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Asbestos in Fertilizer and Other Gardening Products

Asbestos was not intentionally added to fertilizers and other gardening products. Instead, asbestos was an accidental contaminant of a very popular gardening product known as Zonolite.

Zonolite was a product of the W.R. Grace Corporation, one of the largest asbestos producers in the United States prior to 1990. Their mining and processing operations were centered on the northwestern community of Libby, Montana, where most of the nation's supply of chrysotile (common "white" asbestos) was produced during the 20th century.

Zonolite was not asbestos; it was made from a mineral called vermiculite. Still mined in many countries and available in retail outlets, vermiculite is a harmless and very useful mineral that expands into a soft, spongy material when heated. Used as a soil conditioner as well as for insulation, vermiculite is usually found near asbestos deposits and is frequently contaminated with an asbestiform mineral called tremolite. This is a highly toxic amphibole type of asbestos, similar to crocidolite and amosite (but unlike these two, never exploited commercially). Amphibole asbestos is made up of hard fibers that when ingested, puncture the internal organs from the inside and migrate to the outer surfaces and the viscera. Exposure to amphibole asbestos is likely to cause cancer in susceptible individuals.

Zonolite and other vermiculite products are no longer contaminated by asbestos, as the companies producing vermiculite agricultural and gardening products now screen for the presence of tremolite asbestos in their mining operations.

Hazards Associated with Fertilizer Products

Gardeners and agricultural hobbyists working with Zonolite were exposed to asbestos fibers as a result of the presence of tremolite. However, most Zonolite was buried in gardens under topsoil and the opportunities for asbestos inhalation would have been limited. The more serious risk occurred from the use of Zonolite in household products like insulation and aggregates; some estimates are that 35 million buildings in the United States may contain Zonolite. While this material poses relatively low risk when intact, as the insulation or other material wears or is damaged it can become friable, releasing individual asbestos particles into the air. The heaviest exposure to asbestos from Zonolite was borne by the miners and residents of Libby, Montana, where a great deal of U.S. vermiculite was mined, as well as those working or living near a similar vermiculite mine in Virginia.



Bowker, Michael. Fatal Deception: The Untold Story of Asbestos (New York: Touchstone, 2003)

N/A. "Libby Site Background." Environmental Protection Agency Website
( Retrieved 6 January 2011.

Schneider, Andrew. "Virginia Miners At Risk From Asbestos." Seattle Post-Intelligencer, 4 October 2000.

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