February 8, 2019 by Locard's Lab

Tracking Movements with Fingernails

When human remains are discovered, investigators will often turn to routine methods such as fingerprinting, DNA profiling and the use of dental records to identify the individual. But in the absence of database records for comparison, such traditional techniques may not prove all that useful, and forensic scientists must look for new ways to identify the unknown.

In recent years the use of stable isotope analysis has aided forensic investigations, particularly in establishing the geographic origin of unidentified human remains. Isotopes are different forms of an element. For example, oxygen has three naturally occurring stable isotopes: O¹⁶, O¹⁷ and O¹⁸. These isotopes are incorporated into substances in the environment (such as water) in varying ratios. The relative abundance of isotopes can be influenced by various factors in a process known as isotopic fractionation. It has been found that isotopic ratios can be related to different regions of the world. For example, the tap water in one country may have a completely different isotopic signature in comparison to water in another country. How does this relate to the isotopes found in our bodies? Well, you are what you eat. As you consume food and water from a particular area, the atoms in our bodies express abundances similar to the food and water consumed.

This provides the basis for using isotope analysis to trace materials back to a certain geographic region. It has already been demonstrated that the isotopic analysis of bones, teeth and other bodily tissues can allow for individuals to be traced to particular locations, typically through the analysis of oxygen, hydrogen and sulphur isotopes. However last year, researchers at the University of Utah took a different approach, this time focusing on fingernails.

As with bones and teeth, the isotopic content of our fingernails will be affected by factors such as the food and water we consume. As fingernails are estimated to grow at a rate of 3-4mm per month, they are a prime target for studying isotopic patterns in an individual over a shorter timespan (less than six months as oppose to years). This is by no means the first study of isotope abundances in fingernails, but previous research has typically focussed on single timepoints rather than tracking the same individuals over time. As global travel becomes more commonplace, it is increasingly likely that human remains could have originated from any part of the world. Therefore, we need to understand how travel can cause changes in isotope abundances within the body.

This study aimed to establish whether fingernail isotope ratios were different in a group of local people in comparison to non-locals who had recently moved to the area (in this case Salt Lake City in the United States). Over a period of a year, fingernail clippings were collected at multiple timepoints from a group of volunteers, about half of which were local residents and the rest individuals who had recently arrived from various locations across the US and the world. The fingernail clippings were cleaned (to remove surface components and contaminants that could interfere with the analysis) and subjected to analysis by isotope ratio mass spectrometry (IRMS). IRMS is a particular type of mass spectrometry that allows us to measure the isotopic abundance of certain elements typically hydrogen, carbon, nitrogen, and oxygen. You can read more about IRMS here.

The isotope values of samples from residents were used to construct a baseline of expected values for the area, with isotope values from non-residents’ samples being compared with these. Initially, samples from non-residents showed a wide range of isotopic values, which is to be expected given they had only recently moved to the area. Some residents did fall within the expected range of locals, but these participants had moved from relatively nearby locations, which could explain the similar relative isotopic abundances. However after about 3 months, the fingernail isotopic patterns shifted until the non-residents could no longer be distinguished from the residents. This indicates that although the relative abundance of isotopes in our fingernails can shed some light on geographical movement, it can only provide information relating to the past few months. Inevitably there will always be a certain amount of error associated with such analyses, with variation from the likes of short-term travel and random dietary changes being impossible to account for.

Mancuso, C. J, Ehleringer, J. R. Resident and Nonresident Fingernail Isotopes Reveal Diet and Travel Patterns. Journal of Forensic Sciences. 2019, 64(1).

August 9, 2017 by Locard's Lab

Tracking Illicit Drugs with Strontium Isotope Analysis

The manufacture and distribution of illicit drugs such as heroin is a primary focus of many major law enforcement organisations worldwide, including the Drug Enforcement Agency (DEA) in the United States and the National Crime Agency (NCA) in the United Kingdom. Unfortunately, as drug shipments pass hands between dealers and cross borders so rapidly, it can be difficult if not impossible to trace a batch of drugs back to an initial manufacturer. As a result of this, the chances of locating and arresting the manufacturers of illicit drugs can be slim.

