Recent applications of isotope analysis to forensic anthropology

Abstract

Isotope analysis has become an increasingly valuable tool in forensic anthropology casework over the past decade. Modern-day isotopic investigations on human remains have integrated the use of multi-isotope profiles (e.g. C, N, O, H, S, Sr, and Pb) as well as isotopic landscapes ("isoscapes") from multiple body tissues (e.g. teeth, bone, hair, and nails) to predict possible region-of-origin of unidentified human remains. Together, data from various isotope analyses provide additional lines of evidence for human identification, including a decedent's possible region-of-birth, long-term adult residence, recent travel history, and dietary choices. Here, we present the basic principles of isotope analysis and provide a brief overview of instrumentation, analytical standards, sample selection, and sample quality measures. Finally, we present case studies that reflect the diverse applications of isotope analysis to the medicolegal system before describing some future research directions. As shown herein, isotope analysis is a flexible and powerful geolocation tool that can provide new investigative leads for unidentified human remains cases.

Keywords: Forensic sciences; forensic anthropology; isoscapes; provenancing; stable isotope analysis.

Figure 1.

A simple schematic of the analysis of bio-elements (e.g. H, O, C, N) via continuous flow-isotope ratio mass spectrometry (CF-IRMS). Redrawn from [78] with permission granted by the FIRMS’ Board of Directors.

Figure 2.

Bivariate plot of bone collagen stable carbon and nitrogen isotope values of prehistoric hunter-gatherers from Central California. Unidentified bone sample (labeled as “Case”) plots closest to San Francisco Bay Area Native Americans from the northern San Francisco Bay Area. AIR: Atmospheric Nitrogen; VPDB: Vienna-Pee Dee Belemnite.

Figure 3.

(A) Region-of-origin prediction map for Case Study 2 using the oxygen isotopic composition of hair. (Water base layer data used for region-of-origin prediction from [20].) The highlighted areas indicate locations where the decedent may have obtained her drinking water (based on measured oxygen isotope ratios of hair) between 13 and 3 months prior to death (Region 1). These possible regions include areas within the Western U.S. (Washington State, Oregon, California, southern Nevada, Colorado), the Southwest (Arizona, New Mexico), the Midwest (Kansas, Nebraska, the Dakotas, Minnesota, Michigan), the Mid-Atlantic States, West Virginia, and most of the Northeast. (B) Region-of-origin prediction map for Case Study 2 using the oxygen isotopic composition of hair. (Water base layer data used for region-of-origin prediction from [20].) The highlighted areas indicate locations where the decedent may have obtained her drinking water (based on measured oxygen isotope ratios of hair) between approximately 3 and 1 months prior to death (Region 2). These possible regions include areas within the South (Texas, Oklahoma) and South Atlantic (Florida). (Maps created by E.L. Kipnis, IsoForensics, Inc.).

Figure 4.

Box-and-whisker plot comparison of bone collagen stable carbon isotope data for a sample of UBC remains from South Texas and a sample of U.S. Americans (partial data set derived from [105], Figure 15.1, P. 179). Box represents the interquartile range (IQR) and whiskers are 1.5 × IQR. Unidentified bone sample (labeled as “OpID 0381”) is more similar to U.S. Americans than other UBC remains. VPDB: Vienna-Pee Dee Belemnite. UBC: unidentified border crosser; USA: U.S. American.

Figure 5.

Region-of-origin prediction map for Case Study 3, remains of an unidentified border crosser (OpID 0381), using the oxygen and strontium isotopic compositions of tooth enamel. (Water base layer data used for region-of-origin prediction from [20] and [60].) The darkest gray highlighted areas indicate locations where the individual may have obtained their drinking water (based on measured oxygen isotope ratios of tooth enamel). The lighter gray highlighted areas indicate locations where the individual may have obtained their food (based on measured strontium isotope ratios of tooth enamel). The red highlighted areas indicate locations where both oxygen and strontium isotopic compositions overlap, representing the most likely regions-of-origin. These possible regions include several areas within the Western U.S., the Southwest, the Midwest, and the Northeast. (Map created by B.J. Tipple, IsoForensics, Inc.).