Study of the incorporation and release of cocaine and THC in damaged hair samples

Aims: Hair analysis is consistently requested within forensic investigations as a necessary step to prove exposure to various types of drugs. However, interpretation of hair analysis results may be affected by several sources of bias. Among these, chemical or physical cosmetic hair treatments can lead to morphological changes of the hair structure with possible effects on drug incorporation/release to/from the hair. Target of this study was the alleged correlation occurring between repeated cosmetic treatments, hair damage, and exchange of drugs inwards and outwards of the hair matrix, in terms of external contamination (incorporation) and loss (release) of the drugs from the hair structure. Cocaine and THC were utilized as target substances, for both their widespread diffusion among drug abusers and high risk of environmental incidence of contamination. Methods: To investigate incorporation phenomena, different types of drug-free hair were submitted to bleaching, dyeing and straightening and then exposed to marijuana smoke or soaked in a cocaine solution for 60 min. To study release phenomena, hair from cocaine and THC consumers were submitted to the same cosmetic treatments. Drug concentrations were always determined before and after the cosmetic treatments, using common washing and decontamination procedures followed by GC-MS detection, routinely employed in our laboratory. Morphological changes of hair submitted to cosmetic treatments were evaluated by scanning electron microscopy (SEM) and compared with untreated hair strands. Results and Discussion: Cocaine incorporation: non-treated hair and straightened hair (slight damage on the hair surface was observed by SEM) did not show significant incorporation of cocaine, once the contamination on the hair surface was washed out; in contrast, bleached and dyed hair showed considerable cocaine uptake, resulting in concentrations above the cut-off value of 0.5 ng/mg. In the latter case, substantial morphological changes of the hair structure was observed by SEM. THC incorporation after exposure to marijuana smoke was observed for both treated and untreated hair, but no correlation between hair structure damage and drug incorporation was evidenced. Cocaine and THC release: for both drugs, relevant loss was observed from chemically treated hair (bleaching and dying), while hair straightened by repeated heating treatments showed no appreciable decrease of the drugs concentration with respect to untreated hair, despite the structural damages occasionally observed by SEM. Conclusion: The morphological changes produced in the hair cuticle by cosmetic treatments definitely modifies the hair permeability to drugs in both directions, capture and release, but the extent of these effects also appears to depend on the chemical properties of the drugs. Further studies on different substances are in progress to better define the dependence of drug incorporation and release from the observed damage of the hair structure.