The effectiveness of decontamination procedures used in forensic hair analysis

Hair is a mainstream specimen used in forensic toxicology to determine drug use and exposure. However, the interpretation of an analytical hair result can be complicated by the presence of external drug contamination. Decontamination procedures are included in hair analysis methods to remove external contamination, but the capacity of these washes to completely remove contamination for all drugs is controversial. It is evident that there is no consensus on the most effective decontamination procedure, nor can decontamination procedures consistently remove external drug contamination to less than reportable cut-offs for all analytes. ∆9-tetrahydrocannabinol deposited from cannabis smoke is mostly removed by organic solvents, whereas ionizable drugs are more effectively removed by an aqueous wash. Organizations such as the Society of Hair Testing recommend a hair decontamination procedure should include both an organic and aqueous washing step, which is in accordance with the reviewed literature. Studies involving a systematic evaluation of various solvents have shown that the most effective organic solvent was methanol and the most effective aqueous solvent contained sodium dodecyl sulfate detergent. If future systematic studies can demonstrate similar findings, a consensus on the most effective decontamination procedure for forensic hair analysis may be established.