Thallium distribution along segmented single hairs in a case of a criminal poisoning

In this study, six single hairs, each measuring 9-11 cm in length, from a victim of a single criminal thallium (Tl) poisoning incident were analyzed in 0.3 cm segments applying a validated inductively coupled plasma mass spectrometry (ICP-MS) method. The results hold significant forensic value, particularly in cases involving limited sample materials. Despite the very low weight of 0.3-cm single hair (12-16 µg), we found that the sensitivity of ICP-MS is sufficient to carry out the section-by-section analysis even in one single hair for determining Tl in poisoning cases. The measured Tl concentrations in this case were determined to be in the range of 0.6-6.5 µg/g hair, which are 100-fold beyond what is normally found in the German population. The consistent decrease in concentration from proximal to distal segments could be interpreted by predominant Tl incorporation via sweat. This finding is discussed in comparison with previous studies on Tl hair concentrations and in relation to the toxic effects of thallium on hair growth and sweat gland function. Due to the low limit of detection of 0.008 µg Tl/g hair, we conclude that Tl poisoning can be detected by the analysis of single hairs in 0.3 cm segments. However, proving repeated or continuous exposure to the toxin may be challenging due to its incorporation from sweat.