Distribution of Stable Hydrogen Isotopes in New Zealand Human Hair and the Effect of an Explosion

Abstract

Suicide bombers cause mass destruction including death and injury to hundreds of people. It can be difficult to identify the perpetrator of the bombing due to the large destruction and chaos that can surround a bombing site. The remains of a suicide bomber can be almost completely unidentifiable or indistinguishable from the remains of victims, making it hard to identify the perpetrator. Traditional methods of identification might be difficult to employ if there is no ante-mortem information available for comparison. A suggested technique in these circumstances is to measure the hydrogen isotope ratio composition of a person’s hair to predict their geographic movements.

Stable isotopes of hydrogen (δ2H), and oxygen (δ18O), vary around the world on a predictable scale due to partitioning of the isotopes of water within air masses, during various periods of condensation. The predictable nature of isotope distribution is due to cycling of air masses that go through constant periods of condensation and depletion of the heavier isotope. Leading to a trend of decreased δ2H following the movement of an air mass which is reflected in meteoric water. These differences in δ2H of ground water are reflected in materials that take up groundwater. For example, plants will have leaves that are reflective of the δ2H composition of their environment. The same is true for human hair. When a person consumes water, the δ2H composition of that water is reflected in their hair which can reveal information about their recent geographic locations. Therefore, by measuring the δ2H of a person’s hair, predictions can be made of their recent geographical movements. This can aid in a forensic investigation of a suicide bomb as can provide intelligence about the recent geographic movements of the perpetrator.

Although measuring the δ2H of a person’s hair and making predictions about their geographic origins can be useful for an investigation of a suicide bomb, there is no evidence to suggest the δ2H remains unchanged by exposure to an explosion in such close proximities. It is not known if being at the centre of an explosion would cause changes to the δ2H in human hair. The present research investigated if any changes were observed in the δ2H composition of human hair before and after exposure to an explosion of ammonium nitrate fuel oil (ANFO) which best mirrored a suicide bomb scenario. The results found there were no changes to the δ2H measured in the human hair before and after the explosion, suggesting that this is a viable technique to be used in the forensic application of an investigation to a suicide bomb. However the experimentation in this study was very simple and crude and only two explosive experiments were carried out. More robust testing of this is required to make any further conclusions about the effects of an explosion on the δ2H measured in human hair.

To investigate the distribution of δ2H in human hair across the country of New Zealand (NZ), hair from thirteen locations were collected by hairdressers of clippings from clients who were local to their region. Water was also collected from the locations to compare with an already established meteoric water line. The results show that although geographical features such as latitude can have an influence on the measured δ2H of biological materials, other meteorological parameters have a stronger influence on the δ2H in hair and the relationship with groundwater.

The differences in δ2H measured in hair collected from the 13 sampling locations, allowed for the development of an isoscape model that can predict the distribution of δ2H for the entire country. The developed models allowed predicting a particular region of origin of a person with a hair sample of known δ2H. This can help in the possible identification of regions of origins for an unidentified person. This research illustrates the usefulness of the technique of δ2H measurement in a forensic context such as providing intelligence in an investigation of a suicide bomb.