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?
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 ). 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…
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.
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.
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.)
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.
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.
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.
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.