Whether it be cordierite, mullite or other types of refractory materials they all are fused at such high temps that they become, for all practical purposes, inert. Also their chemical composition contains no toxic metals such as lead. It is the ceramic glazes that may contain lead, not the ceramic itself that poses a danger. More inert than say a cast iron skillet which does release perhaps a few harmless molecules of free iron each time it's used. Man has eaten from ceramic plates and bowls for thousands of years with no ill effects unless it has a lead based glaze on it.