As chemists throughout the world have studied the occurrence of different elemental isotopes and developed new techniques to measure the proportions of isotopes present in different parts of the world, this knowledge has developed into a useful tool for forensic scientists. Referred to as isoscapes, a merging of “isotope” with “landscape” this field allows the geographical origin of a sample to be determined by looking at the different proportions of stable isotopes which are present.
Isotopes are atoms of the same element which differ slightly in their mass, due to the presence of a different number of neutrons. For example, while the majority of oxygen atoms on earth have a relative atomic mass of 16, a small proportion have a mass of 18. And this proportion has been found to vary throughout the world. Similarly geographical variations in the proportion of carbon, hydrogen, nitrogen and sulfur isotopes can be detected and this can be used as the basis for forensic investigations including the detection of fake products and identification of bodies.
Variations in Oxygen-18 isotopes in leaves through out the world (Values are relative to standard sea water) https://sites.google.com/site/westlabgroup/isoscapes-home
Isoscaping was used to help determine the movements of a Vietnamese man who was dumped at a hospital room in England, and subsequently died. By applying isoscaping to different sections of a 14 cm hair from his head, it was determined that the dead man had been in the Ukraine a year before his death, then travelled to Germany before finally ending up in the UK. This evidence, along with other information was later used to help convict two men of his murder.
Isoscaping has also been applied to determining the geographical origin of drugs such as cocaine, marijuana and heroin, and has been used by antiterrorism agencies to determine the source of explosives. Carbon isotopes can be used to track migrating salmon, as isotope proportions vary with ocean temperatures which can be correlated to geographical locations. Other isotope ratios can be used to identify counterfeit Scotch whiskey, trace the source of foods, water and fragrances. It is developing into a very useful forensic tool.
Of course given the sensitivity of this technique there are challenges in that standardised data is required in order to make comparisons. Currently there are databases which provide a lot of good data for Europe and North America, however, data for other parts of the world can be quite sparse. However, as this technique grows in use these gaps will no doubt be filled providing more potential applications.
This blog is based on information contained in “Isotopes mark the Spot” by Sarah Everts, Chemical and Engineering News, 2011, June 27, pg 32-35.