http://en.wikipedia.org/wiki/Diatomaceous_earth
Pest control[edit]
Diatomite is used as an insecticide, due to its abrasive and physico-sorptive properties.[8] The fine powder absorbs lipids from the waxy outer layer of insects' exoskeletons, causing them to dehydrate. Arthropods die as a result of the water pressure deficiency, based on Fick's law of diffusion. This also works against gastropods and is commonly employed in gardening to defeat slugs. However, since slugs inhabit humid environments, efficacy is very low. It is sometimes mixed with an attractant or other additives to increase its effectiveness. Medical-grade diatomite is sometimes used to de-worm both animals and humans.[9][10] It is commonly used in lieu of boric acid, and can be used to help control and possibly eliminate bed bug, house dust mite, cockroach, ant and flea infestations.[11] This material has wide application for insect control in grain storage.[12]
In order to be effective as an insecticide, diatomaceous earth must be uncalcinated (i.e., it must not be heat-treated prior to application)[13] and have a mean particle size below about 12 µm (i.e., food-grade – see below).
Although considered to be relatively low-risk, pesticides containing diatomaceous earth are not exempt from regulation in the United States under the Federal Insecticide, Fungicide, and Rodenticide Act and must be registered with the Environmental Protection Agency.
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