Diatomaceous Earth is often mentioned in organic pest control articles as a safe insecticide. It is approved for organic food production.
What is Diatomaceous Earth, is it dangerous or poisonous to cats and pets? How can it help me keep insects and slugs out of the garden? What is food grade diatomaceous earth? Can I use it on my pets to control fleas?
What is Diatomaceous Earth
It is the dried out skeletons/cell wall/shells of a group of microscopic aquatic algae called Diatoms.
Diatoms are not a single organism but rather a whole range of algae with a wide variety of shapes to their shells. Some are round others elongated and very sharp. When they are alive they form a browny green layer in the bottom of lakes. As they die the skeletons sink to the bottom and gradually accumulate and can form deep layers over the years. These accumulated skeleton persist for long times and many beds are found no longer in water but essentially as fossilized deposits of whitish cream coloured powder or soft easily pulverized rock. Geologists refer to these mineral deposits as DIATOMITE.
The type of skeleton can be very specific to an area and water samples can sometimes be identified as to location by identifying the diatoms it contains.
Diatomite is often found in peat and muck soils and can be harvested from the soil. In this case the organic matter is burned off (calcined) and the remaining powder used. This is NOT a process that is useful for making insecticide powder however since the sharp diatom skeletons are damaged and not effective. This process is done in Florida and other places to produce Diatomaceous earth.
Diatomite deposits are widely scattered in areas where prehistoric lakes existed, particularly if there was a source of silica available. Volcanic ash often supplied the required silica.
Diatomaceous earth that is intended for pest control use is usually crushed and milled so that the particle size is between 10 µm to 50 µm.
Chemical Composition of Diatomaceous Earth
It is mainly made up of amorphous SiO2·nH2O. Amorphous is non crystalline material. Older deposits can gradually change and the silica can have a portion of crystalline silica. Amorphous silica is the same material that makes up Opal.
There is also a variable small proportion of crystalline silica found in diatomaceous earth deposits. The proportion becomes larger in older deposits that have had a chance to recrystallize.
I Diatomaceous Earth Dangerous?
The dangers of CRYSTALLINE SILICA are well documented. These include an increased risk for pulmonary diseases such as silicosis, chronic bronchitis, (COPD) chronic obstructive pulmonary disease tuberculosis, and lung cancer
Amorphous Silica which has been manufactured and is pure with no crystalline contamination, has also been researched and showed at least partially reversible inflammation, granuloma formation and emphysema, but no progressive fibrosis of the lungs. This was in long term exposure.
Although there are several studies for amorphous silica toxicity in vitro and with animal studies (also it is used in animal feed to prevent caking, so there is widespread use) there is not a lot of good research with humans regarding the toxicity of long term exposure.
In every day speak this translates to some forms of amorphous silica, in long term exposure can cause irritations and inflammations, possibly severe, but not cancer.
Amorphous silica is used by boatbuilders to thicken epoxy. It is known as coloidal silica. Here is my page on this filler. There are links to safety data sheets and research
Problem is that Diatomaceous Earth has SOME Crystalline Silica
Naturally occurring diatomaceous earth is not purely Amorphous but rather contains some silica crystals and can pose a health risk in long term exposure. Most natural diatomaceous earth used for pest control contain less than 3% crystalline silica or less.
Here is an Australian Material Safety Data Sheet for Diatomaceous Earth. Here is one from American sources There are more on the side bar.
Bottom line is that with reasonable care such as not breathing the dust for long periods or repeatedly, diatomaceous earth is a safe material. All dust will cause irritation to the lungs so this is not related only to diatomaceous earth but is a characteristic of almost all dusts. To get proper perspective it's use must be contrasted to using other pesticides. The usual advice is to wear gloves and a fine particle dust mask or respirator. Smokers or people with a pre disposition for pulmonary problems such as asthma should be particularly careful. Otherwise it is a safe material for use in the home garden.
How does Diatomaceous Earth work?
Diatomaceous earth work by contact. It's action is physical. Since by itself it is not poisonous, it needs to touch to insect to be effective. The powder is abrasive and absorbs oils and fats from the insect cuticle. This causes the insect to dry out and die. Some of the shells which make up the will also pierce the cuticle and speed up the process.
It works best when dry. There is not much hope of success if you wet a product that is intended to dry something out namely insects.
Common Additives in Diatomaceous Earth
Diatomaceous earth is often mixed with other substances to improve it's bug killing ability. The more common additives are pyrethrins and piperonyl-butoxide.Material safety Data sheet for Perma Guard Diatomaceous earth with Pyrethrins and piperonyl butoxide.
Pyrethrins are common additives to Diatomaceous Earth
Diatomaceous Earth is sometimes combined with pyrethrin to increase its efficacity.
Pyrethrins MSDS material safety data sheet. (PYGANIC) This is an insecticide for Organic Crop Protection.
Pyrethrins are a mixture of 6 chemicals, naturally found in some plants including chrysanthemum flowers. These are toxic to a large number of insects, gastropods (snails and slugs) and some nematodes.
To produce pyrethrins sometimes the liquid is extracted from the flowers but sometimes the flowers are simply ground into pyrethrum powder.
This is a link to the National Pesticide Information Center on Pyrethrins
Pyrethins act on the nervous system of insects.
Pyrethrins are relatively non toxic to human and animals so they are widely used for fleas, mosquitoes, head lice and garden pests. It is a common ingredient of pet flea shampoo. It is one of the more common insecticide permitted in organic production.
Besides being poisonous to insects pyrethrins are very poisonous to fish.
