Asbestos in Potting Mixtures

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Most people consider gardening a relatively safe activity, but there can be hidden risks to digging around in the soil. Many people are unaware that their innocent-looking potting mixtures could contain something as potentially dangerous as asbestos.

For potting mixes that contain vermiculite, asbestos contamination is a major concern. Vermiculite is a naturally occurring mineral that expands up to 15 times its normal size when exposed to heat. Vermiculite is also very absorbent. It has a flaky appearance that is often compared to that of mica. Usually, vermiculite is mined specifically for insulating and gardening purposes. The vermiculite itself is not risky for gardeners; however, it can become contaminated by asbestos, leading to potential health problems for those who use it.

When used in potting mixtures, vermiculite retains water, helping plants to get the moisture they need to grow. It may also be used in gardens that have significant clay content, loosening the soil. In the past, a vast majority of the vermiculite used in the United States was mined in Libby, Montana and sold under the name “Zonolite.” In fact, up to 80 percent of the commercially available vermiculite came from Libby.

This changed in 1990 when the plant, then owned by W.R. Grace, was closed down due to instances of asbestos-related illnesses among the employees of the plant. High numbers of lung cancer and mesothelioma cases had become apparent in the plant’s workers. There was a high rate of asbestosis as well. Unfortunately, these health problems occurred not just in the plant’s workers, but also in their family members. It is thought that the plant’s workers unwittingly carried asbestos fibers home on their clothing and attached to their hair, putting their loved ones at risk.

Today, vermiculite is mined in places like South Carolina, Virginia, Brazil, China, Egypt, and Russia. While there is potential for asbestos contamination in vermiculite that comes from such places, many involved in the mining industry assert that there is no significant cause for concern among consumers.

Most environmental experts agree that the amount of asbestos found in potting soil is likely to be minimal. Such a small amount may not pose a significant health risk to gardeners. It is possible though for asbestos fibers to be released into the air during use, creating the potential for the consumer to inhale them. Since no one knows exactly how much exposure it takes to cause cancer, some consumers may decide to avoid potting mixtures that contain vermiculite altogether.