Examination of Firearms Review: 2007 to 2010 - Interpol

The differentiation between systemic exposure and external contamination for
certain drug groups has been frequently referred to as one of the limitations of
drug testing of hair. Difficulty in the interpretation arises when metabolites are
not detected which may either be due to external contamination of the hair, or
low doses of the drugs used, in particular when the drugs are administered by
smoking, sniffing or inhalation. Hair samples of eight pre-Columbian mummies
were analyzed for drugs using GC-MS. Nicotine was detected in 3 of the hair
samples, with measured concentrations of 11.4-57.5 pg/mg, but all 3 cases
revealed negative results for cotinine [444]. Thus, an active consumption of
tobacco could not be confirmed based on the results of the analysis. The
determination of the ratio of drug(s) in wash residue (W) to that in hair (H), i.e.,
W/H ratio, is proposed to differentiate system exposure to external
contamination [445]. When the W/H ratio is less than 0.1 or null, it would tend
to indicate drug use. Where the W/H ratio is above 0.1 but less than 0.5, it is
likely to indicate possible use possibly combined with a level of external
contamination. A W/H ratio greater than 0.5 is likely to indicate that the source
of most of the drug in the wash residue is from external contamination. The
W/H ratios of 891 results were evaluated over 13 analytes. Between 74 and
100% of the analytes studied produced W/H ratios less than 0.5, in particular
for cannabis (93%) and cocaine (95%), where external contamination is more
likely because of the way the drug is used. Hair samples from cocaine users
and seized cocaine samples were compared for the possible profiles of
metabolites/chemical degradation products [446]. It was found that norcocaine,
cocaethylene and anhydroecgonine methyl ester (each normalised to cocaine)
were significantly increased in the incorporation group (i.e., hair samples from
cocaine users). Hair samples were contaminated by rubbing with cocaine
followed by sweat application, multiple shampoo treatments and storage to
study criteria to differentiate the use of cocaine from contamination [447]. All
contaminated samples were correctly identified as contaminated by cutoff,
benzoylecgonine presence, percent of benzoylecgonine, and/or the wash
criterion.
3.4.3 Sweat
A controlled administration of MDMA to 15 volunteers with histories of MDMA
use was conducted to understand the excretion of MDMA and metabolites in
sweat [448]. MDMA was the primary analyte detected, with concentrations up
to 3007 ng/patch. 35.0% and 9.4% of the samples were positive for MDMA and
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