Forensic Botany is a branch of forensic science that utilizes botanical information to solve crimes. The field has relied heavily on the sub-disciplines molecular biology, ecology, plant pathology, and microscopy. However, the evidentiary value of the unique chemical signatures that botanical evidence can lend to criminal investigations is underexploited. This is primarily because few systematic studies that correlate plant chemotaxonomic markers and secondary metabolite chemical signatures to specific plant species have been conducted. Consequently, when plant material found at a crime scene cannot be identified visually or through the use of techniques in molecular biology, its evidentiary value can be greatly reduced.
We have coined the term “Forensic Chemical Taxonomy” to refer to the identification of plant material in a forensic context through multivariate statistical analysis of its unique metabolomic signature. By building a comprehensive database that contains information on plant species and their corresponding chemotaxonomic markers, mass spectrometric analysis of plant material “unknowns” and comparison of the results to database information can enable identification of plant material at a crime scene and inform further investigations and conclusions.
Applications of Forensic Chemical Taxonomy
Being able to identify plant-based material in the manner proposed above would have a number of applications. For example, there is a tremendous need to be able to identify plants with psychotropic activity that are being abused. For millennia, humans have exploited the use of psychoactive substances to induce altered states of consciousness that were deemed important for communication with supernatural spirits and deities in religious and shamanic contexts. These substances were most often natural products derived from plant or animal sources. Examples include the bufotoxins excreted from the parotid glands of toads of the genus bufa, psychedelic mushrooms that contain hallucinogens, and the peyote cactus that contains mescaline. In recent times, with the advance of analytical technologies, the specific compounds responsible for the mind altering effects have been determined. One result has been the development of synthetic methods that enabled production of highly purified active compounds which, although used medicinally in some cases, are nevertheless abused in others. Thus, many of these drugs have become highly regulated and their sale, possession and ingestion are criminal acts. A case in point is marijuana, where the easily identified plant from which it is derived (cannabis), as well as its psychoactive constituents (tetrahydrocannabinol and related compounds) are scheduled. In response, drug manufacturers have gone back to basics, and are exploiting the fact that the vast majority of plants known or thought to contain psychoactive substances are not scheduled. These plants are prepared for inclusion in “herbal blends” that contain other mind altering ingredients, or are extracted with solvents to yield crude residues that purportedly contain higher concentrations of active ingredients and are incorporated into finished products.
Since the world of psychoactive plant and animal derived drugs is vast, it has become increasingly difficult in a forensics context to distinguish between innocuous plant-based food material (e.g. spices or coffee grounds), and a plant that is being abused. Our work is demonstrating that ambient mass spectrometry can be a powerful tool for the identification and differentiation of plants of abuse. Our most recent work in this area is featured in Forensic Science International articles.