To a forensic drugs analyst, a whole range of characteristics can be examined and used to classify and compare different batches of the same drug, including physical appearance, packaging, and chemical composition. To an extent, heroin chemical signatures are already beneficial in comparing different batches of the drug in attempts to establish links and possible sources of the narcotics. This may be based on agents or adulterants a product has been cut with, and the relative concentrations of those substances. The manufacturing process itself can vary in terms of chemicals and apparatus used and the skills of the manufacturer, resulting in further characteristic differences in the chemical profile. However these differences may not be distinct enough to be valuable and are certainly not able to pinpoint the country from which a batch originated. Though there is still no reliable method of tracing an illicit drug back to a particular location, ongoing research is aiming to change this.

One method of studying the history and even origin of a sample is to use isotopic composition. Isotopes are different forms of elements that are incorporated into substances in the environment in varying ratios and abundances, influenced by a number of factors that can alter these ratios. These processes can be described as isotopic fractionation. Interestingly, isotopic ratios can be characteristic to different regions of the world, enabling certain materials to be traced back to the geographic region based on the ratios of particular isotopes contained within that material. With this in mind, they have often been used to trace unidentified human remains to a particular location or study the origin of food products. Focusing on isotopes allows for heroin samples to be studied and compared based on regional characteristics as oppose to the variation caused by the production process.

For the first time, researchers at Florida International University have utilised strontium isotope ratio analysis to determine the provenance of illicit heroin samples. 186 unadulterated, undiluted heroin samples of known origin were obtained from a number of geographic regions including Southeast Asia, Southwest Asia, South America, and Mexico. Of a particularly challenging nature is South American heroin and SA-like Mexican heroin, which can be extremely difficult to differentiate based on their chemical compositions alone. Heroin samples were dissolved via a microwave-assisted acid digestion method before being subjected to a technique known as a multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS). This instrument utilises an inductively coupled plasma ion source to ionise target analytes, which are then separated and analysed by the mass spectrometer. The use of MC-ICP-MS allows for the strontium concentration of particular samples to be determined. The strontium isotope ratio (⁸⁷Sr/⁸⁶Sr) value of each individual sample was then compared with the overall mean values of ratios from different regions in order to establish the likely origin of that particular heroin sample. Samples from the same geographic region would be expected to exhibit a similar isotope ratio.

Multi-collector inductively-coupled plasma mass spectrometer (MC-ICP-MS) Source: www.thermofisher.com

The results demonstrated the possibility of differentiating between heroin of different geographic origin. South American and Mexican heroin samples were correctly classified 82% and 77% of the time respectively. South East and South West Asian heroin samples were somewhat more difficult to differentiate due to more of an overlap between strontium isotope ratio values. SE Asian samples were correctly classified 63% of the time and SW Asian samples only 56% of the time. It is not clear whether this elemental strontium is endogenous or the result of external contamination, but either way it is sufficiently characteristic to be associated with a particular geographic location.

The strontium isotope composition of heroin can be affected by a number of factors, including the soil in which components are grown and groundwater in the area, which can result in region-specific isotope compositions. The use of strontium isotope ratio analysis has presented promising results in the origin determination of illicit heroin. Although a larger scale study incorporating samples of a more worldwide origin would be ideal, initial results suggest that this technique could allow for an unknown illicit drug sample to be traced back to a country of origin, aiding criminal intelligence agencies in the war against drugs.

Debord, J., Pourmand, A., Jantzi, S., Panicker, S. & Almirall, J. Profiling of Heroin and Assignment of Provenance by ⁸⁷Sr/⁸⁶Sr Isotope Ratio Analysis. Inorg Chim Acta. In press (2017).

