Permethrin/Poultry Dust - How long until it breaks down?

I just used permethrin/poultry dust for the first time, as well. Am waiting to see if it works.
However, some experts warn against using anything in the pyrethroid family (synthetic compounds that mimic naturally found compounds that were once dervied from chrysanthemum plants). Here is information on Safe2Use:

http://www.safe2use.net/poisons-pesticides/pesticides/permethrin/cox-report/cox.htm

To be even handed, a case could probably be made for the use of any chemical in excess. I don't know whether Sevin's compounds are safer, but my understanding of the chemical in Sevin (carbaryl) is that it affects invertebrates (such as mites, lice) but breaks down fairly quickly in vertebrates such as chickens although it is toxic in sustained or excessive use.