Vermiculite
We don’t use vermiculite in our soil mixes because it is energy-intensive. Turns out there are other problems with it too. The Straight Dope tells all.
The trouble with vermiculite has nothing to do with the substance itself, but rather with a contaminant that’s sometimes found in vermiculite ores: asbestos….
Technically, it’s not just insulation that poses such potential threat, as there are plenty of vermiculite-bearing gardening products around too — it’s added to potting soils to help them hold more water. In 2000 the EPA tested 54 of these: 22 contained asbestos, it turned out, with 8 containing significant amounts and 1 actually releasing asbestos fibers into the air when used. Overall, though, the exposure level for the average gardener was found to be quite low
