Hair and drinking water: A forensic tool

Hairs at crime scenes have implicated many criminals, or helped identify human remains. In most cases, it was DNA in the hair that cracked the cases. Unfortunately hair contains very little DNA, and for most forensic investigations, no useful amounts. Fortunately, scientists found an alternative way of extracting useful information from hair found at crime scenes. Drinking water. The water you drink tells a story, and that story is imprinted in your hair. A correlation was found between the ratio of hydrogen (H) and oxygen (O) isotopes in drinking water, and that found in a person’s hair.

Isotopes are different forms of the same chemical element that differ with respect to atomic weight. Isotopes may be stable (non-radioactive) or unstable (radioactive). Water is made up of stable hydrogen and oxygen isotopes. The hydrogen isotopes are H2, which is rare and heavier than the more common H1. O18 is the rare heavier isotope of oxygen, while O16 is the more common one.

The ratios of the hydrogen and oxygen isotopes in drinking differ due to geographical location, and various aspects of the water cycle explain this. For example, when rain clouds that formed over the ocean move inland, the first raindrops are mostly those with the heavier isotopes, H2 and O18. It would stand to reason that as the clouds moves further inland, the ratios of the heavier isotopes in the rainfall decrease. Seasonal changes also affect isotope ratios in water, e.g. it differs between snow and rain. Another factor is the rate of evaporation from soil and plants. Despite all the contributing factors, underground and reservoir drinking water contain the average isotope ratios from that particular geographical region.

Saltair Sally Cold Case

The remains of a female murder victim were found in October 2000, on the south end of the Great Salt Lake in Utah. The remains comprised 26 bones, a skull with long hair, a T-shirt, and a necklace. A facial reconstruction was done, and publicized on national television but no one could identify her. Dental records also did not produce any useful leads. All they knew was she was between the ages of 17 and 20, and she was five feet tall. She became known as “Saltair Sally”.

In 2008, investigators contacted IsoForensics, a company that specializes in stable isotope analysis. The results of the hair analysis revealed that she lived between two places during the last two years of year life. They concluded that she moved around repeatedly somewhere in the Northwest, more specifically between the Pacific Northwest and the Salt Lake City area. This geographical information narrowed down who she could have been out of the missing persons reported across the country. Four years later, and 12 years after her disappearance, a subsequent DNA analysis between “Saltair Sally’s” remains and those of her mother confirmed the identity of Nikole Bakoles. It was later confirmed that her geographical movements predicted by the hair isotope analysis were due to the fact that she had been visiting her family. Though Nikole’s murder has not been solved, her family now knows what happened to her.

Michelle Mukonyora

16 May 2016