February 7, 2017 by Locard's Lab

Interview with President of IsoForensics Inc., Lesley Chesson

southern-utah Different forms of elements–called isotopes–are found everywhere in the environment. These isotopes are incorporated into materials in varying ratios and the abundances of different isotopes thus serve as a record of the material’s formation. Analysis of a material for its distinct isotope signature can subsequently be used to reveal its history. Investigators have applied stable isotope analysis to a variety of materials of forensic interest including drugs, explosives, money, food, ivory, and human remains. For example, the isotopes in human hair protein can reveal the age of an individual, what s/he ate, and even how often (and where) s/he travelled.

What is your professional background and how did you come to be involved in IsoForensics?

I have a master’s degree in biology, with a lot of microbiology and chemistry experience. I entered the world of isotope forensics when I was hired to raise Bacillus subtilis (a cousin of the anthrax bacterium) under a variety of conditions – in liquid media, on agar plates, with different nutrients, etc. Because organisms record information about the environment in the isotopes of their tissues, the goal of this project was to develop models that allowed investigators to predict the growth conditions of a dangerous bacterium–such as anthrax–from its isotopic characteristics.

From its start in academia, IsoForensics developed into a private analytical services and research firm that explored novel forensic applications of isotope analysis. I enjoyed the challenges offered by that exploration. Since my first work on the B. subtilis project, I’ve been involved in other projects on human remains, foods and beverages, illicit drugs, and explosives.

Tell us about the work IsoForensics is involved in and what kind of clients do you typically work with?

Currently, IsoForensics provides a lot of human remains testing in unidentified decedent cases. The goal is to use the isotope records contained in hair, nails, bone, and teeth to reconstruct the travel history of individuals and provide new evidence on their origins: Were they local to the area of discovery? Had they traveled prior to death? Where might they have traveled? We work with a variety of law enforcement groups in this casework.

In addition to service work, we conduct basic and applied research through funded grants and contracts. One recent project has started to investigate the origins and ages of seized elephant ivory to understand the structure of illegal trade networks in Africa and Asia.

What are some of the most common sample types you are asked to analyse, and does anything pose a particular challenge?

In any given month, we can analyze a variety of materials – human and wildlife remains, illicit drugs, explosives, etc. One of the most challenging measurements we make is for strontium isotope ratios. There is so little strontium contained in organic materials that prep work takes place in clean lab settings. The preparation of materials for radiocarbon dating is also challenging since we must be extremely careful about contamination of “old” materials with “modern” carbon. However, these challenges are worthwhile since strontium isotopes can provide potentially useful geolocation data about materials while radiocarbon dating provides quantitative information on the “age” of materials.

Are there any areas of isotopic analysis that could benefit from further research and development?

Yes. Isotope forensics benefits from better and better models/methods for interpreting data. It’s one thing to compare isotope measurement results from sample to sample or from sample to a reference databank, but it’s another thing altogether to understand the process(es) driving isotopic variation in materials. For example, are the results we observe due to differences in TNT manufacturing process? Or coca plant physiology? Or elephant diet?

Isotope analytical techniques also change over time as better instrumentation is developed. Understanding the impact of different analysis techniques on measured isotope ratios is extremely important when comparisons are made – especially in legal settings. A major focus of the field is the standardization of practices and protocols, to generate comparable results over time and space (e.g., from lab to lab).

How has the need for isotope analysis in forensic investigations changed over the years, if at all?

The forensic application of isotope analysis has been increasing the past 10-20 years. This is partly due to changes in analytical techniques, which have made isotope ratio measurements faster and cheaper. In addition, those who could benefit most from forensic isotope data–law enforcement, regulators, etc.–have become more aware of the technique and it potential usefulness in various types of investigations. We as forensic scientists and isotope analysts can do even more to spread awareness about the technique and its many applications.

Finally, do you have any advice for students hoping to pursue a career in this field of work?

Isotope analysis is one (extremely useful!) tool in a forensic scientist’s toolbox. Having a background and training in other areas–such as anthropology, analytical chemistry, biology, biochemistry, geology, law, or statistics–can be very important when applying isotope analysis techniques and interpreting the resultant data. The field of isotope forensics is relatively small compared to some other forensic disciplines, so be sure to read papers, attend meetings, and network with scientists working in the field.

