# Diatomaceous earth **URL:** \ **Category:** Factual Questions\ **Created:** [July 24, 2009, 5:50pm UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144 "2009-07-24T17:50:50Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![cainxinth](https://avatars.discourse-cdn.com/v4/letter/c/7bcc69/32.png) [@cainxinth](https://boards.straightdope.com/u/cainxinth)\ **Post date:** [July 24, 2009, 5:50pm UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/1 "2009-07-24T17:50:50Z")
I’ve read that diatomaceous earth is sprayed on plants and used as an insect repellent, but that the diatomaceous earth sold for use in swimming pools should not be used this way because it is heat treated and contains large quantities of free silica. First, what is free silica and why is bad for plants? Second, exactly how bad is pool grade diatomaceous earth for plants? I ask because when I backwash my pool a good amount of water finds its way into the surrounding greenery. Should I be taking more care to prevent this? ---
**Author:** ![psycat90](https://avatars.discourse-cdn.com/v4/letter/p/7ea924/32.png) [@psycat90](https://boards.straightdope.com/u/psycat90)\ **Post date:** [July 24, 2009, 6:34pm UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/2 "2009-07-24T18:34:06Z")
It’s not bad for the plants, it’s bad for you. Your pool water containing DE won’t harm your plants, but using pool grade DE to sprinkle on your lawn could cause you lung problems. It is a respiratory hazard - From wikipedia - > [@](#): > > The type of hazard posed by inhalation depends on the form of the silica. Crystalline silica poses a serious inhalation hazard because it can cause silicosis. Amorphous silica can cause dusty lungs, but does not carry the same degree of risk as crystalline silica. Natural or dried diatomite generally contains very low percentages of crystalline silica. Diatomite produced for pool filters is treated with high heat (calcining) and a fluxing agent (soda ash), causing the formerly amorphous silicon dioxide to assume its crystalline form. > > In the United States, the crystalline silica content in the dusts is regulated by the Occupational Safety and Health Administration (OSHA), and there are guidelines for the maximum amounts allowable in the product and in the air near the breathing zone of workers.[5] ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 25, 2009, 5:14am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/3 "2009-07-25T05:14:24Z")
OH, I can tell you about diatomaceous earth… I recently ordered some on Ebay that I intended to use for some lab work. It was “food grade.” What they sent me was GROUND DE. For anyone joining this discussion, let me explain how fucking preposterous this is. Diatoms are tiny sea creatures that encase themselves in incredible silicon exoskeletons (see: [http://images.google.com/images?q=diatom](http://images.google.com/images?q=diatom) ). These exoskeletons have many tiny, regularly-sized pores. These pores give diatomaceous earth (fossilized dirt mined from the ancient bottoms of long-gone oceans) various useful properties. Diatom exoskeletons can be used for filtering, as a dessicant, and they will cut up the stomachs of parasites that try to feed on them. But if you grind them up into a powder, all you get is sand flour! The ebay seller didn’t see my logic, which is quite startlingly poor customer service for ebay. I think he needs to be introduced to the meaning of negative feedback… ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 25, 2009, 5:17am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/4 "2009-07-25T05:17:47Z")
Long story short, make sure your DE is clean and not ground up. I don’t know about pool-grade, but the DE used in labs fits both requirements. A popular brand is Celite. I wonder if it is heat-treated the same way. In any case, don’t do lines of it. ---
**Author:** ![Alex\_Dubinsky](https://avatars.discourse-cdn.com/v4/letter/a/dbc845/32.png) [@Alex\_Dubinsky](https://boards.straightdope.com/u/Alex_Dubinsky)\ **Post date:** [July 25, 2009, 5:30am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/5 "2009-07-25T05:30:52Z")
Btw, this is another example of a folk remedy that someone went out and tried to “improve” and totally f’d up. I guarantee that ground DE won’t do anything. Silica is an inert substance. All its function comes from its physical structure. ---
**Author:** ![gonzomax](https://avatars.discourse-cdn.com/v4/letter/g/e8c25b/32.png) [@gonzomax](https://boards.straightdope.com/u/gonzomax)\ **Post date:** [July 25, 2009, 3:44pm UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/6 "2009-07-25T15:44:09Z")
I used to have a diatom filter for aquariums. It used diatomaceous earth in the filter. It could clean the ugliest foggiest tank crystal clear in about 10 minutes. ---
