Diatomaceous earth (DE) is a fine, powdery, naturally occurring sedimentary rock. This substance is derived from the fossilized remains of ancient, single-celled aquatic organisms known as diatoms. Significant differences exist between various types of diatomaceous earth, arising not from the original source material, but from the specialized processing steps applied after the material is mined. Understanding these distinctions is necessary for safe and appropriate use.
The Geological Origin and Basic Composition
Diatomaceous earth originates from the microscopic skeletons of diatoms, a type of hard-shelled protist that lived in bodies of fresh or salt water millions of years ago. When these organisms died, their shells, called frustules, settled at the bottom of the water source, accumulating over geologic time to form large deposits of diatomite. This naturally mined rock is primarily composed of amorphous silica, which is silicon dioxide with an irregular, non-crystalline structure. A typical oven-dried sample is 80–90% silica, with the remainder consisting of trace minerals like iron oxide and alumina.
The effectiveness of raw diatomaceous earth, particularly as a mechanical insecticide, stems from the structure of these fossilized shells. Diatom frustules are incredibly intricate and porous, resembling microscopic honeycombs. This structure gives the material a very low density and high surface area, while the edges of the silica shells are microscopically sharp. When insects come into contact with this powder, the edges scratch the waxy outer layer of their exoskeletons, causing them to dehydrate and perish.
The Critical Distinction: Processing and Grades
The most significant factor determining the final product is the post-mining treatment, which separates diatomaceous earth into distinct commercial grades. The primary difference centers on the application of intense heat, a process known as calcination. The subsequent thermal treatment fundamentally alters the material’s chemical and physical characteristics.
Food Grade DE
Food Grade diatomaceous earth is uncalcined or minimally processed, meaning it is not subjected to high heat and retains its original chemical state. It is regulated to contain less than 1% crystalline silica and must meet strict purity standards for heavy metals like arsenic and lead. The silica in this grade remains in its amorphous, non-toxic form, making it safe for internal use in animals and humans, as well as for domestic pest control.
Filter Grade DE
In contrast, Filter Grade diatomaceous earth, frequently used for pool or industrial filtration, is treated at temperatures exceeding 1,000 degrees Celsius. This calcination process hardens the diatom particles, which improves their efficiency as a filter medium by creating a higher flow rate. This extreme heat causes a chemical change, converting the amorphous silica into highly structured crystalline silica, specifically a form called cristobalite. This conversion is substantial, with some calcined products containing up to 70% crystalline silica.
Practical Applications and Safety Considerations
The chemical composition dictated by processing directly determines the product’s intended uses and necessary safety protocols. Food Grade DE is utilized as a dietary supplement, a natural anti-caking agent in animal feed, and a non-chemical pesticide for home and garden use. Its mechanism of action against pests relies on physical abrasion and moisture absorption.
Filter Grade DE is engineered for superior liquid purification and is the standard medium for filtering swimming pool water and various industrial liquids. The robust particle structure allows it to trap particulate matter down to a few microns in size. The presence of high concentrations of crystalline silica makes this grade unsuitable for any application involving ingestion or widespread dusting.
The most significant safety consideration is the inhalation hazard associated with the crystalline form of silica found in Filter Grade DE. Prolonged inhalation of this dust is a known health risk, capable of causing silicosis, a serious, progressive lung disease, and it is classified as a human carcinogen. Consequently, users must never use Filter Grade DE for pest control or any purpose intended for the Food Grade material. Proper handling of calcined DE requires minimizing dust generation and using personal protective equipment, such as a respirator.