Forensic science international

Segmental hair analysis can demonstrate external contamination in postmortem cases.

PMID 21354729


Excluding laboratory mistakes, a false positive hair result can be observed in case of contamination from environmental pollution (external contamination) or after drug incorporation into the hair from the individual body fluids, such as sweat or putrefactive fluid (post mortem artifact). From our 20 years experience of hair testing, it appears that artifact(s) cannot be excluded in some post mortem cases, despite a decontamination procedure. As a consequence, interpretation of the results is a challenge that deserves particular attention. Our strategy will be reviewed in this paper, based on six cases. In all cases, a decontamination procedure with two washes of 5 ml of dichloromethane for 5 min was performed and the last dichloromethane wash was negative for each target drug. From the histories, there was no suspicion of chronic drug use. In all six cases, the concentrations detected were similar along the hair shaft, irrespective of the tested segment. We have considered this as indicative of external contamination and suggested to the forces or the judges that it is not possible to indicate exposure before death. In contrast to smoke, it seems that contamination due to aqueous matrices (sweat, putrefactive fluid, blood) is much more difficult to remove. To explain potential incorporation of 7-aminoflunitrazepam via putrefactive material, the author incubated negative hair strands in blood spiked at 100 ng/ml and stored at +4°C, room temperature and +40 °C for 7, 14 and 28 days. After routine decontamination, 7-aminoflunitrazepam tested positive in hair, irrespective of the incubation temperature, as early as after 7 days (233-401 pg/mg). In all periods, maximum concentrations were observed after incubation at room temperature. The highest concentration (742 pg/mg) was observed after 28 days incubation at room temperature. It is concluded that a standard decontamination procedure is not able to completely remove external contamination in case of post mortem specimens. Homogenous segmental analyses can be probably indicative of external contamination and therefore a single hair result should not be used to discriminate long-term exposure to a drug. Nor should the presence of a metabolite be considered as a discrimination tool, as it can also be present in putrefactive material.