**Author:** ![asterion](https://avatars.discourse-cdn.com/v4/letter/a/4da419/32.png) [@asterion](https://boards.straightdope.com/u/asterion)\ **Post date:** [July 25, 2009, 4:19pm UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/7 "2009-07-25T16:19:52Z")
> [@Alex\_Dubinsky](#): > > Long story short, make sure your DE is clean and not ground up. I don’t know about pool-grade, but the DE used in labs fits both requirements. A popular brand is Celite. I wonder if it is heat-treated the same way. In any case, don’t do lines of it. Of course, it seems like there’s about 50,000 kinds of diatomaceous earth out there. Heck, I think Aldrich sells 30 types of Celite alone. Don’t breathe it in when applying and don’t get it on your skin. Use at least a particle mask and if you’re going to be using a lot, it may be worth getting a $30 respirator with the appropriate cartridges. (Ace was having a sale last week on respirators that looked just about like what I use in the lab.) ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [July 27, 2009, 3:27am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/8 "2009-07-27T03:27:02Z")
I worked for a few years with a fellow who was a major authority on DE, and always had the impression from him that grinding it into a powder in no way interferes with its function, as the powder size is still quite large compared to the cell or pattern size in the little skeletal plates and flakes. Think of it like using scissors to cut window screen into little pieces that are a few inches, an inch, even a quarter of an inch. They still look screenlike and when you drop them in a pile it’s still porous. And I did spend some years using various grades of the stuff myself in filtration. Evaluation grades from Johns Manville came in plastic tubs and were ground differently. They were very popular as body feeds and as filter precoats, especially in removing fruit juice haze (which tends to form a slimy coat that blinds filters quickly). The resulting fruit-slimy filter cake, which contained a lot of diatomite, was fed to cattle. ---
**Author:** ![Stoid](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/stoid/32/272_2.png) [@Stoid](https://boards.straightdope.com/u/Stoid)\ **Post date:** [July 27, 2009, 4:18am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/9 "2009-07-27T04:18:55Z")
That’s what they put in the tooth polishing powder I use… ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [July 27, 2009, 4:30am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/10 "2009-07-27T04:30:08Z")
IIRC, adding Nitro-Glycerine to DE stabilizes it enough to be handled; thus you can package it into sticks of Dynamite. BTW, can DE clarify oil the same way as pool and aquarium water? ---
**Author:** ![achill1016](https://avatars.discourse-cdn.com/v4/letter/a/ad7895/32.png) [@achill1016](https://boards.straightdope.com/u/achill1016)\ **Post date:** [August 9, 2011, 10:04pm UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/11 "2011-08-09T22:04:07Z")
I found a journal article that’s especially relevant to your question called “Surface Reactivity, Cytotoxic, and Morphological Transforming Effects of Diatomaceous Earth Products in Syrian Hamster Embryo Cells” published in 2006 by Toxicological Sciences. In this study, they found that heat-treated diatomaceous earth increases the release of free-radicals in hamster embryo cells. There were more heat effects than that, but I don’t want to say too much about it because I’m not well-versed in the bio-sciences. I encourage someone who actually knows something about biology who’s interested in the effects of diatomaceous earth to read it and summarize it for those of us who don’t know anything about biology. From what I can tell, that seems to be pretty much all of us. ---
**Author:** ![mac\_bolan00](https://avatars.discourse-cdn.com/v4/letter/m/b3f665/32.png) [@mac\_bolan00](https://boards.straightdope.com/u/mac_bolan00)\ **Post date:** [August 10, 2011, 2:39am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/12 "2011-08-10T02:39:05Z")
any fine-silica medium that could be inhaled is very bad for you, just as bad as asbestos. asbestos is a silica and is chemically inert with respect to the human body. it is its physical property (very fine fibers) that’s dangerous. if you’re going to use diatomite in any manner, make sure it is bonded, sealed or confined in a manner to prevent escape (like in filters.) applying it on plant leaves risks inhalation. if it’s to be applied to the soil. it should be dampened immediately. ---
**Author:** ![R.P.McMurphy](https://avatars.discourse-cdn.com/v4/letter/r/7993a0/32.png) [@R.P.McMurphy](https://boards.straightdope.com/u/R.P.McMurphy)\ **Post date:** [August 10, 2011, 3:30am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/13 "2011-08-10T03:30:44Z")
Good info all, but let’s get back to the OP. I’ve heard that DE can be very beneficial to plants but is it only because it kills invading insects? Does it provide any nutrients or other benefits? You have convinced me not to mess with it. (I used to use it when I had a large fish tank many years ago but that is now gone.) I now understand that the crystalline structure can be harmful to human lungs. I didn’t know that and wasn’t careful. So what does it do and what doesn’t it do? Is there a benefit to plants, gardens and lawns if it is handled properly, and in what form? Maybe those questions have been answered but I’d like something succinct. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [August 10, 2011, 5:45am UTC](https://boards.straightdope.com/t/diatomaceous-earth/504144/14 "2011-08-10T05:45:07Z")
Did someone specifically say pool grade DE was bad for plants, or did you read that into instructions not to use it on plants? See if this answers your questions: [http://www.ghorganics.com/DiatomaceousEarth.html](http://www.ghorganics.com/DiatomaceousEarth.html)