Forensic stable isotope signatures: comparing, geo-locating, detecting linkage.

Stable isotope signatures or profiles of physical evidence such as illicit drugs,explosives or human tissue provide information on source, origin, even sample his-tory not obtainable by traditionally applied analytical techniques of forensic chemistry. The discriminatory power, calculated as random match probability, of multivariate stable isotope signatures able to distinguish two cocaine samples from different regions in Colombia can range from one in tens of thousands to one in several million if based on the stable isotope abundances of carbon, nitrogen and hydrogen or carbon, nitrogen, hydrogen and oxygen, respectively. Stable isotope signatures of physical evidence have therefore at the very least great potential to provide invaluable forensic intelligence for intelligence led policing. They may even be of great evidentiary value, especially if corroborated by results from independent analytical techniques. This review aims to offer a glimpse into the fascinating world of forensic stable isotope analysis by discussing the various levels of information stable isotope signatures can provide. For reasons easily appreciated,only a select few instances of its application to criminal investigations have been reported in scientific journals thus far. The various applications of this technique presented in this review are therefore predominantly taken from peer-reviewed work published in scientific books and journals

From stable isotope ecology to forensic isotope ecology: isotopes' tales.

Stable isotope ecology and forensic isotope ecology are not only linked by name. More often than not, knowledge and insights gained through the former serve as a springboard for application focused work of the latter. This review aims to offer a glimpse into the fascinating world of both though with more emphasis on forensic isotope ecology. To this end a selection of past and recent published work is presented and discussed to highlight both potential and limitations of isotopic analytical approaches to the detection of illegal trade in plants and animals

Stable isotope analysis of human hair and nail samples: the effects of storage on samples

When submitting samples for analysis, maintaining sample integrity is essential. Appropriate packaging must be used to prevent damage, contamination or loss of sample. This is particularly important for stable isotope analysis by isotope ratio mass spectrometry as this technique is capable of detecting subtle differences in isotopic composition with great precision. In a novel study, scalp hair and fingernail samples were placed in five different types of packaging, routinely used in forensic laboratories and stored for 6 weeks and 6 months. Samples were subsequently cleaned and submitted for 13C/12C, 15N/14N, 2H/1H and 18O/16O analysis. Results from 13C analysis indicate that type of packaging can cause slight changes in 13C abundance over time. Differences were noted in the 15N isotope signatures of both hair and nail samples after 6-week storage, but not after 6 months. This apparent discrepancy could be a result of the packaging not being properly sealed in the 6 weeks study. Fewer differences were noted when analyzing samples for 2H and 18O abundance

Identification of Ajnala skeletal remains using multiple forensic anthropological methods and techniques: a bioarchaeological report.

Fragmented and badly damaged commingled human remains present a tough challenge for their identification pursuits in forensic anthropology. Thousands of unknown human remains along with items of contextual identity, reportedly belonging to 282 Indian sepoys killed in 1857, were exhumed non-scientifically from a disused ancient well at Ajnala (Amritsar, India). In this manuscript, the non-scientific excavation of unknown human remains from the abandoned well, their forensic anthropological strategies for identification purposes, challenges being faced and future possibilities of their biological profiling have been discussed. Multiple methods and techniques like anthropological examinations, odontological profiling, radiological analyses, stable isotope and mitochondrial DNA (mtDNA) analyses were applied to few bones and teeth collected from the Ajnala skeletal assemblage. Though majority of studied bones and teeth were found belonging to adult males, very few of them had morphological, osteological and molecular features questioning the authenticity and validity of the written records. Due to certain ambiguous findings or gaps observed between the anthropological analyses of the Ajnala skeletal remains and the reported versions about their affiliations; certain advanced radiological, chemical and molecular techniques were applied to estimate their probable age, sex and populational affinity. The obtained radiological, isotopic and molecular signatures of the remains were compared with the available databases to estimate their affinity with the individuals of geographic area to whom the remains reportedly belonged to. The maternally inherited mtDNA haplogroup assignments, and stable isotope analysis of carbon and oxygen suggested that the studied human remains belonged to the individuals from West Bengal, Bihar, Odisha, Awadh (presently in Uttar Pradesh) and parts of Meghalaya and Manipur as potential regions of their geographic identity and thus, attributing the victims to be non-local to the site. However, merely on the basis of forensic anthropological examinations of very few bones and teeth (collected out of a huge collection of thousands of bones and teeth); it would be just an unqualified and sweeping conclusion to claim their identity as adult or non-adult, male or female, local or non-local, victims of 1857 mass killings or to the victims of ceremonial sacrifices or criminal activities committed in the past. A sufficient number of bones and teeth along with items of personal identity needs to be examined with multiple scientific techniques to arrive at some valid conclusions about their biological identity

Recent advances in the application of stable isotope ratio analysis in forensic chemistry

This review paper updates the previous literature in relation to the continued and developing use of stable isotope ratio analysis in samples which are relevant to forensic science. Recent advances in the analysis of drug samples, explosive materials, and samples derived from human and animal samples are discussed. The paper also aims to put the use of isotope ratio mass spectrometry into a forensic context and discuss its evidential potential

A guide for proper utilisation of stable isotope reference materials.

