Applying the principles of isotope analysis in plant and animal ecology to forensic science in the Americas.

The heart of forensic science is application of the scientific method and analytical approaches to answer questions central to solving a crime: Who, What, When, Where, and How. Forensic practitioners use fundamentals of chemistry and physics to examine evidence and infer its origin. In this regard, ecological researchers have had a significant impact on forensic science through the development and application of a specialized measurement technique-isotope analysis-for examining evidence. Here, we review the utility of isotope analysis in forensic settings from an ecological perspective, concentrating on work from the Americas completed within the last three decades. Our primary focus is on combining plant and animal physiological models with isotope analyses for source inference. Examples of the forensic application of isotopes-including stable isotopes, radiogenic isotopes, and radioisotopes-span from cotton used in counterfeit bills to anthrax shipped through the U.S. Postal Service and from beer adulterated with cheap adjuncts to human remains discovered in shallow graves. Recent methodological developments and the generation of isotope landscapes, or isoscapes, for data interpretation promise that isotope analysis will be a useful tool in ecological and forensic studies for decades to come.

Stable isotope models to predict geographic origin and cultivation conditions of marijuana.

Here we describe stable isotope based models using hydrogen and carbon isotope ratios to predict geographic region-of-origin and growth environment for marijuana, with the intent of applying these models to analyses of marijuana trafficking in the USA. The models were developed on the basis of eradication specimens and border specimens seized throughout the USA. We tested reliability of the geographic region-of-origin and growth environment models with a "blind" set of 60 marijuana eradication specimens obtained from counties throughout the USA. The two geographic region-of-origin model predictions were 60-67% reliable and cultivation environment model predictions were 86% accurate for the blind specimens. We demonstrate here that stable isotope ratio analysis of marijuana seizures can significantly improve our understanding of marijuana distribution networks and it is for that purpose that these models were developed.

Tracing retail cannabis in the United States: geographic origin and cultivation patterns.

BACKGROUND: Although cannabis is the most readily available and widely used illicit drug in the United States, there remains significant uncertainty about the importance of different production regions and trafficking patterns. METHODS: We analysed 628 "retail" cannabis seizures from over 50 municipalities across the United States for hydrogen and carbon isotope ratios to predict their growth locations and environments. RESULTS: Results are presented for 22 consolidated retail locations across the United States. Evaluation of specimens from within these retail areas suggested that cannabis seizures had region-dependent origins, often from both domestic and foreign sources, and although indoor growth was common in many areas, there was also regional dependence in the proportions cultivated under indoor versus outdoor conditions. CONCLUSION: Street-available cannabis exhibits region-specific trafficking patterns, both Mexican- and Canadian-grown cannabis are apparently widely available, and indoor-grown cannabis appears to be cultivated and trafficked in both warm and cool weather localities throughout the United States.

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.

Stable isotope ratios of marijuana. I. Carbon and nitrogen stable isotopes describe growth conditions.

There remains significant uncertainty in illicit marijuana cultivation. We analyzed the delta(13)C and delta(15)N of 508 domestic samples from known U.S.A. counties, 31 seized from a single location, 5 samples grown in Mexico and Colombia, and 10 northwest border seizures. For a subset, inflorescences and leaves were analyzed separately. These data revealed a strong correspondence, with inflorescences having slightly higher delta(13)C and delta(15)N values than leaves. A framework for interpreting these results is introduced and evaluated. Samples identified as outdoor-grown by delta(13)C were generally recorded as such by the Drug Enforcement Administration (DEA). DEA-classified indoor-grown samples had the most negative delta(13)C values, consistent with indoor cultivation, although many were also in the outdoor-grown domain. Delta(15)N indicated a wide range of fertilizers across the dataset. Samples seized at the single location suggested multiple sources. Northwest border delta(13)C values suggested indoor growth, whereas for the Mexican and Colombian samples they indicated outdoor growth.