APPROVED FOR USE ON: Dairy cattle, beef cattle, horses, sheep, goats, dogs, swine, poultry, livestock premises and homes [Emphases added here and above]
It gets even worse. Permethrin is prescribed as a treatment for scabies. Cover yourself head to toe with 5% permethrin cream, for 8 to 14 hours, and that will get rid of scabies, and then ... Here is a report of rapid onset of Parkinson’s shortly thereafter:
I had scabies...when I was pregnant. I worked with low income families in their homes at the time and got it from one of their residences. I had to cover my entire naked body with Permethrin overnight. Soon after, the terrible, terrible insomnia started....which turned out to be the early sign of PD. I never made any connection to Permethrin until now.....17 years later. [Emphases added]
Insomnia is a known Parkinson's symptom. Note the last sentence — not realizing a connection with permethrin use. Per Wikipedia:
Permethrin was discovered in 1973.[5] ... In 2017, it was the 410th most commonly prescribed medication in the United States, with more than 150 thousand prescriptions.[7]
Heavy exposure associated with about a half year to diagnosis:
In preparation for an African safari, I spent a few hours spraying all of our outer clothing with permethrin. I didn't consider any safety issues; I didn't wear gloves or a mask. Then we wore the clothing for two weeks. This was in February and I was dx with PD in August of that year...
Permethrin is also available as the active ingredient in the household "flea bomb" canister that emits insecticide vapor. Here are the directions for a typical permethrin home insect fogger: "Cover or remove all food related items, surfaces and children’s toys, stay out of the area during treatment and until the treated area has been thoroughly ventilated. Wait two hours after treatment, ventilate for another two hours." For a treatment that was considered to be non-toxic this would be sufficient. Unfortunately that is not the case.
Given the wait times specified above a person might think that permethrin was not persistent. If so that would be mistaken. Studies of permethrin in soils have yielded half lives ranging from 11 to 36 days. In cropland soils we have bacteria, fungi, nematodes and plant roots all actively participating in soil chemistry, unlike interior surfaces of a home. So the half-life of permethrin in the home is likely a month or more. Exposure will continue over many half lives.
A user may have covered all the food surfaces but there is permethrin residue on the floors, walls and furniture, exposed fabric and bedding and it’s going to be there for some time. For a consumer who uses permethrin in clothing, exposure is even more intimate.
Are other pyrethroids any less toxic?
Permethrin is a relative of the natural pyrethrin insecticides produced by chrysanthemums. Such relatives are known as pyrethroids, and there are many. Here are the results of a study that assessed relative toxicity of different pyrethroids using a rodent model of motor impairment:
ED30:
ED30 was the dose required to induce a 30% decrease in total motor activity [of rats] in figure-eight maze as compared to the corresponding vehicle-treated control group
Note that 8 of the 10 other pyrethroids were more potent (i.e. toxic), at causing motor impairment, than permethrin. Deltamethrin was more than 10 times as toxic. Cypermethrin was about four times more toxic.
Cats
Pesticide-grade permethrin is toxic to cats. Many cats die after being given flea treatments intended for dogs, or by contact with dogs having recently been treated with permethrin.[33] In cats it may induce hyperexcitability, tremors, seizures, and death.[34]
Toxic exposure of permethrin can cause several symptoms, including convulsion, hyperaesthesia, hyperthermia, hypersalivation, and loss of balance and coordination. Exposure to pyrethroid-derived drugs such as permethrin requires treatment by a veterinarian, otherwise the poisoning is often fatal.[35][36] This intolerance is due to a defect in glucuronosyltransferase, a common detoxification enzyme in other mammals, that also makes the cat intolerant to paracetamol (acetaminophen).[37] The use of any external parasiticides based on permethrin is contraindicated for cats.
Aquatic organisms
Permethrin is listed as a "restricted use" substance by the US Environmental Protection Agency (EPA)[38] due to its high toxicity to aquatic organisms,[39] so permethrin and permethrin-contaminated water should be properly disposed of. Permethrin is quite stable, having a half life of 51–71 days in an aqueous environment exposed to light. It is also highly persistent in soil.[40]
Crossposted in part here.