There is a lot of conversation these days about diatomaceous earth. DE is a form silica. It is a natural material composed of diatom skeletons. Diatoms are aquatic phytoplanktons which are one-celled plants that are responsible for much of the food and most of the oxygen that is consumed on earth. Diatoms represent the major process where silicates from the earthís crust are recycled. Diatoms absorb silica acid and use it to make porous microscopic shells composed mostly of silica dioxide (SiO2). When these living creatures die, the shells sink to the bottom of oceans, rivers or lakes and accumulate. Over millions of years the sediments become diatomaceous earth deposits. These large deposits are mined, ground into a powder form and sold as natural diatomaceous earth.
Insects are killed by desiccation due to the dustís highly porous nature. DE is one of the most effective of all natural inert dusts. It absorbs waxy fats and oils (lipids) from the epicuticle (skin) of insects and other invertebrate pests. Once the waxy, oily coating is removed, insects cannot retain water and die due to dehydration. Silica gel and fumed silica are synthetic silicas that also kill insects in this way, but I donít recommend these or any other processed forms of DE. Silica gel is not as useful because the small particle size that gives it greater adherence and greater oil absorption properties also makes it more difficult to apply. It also contains a higher level of crystalline silica dioxide, a form that is dangerous to breathe.
Freshwater diatomaceous earth is composed of fossilized Melosira sp. Diatoms. These microscopic particles of amorphous silica, shown here, absorb an insectís protective oil coating, causing water loss and death from dehydration.
Under a scanning electron microscope Melosira sp. looks like little barrels full of holes or a white breakfast cereal. Freshwater DE products contain a high percentage of intact shells with both an interior void space along with interior and exterior surfaces. This large surface area is key to its effectiveness. Marine diatoms tend to be larger, lacy and fragile. They are beautiful in design and many look like snowflakes. Few survive the compaction of deposition and the impact of mining, drying, milling and classifying. Marine DE also has larger amounts of crystalline silica, but in most cases is still less than 3% which minimizes the breathing danger. Marine DE tends to contain a high percentage of shell fragments with almost no interior void spaceóthus not as good for our organic purposes.
Both freshwater and marine DE can be caclcined which means heated to high temperatures and partially melted. This material should be avoided for stored grains, pest control and for animal feeds. The heating process makes DE a better filtration material, but destroys its desiccating insecticidal properties. It also increases the crystalline silica content to 25% or sometimes much more. Inhalation of significant amounts crystalline silica over long periods can lead to lung cancer. Breathing small amounts can cause nose bleed.
Up to 2% of natural amorphous DE is added to a variety of processed foods as an anti-caking agent and 90-day rat feeding experiments showed that up to 5% in the daily diet created no problems. In my opinion, the most important use of natural DE is in animal feeds. It can and should be added to any animal feed at the same 2% rate. It will help with internal pest control, and improved digestion. It will also aid detoxification and provide a wide range of trace minerals. There are still many people who bad-mouth the use of natural diatomaceous earth, even an alarming number of veterinarians. If there were anything dangerous about this wonderful natural material, there would be a lot of sick pets and livestock as a result of its use. Just the opposite is the case.
From Sept 06 DIRT Revised July 08