The goal of this study was to evaluate cocaine analytes in hair of different color (e.g., light, dark) and ethnic origin (e.g., Caucasian, African American) after the hair was subjected to surface contamination with cocaine and subsequent laboratory decontamination.
Research data suggest that hair color may affect cocaine's incorporation into and retention in the hair matrix. The possibility that differences in hair color may cause one individual to be more likely to test positive for a drug than another, despite both having ingested or having been exposed to the same amount of a drug, greatly concerns policymakers and forensic practitioners. If it is shown that hair color influences drug permeability, the current drug-testing methods may need improvement to take these variations into account and remove any potential for bias and false-positive results. While our previous cocaine surface contamination studies were designed to provide an estimate of intra, or within-individual, variation, this study includes sufficient samples to determine differences between ethnic groups or hair color with statistical significance. These data suggest there is no apparent simple relationship between concentration and ethnicity by this in vitro cocaine surface contamination model. While these results are statistically significant, the current study is limited to a small population. Additional results demonstrate that methanol laboratory hair decontamination is much less effective compared to extended phosphate buffer decontamination by this in vitro surface contamination model. This study demonstrates a lack of relationship between morphology and hair color or ethnicity, as well as no relationship between dye staining of hair and cocaine concentration or positive results of the hair. The results suggest that while cocaine analyte concentrations may be significantly higher in dark hair types use of benzoylecgonine/cocaine ratios and extensive decontamination wash criteria greatly reduce positive hair testing results in this in vitro surface contamination model. These findings could have a significant impact on whether national agencies use hair testing.