Pyrethrins are toxic to beneficial insects as well as garden pests. This sould be taken in consideration when being applied. An evening application is less likely to contact honey bees. Luckily pyrethrins have some repellant activity that helps keep good and bad insects away from it.
Perythins are not very persistant and if exposed to sunlight will break down almost completely in a couple of days. If not exposed to sunlight then it might persist for 3-4 weeks. It will persist better if it settles in the bottom of a pond in the sediment.
Pyrethrins are not the same as Permethrin, Do not use near cats, ever.
Permethrin are synthetic (man made) insecticides, generally called pyrethroids, which show similar structure to pyrethrins. It is more toxic, more persistant and a possible carcinogen, The U.S. EPA decided that permethrin was "likely to be carcinogenic to humans" if it was eaten. It is very toxic to CATS and should never be used near them. It is also highly toxic to fish and water animals.
Treat pyrethrin with care
When using diatomaceous earth with pyrethrin, take the usual precautions. Don't breathe the dust, don't get it on your skin or eyes. Wear gloves, dust mask, keep out of strong wind. It's not deadly but it's not good for you either.
Some people including kids are more sensitive.
Some insects can gradually break down the poison and can recover. The insect might fall down and stop moving, then gradually some might actually get back up.
In order to make the diatomaceous earth/pyrethrin mixture more effective other ingredients are sometimes added. Some of these just improve the flow of the material, or make it stick better, or slows down the break down of the pyrethrin by insects. These additives, called Synergists actually improve the effectiveness. By themselves they are not good pest control materials. A common synergistic material is piperonyl butoxide.
Piperonyl butoxide is a chemical originally derived from sassafras, that has no insecticide activity of its own but is a common ingredient added to improve the success rate of insecticide. When used with pyrethrins it slows down the rate at which insects can break down the insecticide so that it is more poisonous to them.
Toxicity to humans is low. PBO has a low acute toxicity by oral, inhalation and dermal routes. It is minimally irritating to the eyes and skin. It is a not a dermal sensitizer.
No evidence suggests that PBO disrupts the normal functioning of the endocrine system. The USEPA, determined that there were "no risks of concern" for householders mixing, loading, handling, or applying PBO-containing products. The EPA considers it unlikely the pesticide will cause cancer in humans.
Toxicity is very much a function of amount of exposure. There is no evidence that piperonyl butoxide is toxic in the concentrations used. It's toxicity in large quantities is also quite low.
Borates are also sometimes added.
Borax is used widely in cockroach formulations and is sometimes added to diatomaceous earth. It is not considered toxic in concentrations found for this purpose.
What is food grade Diatomaceous Earth?
Food grade diatomaceous earth does not have any toxic additives that some insecticide grades do. It is added to feed and grains to help protect against insect attack but also to improve flow and prevent caking and hardening.
It is chosen for its small amount of crystalline silica present, less than 1%. I don't think it is possible to get natural diatomaceous earth that is completely free from it but food grade has only a small amount.
Food grade Diatomaceous Earth has not been calcined (a heating process). For this reason diatomite that is intended for pool filters is not suitable since it is calcined and soda ash added, causing a significant proportion of crystalline silicon dioxide to be formed 60-70%.
Food Grade diatomaceous earth must not contain more than 10mg/kg of arsenic and no more than 10mg/kg of lead.
Using Diatomaceous Earth
To be effective it has to come in contact with the insects. It is usually applied by either shaking the powder on a plant or around the stems or by using a blower/puffer of some kind to blow the powder onto the plant.
Since it can be irritating to the skin, eyes and lungs, you need to avoid contact. Wear gloves, glasses and a dust mask or dust respirator.
Using safety gear becomes even more important if there are other additives to the diatomaceous earth. These are much more toxic.
If there are additives such as pyrethrin then applying out of the sun to slow down the breakdown of the pyrethrins is more effective. Applying in the evening when the bees have gone home for the day will also help prevent damage to the good insects.
For application to a small area such as on house plants, a make up brush used for powders can work very well.
Since pyrethrins are very poisonous to fish keep it away from ponds, and waterways.
A common use is for flea control. Be very careful if you apply to an animal that the dust does not get in their lungs and eyes. Discourage grooming if you can. It is a better practice to apply the flea dust to the bedding and other places where the animal goes and sleeps. NEVER USE PERMETHRIN ON CATS. IT IS A COMMON INGREDIENT OF FLEA DUST FOR DOGS BUT IT IS VERY POISONOUS TO CATS.
Other uses of Diatomaceous Earth
It used to be a common component of toothpase because it is mildly abrasive. It is also a component of some silver and brass polishes.
It has many applications as filter material. Most people have heard of it for pool filters but it is also used to filter water, beer and wine, sugar and honey syrups and many other things that would pass through regular filter paper.
Because it is full of small air spaces trapped in the diatom shells, diatomaceous earth is useful as an insulator, where conditions would damage other materials.
Diatomaceous Earth is widely sold for ants and bedbugs, as well as cockroaches.
Again because of it's many pores, it can be used to prevent dangerous liquids from sloshing around. Nitroglycerine is very sensitive to shocks and had the bad habit of exploding. When it was placed in diatomaceous earth it became safe to handle and this improvement paved the way to the development of dynamite.
Many people take diatomaceous earth supplements. Many benefits are claimed including nutrition, parasite control and disease control. Many claims are made but scientific research of high quality trials, large, double blind, placebo, etc. are not many and have not generally supported its use.
I try to be accurate and check my information, but mistakes happen.email me if you find mistakes, I'll fix them and we'll all benefit: Christine