Visit the Isoforensics Inc. website for more information.

April 30, 2015 by Locard's Lab

Geochemistry and Clandestine Graves

Perpetrators of fatal crimes will on occasion attempt to conceal their wrongdoings by burying the evidence – that is, attempting to bury human cadavers. This can be problematic during a forensic investigation for a number of reasons. Firstly, the search for a victim’s body may well be relatively blind, with investigators having little or no idea as to where a body has been buried. In some instances, a body may well be so damaged or decomposed that little recognisable human remains are present. The perpetrator may later remove the body from the burial site, perhaps fearing discovery, leaving behind no obvious trace that a body was ever buried there.

So what can investigators do to determine if an area of soil was the site of a clandestine grave (illicit burial site)? A number of methods that have been developed to tackle this question.

Certain chemical compounds may be indicative of decomposing flesh. Sterols have been suggested as a potential biomarker for decomposition fluids – that is, the presence of them in soil could indicate whether or not a body has decomposed in that location, depending on the types of sterols present and in what amounts. Sterols are a class of organic compound, of which cholesterol is perhaps the most well-known sterol present in animal cells. This compound can be found in plants too, but in a significantly smaller amount, thus the unexpected presence of cholesterol in soil will typically indicate some kind of animal-related activity. Research examining the decomposition fluids in soils found sterols to be beneficial in this application (Von der Luhe et al, 2013). A number of pig carcasses were buried over a few months, with soil samples being collected from underneath the cadavers at different time points after burial. Cholesterol and coprostanol were detected in the soil, and it is these substances that were of particular interest to the researchers. Coprostanol is formed via hydrogenation of cholesterol in the intestinal tract of higher mammals, thus it is considered a useful biomarker associated with the faecal matter of animals such as humans and pigs. The concentration of these compounds was greater during the time period in which the pigs were undergoing the putrefaction stage of decomposition, at which point fluids would be leeching into the soil. This suggests a certain time frame in which these compounds are useful as indicators of decomposition fluids.

Cholesterol

The research suggested that, as the cadaver decomposes, decomposition fluids leak into the soil, depositing cholesterol and coprostanol (and a whole range of other substances). Thus the presence of these compounds in a particular area of soil, particularly if nearby similar areas did not contain them, could indicate previous decomposition of a human (or equally a pig or other animal) in the area. However it is vital to note that these compounds could equally be detected in the soil as a result of faecal matter, though potentially in considerably lower concentrations than those produced by a whole decomposing body.

Other compounds resulting from decomposition are of equal interest in detecting potential gravesites. Adipocere, also known as grave wax, is an insoluble, white substance known to form if a body decomposes in very specific conditions. The presence of this substance in soil can of course indicate the decomposition of a body, but how does one distinguish between the decomposition fluids of a human and those of another mammal? Research has aimed to answer this question using isotopes (Bull et al, 2009). By focusing on the ratio of ¹³C to ¹²C content of particular fatty acids from the fats of various animals, it was suggested that it is possible to distinguish between adipose fats from humans and those from other animals, such as pigs, though further work may be required to develop this application.

Other researchers are applying existing forensic techniques in a novel manner to the detection of clandestine graves. When the body decomposes, a significant amount of nitrogen is released, typically in the form of ammonium and nitrate (Hopkins et al, 2000). Ninhydrin, a compound already readily available to law enforcement due to its use as a method of fingerprint development, can produce a blue or purple pigment upon reaction with certain nitrogen-containing compounds.

Ninhydrin is typically used for visualising fingerprints (http://daten.didaktikchemie.uni-bayreuth.de)

One particular study examining ninhydrin reactive nitrogen (Carter at al, 2008) left a number of mammalian cadavers to decay over a period of a month, after which soil samples from the burial sites were collected and analysed for ninhydrin reactive nitrogen. This work discovered that cadaver burial resulted in the concentration of NRN in the soil approximately doubling, thus concluding that it may be possible to use ninhydrin as a presumptive test for gravesoil. Of course this particular method is somewhat limited by the fact that any mammalian cadaver (and plants or faeces for that matter) will most likely produce this increase in nitrogen-containing compounds which will react with ninhydrin, but an interesting application of an existing indicator nonetheless.

