Bank of England banknotes sampled from different locations in the UK have been analysed for the presence of cocaine, diamorphine (DAM), Delta(9)-tetrahydrocannabinol (THC) and 3,4-methylenedioxymethamphetamine (MDMA). A database of the contamination detected is routinely used as a benchmark against which the contamination detected on seized banknotes can be compared. Evidence presented at court details how banknotes seized from a suspect may differ from banknotes in general circulation in terms of their contamination with controlled drugs. A question arising from such evidence is whether seized banknotes could have become contaminated through being in circulation in drug "hot spots". In order to address this issue, a Plackett-Burman experimental design was used to investigate the influence of source location and other factors on banknote contamination with drugs of abuse. Banknotes were drawn from banks in eight regions throughout the UK. Each location could be described by a unique combination of the factors under investigation, namely whether the location was rural or urban, in the North or South of the UK, and whether it was a port of entry. The socio-economic class and the proportion of drug offenders in the area and the denomination of the banknotes were also considered as potentially influential factors. Indices were calculated to describe the degree to which samples were contaminated with different drugs, and normal probability plots were used to identify the factors that could account for the contamination observed. Whilst some factors were more influential than others, it was shown that, at the 95% confidence level, none of the proposed factors were significant influences on the contamination. Cocaine contamination on banknotes has been shown to follow a log-normal distribution. It was, therefore, possible to calculate F- and t-statistics to compare the cocaine contamination on the entire sample set with that detected on a second sample set consisting of banknotes all drawn from a single bank branch. It was shown that both inter-bank samples and intra-bank samples had similar variance and similar contamination levels at the 95% confidence level. This suggests that there are no significant regional trends in the contamination of banknotes with drugs of abuse across the UK.

In many countries, monies suspected of being associated with drug trafficking can be seized by the authorities. One of the ways of investigating this association is through the analysis of seized banknotes for traces of controlled drugs. We report three studies which may assist the expert in assessing whether banknotes contaminated with diamorphine are part of the general population of notes in circulation or whether they show unusual contamination patterns which require explanation. Study 1 is based on three plausible contamination scenarios as they may occur during the various stages of an illicit drug transaction and seizure. It shows that notes which have been in direct contact with visible traces of diamorphine show significantly higher contamination to those in more indirect contact with the drug. Study 2 investigates the transfer of diamorphine from one highly contaminated note to other notes in a bundle over a period of 10 weeks with and without agitation. It was found that the total amount of drug transferred was smaller than 6% and no more than 4 out of a bundle of 10 previously clean notes became lightly contaminated. Based on extensive background data, study 3 proposes a probabilistic model to assess whether an observed proportion of diamorphine bearing banknotes is likely to have been contaminated by chance. The model predicts that there is only a 0.3% chance that a bundle of 100 notes from the general banknote population contains more than six contaminated specimens. Jointly, the three studies give useful indications for the spread of contamination throughout a sample and the amounts of heroin which may be expected given plausible contamination scenarios.