The Passionate Gardener: July 2016
By: Ron Kushner
Diatomaceous earth (DE) is an inert dust and type of rock composed of skeletons of fossilized diatoms. These diatoms were tiny, one celled marine and freshwater plant organisms that are composed mainly of silica, a naturally occurring mineral. When crushed, these skeletons break up into tiny pieces of a glass-like material, so tiny that the material feels like talcum powder. This is easily picked up by the hairy bodies of most insects, whereupon it scratches through their protective wax layers; and they also absorb some of this material resulting in the insect losing water rapidly, drying up and dying.
DE is mined for use in industrial filtration applications but its oldest and best known commercial use is as a very mild abrasive in metal polishes and toothpaste. It has also been used as an exfoliant in skin products, a source of detoxification and mineral additive in pet food and an extremely effective reduced-risk pesticide.
Large deposits occur in California, Nevada, Washington and Oregon but it is harvested from sediments at the bottom of oceans, lakes and rivers around the globe.
There is no evidence that DE or the silica that it is composed of is toxic to humans or animals, including experiments with cancer research. That being said, there is a particular form of silica that could pose a health hazard but the amount occurring in natural DE is so small that any health hazard has been totally ruled out.
When DE is heated to high temperatures, the silica is changed chemically and becomes a potentially harmful form but only if inhaled at high levels for a long time (years) and only under occupational conditions. It should be noted that the “pool filter grade” DE is processed differently and not recommended for use in pest control.
The naturally occurring DE sold in garden centers and other retail outlets labeled “food grade” poses no more of a health hazard than inhaling dust in general; for most people, nothing more than an unpleasant nuisance. Food grade DE is non-toxic and safe for human consumption. It is also allowable on “organic” labeled foods by the US Dept. of Agriculture. Still, it is recommended that DE be applied with a bulb duster and protective equipment such as a dust mask.
DE is in no way harmful to rivers, lakes, fish or other aquatic life. In water, it is basically the same as plain sand. Remember, it was actually created by living marine organisms.
Natural DE is used as an insecticide, where it works in a purely physical manner and not through any chemical toxicity. The abrasive diatom skeletons act like tiny razor blades and rub holes in an insects’ soft parts, causing a loss of bodily fluids resulting in the death of the insect. All other animals and humans are immune to this effect. It is effective on anything with an exoskeleton; any insect (with six legs) and non-insect arthropods (eight or more legs).
DE is not in any way harmful to plants (although it is probably not good to allow the plants to become smothered in the dust).
The use of insect dusts such as DE to control insects has been around for thousands of years. Ancient cultures around the world used them to protect stored grains against pantry pests like moths and beetles. The same mode of action is used by birds and other animals that take dust baths-they are ridding themselves of their insect parasites.
Another use of DE is in animal production units for control of external parasites and flies. This control is achieved by dusting the animals and the litter or bedding area. It has also been included in the diet (two percent in the grain ratio) to control certain internal parasites and this practice is said to result in lower fly populations in the resulting manure.
According to Professor Stuart B. Hill of McGill University in Canada “….It is perhaps the safest effective pesticide for use in the home and has a valuable place in the protection of stored food and control of insects in animal production units”.
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