FORENSIC GEOLOCATION USING ENVIRONMENTAL ISOTOPES

Natural geospatial variation in the abundance of biologically relevant isotopes represents a source signal allowing geolocation of animal and plant samples. The isotopic composition of tissues reflects the composition of a plant or animal's growth environment integrated over the time of tissue growth and modified by biosynthetic and physiological mixing processes. Accurate and precise application of environmental isotopes for forensic geolocation thus requires 1) knowledge of the geospatial patterns of isotopic variation in the environment, 2) robust models for the incorporation of environmental isotope signatures in plant and animal tissues, and 3) the ability to precisely and accurately determine the isotopic composition of tissue samples. Our presentation will focus on issues 1 & 2, which form the foundation on which isotopic measurements of forensic samples can be interpreted. The H, C, N, O, and Sr isotope systems each exhibit geospatial variation useful for forensic geolocation over a range of spatial scales. The environmental distributions characterizing these systems can be merged with empirical or process-based biological models in order to create predictive distributions for the isotopic ratios of a variety of organisms and tissue types. These predictive distributions provide a context by which the origin of forensic samples can be constrained. Commercially available GIS provides a workspace and toolset with which spatial modeling and integration of diverse datasets can be combined in order to develop powerful forensic geolocation tools. Application of these tools to modern and pre-modern forensic investigations will be advanced through the continuing development of databases and models relevant to the issues described here.