The various methods of using the chemical analysis of soil to detect clandestine graves are plentiful and fascinating. Despite the limitations, namely the possibility of animal faeces and non-human decomposition providing false positive results, these techniques may at the very least act as a kind of presumptive or complimentary test for possible burial sites.

References

Von der Luhe, B. Dawson, L. A. Mayes, R. W. Forbes, S. L. Fiedler, S. Investigation of sterols as potential biomarkers for the detection of pig (S. s. domesticus) decomposition fluid in soils. Forensic Sci Int. 230 (2013), pp. 68-73.

Bull, I. D. Berstan, R. Vass, A. Evershed, R. P. Identification of a disinterred grave by molecular and stable isotope analysis. Sci Justice. 49 (2009), pp. 142-149.

Carter, D. O. Yellowless, D. Tibbett, M. Using ninhydrin to detect gravesoil. J Forensic Sci. 53 (2008), pp. 397-400.

February 13, 2015 by Locard's Lab

Food for Thought: Forensics & Food Fraud

Recently, organisation Food Forensics became the first laboratory of its kind in the UK to receive UKAS accreditation, which brings me to this post. Some might ask, what does food have to do with forensics? Perhaps a perfectly valid question with the traditional bloodied crime scene on a dark night in mind. However the application of forensic science is growing continuously, including in tackling problems of food fraud.

Many Europeans will remember the food scandal arising in 2013 in which horsemeat was somewhat shockingly detected in a range of food products (obviously in products where horsemeat should not have been popping up). Or perhaps less well-known, the 1858 Bradford sweets poisoning, in which a batch of humbugs was accidentally made using arsenic instead of a sugar substitute, resulting in the poisoning of numerous people. Common mistake to make I’m sure! Concerns over foodstuffs have always been prevalent, but it is only in relatively recent years that advanced analytical techniques have been available to apply to this field of work.

Organisations are now carrying out research and analyses of food and beverages to validate their composition. Of particular note is the use of stable isotope analysis to determine the isotopic composition of a sample. As a brief reminder, isotopes are atoms of the same chemical element (same number of protons but different number of neutrons, thus giving them slightly differing masses). Stable isotopes have a natural abundance which is altered in different locations to a different extent, a process known as fractionation. This will result in samples (whether it be samples of food, plants or anything else) acquiring different ratios of isotopes. Stable isotope analysis examines these non-radioactive isotopes to help establish the isotopic composition of a sample, which can then be compared to others.

With this information available, it is possible to establish the origin of food products. Whereas the origin of a product may seem benign, realistically if you don’t know where your food has come from, you can’t say much about the safety of food. By determining the stable isotopic compositions of food samples and comparing them to known standards, the contents of a sample can be validated or refuted. Some researchers have compiled isotopic data for different regions into a kind of map (sometimes referred to as an “isoscape”) which shows the varying isotopic data throughout different areas. With data such as this at hand, it may be possible to establish the origin of a food sample based on its isotopic composition and how that compares with the isotopic data of particular areas. Using this analytical method, it may be possible to not only investigate the country or even region of origin of a food product, but also further details such as if it is organic.

As an example, the James Hutton Institute based in Scotland has conducted research into the hydrogen and oxygen isotopic composition of Scotch whisky, aiming to prove that fraudulently-produced whisky made outside of Scotland will be detectable if not made with water from within and around Scotland. Whisky made from water sourced elsewhere will have a different isotopic “fingerprint”. It is applications like this that allow for scientists and regulators to crack down on food fraud, ensuring both safety in food supply and preventing food-related criminal activities.