Many scientific publications about stable isotope ratios suffer from flawed practices regarding calibration and normalisation of raw δ values in conjunction with prescribed δ values of reference materials. Violations of the Identical Treatment principle with regards to samples and standards (i.e. reference materials) and lack of adherence to SImandated and IUPAC-recommended nomenclature exacerbate the widespread problem of lackadaisical analytical practice and reporting. Science is supposed to strive for exactness, whereas ambiguity and jargon confound interdisciplinary communication. This contribution aims to expose typical misconceptions and avoidable errors and offers guidance toward reproducible generation of isotope data, isotopic scale normalisation, and proper data reporting. We offer a comprehensive overview of sources of light stable isotope reference materials to best match sample matrices encountered by stable isotope practitioners with chemically similar reference materials

Highlighting the effects of co‐eluting interferences on compound specific stable isotope analysis of polycyclic aromatic hydrocarbons using comprehensive two‐dimensional gas chromatography

Accuracy is the most important issue when carrying out compound specific stable isotope analysis of polycyclic aromatic hydrocarbons extracted from complex samples. It depends on two main factors: the possible isotopic fractionation of the compounds during extraction and the potential co‐elution with interfering compounds with different isotopic signatures. We present here a simplified pressurised liquid extraction method for compound specific stable isotope analysis of polycyclic aromatic hydrocarbons (PAHs) in non‐aqueous phase liquids of coal tar. Samples extracted using the new method and using fractionation on silica gel column were analysed using comprehensive twodimensional gas chromatography. We were able to evaluate the effect of coelution on carbon and hydrogen stable isotope signatures of the 16 US EPA priority PAHs in the coal tars with various proportions of aromatic and aliphatic content. Even in samples that presented a good baseline resolution, the PAHs of interest co‐eluted with other aromatic compounds with a notable effect on their stable isotope values; it demonstrated the necessity to check the quality of all extraction and clean‐up methods (either the simplified pressurized liquid extraction or more traditional labour‐intensive methods) for the more complex samples prior to data interpretation. Additionally, comprehensive twodimensional gas chromatography enabled visualisation of the suspected coelutions for the first time

Dietary Differentiation and the Evolution of Population Genetic Structure in a Highly Mobile Carnivore

Recent studies on highly mobile carnivores revealed cryptic population genetic structures correlated to transitions in habitat types and prey species composition. This led to the hypothesis that natal-habitat-biased dispersal may be responsible for generating population genetic structure. However, direct evidence for the concordant ecological and genetic differentiation between populations of highly mobile mammals is rare. To address this we analyzed stable isotope profiles (δ13C and δ15N values) for Eastern European wolves (Canis lupus) as a quantifiable proxy measure of diet for individuals that had been genotyped in an earlier study (showing cryptic genetic structure), to provide a quantitative assessment of the relationship between individual foraging behavior and genotype. We found a significant correlation between genetic distances and dietary differentiation (explaining 46% of the variation) in both the marginal test and crucially, when geographic distance was accounted for as a co-variable. These results, interpreted in the context of other possible mechanisms such as allopatry and isolation by distance, reinforce earlier studies suggesting that diet and associated habitat choice are influencing the structuring of populations in highly mobile carnivores

Stable isotope relationships between apatite phosphate (δ18O), structural carbonate (δ18O, δ13C), and collagen (δ2H, δ13C, δ15N, δ34S) in modern human dentine

Rationale The use of multi‐isotopic analysis (δ2H, δ13C, δ15N, δ18O, and δ34S values) of modern human body tissues for provenancing of unknown individuals in forensics is increasing. Tooth dentine develops during childhood and adolescence, therefore providing geographical information from that period of life. Tooth apatite δ18O values are commonly used for the reconstruction of drinking water values, and H–C–N–S isotope ratios in collagen supply additional information about the composition of diet. We tested if dentine collagen δ2H values provide similar information to apatite δ18O values with a proof‐of‐concept study. Methods Tooth samples were taken from modern‐day individuals born in different regions of the world. Apatite and collagen were prepared from dentine. Stable isotope analyses were performed on apatite phosphate oxygen (δ18Ophos); oxygen and carbon of the structural carbonate (δ18Ocarb, δ13Ccarb); and hydrogen, carbon, nitrogen, and sulfur of the collagen (δ2Hcoll, δ13Ccoll, δ15N, δ34S). Results δ18Ophos, δ18Ocarb, and δ2Hcoll values are highly correlated in modern human dentine. There are significant relationships of δ18O values in the apatite fraction and δ2H values in the collagen fraction with local δ18O and δ2H precipitation values, respectively. Pearson correlation coefficients indicate no direct relationship between δ15N values and the isotope ratios of any other element. Weak relationships exist between collagen δ34S values and δ18Ocarb or δ18Ophos values. Conclusions The highly significant correlation of δ18Ophos, δ18Ocarb, and δ2Hcoll values in the modern human dentine implies that measurement of δ2H values in collagen or δ18O values in bioapatite will provide reliable information about the climate at the person's whereabouts

Simplifying and improving the extraction of nitrate from freshwater for stable isotope analyses

Determining the isotopic composition of nitrate (NO3_) in water can prove useful to identify NO3_ sources and to understand its dynamics in aquatic systems. Among the procedures available, the ‘ionexchange resin method’ involves extracting NO3_ from freshwater and converting it into solid silver nitrate (AgNO3), which is then analysed for 15N/14N and 18O/16O ratios. This study describes a simplified methodology where water was not pre-treated to remove dissolved organic carbon (DOC) or barium cations (added to precipitate O-bearing contaminants), which suited samples with high NO3_ ($400 mM or 25 mg L_1 NO3_) and low DOC (typically <417 mM of C or 5 mg L_1 C) levels. % N analysis revealed that a few AgNO3 samples were of low purity (compared with expected % N of 8.2), highlighting the necessity to introduce quality control/quality assurance procedures for silver nitrate prepared from field water samples. Recommendations are then made to monitor % N together with % O (expected at 28.6, i.e. 3.5 fold % N) in AgNO3 in order to better assess the type and gravity of the contamination as well as to identify potentially unreliable data