Others are the approximately- corresponding figures of 818 pCi/g, 30 kBq/kg (800 pCi/g, or 810 pCi/g, depending on which converter you use) and 8.54E-10, one of which is cited in the National Research Council book, Evaluation of Guidelines for Exposures to Technologically Enhanced Naturally Occurring Radioactive Materials...the basis of the EPA Guidelines for Exposure to Naturally Occurring Radioactive Materials.
Me and my buds were talking about that very subject last night in the bar after bowling.........I wish I could remember what they said since they may have had the answer you're looking for.