References

Food Forensics. [online][Accessed 12 Feb 2015] Available:http://www.foodforensics.co.uk

Earth Magazine. Cold case files: forging forensic isotopes. [online][Accessed 12 Feb 2015] Available:http://www.earthmagazine.org/article/cold-case-files-forging-forensic-isoscapes

Cambridge Network. Food forensics achieves UKAS accreditation focussed on combating food fraud. [online][Accessed 12 Feb 2015] Available:http://www.cambridgenetwork.co.uk/news/food-forensics-achieves-ukas-accreditation-focused-on-combat530

Image Sources: https://www.flickr.com/photos/xiekitchen/269285157

November 21, 2014 by Locard's Lab

Ammo Analysis: Using Isotopes to Match Bullets

We’ve all seen the classical TV crime drama clip where the over-worked genius detective throws a couple of bullets under the comparison microscope, lines up a set of striations and declares that the two bullets were fired from the same gun or maybe they came from the same box of bullets. Whilst this may be the crux that solves the case in fiction, and very occasionally in reality, linking bullets is typically not so simple. A more accurate method of connecting objects such as projectiles is to study them at an elemental level or, in the case of this research, at an isotopic level.

Elements exist as a number of different stable isotopes (atoms of the same element differing in the number of neutrons present in the nucleus). Lead, a common component in bullets, exists as four isotopes in nature; ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb and ²⁰⁸Pb. When lead occurs naturally in ore (a type of rock containing minerals and metals), different sources of lead will vary in their isotopic compositions. Further dissimilarity arises through recycling of lead products, meaning that lead from numerous sources may be mixed together into a new product. This variation can be utilised to distinguish between lead bullets from different batches or conversely establish that two bullets are likely to have originated from the same source.

The research we’re talking about here, led by a team at the University of Oslo in Norway, used an analytical technique called MC-ICP-MS to analyse the lead isotopic compositions of a range of bullets, cartridge cases and firearm discharge resides.

What’s MC-ICP-MS, I hear you ask?

MC-ICP-MS stands for multiple-collector inductively coupled plasma mass spectrometry. Put simply, a conventional ICP-MS involves the introduction of the sample as a fine aerosol, using an inductively coupled plasma source to ionise the sample, after which the newly ionised components are separated based on their different mass-to-charge ratios. The ions impact with a dynode of an electron multiplier, resulting in the release of an electron for each ion strike. This can then be amplified until an intensity significant enough for measurement is achieved. The signal is ultimately proportional to the ion concentration, therefore allowing for the amount of a substance present to be determined. Multiple detectors (such as MC-ICP-MS) use multiple detectors to simultaneously measure separated isotopes.

ICP-MS Schematic (http://www.spectro.com)

Okay, that concludes our technical talk! But now just what did this research find, and why is it useful?

After extracting lead from a wide range of bullet samples using nitric acid and subjecting the specimens to MC-ICP-MS, researchers could examine the distribution of isotopic ratios in bullets across a variety of manufacturers. Not only did it seem possible to distinguish between bullets from different manufacturers based on lead isotopic composition, but also between boxes of bullets from the same manufacturer produced at different times. In many instances fired bullets will become disfigured upon impact, making microscopic examination difficult if not impossible. But by studying the bullet at an isotopic level and even determining a kind of isotopic fingerprint, analysts may be able to distinguish between bullets produced in different regions of the world, by different manufacturers, and even between individual batches from the same company. The ability to do this could prove invaluable to forensic investigators.

Though naturally there was a certain amount of uncertainty associated with the work, the use of isotope ratios in the study of bullets proves promising. The idea of utilising isotopic ratios to distinguish between bullets is not a new concept, with researchers investigating the theory as early as 1975. But as analytical techniques progress and improve, forensic scientists are able to obtain much more from their evidence, bettering the criminal justice system one isotope at a time.

References

Sjastad, K-E. et al. Lead isotope ratios for bullets, a descriptive approach for investigative purposes and a new method for sampling of bullet lead. Forensic Sci. Int, 244 (2014), pp. 7-15.

Perkin Elmer. The 30-Minute Guide to ICP-MS. [Online][Accessed 20 November 2014] Available from: http://www.perkinelmer.co.uk/PDFs/Downloads/tch_icpmsthirtyminuteguide.pdf