Most people know vermiculite as that foam-like mineral that gets mixed into potting soil or poured into attic spaces as lightweight insulating pebbles. Last week, the Environmental Protection Agency and the federal Agency for Toxic Substances and Disease Registry issued a joint warning about vermiculite: If it's a decade or more old, it may be laced with asbestos, a potent lung carcinogen.
The federal agencies report that most U.S. vermiculite mined prior to 1990 came from a site near Libby, Mont., where a natural asbestos deposit ran through the mine, tainting much of the vermiculite.
Based on just-released data from a study conducted 2 years ago in six Vermont homes with vermiculite insulation, EPA reports that "the asbestos content of the vermiculite was as high as 2 percent in bulk samples . . . yet asbestos was not detected in the air or dust."
What led to the federal warning were the results of additional tests, such as a simulation of a homeowner wiring a c