The stable isotope ratios of marijuana. II. Strontium isotopes relate to geographic origin.

Effectively addressing marijuana trade is aided by understanding marijuana geographic sources. We analyzed the (87)Sr/(86)Sr of marijuana samples grown in 79 counties across the United States to determine if a primary geologic signal is retained in marijuana, which could therefore be useful for geographic sourcing. The marijuana results were compared with modeled bedrock (87)Sr/(86)Sr values based on (87)Rb decay rates and a generalized geologic map of the U.S.A. A significant correlation was observed between marijuana (87)Sr/(86)Sr and modeled bedrock (87)Sr/(86)Sr. Although values clustered near the 1:1 relationship, there was a predominance of positive anomalies, perhaps attributable to carbonate bedrock. A small number of negative anomalies were also observed, which were generally associated with granitic bedrocks. These results suggest that strontium isotopes in marijuana record the geographic origins of marijuana, and that refinement of the base strontium map (or strontium isoscape) and improved understanding of other strontium sources would be productive.