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

Abstract

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.

Keywords: Criminal investigation; Drug; Food and beverage; Human remains; Wildlife.

Figure 1.

A spatial representation of global annual average precipitation δ¹⁸O values, estimated using the Online Isotopes in Precipitation Calculator (OIPC v3.0). Figure reprinted with permission. Copyright (2017) waterisotopes.org. This figure is available in color in the online version of the journal.

Figure 2.

(a) Global map of predicted δ¹⁸O values of cotton based on leaf-water modeling coupled with local climate and δ¹⁸O values of local meteoric waters. Only regions where cotton is produced are shown. (b) A crossplot of δ²H (δD) and δ¹⁸O values of paper from genuine US$100 bank notes (green square) and high-quality counterfeit bank notes from multiple series. Figure reprinted with permission from Cerling et al. (2016a). Copyright (2016) Annual Reviews. This figure is available in color in the online version of the journal.

Figure 3.

(a) Absolute frequencies of carbon isotope ratios of C₃ and C₄ plants. (b) Absolute frequencies of carbon isotope ratios of beers brewed in the U.S and in Canada. (c) Absolute frequencies of carbon isotope ratios of beers brewed in Europe, Mexico, Brazil, and the Pacific Rim (Japan, Australia). Arrows indicate average δ¹³C values for two main beer ingredients, malted barley and corn sugar. Figure reprinted with permission from Brooks et al. (2002). Copyright (2002) American Chemical Society.

Figure 4.

Sites of tap water sample collection (gray circles), displayed on an isoscape of inferred ⁸⁷Sr/⁸⁶Sr ratios in the coterminous USA. Isoscape from Bataille and Bowen (2012) and based on the bedrock age model of Beard and Johnson (2000). Figure from Chesson et al. (2012), reprinted under Creative Commons license. This figure is available in color in the online version of the journal.

Figure 5.

Box and whisker diagram for median lag times (difference between date of death and seizure date) of confiscated ivory specimens; the number of specimens with F¹⁴C measurements for each grouping is given in parentheses. Figure reprinted with permission from Cerling et al. (2016b). Copyright (2016) National Academy of Science. This figure is available in color in the online version of the journal.