It is easy to find in florists and nurseries, along with herbicides, insecticides, fungicides, fertilizers and other phytosanitary products, some bottles filled with a fine, whitish, yellowish or sand-colored powder, labeled as ” diatomaceous earth “. This product, in addition to its versatility, has a curious origin: they are exoskeleton fossils of diatom algae.
What are diatoms?
Diatom algae are a very diverse group of unicellular algae. Each cell body is covered by a silica exoskeleton, called a frustula , made up of two pieces, called thecae , that fit together like the lid on a box. And when the alga dies, its frustula is deposited in the sediment.
These teaks present complex porous ornamentations , which generate very striking and characteristic patterns. Over time, more and more sediment falls on the empty frustules of diatoms and, millions of years later, the shells fossilize and form a rock called diatomite, from which the famous ‘diatomaceous earth’ is extracted.
At this point it is important to define “ adsorption ”, not “absorption”. Absorption, with B, implies the attraction and retention of a substance by a solid or liquid, which becomes part of its structure. Adsorption, with D, —which only occurs in solids— also involves the attraction of substances, but they are retained on the surface of the attractor body, not inside.
The high porosity of diatom frustules —and therefore, of diatomaceous earth— allows the adsorption of a large number of substances: mineral salts, metals, organic matter and even water, due to the hygroscopic effect . And this property, high porosity, makes diatomaceous earth a product with a host of practical uses.
diatomaceous earth in gardening
Diatomaceous earth has some fertilizing capacity. Generally, the frustules of the algae, when dying, adsorb substances that are diluted in the water and are preserved in the fossilization. Phosphorus, calcium, carbonates , or silica itself are held in diatomaceous earth, and nourish the soil.
But it is not the only function in gardening. Thanks to the property of adsorbing the lipids that cover the cuticle of insects, mites and other arthropods, it kills them by desiccation. In addition, it has a certain abrasive capacity that can damage or eliminate insects and mites. Hence, diatomaceous earth is also used as an insecticide and acaricide. This application is not only effective for the treatment of plants affected by these animals, but also to prevent pests in stored products.
Other Uses for Diatomaceous Earth
Another very promising use of diatomaceous earth is related to water purification . Especially, to remove heavy metals from wastewater and water bodies present in the natural environment. This purifying capacity increases when diatomaceous earth is treated with manganese oxide. A certain capacity for adsorption of colorants and dyes has also been observed in wastewater from the textile industry.
Also in the construction industry diatomaceous earth can have interesting applications. A research group from the University of Ghent, Belgium, has studied the use of diatoms as a method of protecting bacteria used in self- curing concrete . The main cause of the decrease in the useful life of concrete structures is cracks. One of the proposals to prolong this useful life is the use of bacteria that produce calcium carbonate, such as Bacillus sphaericus , which are present within the concrete matrix. In this way, before a crack, it is the bacteria that fill it with their excretions. Concrete treated in this way would repair itself—at least to some extent.
However, the alkaline environment that occurs during the production of the concrete mass is fatal for these bacteria. And that’s where diatomaceous earth comes into play. This substance has shown the ability to protect bacteria, and keep them in the concrete. The results of the study revealed that, in concrete pieces made in this way, cracks up to 0.17 mm wide were completely filled with calcium carbonate excreted by bacteria.
Ni milagroso, ni inocuo
The insecticidal or fertilizing capabilities of diatomaceous earth are real, but they are far from the miracle cure that many try to sell. There are much more effective insecticides and acaricides on the market.
However, the most important thing is that it is not a harmless substance for humans. It must be handled with caution. Inhaled diatomaceous earth particles can accumulate in the bronchi, alveoli of the lungs, liver tissues, and lymph nodes, and are not always eliminated from the body.
Chronic and repeated exposure to diatomaceous earth without adequate protection is potentially associated with health problems , especially respiratory ones, from mild to very serious, such as silicosis or lung cancer.
Therefore, to handle diatomaceous earth in any of its multiple applications, you should always use a mask to protect against particles, type PM 2.5 or higher, as a measure to prevent future health problems.
References:
Akhoundi, M. et al. 2019. Harmful Effects of Bed Bug-Killing Method of Diatomaceous Earth on Human Health. Journal of Insect Science, 19(5), 13. DOI: 10.1093/jisesa/iez095
Al-Ghouti, M. A. et al. 2003. The removal of dyes from textile wastewater: a study of the physical characteristics and adsorption mechanisms of diatomaceous earth. Journal of Environmental Management, 69(3), 229-238. DOI: 10.1016/j.jenvman.2003.09.005
Bello, O. S. et al. 2014. Insights into the Adsorption of Heavy Metals from Wastewater using Diatomaceous Earth. Separation Science and Technology, 49(12), 1787-1806. DOI: 10.1080/01496395.2014.910223
Shah, M. A. et al. 2014. Use of diatomaceous earth for the management of stored-product pests. International Journal of Pest Management, 60(2), 100-113. DOI: 10.1080/09670874.2014.918674
Wang, J. Y. et al. 2012. Diatomaceous earth as a protective vehicle for bacteria applied for self-healing concrete. Journal of Industrial Microbiology and Biotechnology, 39(4), 567-577. DOI: 10.1007/s10295-011-1037-1
Zeni, V. et al. 2021. Diatomaceous Earth for Arthropod Pest Control: Back to the Future. Molecules, 26(24), 7487. DOI: 10.3390/molecules26247487
