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Ah, spring! People everywhere are putting spades to soil and planting their favorite new flowers, shrubs and vines. But beware if you use vermiculite to amend your soil! Vermiculite is a puffy, lightweight granule applied as a soil conditioner to improve aeration and drainage when planting. You must be sure you are opening a recently purchased bag and not unsealing an old product that has been in your gardening shed for decades. Amazingly, much of the vermiculite sold as a common gardening supplement up through the 1980s was contaminated with deadly, cancer-causing asbestos.
Vermiculite, a naturally occurring mineral was, until 1990, mined from the same ore deposits as the deadly mineral fiber asbestos. Asbestos ore is made up of long, thin fibers that can only be seen through a microscope. When these tiny fibers become airborne, they can be inhaled into the lungs, where they might eventually cause asbestosis, lung cancer, and even the deadly asbestos cancer mesothelioma.
Vermiculite was first identified in 1881 in a mine near Libby, Montana. In 1919, Dr. Edward Alley discovered that vermiculite expanded (popped like popcorn) when heated. This expansion created pockets of air that made the material suitable for use as insulation and provided better drainage in dense garden soils.
Dr. Alley founded the Zonolite Company and developed a processing facility north of Libby, producing expanded vermiculite. His Zonolite vermiculite was both lightweight and inexpensive to process. It was used in everything from construction insulation to school craft projects from the early 1940s through the late 1970s.
Unfortunately, asbestos ore was abundant in the same mine, a particularly dangerous type of asbestos known as amphibole asbestos or Tremolite. Tremolite asbestos fibers are generally longer and break apart more easily than other asbestos fibers. They are also believed to be more toxic. The veins of this toxic and extremely friable form of asbestos-contaminated most, if not all, of the vermiculite taken from the Libby mine. Milling removed some of the asbestos from the finished product, but a significant amount remained.
When subjected to heat, vermiculite has the unusual property of expanding into worm-like pieces (the name vermiculite is derived from the Latin ‘vermiculare’ – to breed worms). Vermiculite has been employed in various industries for more than 80 years. It is used in construction as a lightweight filler in concrete blocks, in home attic insulation, in commercial fireproofing spray, and in agricultural and horticultural markets for seed germination, bulb storage, and as a soil conditioner. It’s even used as a filter in fish aquariums!
It is estimated that the Libby mine was the source for almost 80 percent of all vermiculite sold in the U.S. from 1923 until the mine closed in 1990. While the Libby mine is no longer operating, vermiculite-mining operations are still found worldwide. The largest vermiculite mines continue in Brazil, China, and South Africa.
As of 2017, there were only two vermiculite mines still operating in the United States, both in the eastern Appalachian mountain ranges of Virginia. While vermiculite from these mines is thought to be “safe”, the layers of igneous rock where vermiculite is found almost always contain asbestos.
Although testing of vermiculite mined in the U.S. is stringent, the examination of vermiculite in other countries is not always so rigorous. If you do use vermiculite when gardening, you should confirm that it was sourced in the U.S.
The Agency for Toxic Substances and Disease Registry (ATSDR) says that homeowners should assume any vermiculite insulation in their attics is contaminated with asbestos. It should not be disturbed. The Environmental Protection Agency (EPA) estimated in 1985 that 940,000 American homes contained asbestos-laden Zonolite attic-fill from the contaminated Libby mine in Montana.
If you have bags of old or imported vermiculite soil amendment in the garage, it would be best to throw them out. Bags of horticultural vermiculite produced from mines in the United States after 1990 are probably safe to use. But as with any fibrous material that creates dust when disturbed, you should always wear a mask, take the vermiculite outside before using it, and dampen it with water before mixing it into your soil.
If you are getting out into your garden to do some planting this spring, be sure the vermiculite you choose for your flowers is brand new and made in the U.S.A. If you have been diagnosed with mesothelioma, please contact the knowledgeable lawyers at Baron & Budd to find out if you can seek compensation from the manufacturers who made the products that exposed you to their toxic asbestos fibers.