Exploring regional differences in trace metal isotopes found in hair samples

Abstract

Introduction: Cancer is classified into several stages, being more difficult to cure in later stages. Thus, early detection is important. This project aims to help the development of a non-invasive method for early cancer detection using hair samples.
Background: Isotopes are known to leave a temporary and geographical signature in different samples. Capillon Analytics AB uses isotopes to detect cancer but there have been few studies on isotopic fractionation in low abundant elements in hair due to location.
Aim(s): The aim of this study was to find which elements have statistically significant different or similar isotopic fractionation in hair samples from individuals from the US and from Sweden while optimizing the existing method.
Methods: After testing several microwave-assisted acid digestion methods using certified reference materials (CRM), and conducting stability and repeatability studies, hair samples were digested using HNO3 and analysed by Inductive-Coupled Plasma-Mass Spectrometry (ICP-MS). Results were treated by using t-tests for differences, two one-sided t-tests (TOST) for similarities, and analysis of variance (ANOVA) for method comparison. Multivariate analyses, such as principal component analysis (PCA) and Ward’s hierarchical clustering were used.
Results: Digestions using HNO3 with H2O2 presented slightly better accuracy than digestions using only concentrated HNO3. However, since the use of H2O2 implies the addition of one step in the process, and the results were comparable, concentrated HNO3 was used for practical reasons for following studies. T-tests showed that 60 out of 89 isotopes presented differences in concentrations between US and Sweden with a power higher than 0.99. However, when using fractional abundance, only 13 isotopes showed significant differences with power higher than 0.99. TOST did not reveal any similarities in concentration or fractional abundances between different regions when using an equivalence margin of 0.2 times the pooled standard deviation.
Conclusion: In conclusion, a microwave-assisted digestion method using only concentrated HNO3 was proved to be optimal for the analysis of hair samples using ICP-MS. Finally, fractional abundances proved to be more robust between hair origin than concentrations. However, studies of the deconvolution of isobaric data and interferences present are still needed.

Popular Abstract

Exploring isotopic differences in non-abundant elements in hair from different geographical locations
Cancer detected in a late stage is largely lethal. Since early detection can save lives, there is a need for simple, non-invasive and inexpensive detection techniques. The company Capillon Analytics AB developed a non-invasive method to detect cancer early by using hair. The idea is to take some strands of hair, analyse their chemical composition, and check for the presence of cancer in the body.
Hair is a byproduct of the cell metabolism processes which transform food and water into energy. These metabolic processes differ from cell to cell, especially in cancer cells, which are hungry for nutrients. Cancer cells have a faster turnover rate than normal cells. It is this turnover rate and need of nutrients that eventually lead to a chemical sign of cancer signals in hair. Some of the elements that can be altered are zinc, lead, strontium or calcium. However, the amount of nutrients and elements within a body also varies due to diet or environmental conditions. Since it might be very difficult to determine the presence or absence of cancer, we need to understand how the environmental factors also alter the chemistry in hair.
Chemical elements can have several versions of themselves where the mass differs a little – isotopes. An analogy could be a T-shirt with different sizes. It is still the same T-shirt but with a small difference; thus, the element is the same, but it has isotopes. The concentration of each isotope, with its specific mass, can be measured. Then the proportion of each isotope for an element can be calculated, called fractional abundance. Their different masses affect the rate in the biological processes. And as mentioned, cancer cells reproduce faster, consuming then a larger amount of the less reactive isotope.
Food and water are different across the globe, meaning that also the concentrations and the abundance of isotopic elements may differ among human living, eating, and drinking in these regions. The aim of this study is to explore if differences exist in concentrations and fractional abundances of isotopes in the hair between healthy individuals living in the US and Sweden.
To measure the concentration of trace elements in hair, we used equipment that atomizes and ionizes the sample. This means that all molecules present become single atoms and then ions. Then the formed ions are separated by mass-to-charge ratio, obtaining a concentration for each mass. To be able to determine the isotopes present in hair, it needs to be digested by using acid and microwave heating. Several acids were tested, and concentrated nitric acid gave the best results while being an optimized process. Different statistical tests were used to determine the differences and the similarities in concentrations and fractional abundances between the two countries, including t-test and two one-sided t-test (TOST) respectively.
Our results show that differences in concentrations were found in 77 out of 89 isotopes with an 80 % probability of being true. In the US, the concentrations were higher than in Sweden for all isotopes except the two uranium ones. Some isotopes had a low probability of giving the correct result, likely caused by interferences from elements or molecules having the same mass as the isotope analysed and being measured at the same time being indistinguishable. Regarding fractional abundances, only 22 isotopes showed differences between the countries with a 60 % probability of being true. This implies that fractional abundances are more consistent between US and Sweden than concentrations and would be a better option to determine the presence of cancer.
Finally, the TOST results were not successful, since there is too much variation between individuals to be able to determine whether similarities exist. Future studies will focus on the separation of interferences from analytes (the isotopes we are interested in), and comparisons between individuals’ ethnicity, diet, or the part of the body where the hair was taken.

• author: Pascual Massip, Ines
• supervisor: Emma Hammarlund; Jürgen Kuhn
• organization: Centre for Analysis and Synthesis
• course: KAKM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Hair, Inductive-Coupled Plasma – Mass Spectrometry, Microwave-assisted acid digestion, Sample Origin, T-test, Analytical chemistry
• language: English
• id: 9196229
• date added to LUP: 2025-06-23 15:29:52
• date last changed: 2025-06-23 15:29:52