There is some concern about this being in ball clays.
Tennessee-Kentucky Ball Clay Co. are still
researching this situation, and will put out an official statement at a
later date, but for now here's the scoop: they have discovered
naturally occuring dioxin in all ball clay deposits. The level slightly
higher at the Mississippi mine where the bentonite that went into the
chicken feed was found. But he says the levels that are found in ball
clay are well under federal safety limits. He said that MSDS's for ball
clay and bentonite now list dioxin as a trace ingredient. They don't
have any worries about the safety of potters using these clays, but
consider that ingestion by mouth would be of concern. As for fired pots,
dioxin breaks down at 800 degreed F., so there is no worry about kiln
fumes, or dioxin in the fired pots. They are working with federal
agancies on this issue, and no clay from the Mississippi mine is being
disributed to potters now.