From the various websites I've read, it seems permethrin is highly toxic and persistent in the environment and you would be wise to reconsider its use, not only to protect your cats but yourself. I took an interest in this question, because I had been exposed to bed bugs in a hotel room, and when I got home, I was prescribed by my doctor, a permethrin creme (5%) to apply all over my body, which I left on for one day before washing off and then washing my bedding. Now I regret using it because of its possible link to other diseases, such as cancer and Parkinsons. At the very least, apply the treatment to plants outdoors, and then bring them inside.

"Permethrin is toxic to cats. Many cats die after being given flea treatments intended for dogs, or by contact with dogs who have recently been treated with permethrin." (I assume because cats like to lick their fur.)

"Permethrin, like all synthetic pyrethroids, kills insects by strongly exciting their nervous systems. Permethrin makes the nervous system hypersensitive to stimuli from sense organs. Rather than sending a single impulse in response to a stimulus, permethrin-exposed nerves send a train of impulses. This excitation occurs because permethrin blocks the movement of sodium ions from outside to inside of the nerve cells. Permethrin’s mode of action is similar to that of the organochlorine insecticide DDT."

"Ingestion of permethrin reduces the ability of immune system cells called T-lymphocytes to recognize and respond to foreign proteins. Doses equivalent to 1/100 of the LD (Lethal Dose), inhibited T-lymphocytes over 40 percent. Permethrin ingestion also reduced the activity of a second type of immune system cell, natural killer cells, by about 40 percent. In tests using mouse cell cultures, permethrin had similar effects on the immune system, inhibition of two kinds of lymphocytes. Researchers concluded that “the immune system is exquisitely sensitive … at exposure levels that cause no overt toxicity.”

"Environmental Fate:
Soil
The average half-life of permethrin in aerobic soils is 39.5 days, with a range from 11.6 to 113 days. "

"Half-life.
Permethrin binds tightly to soil and is broken down primarily by microorganisms, but also by photolysis."

"Water
When permethrin enters an aquatic system, some is degraded by sunlight while in the water column but the majority binds tightly to the sediment. In water, permethrin is broken down by photolysis into 3-phenoxybenxzyl alcohol (PBA) and dichlorovinyl acid (DCVA). The average half-life range for permethrin in the water column is about 19-27 hours, however permethrin adsorbed to sediments can persist more than a year."

"Indoor
Permethrin was applied in a thin layer to an indoor surface beside a window and exposed to daylight. After 20 days, 60% of the permethrin remained on the surface."

"Food Residue
In the FDA’s Total Diet Study of 2003, permethrin residues were detected in 3% of the 1039 food samples tested. The range of permethrin levels found was 0.0008-4.7130 ppm" (0.8-4713 ppb). "Permethrin is very highly toxic to lobster; the LC50 is less than 1 ppb. (LC50: the concentration that kills 50 percent of a population of test animals)

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